THAT WAS SO LAST MILLENNIA…

EVOLUTION OF THE HUMAN RACE

Steven Pinker is Harvard College Professor in the Department of Psychology at Harvard University. He conducts research on language and cognition, writes forpublications such as the New York Times, Time and The New Republic, and is the author of eight books, including The Language Instinct,

How the Mind Works,Words and Rules, The Blank Slate, The Stuff of Thought, and most recently

The Better Angels of Our Nature: Why Violence Has Declined. The following is

a transcript of Steven being interviewed for a television series called “Evolution

of the Mind”.

Q: Can you talk about our origins in Africa?A: The
genetic evidence suggests that we evolved in Africa. We know that people
reached Australia by forty thousand years ago, maybe earlier, which required
travelling across sixty miles of open ocean, and it would have required a
species with considerable intelligence to put together some kind of canoe or
dugout that could have traversed that distance.Also, probably the longer welook the more we’ll find evidence
for signs of human creativity and ingenuity in Africa. Europe is where you
have a lot of caves, which preserve stuff, and Europe is where you have a lot
of archaeologists out looking for human remains, and so I think there’s a bit
of a bias toward the European landscape. As people get cleverer about finding
things in Africa and look longer, I suspect that we will see things beyondthe age at which the European artifacts appear.
We also know that a lot of our evolution had to have taken place
before the human races diverge because we’re pretty much birds of a feather.
If you took a bunch of human babies from anywhere around the world — from
Australia, New Guinea, Africa, Europe — and scrambled the babies at birth
and brought them up in any society, they’d all be able to learn the same
languages, learn how to count, learn how to use computers, learn how to make
and use tools. It suggests that the distinctively human parts of our
intelligence were in place before our ancestors split off into the different
continents.

So in a sense we’re all Africans, and if the first group that
budded off from the African population and ended up in Australia did so sixty
or seventy thousand years ago, then our evolution had to have been pretty
much complete by then, because today’s Australians and today’s Europeans and
today’s Asians and Africans are all the same species with pretty much
indistinguishable cognitive abilities.

Q: So what happened fifty thousand years ago?

A: Human
evolution, at first, seems extraordinary. How could the process that gave
rise to slugs and oak trees and fish produce a creature that can fly to the
moon and invent the Internet and cross the ocean in boats? Was it some kind
of divine spark that made our brains special? Well, I don’t think so, because
I think that you can understand human evolution in terms of the ordinary
process of Darwinian natural selection.

The way to understand how different species evolved is to think
about the niches that they fill in an ecosystem — basically, how they make a
living. And how do humans make a living? Well, with their brains. You could
think of an ecosystem as a bunch of antagonistic arms races, almost:
Everything that an animal depends upon for food is the body part of some
other animal or plant who would just as soon keep that body part for itself.

And so all the things that we depend on for food evolve defenses
against being eaten. Animals run away, they develop spines or poisons. Plants
can’t very well defend themselves by their behavior, so they resort to
chemical warfare, and plants are saturated with toxins and irritants to deter
creatures like us who want to eat them. Now, whenever you have some kind of
defensive weapon in nature, you get an offensive weapon, and vice versa. So
as the hide gets thicker, the fangs get stronger and sharper, which makes the
hides get thicker still, and so on.

This arms race, though, is played out in evolutionary time, and
the animal can’t will its skin to get thicker in its own lifetime. Now,
here’s the trick, I think, behind humans: We participate in this arms race —
but in our own lifetime, not in evolutionary time — by using our brains, by
developing a model of how the world works, what causes lead to what effects,
and figuring out ways of defeating the defenses of other plants and animals
before they can evolve countermeasures in response.

So we invent snares or camouflaged pits, or we coordinate our
behavior to drive large animals and stampede them over a cliff, or ways of
detoxifying plants by cooking them or fermenting them or soaking them. And
because we can figure these things out in our mind’s eye by learning how the
world works, we can figure out how to use more of the ecosystem to our
advantage, and I think that explains why these big-brained creatures became
as successful over the planet as they did.

Q: How did evolution, for humans, happen so quickly? We
[already] had a big brain, but how did the big brain suddenly start working?

A: Certainly
humans didn’t evolve to their present state in one instant, in one fell
swoop, because we know that our ancestors, the species like Homo erectus
and Homo habilis already had a pretty big brain for a primate of that
size. They were already using tools. They were almost certainly cooperating
with one another. So it’s not as if our species was the first to do it; it
was building on some earlier stepping stones.

And it’s unlikely that it happened all at once. You have to
remember that not every creature that was evolving left behind its skull or
its tools for our convenience tens of thousands of years later. Most bones or
most tools rot or get buried and are never found again. So the earliest date
at which we find some fossil or artifact is not the point at which the
species first appeared; it was probably doing its thing for many tens of
thousands of years before we were lucky enough to find something that it left
behind that lasted to the present day.

Q: Can you talk about the rewiring of the human brain?

A: You have
to remember that human intelligence and intelligent behavior don’t just come
from having a whole bunch of stuff packed into our skull like meatloaf.

The actual organization of behavior goes on the level of the individual nerve
cells and their connections, and we have a hundred billion nerve cells,
probably a hundred trillion connections. It’s just mind-boggling to think of
all the different ways in which they’re arranged in a baby’s head. And a lot
of our evolution consisted not just in getting more of this stuff, but in
wiring it in precise ways to support intelligence.

Q: Does Darwinian evolution allow for such internal rewiring as
part of its process?

A: There are
lots of ways in which Darwinian natural selection could rewire a brain. There
are chemicals that are released in the growing brain that attract nerve
cells, encouraging them to grow in certain pathways versus others. There are
molecules at the tips of the growing neurons that can engage or not engage
some target, like a lock and a key. There are rules for when brain cells die
in what part of the brain, so that they might grow in one part, die off in
another. All of these are under the control of genes, and as genes evolve,
the way they do throughout evolution, the wiring of the brain can change.

Q: So this rewiring pattern happened progressively?

A: Yes. It’s
very likely that the changes in the brain didn’t happen overnight. There
wasn’t one magical mutation that miraculously allowed us to speak and to walk
upright and to cooperate with one another and to figure out how the world
works; evolution doesn’t work that way. It would be staggeringly improbable
for one mutation to do all that. Chances are there were lots and lots of
mutations over a span of tens, maybe even hundreds of thousands of years that
fine-tuned and sculpted the brain to give it all the magnificent powers that
it has today.

I don’t think there was a thunderclap or a divine spark that
suddenly made one species smart. You can see, in our ancestors, there was a
gradual expansion of the brain, there was an expansion of the complexity of
tools. Even when our species evolved, it surely was spread out over tens of
thousands of years. The fact that we find a whole bunch of artwork or tools
in one place just means that that’s when they arrived there and left some
garbage that survived to the present time. But it’s virtually certain that it
was extended over many, many generations before that.

Q: What is a “cognitive niche”?

