Re: Beyond stones and bones

On May 5, 10:46 am, Peter Pan <peterpan55...@xxxxxxxxx> wrote:
http://www.msnbc.msn.com/id/17542627/site/newsweek/page/2/

"Fossils never resolved when the lineages split. DNA might. Human DNA
and chimp DNA differ by no more than 1.2 percent, and DNA changes at a
fairly regular rate. That lets scientists use this rate to calibrate a
"molecular clock" whose tick-tocks measure how long ago a genetic
change occurred. The fact that the DNA of living chimps and humans
differ by about 35 million chemical "letters," for instance, implies
that the two lineages split 5 million to 6 million years ago. That
fits with the discovery that Earth became cruelly colder and drier 6.5
million years ago, just the sort of climate change that coaxes new
species into being. The apes that stayed in the forests hardly
changed; they are the ancestors of today's chimps. Those that ventured
into the newly formed habitat of dry grasslands had taken the first
steps toward becoming human.

Now the contentious part. In 2001, a team digging in Chad unearthed
what it claimed was the oldest fossil of an ancestor of humans but not
chimps. If so, it must have lived after the two lineages split.
Trouble was, Sahelanthropus tchadensis (nicknamed Toumai, the local
word for "child") lived close to 7 million years ago. The genetic
data, pointing to a human-chimp split at least 1 million years later,
suggest that Toumai is not the ur-hominid-the first creature ancestral
only to human and not our chimp cousins-after all.

If Toumai is not our ancestor, what is he doing with such a humanlike
face and teeth, which look like those of species 5 million years his
junior?

This is stunning fossil record confirmation of my
hypothesis that man and chimp did not have
a common ancestor, and it predates Peter
Pan, which does not exist.

"A 7 million-year-old hominid should be just starting to look
like a hominid, not have a trait you see so much later in the fossil
record," says paleoanthropologist Bernard Wood of George Washington
University. Even if he is not our ancestor, Toumai is valuable because
he undermines the "begat" model of human evolution-that Toumai begat
Australopithecus who begat Homo habilis who begat Homo erectus who
begat Homo sapiens. That model assumes that each biological
innovation, whether bipedality or a large brain or any other, evolved
only once and stuck.

Instead, evolution played Mr. Potato Head, putting different
combinations of features on ancient hominids then letting them vanish
until a later species evolved them. "Similar traits evolved more than
once, which means you can't use them as gold-plated evidence that one
fossil is descended from another or that having an advanced trait
means a fossil was a direct ancestor of modern humans," says Wood.
"Lots of branches in the human family tree don't make it to the
surface."

In fact, starting 4 million years ago half a dozen hominids belonging
to the genus Australopithecus called Africa home. Best-known for the
fossil named Lucy, which was discovered in 1974, Australopithecus
afarensis had apelike features such as a large jaw and jutting face,
and probably scrambled up trees for safety and shelter. But she also
strode the grasslands erect, a hallmark of modern humans. Footprints
preserved in volcanic ash 3.6 million years old are mute testimony to
how one larger afarensis and a smaller companion-woman and mate, or
parent and child-walked across a plain in what is now Tanzania.

http://www.msnbc.msn.com/id/17542627/site/newsweek/page/3/

"And it helps explain why Lucy's kind were the way they were.
Afarensis women and men stood three to five feet tall and weighed 60
to 100 pounds. They had small teeth good for fruits and nuts, but not
meat. (The available prey was enough to make one a confirmed
vegetarian: hyenas the size of bears, saber-toothed cats and other
mega-reptiles and raptors.) That suggests that early humans were more
often prey than predators, says anthropologist Robert Sussman of
Washington University, coauthor of the 2005 book "Man the Hunted." The
evidence is as stark as the many fossil skulls containing holes made
by big cats and talon marks from raptors.

http://www.msnbc.msn.com/id/17542627/site/newsweek/page/4/

"The realization that early humans were the hunted and not hunters has
upended traditional ideas about what it takes for a species to thrive.
For decades the reigning view had been that hunting prowess and the
ability to vanquish competitors was the key to our ancestors'
evolutionary success (an idea fostered, critics now say, by the male
domination of anthropology during most of the 20th century). But prey
species do not owe their survival to anything of the sort, argues
Sussman. Instead, they rely on their wits and, especially, social
skills to survive. Being hunted brought evolutionary pressure on our
ancestors to cooperate and live in cohesive groups. That, more than
aggression and warfare, is our evolutionary legacy.

http://www.msnbc.msn.com/id/17542627/site/newsweek/page/5/

"Although erectus spread across Eurasia between 2 million and 1
million years ago, DNA makes clear that the species was almost
certainly a dead end and not our ancestor, as some scientists had
argued. According to this idea, groups of erectus scattered across the
Old World all accrued the same mutations and underwent the same
natural selection that led to Homo sapiens. The Y chromosome begs to
differ. The Y is passed intact from father to son; in that sense, it's
like a last name and so can be used to trace ancestries. But like
surnames that got Anglicized at Ellis Island, sometimes a Y changes,
with the altered version being passed to all male descendants. Peter
Underhill, a molecular anthropologist at Stanford University, tracked
160 such changes in the Y's of 1,062 men from 21 populations across
the world. Applying the molecular-clock technique, he concludes that
the most recent common ancestor of all men alive today lived 89,000
years ago in Africa. The first modern humans-and therefore, unlike the
earlier wave of Homo erectus into Asia a million years ago, the
ancestors of everyone today-departed Africa about 66,000 years ago.

These pilgrims were strikingly few. From the amount of variation in Y
chromosomes today, population geneticists infer how many individuals
were in this "founder" population. The best estimate: 2,000 men.
Assuming an equal number of women, only 4,000 brave souls ventured
forth from Africa. We are their descendants.

A curious thing about early Homo species is that they looked quite
human early on. "By 600,000 years ago everyone had a big brain, and by
200,000 years ago people in Africa looked like modern humans," says
archeologist Richard Klein of Stanford. "But there was no
representational art, no figurines, no jewelry until 50,000 years ago.
Some kind of cognitive advance was required, probably in language or
working memory. But since size hardly changed, the brain change that
produced behaviorally modern humans must have been in structure."

The source of such structural changes must come, like every aspect of
our physiology, from genes. Combing the genome for genes that emerged
just when language, art, culture and other products of higher
intelligence did, researchers have found three with the right timing.

The first, called FOXP2, plays a role in human speech and language,
but it must do something else in other species, because the decidedly
nonverbal mouse has a version of it. Using the standard molecular-
clock tactic, Svante Paabo and colleagues at the Max Planck Institute
estimate that the human version of FOXP2 appeared less than 200,000
years ago-about when anatomically modern humans stepped onto the world
stage-and maybe as recently as 50,000. If so, then it is only humans
as modern as those in the last diaspora out of Africa who developed
advanced, spoken language. Another gene with interesting timing is
microcephalin, which affects brain size. It carries a time stamp of
37,000 years ago, again when symbolic thinking was taking hold in our
most recent ancestors. The third, called ASPM and also involved in
brain size, clocks in at 5,800 years. That was just before people
established the first cities in the Near East and is well after Homo
sapiens attained their modern form. It therefore suggests that we are
still evolving."


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