archive: SETI Until this big black Monolith came along and...

SETI Until this big black Monolith came along and...

Larry Klaes ( lklaes@bbn.com )
Thu, 27 May 1999 11:39:35 -0400

HOMO SAPIENS CAME CLOSE TO EXTINCTION - SEVERAL TIMES

>From ABC News Online, 26 May 1999

http://abcnews.go.com/sections/science/DyeHard/dye990526.html

We Dodged Extinction

By Lee Dyw
Special to ABCNEWS.com

A worldwide research program has come up with astonishing evidence
that humans have come so close to extinction in the past that it's
surprising we're here at all.

Pascal Gagneux, an evolutionary biologist at the University of
California at San Diego, and other members of a research team studied
genetic variability among humans and our closest living relatives, the
great apes of Africa.

Humanoids are believed to have split off from chimpanzees about 5
million to 6 million years ago. With the passage of all that time,
humans should have grown at least as genetically diverse as our
"cousins." That turns out to be not true.

"We actually found that one single group of 55 chimpanzees in west
Africa has twice the genetic variability of all humans," Gagneux says.

"In other words, chimps who live in the same little group on the Ivory
Coast are genetically more different from each other than you are from
any human anywhere on the planet."

The Family Bush

"The family tree shows that the human branch has been pruned," Gagneux
says. "Our ancestors lost much of their original variability."

"That makes perfectly good sense," says Bernard Wood, the Henry R. Luce
Professor of Human Origins at George Washington University and an
expert on human evolution.

"The amount of genetic variation that has accumulated in humans is just
nowhere near compatible with the age" of the species, Wood says. "That
means you've got to come up with a hypothesis for an event that wiped
out the vast majority of that variation."

The most plausible explanation, he adds, is that at least once in our
past, something caused the human population to drop drastically. When
or how often that may have happened is anybody's guess. Possible
culprits include disease, environmental disaster and conflict.

Almost Extinct

"The evidence would suggest that we came within a cigarette paper's
thickness of becoming extinct," Wood says. Gagneux, who has spent the
last 10 years studying chimpanzees in Africa, says the implications are
profound.

"If you have a big bag full of marbles of different colors, and you
lose most of them, then you will probably end up with a small bag that
won't have all the colors that you had in the big bag," he says.

Similarly, if the size of the human population was severely reduced
some time in the past, or several times, the "colors" that make up our
genetic variability will also be reduced.

If that is indeed what happened, then we should be more like each
other, genetically speaking, than the chimps and gorillas of Africa.
And that's just what the research shows.

"We all have this view in our minds that we [humans] started
precariously as sort of an ape-like creature" and our numbers grew
continuously, adds Wood. "We're so used to the population increasing
inexorably over the past few hundred years that we think it has always
been like that." But if it had, Gagneux notes, our genetic variability
should be at least as great as that of apes.

A Stormy Past

Gagneux is the lead author of a report that appeared in the April 27
issue of the Proceedings of the National Academy of Sciences. The
study, carried out with researchers in Germany, Switzerland and the
United States, is the first to examine large numbers of all four ape
species in Africa.

"We can do that now because new technology allows us to non-invasively
take some hair, or even some fruit that these apes chew, and then we
get their DNA from a couple of cells that stick to a hair or a piece of
fruit they chewed."

Then they compared the DNA variability of apes and chimps to that of
1,070 DNA sequences collected by other researchers from humans around
the world. They also added the DNA from a bone of a Neanderthal in a
German museum. The results, the researchers say, are very convincing.

"We show that these taxa [or species] have very different amounts and
patterns of genetic variation, with humans being the least variable,"
they state. Yet humans have prevailed, even though low genetic
variability leaves us more susceptible to disease.

"Humans, with what little variation they have, seem to maximize their
genetic diversity," Gagneux says. "It's ironic," he notes, that after
all these years the biggest threat to chimpanzees is human intrusion
into their habitats. When he returned to Africa to study a group of
chimps he had researched earlier, Gagneux found them gone.

"They were dead," he says, "and I mean the whole population had
disappeared in five years." Yet as our closest living relatives, chimps
still have much to teach us about ourselves.

Copyright 1999, ABC News