A: Our niche
in nature, the “cognitive niche,” the ability to understand the
world well enough to figure out ways of manipulating it to outsmart other
plants and animals. And there are several things that I think evolved at the
same time to support this way of life. One of them is cause-and-effect
intelligence: How do sticks break, how do rocks roll, how do things fly
through the air? A second is social intelligence: How do I coordinate my
behavior with other people so that we can bring about effects that one person
acting alone, like Robinson Crusoe, could never have done? And I think the
third is language: If I learn something, I don’t get the benefit of it alone,
but I can share it with my friends and relatives, I can exchange it for other
kinds of commodities, I can negotiate deals, I can gossip to make sure that I
don’t get exploited.

So, each one of these abilities — intelligence about the world,
social intelligence, and language — I think reinforces the other two, and
it’s very likely that the three of them coevolved like a ratchet, each one
setting the stage for the other two to be incremented a bit.

Q: Some scientists think that gossip was the only thing driving
language.

A: Gossip is
certainly one of the things that language is useful for, because it’s always
handy to know who needs a favor, who can offer a favor, who’s available,
who’s under the protection of a jealous spouse. And being the first to get a
piece of gossip is like engaging in insider trading: You can capitalize on an
opportunity before anyone else can.

But language is useful for other things, for exchanging technical
know-how — how do you get poison out of the gland of a toad, what’s the best
way to make a spear, where are the berries, what’s the best time of year to
hunt. It’s also good for one-on-one negotiations: “If you give me some
of your meat, I’ll give you some of my fruit”; “You and I can gang
up on the leader: — even though he’s stronger than either of us, he can’t
beat the two of us acting together”; “If you have sex with me, I’ll
help bring up the children.” There are all kinds of ways that language
can be useful. Gossip, I think, is just one of them.

Q: So languages began just about fifty or sixty thousand years
ago.

A: We really
don’t know when language began. It can’t be any later than fifty or sixty
thousand years ago because that’s when the races diverged, and we know that
all the races are interchangeable in their language abilities. Bring up an
Australian Aborigine in New York; they’ll speak English with a New York
accent, or vice versa. So it had to be in place before that; it couldn’t be
later than fifty or sixty thousand years ago.

How much earlier? I think considerably earlier, simply because
language is complicated. It’s like the eyeball or the ear, and complicated
organs can’t evolve in one fell swoop — they need too many mutations in
order to craft this finely engineered organ. So I think language had to have
had a fairly long evolutionary history.

We don’t really know why it took us as long to evolve as we did,
but I think there’s a strong suggestion that language couldn’t have evolved
before other things were in place. First of all, you have to have something
worth saying. What’s the use of having long, flowery sentences if you have
nothing interesting to communicate? If chickens had language, what would they
talk about? Nothing terribly interesting.

And also, you’ve got to be on speaking terms with someone else.
If no one else is interested in what you have to say, or if you tell someone
something and they will take advantage of you and you can’t expect something
in return, there’d be no point in having language. So I think we evolved
language when we also evolved something to say and when we also evolved to be
on speaking terms with one another.

Language evolved over an extended period of time, but it seems
to have coevolved with other things that all came to their present
configuration about the same time, somewhere before fifty thousand years ago.
Our intelligence, our language, our social interactions, all of them seem to
come together at this magic point.

I think human evolution couldn’t just have been driven by social
completion, by people gossiping and plotting against each other, because
that’s the equivalent of taking in one another’s laundry; it doesn’t get you
anywhere. I think social intelligence coevolved with physical intelligence —
figuring out how the world works. It gives you a reason to hang out together
because you can accomplish things that one person couldn’t, and it creates an
environment in which know-how is that much more worth having because you can
share it with your buddies and your kids. And so the costs of a big brain are
repaid if everything you know can be multiplied in terms of sharing it with
other people.

Q: We’re talking about anatomically modern humans —
anatomically modern and behavioral modern are two very different things. Why
didn’t the others make it and why did this new group make it?

A: It’s
possible that once the skull had evolved to the present size, there was still
more evolving to do. And that might explain the gap between the first
anatomically modern human that had the same amount of brain that we had, and
the first behaviorally modern human who created art and fine inventions and
so on. The difference is that there could have been a lot of evolution going
on inside the skull as the brain got rewired.

The actual cause of behavior is not just brain tissue acting en
masse like a muscle, but it’s the wiring diagram of the hundred billion
different brain cells connected by a hundred trillion connections. There are
so many ways in which those could be wired and many ways for the genes to
bias that in one direction or another that, for a long period of time, there
could have been a kind of internal rewiring even if on the outside the skull
looked exactly the same.

Q: We always say that we’re never going to find the answer to
that because the brain doesn’t fossilize. Is that true, or do you think we
may find the answer?

A: We
probably won’t find the answer to that in the fossils because the
neuron-to-neuron connections certainly don’t fossilize. We’ll have to be
awfully clever about reconstructing it, both from the products that they left
behind — what does a functioning brain do? — and perhaps also from clever
use of genetic evidence, working backwards from the genes that build the
brain today to figure out what the genes that built the brain fifty thousand
years ago might have looked like. That’s science fiction today, but who knows
what will happen in ten or twenty or thirty years?

Q: If you look at a Neandertal skull and the skull of the modern
human, they’re about the same size. One failed and one succeeded. Why?

A: We don’t
really know why Homo sapiens succeeded and Homo neandertalensis
didn’t. The brains were the same size, but they may have been wired quite
differently, and it could have been that there was wiring in the Homo
sapiens
brain that supported better language, cleverer know-how, better
social coordination, that gave them an advantage. And it didn’t have to be a
big advantage; even an advantage of a couple of percentage points in survival
rate could, over a few thousand years, have driven the less well-adapted
species to extinction.

Q: What are memes?

A: Certainly,
when we look around us and are amazed at all the things that Homo sapiens
has wrought — rockets that go to the moon and the Internet and modern
medicine and so on — that wasn’t because our brain evolved to do those
things in particular; no Robinson Crusoe thinking by himself on a desert
island could have invented a rocket. It depends on the accumulation of an
enormous number of discoveries that were passed on, not through the genes,
but from one person to another through language and other forms of
communication.

This is called cultural evolution. Some people call the units of
cultural evolution memes — little units of memory or knowledge — and we’ve
been accumulating them for tens of thousands of years.

So we figured out how to make nice sharp tools and our jaws and
teeth became smaller. We figured out how to use the hides of other animals to
stay warm and we lost a lot of body hair. We are now figuring out how to cure
diseases, how to build shelters. And for tens of thousands of years the
products of the human brain have accumulated in almost a parallel course in
evolution to the changes in our bodies and brains.

These memes can be anything from styles that help you fit into a
group, like turning a baseball cap around and wearing the peak in the back,
to figuring out the cure for some disease or how to grow crops. So the
products of the brain that have been transmitted not through the brains but
through language have, for many thousands of years, been as important or more
important than the actual physical stuff that we’re made out of.

A lot of the creations of our brain can make up for physical
deficiencies, and could actually change the course of evolution. Thousands of
years ago, someone who was severely nearsighted probably wouldn’t have had
many descendants; he would have been eaten or fallen off a cliff a long time
ago. But we invented eyeglasses and now being nearsighted has no disadvantage
at all.

There are some people who might say, “Well, isn’t this
interfering with evolution? Wouldn’t we be better off letting the diabetics
and the nearsighted die an early death to improve the physical vigor of the
species?” That really goes against the way that human evolution works,
which is that for tens of thousands of years we’ve depended for our survival
on our own inventions, on our own creation, and this is simply extending this
process.

