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Knowing evolution August 3, 2007

Posted by Sharath Rao in contemplation, science.
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How well do you know something ?

Lets measure ‘grasp of a topic’ by how many minutes you can talk on the topic without prior research, prior notice and slides. The audience of course needs to be defined and this case let it consist of a handful of experts and utter (but open-minded) novices. Your talk should not leave the experts unconvinced of your grasp on the subject and not be completely incredulous to the novices either. ( I will not further complicate things by trying to define ‘serious’ and ‘incredulous’ πŸ™‚ ).

Anyway, from this rather loose definition of ‘grasp’, my grasp of the topic of “Evolution by natural selection” would be perhaps 3 minutes.

While I understand the mechanism of evolution to the first approximation, I have been fed up of my inability it to explain (mostly to myself) in a more substantial way. Yes, its a rather simple and appealing idea for those who are open to ideas such as these but I am really talking about knowing specific examples of evidence, having some domain knowledge (biology), knowledge of the history of the field, counter-examples (if any) and open problems and of course taking questions like – “When biologists say that humans and chimps have evolved from a common ancestor and this happened due to different adaptations in response to the environment (or lack thereof), then why were humans and chimpanzees found in the same geographical area ?” Or more stupidly, “Why are there chimpanzees at all – they should all have become human beings ?”, a question that lingers from my 6th standard class.

Of course, this is no doubting the theory, but merely acting agnostic in order that I can ask questions and seek answers. And thus I went to the Carnegie Library of Pittsburgh and borrowed a book – Ernst Mayr’s “What evolution is”. Now, Ernst Mayr is apparently one of the greatest biologists ever and I had not even heard of him – another necessary but insufficient criterion to knowing a field would be to know the leading lights of it. πŸ˜‰

Anyway, I have completed 3 chapters, but it might take more reading and more focussed at that, to push my grip to something like 30 minutes (by the above definition). I must admit that developing a feel for biology is hard and on second thoughts, I regret not having borrowed the book ‘Evolution for Dummies’ that was sitting alongside Mayr’s book. ( Remember that common grouse among high school students of 90s ( and most certainly even today ) is that biology is rather hard on facts and low on abstract, mathematical reasoning, as compared to er…physics or math ! )

Let us see how far I get but so far from my reading of Mayr’s book I have discerned that the evidence for evolution is so overwhelming (as say, quantum mechanics) that it is suggested that we stop calling it a ‘theory’.

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Comments»

1. Venu - August 5, 2007

If you haven’t tried out Dawkins, you definitely should.

The way I would explain the close proximity of chimps and humans is that at the time of speciation, the two groups were far apart, but after that period, wandering humans have made it over into chimp territories.

2. Sharath Rao - August 5, 2007

Yeah, I thought that would be an explanation – but wondered if its too obvious to be true ….maybe its like one of those things that are true because they are obvious πŸ™‚

3. Ed Darrell - August 6, 2007

Why not turn to the internet to find supplements to keep Mayr understandable?
Here’s one site at HHMI, which should open some other sites:
http://www.hhmi.org/genesweshare/e120.html

Here’s the Berkeley site, Understanding Evolution:
http://evolution.berkeley.edu/

And you should look for the website at the PBS site that accompanies the series “Evolution.” It’s got some nice stuff there that help illustrate what’s going on.

Best of luck to you.

4. kierenlythgow - August 6, 2007

There are different types of speciation. Allopatric speciation refers to geographical isolation of two populations whereas sympatric speciation occurs within the same location but the groups are separated through genetic divergence.

The Selfish Gene is definately worth a read.

5. Roads - August 6, 2007

Your question addresses some of the most critical observations in evolution.

Where the population of species is limited, for example in geographically disconnected communities within remote valleys or on isolated islands, then mutationary adaptations which are found to be favourable in that particular setting have a greater chance of spreading more rapidly throughout the local gene pool.

Eldredge and Gould termed such small environmental subsets ‘peripheral isolates’.

Over time, the successful spread of mutations within peripheral isolates can lead to the emergence of a population which is genetically different from the main gene pool. Depending upon the length of time, the degree of environmental separation and the size of the population within a peripheral isolate, this process can eventually extend through the development of different races and subspecies (which may still be able to interbreed following reconnection with the main population) to the development of new and entirely distinct species and genera.

