Skip to comments.We Dodged Extinction
Posted on 01/29/2002 7:23:19 PM PST by Sabertooth
We Dodged Extinction
Pruned Family Tree Leaves Little Genetic Variety
Just one group of chimpanzees can have more genetic diversity than all 6 billion humans on the planet. (Corel)
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 its surprising were 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 branch lengths illustrate the number of genetic differences, not only between species, but among species as well. The pruned bush for humans shows how little genetic diversity exists. (Marco Doelling/ABCNEWS.com)
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 youve 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 anybodys guess. Possible culprits include disease, environmental disaster and conflict.
The evidence would suggest that we came within a cigarette papers 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 wont 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 thats 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. Were 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.
Its 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.
Lee Dyes column appears Wednesdays on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.
Running for cover.
Fear not. I have nearly perfect my race of atomic supermen.
We will protect you sub-norms.
It's okay. Evolution believes in you.
Guess they never heard of Noah.
That's nice. :)
Gee, brilliant, incisive argument there.
They have, of course, but the problem is there isn't a scrap or shred of evidence, or any logical mechanism, for a simultaneous world-wide flood.
Most likely candidate I've seen for the cause of the almost-extinction was the eruption of the Supervolcano Toba in Indonesia 70,000 years ago...the last Supervolcano to have erupted.
You haven't considered all of the ramifications of the article I sent...
And the LORD said unto Noah, Come thou and all thy house into the ark; for thee have I seen righteous before me in this generation.
Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.
Of fowls also of the air by sevens, the male and the female; to keep seed alive upon the face of all the earth.
For yet seven days, and I will cause it to rain upon the earth forty days and forty nights; and every living substance that I have made will I destroy from off the face of the earth.
And Noah did according unto all that the LORD commanded him.
And Noah was six hundred years old when the flood of waters was upon the earth.
And Noah went in, and his sons, and his wife, and his sons' wives with him, into the ark, because of the waters of the flood.
We almost dodged extinction in that story too.
Well in the Flood story there were eight people left after the flood to populate the world, but only two chimps. I wonder how that would explain the chimps having more genetic diversity when they started with a smaller gene pool in the first place. The Noah story helps not a bit here . . . sorry.
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