Tuesday, October 6, 2009

Evolution: Stealing examples from Dawkins

I've been reading Richard Dawkins' new book 'The Greatest Show on Earth: The Evidence for Evolution' and, I have to say, it is an excellent piece of popular science writing.

Evolution is both simple and complex at the same time - when you understand its complexity, the elegant simplicity shines through, When you misunderstand the simplicity, the complexity seems absurd. A tricky concept to get across.

What Dawkins does so well is to lead the reader through the thought-processes that are necessary to view evolution in the right context and you can tell that he's being very careful to minimize the quote-mine opportunities throughout the book.

A particular example, that I'd like to borrow and adapt, from the book is in dealing with 'transitional forms' in the fossil record; a creationist favourite!

Imagine a country where the voting age, drinking age, driving age and age at which you are tried as an adult in court are all 18. That will be our assumption.

So under-18s are kids and over-18s are adults. That's the best way we have for drawing a distinction between the two, and we have to draw a line somewhere because otherwise you'd have 4-year-olds behind the wheel and 40-year-olds being charged as a minor for crimes.

Now, does this mean that we actually think that kids magically turn into grownups at the stroke of midnight on their 18th birthday? No, of course not. We appreciate that they go through an adolescent phase that can run from 14 - 24, or 17-19 or, in some cases, from 21- 91! But we have to make that distinction for categorical purposes.

So, when creationists demand to see a transitional form in the fossil record, what they are asking for is our 'adolescent'. However, because of our need to categorize, any fossil we find will always fit into one category or another (unless it is distinct enough to form a new category of its own and then we just have two new 'adolescent' positions in the fossil record).

What creationists don't realize (or do realize, but lie about it) is that what they are actually demanding is that we provide them with the 'stroke of midnight' fossil as child-->adult. Of course, this fossil cannot exist; all we can provide is forms that straddle the line.

. . . . . . . l . . . . . . .

Let's say the dots to the far left is Species A and the far right is Species B. Scientists have drawn an imaginary line between the two which is, for all intents and purposes, arbitrary.

Now, a creationist comes along and says; 'where's the transitional form?' Scientists go looking and find the three specimens shown in purple, below;

. . . . . . . l . . . . . . .

The one to the left of the line has more in common with Species A and the two to the right of the line have more in common with Species B. These are transitional forms between Species A and Species B and we have these, in droves, for multiple lines of evolution covering almost every group of organisms know to have existed.

We could, if we looked long and hard enough, find all the 'missing' dots for this particular sequence...

Now here's the kicker.

These dots do not represent individuals, they represent populations of organisms, existing for tens of thousands of years, that can be said to be distinct enough from their neighbouring dots to be recognized as different. Each can just about inter-breed with the one next to it for a relatively short period of time (indeed, they must as that is the period where the one group diverges from the parent group) until speciation occurs and the two populations can no longer interbreed.

Even representing it like this is false because we have arbitrarily separated the populations into dots when, really, it should be a continuous line that gradually changes colour. Like the years of our child-->adult's life, we put an imaginary break at their birthday and say 'now you are 12' but they are almost no different to how they were yesterday and they will be almost no different tomorrow to how they are today. Yet, at some point, they stop being 'child' and become 'adult'. Can you point to the transitional age for a given person going from child-->adult?

The creationist's insistence on 'transitional forms' is founded in a misunderstanding of what the term means and how the process works. It is dishonest either way; to demand evidence for something you don't understand is ignorant, to demand evidence for something you willfully don't understand and have no intention of understanding is a flat-out lie.

I highly recommend Dawkins' book - he puts this stuff far more eloquently than I can.

Any questions, comments or clarifications are welcome.



zilch said...

Just what I need: another book I'll have to buy someday. Dawkins is indeed brilliant at thinking of imaginative ways of explaining biology and evolution. I especially liked his previous book The Ancestor's Tale, in which he inverts the Tree of Life, starting from humans, and going backwards in time until he reaches the next (known) branching point, all the way down to the LUCA, the last universal common ancestor.

ExPatMatt said...

I've not read that one, but having read TGSoE I might have to.

He's much better when he's talking biology than he was talking theology in the God Delusion. You can tell this is his forte and he relishes every nerdy detail!

zilch said...

Indeed. Dawkins and the late S.J. Gould are unexcelled at explaining evolution. I did enjoy The God Delusion, but in the end, it is, as Dawkins admitted, rather a screed than science.