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.
Yup. I think you are correct. However, there have been a number of 'thinning out' periods. There have been five worldwide catastrophies in the last 10k years alone, some refer to these as 'near extinction' events. The last one occurred in 540AD. Toba was the 'butt kicker' though.
Like a really big flood, maybe?
There is also no possible geological or meteorological mechanism for such an event.
There is some evidence, probably overhyped by the media, that a sudden flooding of the shores of the Black Sea from the Mediterranean may have been the source of the various Babylonian and Assyrian flood myths that eventually later made into the Bible as the Noah story, but this would still be a very localized event and couldn't possibly account for the human biodiversity bottleneck. Also, it's much too recent to be the bottleneck, anyway.
But that's not what I'm saying.
Let's set Jesus aside, and let's talk about the non-divine... did the Prophets or Disciples understand every aspect of Genesis, including what happened in the gaps that even a literal interpretation of thousands of years would have to concede?
And getting back to Jesus, did He tell all he knew about all things?
John Baumgardner (B.S, M.S., Ph.D (UCLA)) is a geophysicist employed at the Los Alamos National Laboratory in New Mexico. His work involves detailed computer modeling of the structure and processes of the earth's interior, as well as a variety of other fluid dynamics phenomena. --------------------------------------------------------------------------------
Q: DR Baumgardner, some say that because of continental drift (the idea that the continents have broken apart and moved thousands of miles) one has to believe in 'millions of years'.
JB: Well, I believe there is now overwhelming evidence in favour of continental break-up and large-scale plate tectonic activity. The acceptance of these concepts is an amazing example of a scientific revolution, which occurred roughly between 1960 and 1970. However, this revolution did not go far enough, because the earth science community neglected and suppressed the evidences for catastrophism large-scale, rapid change throughout the geological record. So the timescale the uniformitarian scientists today are using is dramatically too long. The strong weight of evidence is that there was a massive catastrophe, corresponding to the Genesis Flood, which involved large and rapid continental movements. My conclusion is that the only mechanism capable of producing that scale of catastrophe and not wrecking the planet in the process had to be internal to the earth.
I am persuaded it involved rapid subduction (sinking) of the pre-Flood ocean floor, pulling the 'plates' apart at the beginning of the Flood, and was probably associated with the breaking up of the 'fountains of the great deep' described in Scripture.
A 1993 New Scientist article spoke highly of your 3-D supercomputer model of plate tectonics.
JB: There are to my knowledge three other computer codes for modeling the earth's mantle and so on, in the world. These other three use a mathematical method not so well suited for the modern parallel supercomputers. The one I developed uses the finite element technique and performs very well on the new, very large supercomputers. So, many of my colleagues are recognizing it as the most capable code in the world.
Last year NASA funded this effort as one of the nine grand challenge projects for the next three years in their High Performance Computing and Communication initiative, and are supporting two post-doctoral researchers to collaborate with me to improve it, and apply it to study the earth.
This code is comparable to what are called general circulation models for the atmosphere and oceans, which are some of the largest codes in the world in terms of how much machine power they consume. It's got lots of physics in it to model the details of the mechanical behaviour of the silicate rock inside the earth. My present focus is to make the representation of the tectonic plates even more realistic. So the code is in an ongoing state of development, but it's come a long way in the last 15 years.
We understand you've shown that as these floating blocks of rock push down into the material below, things get hotter, so the 'slipperyness' increases and there's a runaway effect. The faster they sink the hotter they get, so the faster they can sink.
JB: Yes rock that represents the ocean floor is colder, and therefore denser than the rock below it and so can sink into the earth's interior. And the properties of the rock inside the earth, especially at the high temperatures that exist there, make it possible for the colder rock from the earth's surface to peel away and sink in a runaway manner down through the mantle very rapidly.
So this 'happens' on your computer model all by itself, from the laws of science over a short time-scale, not millions of years?
JB: That's correct. Exactly how long is something I'm working to refine. But it seems that once this sinking of the pre-Flood ocean floor (in a conveyor-belt-like fashion down into the earth, pulling things apart behind it) starts, it is not a slow process spanning millions of years it's almost certain that it runs to completion and 'recycles' all of the existing floor in a few weeks or months.
You're part of a team of top creation scientists3 which is developing a model of catastrophic plate tectonics based on this mechanism, which believes the continents broke up (from a single landmass) during, not after the Flood as some have proposed.
JB: Yes. There is compelling evidence from the fossil-bearing sediments on the continents that the breakup occurred during the time these sediments were being deposited. We are convinced that this 'continental sprint' as it's been called, was during the time of the Flood, and part of the mechanism for it.