Q: If Darwin could see the modern world, what would he be most
surprised or gratified to understand that we understand?

A: If Darwin
were alive today, the discovery of biology that would have pleased him the
most would have been modern genetics and DNA, because to the day that he died
he was haunted by the worry that his theory wouldn’t work because traits of
organisms blended when they mated, that anything that was advantageous in an
organism would be diluted when it mated with some other organism that didn’t
also have that trait, and there was no way to get evolution off the ground.

We know now that genes survive intact when organisms mate, that
they are particles that don’t get blended but survive in their identical
form. We know that they have a physical basis, the sequence of bases in the
DNA molecule. Those were the missing pieces in the theory of evolution, and
that’s really what convinced scientists that Darwin’s theory was the correct
explanation for the evolution of life on earth.

Q: Do you think he would be surprised to know how much
dissension there still is around his theory?

A: I think
Darwin would be surprised to learn that more than a hundred years after he
proposed his theory there are still people who think it’s just a theory, who
have sincere doubts about it, because the evidence was quite convincing in
Darwin’s time. And now that the last holes of his theory have been plugged by
the discoveries of genetics, by the discovery of the age of the earth, by the
discovery of the chemical basis of life, no reasonable person can deny that
this is overwhelmingly the best explanation we have for the evolution of life
on earth.

Chimpanzees are clearly our close cousins. You cut us both open,
you see the same organs. You look at our DNA and we share 98.5 percent of our
DNA with chimps. But obviously, we’re very different. Chimps are precariously
clinging to a few patches of forest in Africa; humans have taken over the
planet. What could have produced the difference?

Well, there was six million years in which our brains expanded
and got rewired in ways that allow us to do completely different things. We
can exchange information by making noise as we exhale — the gift that we
call language. We figure out how the world works, we make many different
kinds of tools; we coordinate our behavior and exchange information. And all
of these changes in cognitive evolution, in the evolution of the powers of
the brain, account for why humans are making a film in which they can talk
about chimpanzees rather than vice versa.

A friend of mine lived and worked with a chimpanzee for several
years, and tells the story of how the chimp loved to imitate things that she
did. For example, after she washed the dishes the chimp would wash the
dishes, but the chimp’s idea of washing the dishes was very different from
ours. It went through the same muscle movements; it would pick up the sponge,
let the warm water roll over his hands, would rub the sponge on the plate,
but didn’t get the idea that the point of washing the dishes was to get the
dishes clean.

It just liked the feel of rubbing a sponge over the plate. It
could wash the same dish over and over again; it could rub some of the dirt
off and not get all of it off, because what it was imitating was the
particular physical sequence. What it didn’t think about was what the goal of
the human performing the action was. And the ability to guess what other
people’s goals are is a key part of human intelligence, and it makes us very
different from our primate cousins.

http://www.pbs.org/wgbh/evolution/library/07/2/text_pop/l_072_03.html

© 2001 WGBH Educational
Foundation and Clear Blue Sky
Productions, inc. All rights reserved.

The
Evolution of the Human

The universe is constructed from a multitude of various materials. It
is dynamic in form and shape due to a multitude of various processes and
interactions between these materials. To the human, however, in his need to
establish his place and purpose in the universe, the most important material
is biological and the most important process is evolution, far it is only
here that the human can learn to understand himself, an understanding that is
vital to his survival.

Wise men, psychologists, philosophers and theologians have surmised and
conjectured about the human over the centuries, and still do, but the truth
about the human may be found only through factual knowledge. That factual
knowledge lies in a process called evolution. The human is what evolution
made him.

Man
has been a tribal animal since he first walked erect, more than four million
years ago. With the impediment of being bipedal, he could not out-climb or
outrun his predators. Only through tribal cooperation could he hold his
predators at bay.

For
two million years, the early hominid was a herd/tribal animal, primarily a
herd herbivore. During the next two million years the human was a tribal
hunter/warrior. He still is.

All of the human’s social drives developed long
before he developed intellectually. They are, therefore, instinctive. Such
instincts as mother-love, compassion, cooperation, curiosity, inventiveness
and competitiveness are ancient and embedded in the human.

They were all
necessary for the survival of the human and pre-human. Since human social
drives are instinctive (not intellectual), they cannot be modified through
education (presentation of knowledge for future assimilation and use). As
with all other higher order animals, however, proper behaviour may be
obtained through training (edict and explanation followed by enforcement).

The
intellect, the magnitude of which separates the human from all other animals,
developed slowly over the entire four million years or more of the human
development. The intellect is not unique to the human; it is quite well
developed in a number of the other higher animals. The intellect developed as
a control over instincts to provide adaptable behaviour. The human is
designed by nature (evolution) to modify any behaviour that would normally be
instinctive to one that would provide optimum benefit (survivability). This
process is called self-control or self-discipline, and is the major
difference between the human and the lower order animals.

Background and Introduction

The
direct lineage from the ancestor of both man and the modern apes to modern
man is not known. Evidence is increasing. Thousands of relics fit the general
pattern.

The
word hominidae is used to describe the total member species of the
human family that have lived since the last common ancestor of both man and
the apes. A hominid is an individual species within that family. The
field of science which studies the human fossil record is known as pale
anthropology. It is the intersection of the disciplines of palaeontology (the
study of ancient life forms) and anthropology (the study of humans). Each
hominid name consists of a genus name (e.g. Australopithecus, Homo)
which is always capitalized, and a species name (e.g. africanus, erectus)
which is always in lower case.

Controversy
exists over whether brain size alone shows intellectual ability, but our only
measure of intellectual growth in the hominid record is brain size. The
fossil evidence, except for one notable blip, shows a steady growth in brain
size. This can be misleading due to the different sizes of the people. Early
man (with perhaps three exceptions) was quite small and the males were much
larger than the females.

From
a cultural viewpoint, modern man and the other apes are quite similar in some
respects. Sexual practices of modern humans are quite similar to the
chimpanzee (although stoutly denied by some), but with far more homosexual
activity. Although homosexual play is common among the apes, a totally
homosexual ape is rare. It is estimated that about 10% of the human population is so oriented.

The
modern human’s trend toward family dissolution places the human only a few
percentage points from that of the chimp. In fact, unlike man, a gorilla male
must be physically driven away and held at bay before he will leave his
family. A great ape will rarely kill another member of the same species. On
the other hand, music and art are peculiarities of the human and have no
counterpart in any ape society.

SPECIES TIME PERIOD
Ardipithicus ramidus 5 to 4 million years ago
Australopithecus anamensis 4.2 to 3.9 million years ago
Australopithecus afarensis 4 to 2.7 million years ago
Australopithecus africanus 3 to 2 million years ago
Australopithecus robustus 2.2 to 1.6 million years ago
Homo habilis 2.2 to 1.6 million years ago
Homo erectus 2.0 to 0.4 million years ago
Homo sapiens archaic 400 to 200 thousand years ago
Homo sapiens neandertalensis 200 to 30 thousand years ago
Homo sapiens sapiens 200 thousand years ago to present

History
of Man

The
earliest fossil hominid, Ardipithecus ramidus, is a recent discovery. It is dated at 4.4 million years ago.
The remains are incomplete but enough is available to suggest it was bipedal
and about 4 feet tall. Other fossils were found with the ramidus fossil which would suggest
that ramidus was a forest
dweller. A new skeleton was recently discovered which is about 45% complete.
It is now being studied.