This is the process which we see reflected today within the distinct faunas of isolated islands – both on the small scale of an individual Galapagos island, and on the relatively larger scale of Australia.

It was the observation and mapping of such faunal differences across the island chains of Indonesia which led Alfred Russel Wallace to propose the theory of natural selection, in turn encouraging Darwin belatedly to publish his own ideas within The Origin of Species.

Following reconnection of temporarily or more permanently isolated communities, for example during times of sea level fall when isolated islands are linked by the emergence of new land bridges, or as a result of plate tectonics (continental drift), in many cases there will be competition between the different populations as they mix and spread across the reconnected area.

Depending upon the different adaptations which may have developed, following reconnection it may still be possible for both communities successfully to co-exist (as was the case, at least until recently, with chimpanzees and humans), or it may be that either the old or the new population finds itself at a disadvantage to the other.

This may lead to the relatively abrupt wiping out of long-established lifeforms. It also answers one of the classic questions about evolution – namely if evolution is a gradual process which occurs over generations, then why do we typically not see intermediate forms ?

Because the qualities of any large and connected gene pool drift more or less together – all things being equal, then most adaptations will typically spread only very slowly because the gene pool is in equilibrium, most of the time.

In contrast to the slow evolutionary changes possible through gradualism, the process of isolation can be seen to be fundamental to evolution since it results in the creation of distinct subsets of the gene pool. Rapid (geologically instantaneous) and discrete evolutionary ‘jumps’ then occur when populations are reconnected.

This is the concept of ‘punctuated equilibria’ which so characterises the appearance of the fossil record – put simply, there are long periods when nothing much happens in evolutionary terms, and then suddenly new forms can appear and old ones disappear all within a short space of time.

http://en.wikipedia.org/wiki/Punctuated_equilibrium

http://en.wikipedia.org/wiki/Alfred_Russel_Wallace

6. Sharath Rao - August 8, 2007

@Roads : Thats a lot of information …answering questions that would have logically come up next …..thanks much for ur time !

@Ed : the berkeley site is real informative one…

7. 158. How evolution works « roads of stone - August 9, 2007

[…] from one species to another, then how can homo sapiens and chimpanzees co-exist ? That’s a classic question, and one which goes right to the heart of […]

8. Eats Wombats - August 14, 2007

Indeed, the evidence for evolution is overwhelming, which doesn’t mean that we fully understand all evolutionary processes. All of human history is said to be challenge and response. Evolution could be said to be environmental challenge and biological response.

Where species and populations diverge normally depends on environmental (physical separation) and, or ecological factors (e.g., eating different things).

The idea that we should stop calling it a theory is based on a misunderstanding of the idea of a scientific “theory”. People tend to think of a fact as something inconvertibly proved. In science nothing is ever proved with certainty. A theory is an explanation that is open to both falsification and to further refinement or even replacement by a better explanation. We don’t discuss a need to stop calling the theory of gravitation a theory.

9. Eats Wombats - August 14, 2007

BTW http://scienceblogs.com/pharyngula/ is a good blog to have a look at if you want to see some cut and thrust between science and ignorance.

A good number of scientists, including PZ Myers whose blog it is, are atheists, but in fact God and evolution are not incompatible. There are plenty of evolutionary biologists who believe in God and who support the separation of church and state.

Ken Miller (a Catholic biologist) demolishing Intelligent Design

10. eyw (decaffeinated) - August 17, 2007

I’m not going to pretend to know any more than you on this topic :)… althought I did give a 12-min presentation on crossover and mutation once..
I do think, however, that you’ll find Genetic Algorithms a fairly interesting topic to peruse whenever you get tired of biological text :). I’d say it’s the easiest way Evolution can steal a computer engineer’s heart πŸ™‚ Having written up a few of these programs myself, I’m an unquestioning believer. It may also help you whet some of your mathematical appetite.

11. Sharath Rao - August 17, 2007

Bingo ! I admit that my intuition for evolution came from my exposure to machine learning algorithms πŸ˜‰


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