Tuesday, February 15, 2005

Evolutionary timescales

One of my colleagues complained today that my blog has been "all about money" lately, and needed a dose of science :-)

Below is a comment I posted to biophysicist Carson Chow's blog recently:

"The process of evolution has been experimentally verified without question. But has anyone shown that humans could have evolved from complex molecules in the time allowed? (e.g., age of the universe = 10 Gyr?) I think the best claim a creationist (or "intelligent design" enthusiast or whatever) could make is that, sure, evolution works, but without a hidden push every now and then there has not been enough time to achieve the observed complexity of the biological world. Since we can't really estimate the necessary timescales from what we currently know, we can't rule out this possibility.

I once asked a well-known evolutionary biologist at Harvard about this, and was stunned to realize he didn't understand my question. He gave me a BS answer about the observed mutation rate being fast enough to explain the observed complexity of life, but I don't see how anyone could justify that.

Of course Occam's razor suggests that evolution alone is capable of producing humans in the allotted time, but that is not yet verifiable scientifically."

Does anyone want to make a counter-claim? What scientific progress will be necessary for us to be very confident in a quantitative sense that genetic drift + natural selection are enough to explain the incredibly optimized eyes, brains, leaves, tendrils, web-spinners, etc. in the natural world? How about to conclude that 10^{100} years is more than enough time? (Remember, we have to start with molecules and understand the timescales required to get to simple cells (but with genetic coding), then to multicellular beasts, and eventually to Angelina Jolie :-)
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11 comments:

Anonymous said...

There was a time I could have written to Ernst Mayr and asked; no more. I suspect the answer may rest in understanding the evolution acts not on a molecular or cellular level, but on the organism. So, evolution is faster than a physicist or chemist might so carefully anticipate. But, I will read and think and ask and possibly there will be an answer in time :)

Anne

11:38 AM
Anonymous said...

Since you are taking requests :), there are the arts. There really are.

Anne

11:39 AM
Anonymous said...

Well, biology is a beginning :)

Anne

11:39 AM
Anonymous said...

You are correct, that is the best claim a creationist or Intelligent Design aficionado could make. (And most of them have not even done that well.)

But hey, even if someone came up with a compelling argument that, statistically, something like 10^100 years would be required, you could just invoke the string theory "landscape" of vacua and the anthropic principle to smooth all that over.

12:25 PM
Steve Hsu said...

Anne: the hypothesis we would like to disprove is that there is something beyond natural selection at work (an "invisible hand"). If the hypothesis were correct, then Mayr's hard-won intuition would be way off, as he would be seeing the results of the invisible hand, rather than natural selection. This is a quantitative question, so Mayr telling me something like "I've looked at a lot of snails, and there has detfinitely been enough time for humans to evolve" doesn't really answer the question.

Art, huh? I'm not sure whether to inflict on anyone my thoughts on such subjects :-)

Abyss: that's trader, not quant :-)

3:49 PM
Anonymous said...

Ah. There is the reason you are puzzling. Then there must be consideration of the distinct nature of biology in which evolution of organisms can not be experimentally duplicated while another way round is found to add to our understanding of the mechanisms and path.

Anne

6:03 PM
Carson C. Chow said...

You can be even more precise. We know the mutation rates of DNA so we can calculate how long it would take say a bacteria to adapt to a change in the environment like the appearance of a toxin like oxygen. If you do a simple minded calculation you find that there is not enough time if say three mutations are required to adapt for an averaged sized colony (that's why the triple AIDS cocktail works).

There are ways out though. For example, mutation rates do not have to be constant in time or throughout the genome. When an organism is stressed it could up the mutation rate. There are also effects of horizontal gene transfer that can speed things up. The bottom line is that you cannot separate molecular biology from natural selection if you wanted to make such an estimate.

8:27 PM
Anonymous said...

"The bottom line is that you cannot separate molecular biology from natural selection if you wanted to make such an estimate."

But, how would this lead to a proper estimate?

Anne

9:04 PM
Anonymous said...

I must think about Carson's interesting comment carefully. But, why should evolution be "smooth?" What am I missing, Carson?

9:10 PM
Carson C. Chow said...

Hi Anne,

No one knows how to make the estimate but if one were made, constraints from molecular biology such as the average mutation rate must be included.

I'm not sure what you mean by smooth. However, on that thought, if you only look at the genome and followed the phylogenetic tree, my bet is that the transition from species to species looks much more seamless at the genome level. We'll only know for sure when we sequence many more organisms. Thus speciation per se may not be as fundamental a process as is commonly believed. Organisms basically shuffle their genetic material either through sex or gene transfer with some background mutation on top. If this continues long enough, you could say speciation took place although there was not a single event when this happened.

10:46 PM
Anonymous said...

Carson Chow:

I'm not sure what you mean by smooth. However, on that thought, if you only look at the genome and followed the phylogenetic tree, my bet is that the transition from species to species looks much more seamless at the genome level. We'll only know for sure when we sequence many more organisms. Thus speciation per se may not be as fundamental a process as is commonly believed. Organisms basically shuffle their genetic material either through sex or gene transfer with some background mutation on top. If this continues long enough, you could say speciation took place although there was not a single event when this happened.

Wow! How splendid you are....

Anne

8:05 PM

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