A new species, Australopithecus anamensis, was named in 1995. It was
found in Allia Bay in Kenya. Anamensis lived between 4.2 and 3.9
million years ago. Its body showed advanced bipedal features, but the skull
closely resembled the ancient apes.

Australopithecus
afarensis
lived between 3.9 and 3.0 million years ago. It
retained the apelike face with a sloping forehead, a distinct ridge over the
eyes, flat nose and a chinless lower jaw. It had a brain capacity of about
450 cc. It was between 3’6″ and 5′ tall. It was fully bipedal and the
thickness of its bones showed that it was quite strong. Its build (ratio of
weight to height) was about the same as the modern human but its head and
face were proportionately much larger. This larger head with powerful jaws is
a feature of all species prior to Homo sapiens sapiens.

Australopithecus
africanus
was quite similar to afarensis and lived
between three and two million years ago. It was also bipedal, but was
slightly larger in body size. Its brain size was also slightly larger,
ranging up to 500 cc. The brain was not advanced enough for speech. The
molars were a little larger than in afarensis and much larger than
modern human. This hominid was a herbivore and ate tough, hard to chew,
plants. The shape of the jaw was now like the human.

Australopithecus
aethiopicus
lived between 2.6 and 2.3 million years ago. This
species is probably an ancestor of the robustus and boisei.
This hominid ate a rough and hard to chew diet. He had huge molars and jaws
and a large sagittal crest. A sagittal crest is a bony ridge on the skull
extending from the forehead to the back of the head. Massive chewing muscles
were anchored to this crest. See the opening picture of an early Homo
habilis
for an example. Brain sizes were still about 500cc, with no
indication of speech functions.

Australopithecus
robustus

lived between two and 1.5 million years ago. It had a body similar to that of
africanus
, but a larger and more massive skull and teeth. Its huge face
was flat and with no forehead. It had large brow ridges and a sagittal crest.
Brain size was up to 525cc with no indication of speech capability.

Australopithecus
boisei
lived
between 2.1 and 1.1 million years ago. It was quite similar to robustus,
but with an even more massive face. It had huge molars, the larger measuring
0.9 inches across. The brain size was about the same as robustus. Some
authorities believe that robustus and boisei are variants of
the same species.

Homo
habilis

was called the handy man because tools were found with his fossil
remains. This species existed between 2.4 and 1.5 million years ago. The
brain size in earlier fossil specimens was about 500cc but rose to 800cc
toward the end of the species life period. The species brain shape shows
evidence that some speech had developed. Habilis was about 5′ tall and
weighed about 100 pounds. Some scientists believe that habilis is not
a separate species and should be carried either as a later Australopithecine
or an early Homo erectus. It is possible that early examples are in
one species group and later examples in the other.

Homo
erectus

lived between 1.8 million and 300,000 years ago. It was a successful species
for a million and a half years. Early examples had a 900cc brain size on the
average. The brain grew steadily during its reign. Toward the end its brain
was almost the same size as modern man, at about 1200cc. The species
definitely had speech. Erectus developed tools, weapons and fire and
learned to cook his food. He travelled out of Africa into China and Southeast
Asia and developed clothing for northern climates. He turned to hunting for
his food. Only his head and face differed from modern man. Like habilis,
the face had massive jaws with huge molars, no chin, thick brow ridges, and a
long low skull. Though proportioned the same, he was sturdier in build and
much stronger than the modern human.

Homo

sapiens (archaic)provide the bridge between erectus
and Homo sapiens sapiens during the period 200,000 to 500,000 years
ago. Many skulls have been found with features intermediate between the two.
Brain averaged about 1200cc and speech was indicated. Skulls are more rounded
and with smaller features. Molars and brow ridges are smaller. The skeleton
shows a stronger build than modern human but was well proportioned.

Homo
sapiens neandertalensis
lived in Europe and the Mideast between
150,000 and 35,000 years ago. Neandertals coexisted with H.sapiens
(archaic)
and early H.sapiens sapiens. It is not known whether he
was of the same species and disappeared into the H.sapiens sapiens
gene pool or he may have been crowded out of existence (killed off) by the H.sapien
sapien
. Recent DNA studies have indicated that the neandertal was an entirely
different species and did not merge into the H. sapiens sapiens gene pool.
Brain sizes averaged larger than modern man at about 1450cc but the head was
shaped differently, being longer and lower than modern man. His nose was
large and was different from modern man in structure. He was a massive man at
about 5’6″ tall with an extremely heavy skeleton that showed attachments
for massive muscles. He was far stronger than modern man. His jaw was massive
and he had a receding forehead, like erectus.

Homo
sapiens sapiens
first appeared about 120,000 years ago.
Modern humans have an average brain size of about 1350 cc.

History of Man – an Expansion

Evolution
appears to work in bursts of activity. A species may survive for a very long
time, even millions of years, with relatively little change, and then
suddenly, seemingly overnight, a variant species springs from it. Several
such cases are evident among the hominid. When populations are large, species
drift is very slow, regardless of species. Evolution works best when a small
population of a species becomes isolated and faced suddenly with new hazards.
The environment provides early and quick death to quickly weed out
deleterious mutations and the small population provides a small gene pool
across which helpful mutations may quickly spread.

This
is the manner in which the first hominid, the walking ape, appeared. Although
no one knows what specifically happened or where, a small pocket of primates
were somehow isolated in an area where there were no cats (the main primate
predator) and the food supply was short, perhaps even dwindling.

In
warmer and wetter times, huge forests abounded across Africa. Both the
ancient primates and felines were widespread. Then the climate changed.
Forests dwindled. Patches of forests became isolated, causing animal
interchange to become quite difficult. In most such patches, both primate and
feline survived. The shortage of food, perhaps growing worse daily, drove
some of the primates to the forest floor in search of food. There they became
food for the cats. Life was too grim and short for a new ground dwelling
primate species to develop.

But
somewhere there was an unusual valley, one completely isolated from all the
others, and something there eliminated the cat. Perhaps it was a disease.
Perhaps it was a famine of all animal life, with the sole animal survivor
being the primate. There must always be a large numerical ratio between food
supply and predator. Perhaps it was a small valley, too small to support a
large enough cat gene pool for the cat survival, but large enough to support
bare primate survival. Or, more likely, the small valley was over-harvested
by the cats to the point that only the primates, safe high in the trees,
survived, and the cat was starved out of existence. The primate in that
valley was then able to spread safely to the forest floor. The walking ape
was born. The original primate species still ruled the forest canopy, while
this new species, in the absence of felines, was dominant on the forest
floor.

Then
the climate changed, reopening the valley for the transit of both primate and
feline. The tree-top primate rejoined his fellows and their gene pools
blended. The feline was re-introduced to the valley. The bipedal ape on the
forest floor was introduced to his new predator. If that introduction had
been sudden, the bipedal ape could not have survived. Perhaps there were
other valleys in which that actually happened. Luckily, in this one, it was
slow, and the walking ape had time to adjust to his new danger. He formed
defensive groups and developed defensive strategies.

That
first hominid was Ardipithecus Ramidus. He lived on the forest floor.
His close cousin, the primeval ape Ramapithecus, lived overhead.
Ramidus
had become a herbivore. Ramapithecus was an omnivore. Ramidus
had feet on one end. Ramapithecus had hands on both ends. They were
about the same size and had about the same intelligence. When the predator
came, Ramapithecus escaped into the trees. With four hands he could
out climb even the ancient leopard. In spite of the leopard, ramidus
had to stay in the forest, being on the open plains was certain death. He was
neither fast enough nor strong enough to handle the big plains’ cats. While
in the forest, ramidus could at least jump into a tree and escape the
big ground cats, but he was still easy prey for the leopard. The death rate,
especially among the children, was high. A pregnant woman had no chance at
all. Something had to change. Ramidus learned how to cooperate in
defense and he learned how to use a club. His culture became more restricted
and structured.

The
idea of a club was not new. Modern chimps will use one to beat on the ground
in trying to drive off an interloper. The chimp does not need to learn how to
use one well because he can always take to the high trees. Chimps will even
cooperate in driving off interlopers by jumping up and down and screaming.
They do not need to learn how to cooperate in fighting. They can always take
to the trees. Ramidus did not have that choice.

Ramidus now
had two things that kept him out of the trees in times of danger: his feet
and the club. When the leopard came, he had no chance without the club
whether he met the cat on the ground or in the tree. Climbing a tree in a
hurry with two feet that cannot grasp anything and a club in one hand while
trying to escape from a big cat would be an exciting experience. His women
and children had no chance at all without his protection on the ground. Ramidus
learned to get shoulder to shoulder with his friends, club at the ready, in
front of the women and children, and stand his ground, no matter what the
animal was. Now he did not have to live under the trees. He could live
anywhere he pleased. They moved out on the plains.

Meanwhile,
ramidus was also having deep trouble trying to make a living. He was a
herbivore, the available food was coarse and hard to chew and his chewing
apparatus had been designed to fit the needs of an omnivore who ate much
fruit. The women, especially, were having real problems in caring for the
children while foraging. The life style was brutal, and the death rate was
high. Evolution loves a high death rate.

Evolution
had few options. Ramidus could not return to the jungle. He was built
wrong. He was structurally too slow to convert to a plain’s predator.
Besides, he was primarily a vegetarian and did not have the physical
equipment to tear meat off his prey. Birth rate increases would require major
physical changes. Only cultural changes were available. The women needed more
time to take care of the children and the children would fare better if they
did not need to be out on the plains. The males needed to take more of the
burden. The tribe needed a safe haven for the women and children, preferably
one with some protection from the weather. The old men could stand guard and
the young ones could take their clubs with them and forage. Since they were
bipedal, they had two arms to haul the food back to camp.

By
the time Australopithecus afarensis appeared, some structural
improvements had been made. His head was proportionately larger with a much
improved eating apparatus, with molars that were much larger. The size of the
canine teeth had diminished (evolution diminishes things not needed). His jaw
was heavier and had huge chewing muscles attached. The male was also a little
taller and heavier and the female was smaller because of their differing
roles. A slight brain size increase provided improved social interaction.
With the following Australopithecus africanus, they survived, in
balance with nature, for almost two million years. Still, life was short,
child mortality high, and hardship was constant. Evolution had honed the
species to fit the environment and was now in balance. The people were tough,
hard-working and resilient. Man had joined the other plains’ animals in a balance
with nature that appeared stable (not fun, but at least survivable). Many
other plain’s animals had also reached stability in their evolution, one that
exists to this day. If something had not happened to upset this balance, man
would still be there today, mingling with the wildebeests.

Several
things happened to spur further development. With their stronger culture,
they could survive the plains better than the other herd herbivores. Their
population grew. Competition was high for food. Other species branched off:

Australopithecus aethipicus came first, followed by robustus and boisei.
These were bigger and tougher competitors for the same food supply.

Somewhere
along in the last million years of the reign of africanus, someone
sharpened a stick, perhaps to use to dig roots, and discovered that a spear
was a much more effective weapon for some uses than a club. A club is a good
defensive weapon. When a club is used against an animal other than man, it is
immediately available for another swing. It is not too good against another man.
He will usually grab it on the way in and the advantage is lost.

Life
became even more precarious, the favourite working ground for evolution. The
greatest dangers that man now faced were other men. When man goes against
man, and the weapons are the same, cunning is usually the deciding factor. A
spear is a great equalizer in size, so growing bigger was not as effective as
a survival move as growing smarter. Unfortunately, becoming more vicious was
also effective. The docile hominid cow of the plains became a warrior. His
culture was now much more complex, one that needed careful planning and
leadership. This required intelligence and language.

Homo habilis
was the transition man. Starting with a 500cc brain, it grew to a respectable
800cc. Habilis developed from a brutish and dim-witted herd animal to
a competent man. The Broca’s area in his brain became developed showing the
existence of a workable vocabulary. He invented the use of fire for cooking,
warmth and keeping wild animals at bay. He invented the stone axe. He also
may have eliminated the last of that big tough robustus and boisei
bunch. For some reason they disappeared about that time. For sure there was
no one else on the plains that could have done them in.

Then,
about 1.8 million years ago, Homo erectus came: mighty warrior, skilled
hunter, inventor, far-ranging explorer and king of all he surveyed.
The
size of a modern human and standing as straight, he developed a 1250cc brain,
very close to modern man. Along the way he developed many new tools and
weapons, invented clothing, and travelled out of Africa, the first hominid to
do so. He went across southeast Asia, into northern China and south to Java.
He was now an omnivore who ate mostly meat, both animals and fish. He cooked
his food. Evolution had noted the softer food, and degraded his magnificent
chewing apparatus. By the end of his reign, his molars and jaw had shrunk to
almost that of modern man.

The
culmination of man’s evolution was Homo sapiens (archaic). It has been
downhill ever since. He came about 300,000 years ago, straight and tall,
muscular, hardened and practical, with almost a full size brain, the result
of four million years of evolution. Humankind was now a veteran of millions
of deaths and countless hardships, with a population so small that mutations
spread rapidly. His gene pool had little variability. Natural selection
(death and misery) had kept him pared. Only the strongest, the most cunning,
and the most stubborn survived.

Then
came modern man, an anticlimax, about 120,000 years ago. From this point on
his inventive mind would devise method after method to ease his lot. He would
remove his enemies without compassion. He would learn to enslave other
animals and even other men. He would greedily take from the world around him
and from those who were weaker. He would make his life easier, and evolution
would degrade him to match.

The Neandertal

Concluding
this story without giving tribute to an enigma in our history would not be
proper. The Homo sapiens neandertalensis does not quite fit in our
story. They probably came from far northern Europe, the descendants of an
ancient Homo erectus tribe, a tribe that had migrated to that region
many hundreds of thousands of years before. They had many physical characteristics
of the modern Eskimo, who is well tuned to arctic living. They were stocky,
almost massive, in build. The males were about 5’6″ tall but they were
much heavier and stronger than modern man. They had the large pronounced
cheeks usually associated with cold weather adaptation. They walked as
erectly as modern man. Their tools paralleled the coexisting Homo sapiens
sapiens
, but it is not known who copied. Although lacking a forehead,
they had brains that averaged 1450cc, about 8% larger than modern man. They
were the first to bury their dead, complete with flowers and artefacts. Were
they cunning beasts? Or were they gentle and intelligent people? And what
happened to them? Were they of the same species and their genes disappeared
into a much larger pool? Or, (the most likely) did they get in the way of the
early Homo sapiens sapiens and were simply exterminated? Late evidence
in a study of the DNA from fossil remains seems to indicate that the neandertal
was not assimilated into the gene pool of modern man.

How
Evolution Works

Mutations
are accidents in reproduction. The only place where such mutations can occur
is in the production of the haploid cells (cells with a single set of
chromosomes) in the sperm and egg, or in the joining of the two in conception.
A reproduction accident anywhere else in the body will affect only the cell
that suffers the accident. Such accidents will not be added into the gene
pool and thus are not mutations. In such an accident, the sick cell is
quickly replaced by a well one and the incident is over. Yet when such an
accident occurs in the sperm or egg, it will appear in every cell in the
offspring. This mutation then has a 50% chance of occurring in each
grandchild. If the recipient of the mutation has several children, the odds
are that the mutation will join the species gene pool by way of one or more
of his children.

Natural
selection then determines the fate of the mutation in the species gene pool.
The test is not survivability or excellence. The test is in species population
growth. If the mutation aids the growth of the species population then it is
successful and will remain in the gene pool. If it does not, natural
selection will remove it from the gene pool (through death and hardship).

Instinct and Intelligence

What
is instinct? It is the driving force in the behaviour of an organism and is
directly determined by genetic code. Early single-cell organisms, billions of
years ago, developed sensors to detect light and an instinct to swim toward
that light. Others developed poison darts and sensors to tell when another
organism was near. When their sensors said that something was near, their
instinct fired the darts to obtain a meal. With the development of sexual
reproduction, the instinct of sexual desire provided the drive for
reproduction.

The
northern pike is a fish in the lakes of northern North America. It is a
predator. If one is placed in a tank of water and a smaller fish tossed into
the tank, the pike will quickly eat it. If two fish of equal size are tossed
into the pond, it will eat the closest one first. If the two fish are of
unequal size but are placed in the tank equally far from the pike, it will
eat the largest first. If the larger one is farther away, it will still eat
the larger one first up to a certain distance differential. If the larger one
is too far away, it will eat the small one first. It judges the relative
distance of the two fish, juggles that with the size of the fish, and then
optimizes his chance for the most food. This is called reasoning. Yet the
pike can be raised in isolation and it will still do this. This is called
instinct. The parameters of the calculation are fixed in his genetic
description.

Reasoning
of this type in man is indistinguishable to him from intellectual reasoning.
The reasoning mechanism is fixed and is the same one used in both cases. The
only difference in the process is that intellectual reasoning follows a
learned process (program) stored in a learning memory (RAM). The pike follows
a process (program) stored in fixed memory (ROM). Most reasoning by man,
which he considers to be intellectual, is not intellectual at all. All
cultural (emotional) interactive reasoning processes are of the fixed type,
embedded eons ago. Modern data may be fed into these processes from memory or
senses, but the process is instinctive. Anything involving mother love or
sex, for example, will be reasoned following ancient fixed processes.

The
long term result of evolution is bare survival. If the organism is in
distress, the higher death rate removes survival impediments rapidly. An
organism suffering a high mortality rate tends to become stronger to match
its environment. If the organism is better than required, evolution will
degrade it, again matching the organism with the environment. A comfortable
organism has a lower death rate and so does not weed out detrimental
characteristics as quickly. The result is a gradual degradation of function
until the comfort is removed.

Now
back to the pike, with that in mind:

If
the pike is successful in his environment, he will not develop any further
intelligence. He does not need it. It would be of no value to him. If the
environment becomes harsher, he will either develop offsetting ability or
perish. Still, what is the most likely change? He already knows how to hunt.
He does not have a hand to hold a weapon and has no need to understand
Shakespeare. Bigger teeth, a sleeker body for speed, or a quicker reaction
time would solve his problem far better and quicker than a higher IQ. Look at
a pike. He has been gaining those features for millions of years. Pound for
pound there is not a better killing machine on earth (well, maybe with man as
an exception).

Evolution,
through the liberal application of death and hardship, had built a strong
body and a sound mind by the time of the appearance of Homo sapiens
sapiens
. Both were designed for entirely different environments than
experienced by man today. We live longer today for three reasons.

One is our
health care and diet. The second is that our bodies were constructed to last
thirty years under brutally harsh conditions. Removal of those harsh
conditions allows a longer life span. Third is our culture. We cheat
evolution of the deaths that it needs to cleanse the gene pool. In the short
run we will live longer. Eventually mutations will erase these benefits.
Evolution seeks to have us hanging over the edge.

In
modern society, survivability is no longer dependent on the condition of the
mind. In fact, the more successful tend to have fewer children. Mutations
that distort the function or size of the brain are no longer removed by
natural selection from the gene pool. The enormous size of the population
slows the spread of adverse mutations across the gene pool, but if no one
dies of their adverse effects before he has his offspring, alleles from
adverse mutations will accumulate.

The Evolution of the Brain

Any
mutation must be applied to a DNA coding that already exists. It cannot be
applied to coding that does not exist. Is this a silly statement? Not at all.
It leads to the way that evolution changes an organism. Mutations are always
applied to the existing DNA coding. Evolution makes something new out of
something that already exists. If a bear becomes distressed in a given
environment, it does not sprout wings and fly. Instead, such things as longer
legs or claws will be tested. Also, evolution often does not fix the thing
that causes a problem, it patches the problem by doing something unrelated.
If an organism suffers a mutation that shortens its life so that it has
difficulty rearing its children to childbearing age, that mutation will start
being culled from the gene pool. Before that mutation has been completely
removed from the gene pool, another mutation may occur which shortens the
gestation period or child development period. If this shortens the child
caring requirements enough so that the shortened life is no longer a problem,
then both mutations would be acceptable as permanent residents in the gene
pool.

One
must remember that every cell in the human body can perform any function. Two
copies of the entire genome are in every cell. A cell that is in the liver
chooses to do that function. The cells in bone or in the brain choose to do
those functions. When a mutation happens, it is either to the inner function
of a cell, or to the size and shape of the overall cell structure (such as a
skull, heart, etc.).

The
brain did not start with man; there were many examples of single cells that
had simple versions billions of years before the first hominid appeared.
Photosynthesis requires light. If a cell that depended on light drifted too
low in the water or drifted under a land overhang that obscured the sun, it
was in deep trouble. Some developed a light sensor and a method of swimming.
For the system to work, they developed a central control system that would
judge the amount of light and if it was insufficient would turn the cell
toward the light source and swim in that direction. It would keep swimming
until it was bathed with sufficient light. This was all done within a single
cell organism. That early cell had memory (what am I supposed to do?), and
reason (which way do I swim?).

Early
animals developed cells that connected their various muscles to the central
control area. Commands from the brain drive the muscles through these nerve
cells. Every cell in an organism carries all of the information in its DNA
for the entire organism. Each cell is a universal cell and can provide any
service in the body of the organism. Evolution constructed the nerve cell
from the standard cell. It also constructed nerve cells that connect the
various sensors (ears, eyes, nose, and skin) to the central control area.

These nerve cells carried sensor information
to the brain. Further cell adaptations in the central control area provided
functional links. If the ears hear a loud bang then tell the leg muscles
to jump the other way
. If the stomach says it is hungry, go bite
something
.

We refer to these permanent fixed processes as instincts.
Still, the DNA cannot foresee all possible contingencies. It must allow some
leeway. No animal is totally instinctive. All animals have some memory, some
reasoning ability, and some decision making ability. We differ only in
degree. The first hominid had all of the neural elements that we have today,
as do the chimp and your pet poodle. The mutations that built our brain from
that first hominid were more about quantity, shape, and organization than in
substance.

The thing we must remember is that africanus had
a 450cc brain. We now have a 1350cc brain. That africanus brain is
still in there. Evolution patches over. It does not do housecleaning.

Another thing to remember is that evolution has a zero IQ.

It was not being intelligent when it formed the
rest of our brain. It was much more interested in the sex life of our DNA.

Even
that is not the whole story. Africanus was largely instinctive. Most
of the add-ons to his brain have been intellectual. Those original instincts
were strong and uniform. Evolution saw to that. His world was brutally
uniform and required full time participation. Any deviant individual behaviour
would affect the birth-rate. Evolution would not tolerate it. His instincts
were well maintained.

Intelligence
is always at odds with instinct. If the instinct provided proper survival
action, there would be no need for intelligence. Indeed this is the case with
all of the other animals. There are literally thousands of species that
survive quite well with little intellectual ability. Intelligence is supposed
to override instinct to provide action that is more suitable. That is why we
got it in the first place. By controlling our instincts we could provide
action that enhanced our survivability. A little self-discipline provided
great survival dividends, and it worked. Man has conquered the world. He is
the fat cat. He is on top of the heap. Yet now, peak intellectual performance
and self-discipline are no longer requirements for survival. Man has become
self-indulgent and has reverted to satisfying his instincts.

That
is why today we act like africanus though we have a 1350cc brain. Africanus
would object loudly to that statement, because that statement is not quite
true. We would not live an hour in his environment. We have reverted to his instinct,
that is true, but those instincts are now perverted. Through discipline, man
substituted intelligence for instinct over a long period. During that time
the instincts suffered mutations. Since both the original instincts and their
mutations were being overridden by intelligence, the instinct mutations were
not considered detrimental by evolution and so accumulated in the gene pool.

We have now reverted to a set of perverted
instincts and now cater to those perversions by calling them normal. We
excuse behavior now that would horrify africanus.

http://www.onelife.com/evolve/manev.html

big bang theory research

The timeline of human evolution outlines the major events in the development of human species, and the evolution of humans’ ancestors. It includes a brief explanation of some animals, species or genera, which are possible ancestors of Homo sapiens. It presents a possible line of descendants that led to humans. This timeline is based on studies from palaeontology, biology, morphology and from anatomical and genetic data. The study of human evolution is a major component of anthropology. The line of descent of Homo sapiens (modern humans) is as follows:

First living beings

Date

Event

4000 million years ago) The earliest life appears

3900 Ma

Cells resembling prokaryotes appear. This marks the first appearance of photosynthesis and therefore the first occurrence of large quantities of oxygen on the earth.

2500 Ma

First organisms to use oxygen. By 2400 Ma, in what is referred to as the Great Oxygenation Event, the pre-oxygen anaerobic forms of life were wiped out by the oxygen consumers.

2100 Ma

More complex cells appear: the eukaryotes.

1200 Ma

Sexual reproduction evolves, leading to faster evolution.

900 Ma

The choanoflagellates may look similar to the ancestors of the entire animal kingdom, and in particular they may be the direct ancestors of Sponges. Proterospongia (members of the Choanoflagellata) are the best living examples of what the ancestor of all animals may have looked like.They live in colonies, and show a primitive level of cellular specialization for different tasks.

600 Ma

It is thought that the earliest multi-cellular animal was a sponge-like creature.

Sponges are among the simplest of animals, with partially differentiated tissues.

Sponges (Porifera) are the phylogenetically oldest animal phylum extant today.

580 Ma

Animal movement may have started with cnidarians. Almost all cnidarians possess nerves and muscles. Because they are the simplest animals to possess them, their direct ancestors were very likely the first animals to use nerves and muscles together. Cnidarians are also the first animals with an actual body of definite form and shape. They have a circular symmetry. The first eyes evolved at this time.

550 Ma

Flatworms are the earliest animals to have a brain, and the simplest animals alive to have two sided symmetry. They are also the simplest animals with organs that form from three germ layers.

540 Ma

Acorn worms are considered more highly specialised and advanced than other similarly shaped worm-like creatures. They have a circulatory system with a heart that also functions as a kidney. Acorn worms have a gill-like structure used for breathing, a structure similar to that of primitive fish. Acorn worms are thus sometimes said to be a link between vertebrates and invertebrates.

Chordates

530 Ma

Pikaia is an iconic ancestor of modern chordates and vertebrates.  The lancelet, still living today, retains some characteristics of the primitive chordates. It resembles Pikaia.

505 Ma

The first vertebrates appear: the ostracoderms, jawless fish related to present-day lampreys and hagfishes. Haikouichthys and Myllokunmingia are examples of these jawless fish, or Agnatha. They were jawless and their internal skeletons were cartilaginous. They were precursors to the Osteichthyes (bony fish).

480 Ma

The Placodermi were prehistoric fishes. Placoderms were the first of the jawed fishes, their jaws evolving from the first of their gill arches. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked.

410 Ma

The first coelacanth appears; this order of animals had been thought to have no extant members until living specimens were discovered in 1938. It is often referred to as a living fossil.

Tetrapods

390 Ma

Some fresh water lobe-finned fish (Sarcopterygii) develop legs and give rise to the Tetrapoda. The first tetrapods evolved in shallow and swampy freshwater habitats. Primitive tetrapods developed from a lobe-finned fish with a two-lobed brain in a flattened skull, a wide mouth and a short snout, whose upward-facing eyes show that it was a bottom-dweller, and which had already developed adaptations of fins with fleshy bases and bones. The “living fossil” coelacanth is a related lobe-finned fish without these shallow-water adaptations. These fish used their fins as paddles in shallow-water habitats choked with plants and detritus. The universal tetrapod characteristics of front limbs that bend backward at the elbow and hind limbs that bend forward at the knee can plausibly be traced to early tetrapods living in shallow water.

Panderichthys is a 90–130 cm (35–50 in) long fish from the Late Devonian period (380 Mya). It has a large tetrapod-like head. Panderichthys exhibits features transitional between lobe-finned fishes and early tetrapods. Lungfishes retain some characteristics of the early Tetrapoda. One example is the Queensland Lungfish.

375 Ma

Tiktaalik is a genus of sarcopterygian (lobe-finned) fish with many tetrapod-like features. It shows a clear link between Panderichthys and Acanthostega.

365 Ma

Acanthostega is an extinct amphibian, among the first animals to have recognizable limbs. It is a candidate for being one of the first vertebrates to be capable of coming onto land. It lacked wrists, and was generally poorly adapted for life on land. The limbs could not support the animal’s weight.Acanthostega had both lungs and gills, also indicating it was a link between lobe-finned fish and terrestrial vertebrates.

Ichthyostega is an early tetrapod. Being one of the first animals with legs, arms, and finger bones, Ichthyostega is seen as a hybrid between a fish and an amphibian. Ichthyostega had legs but its limbs probably weren’t used for walking. They may have spent very brief periods out of water and would have used their legs to paw their way through the mud.

Amphibia were the first four-legged animals to develop lungs. Amphibians living today still retain many characteristics of the early tetrapods.

300 Ma

From amphibians came the first reptiles: Hylonomus is the earliest known reptile. It was 20 cm (8 in) long (including the tail) and probably would have looked rather similar to modern lizards. It had small sharp teeth and probably ate millipedes and early insects.

Evolution of the amniotic egg gives rise to the Amniota, reptiles that can reproduce on land and lay eggs on dry land. They did not need to return to water for reproduction. This adaptation gave them the capability to colonize the uplands for the first time. Reptiles have advanced nervous systems, compared to amphibians. They have twelve pairs of cranial nerves.

Mammals

256 Ma

The earliest mammal-like reptiles are the pelycosaurs. The pelycosaurs were the first animals to have temporal fenestra. Pelycosaurs are not Therapsids but soon they gave rise to them. The Therapsida were the direct ancestor of mammals.

220 Ma

One sub-group of therapsids, the cynodonts evolved more mammal-like characteristics.

The jaws of cynodonts resemble modern mammal jaws. It is very likely this group of animals contains a species which is the direct ancestor of all modern mammals.

From Eucynodontia (cynodonts) came the first mammals. Most early mammals were small and shrew-like animals that fed on insects. Although there is no evidence in the fossil record, it is likely that these animals had a constant body temperature and milk glands for their young. The neocortexregion of the brain first evolved in mammals and thus is unique to them.

Monotremes are an egg laying group of mammals represented amongst modern animals by the platypus and spiny anteaters.

100 Ma

Common genetic ancestor of mice and humans (base of the clade Euarchontoglires).

Primates

65–85 Ma

A group of small, nocturnal and arboreal, insect-eating mammals called the Euarchonta begins a speciation that will lead to the primate species, tree shrew and flying lemur orders.

40 Ma

Primates diverge into suborders Strepsirrhini (wet-nosed primates) and Haplorrhini (dry nosed primates). Strepsirrhini contain most of the prosimians; modern examples include the lemurs and lorises. The haplorrhines include the three living groups: prosimian tarsiers, simian monkeys, and apes. One of the earliest haplorrhines is Teilhardina asiatica, a mouse-sized, diurnal creature with small eyes. The Haplorrhini metabolism lost the ability to make its own Vitamin C. This means that it and all its descendants had to include fruit in its diet, where Vitamin C could be obtained externally.

30 Ma

Haplorrhini splits into infraorders Platyrrhini and Catarrhini. Platyrrhines, New World monkeys, have prehensile tails and males are colour blind.

25 Ma

Catarrhini splits into 2 superfamilies, Old World monkeys (Cercopithecoidea) and apes (Hominoidae). Our trichromatic color vision had its genetic origins in this period.

Hominidae

15 Ma

Hominidae (great apes) branched out from the ancestors of the gibbon (lesser apes).

13 Ma

Homininae ancestors brach out from the ancestors of the orangutan.  Pierolapithecus catalaunicus is believed to be a common ancestor of humans and the great apes or at least a species that brings us closer to a common ancestor than any previous fossil discovery. Pierolapithecus had special adaptations for tree climbing, just as humans and other great apes do: a wide, flat ribcage, a stiff lower spine, flexible wrists, and shoulder blades that lie along its back.

10 Ma

Hominini speciate from the ancestors of the gorillas.

7 Ma

Hominina speciate from the ancestors of the chimpanzees.

4.4 Ma

Ardipithecus is a very early hominind genus (subfamily Homininae). Ardipithecus ramidus, which lived about 4.4 million years ago during the early Pliocene. Ardipithecus lived largely in the forest where it competed with other forest animals for food, including the contemporary ancestor for the chimpanzees. Ardipithecus was likely bipedal as evidenced by its bowl shaped pelvis, the angle of its foramen magnum and its thinner wrist bones, though its feet were still adapted for grasping rather than walking for long distances.

3.6 Ma

Some Australopithecus afarensis left human-like footprints on volcanic ash in Laetoli, Kenya (Northern Tanzania) which provides strong evidence of full-time bipedalism. Australopithecus afarensis lived between 3.9 and 2.9 million years ago. It is thought that A. afarensis was ancestral to both the genus Australopithecus and the genus Homo. Compared to the modern and extinct great apes, A. afarensis has reduced canines and molars, although they are still relatively larger than in modern humans. A. afarensis also has a relatively small brain size.

3 Ma

Loss of body hair takes place in the period 3-2 Ma, in parallel with the development of full bipedalism.

Homo

2.5 Ma

Appearance of HomoHomo habilis is thought to be the ancestor of the lankier and more sophisticated Homo ergaster. Lived side by side with Homo erectus until at least 1.44 Ma, making it highly unlikely that Homo erectus directly evolved out of Homo habilis.

1.8 Ma

Homo erectus evolves in Africa. Homo erectus would bear a striking resemblance to modern humans, but had a brain about 74 percent of the size of modern man. Its forehead is less sloping and the teeth are smaller. Other hominid designations such as Homo georgicusHomo ergasterHomo pekinensisHomo heidelbergensis are often put under the umbrella species name of Homo erectus.  Control of fire by early humans is achieved 1.5 Ma by Homo ergaster.Homo ergaster reaches a height of around 1.9 metres (6.2 ft). Evolution of dark skin, which is linked to the loss of body hair in human ancestors, is complete by 1.2 Ma.

1.2 Ma

Homo antecessor may be a common ancestor of humans and Neanderthals. At present estimate, humans have approximately 20,000–25,000 genes and share 99% of their DNA with the now extinct Neanderthal  and 95-99% of their DNA with their closest living evolutionary relative, the chimpanzees The human variant of the FOXP2 gene (linked to the control of speech) has been found to be identical in Neanderthals. It can therefore be deduced that Homo antecessor would also have had the human FOXP2 gene.

600 ka

Three 1.5 m (5 ft) tall Homo heidelbergensis left footprints in powdery volcanic ash solidified in Italy. Homo heidelbergensis may be a common ancestor of humans and Neanderthals. It is morphologically very similar to Homo erectus but Homo heidelbergensis had a larger brain-case, about 93% the size of that of Homo sapiens. The holotype of the species was tall, 1.8 m (6 ft) and more muscular than modern humans.

http://en.wikipedia.org/wiki/Timeline_of_human_evolution

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