Monday, June 18, 2012

Misunderstanding Evolution


From this curious unsatisfying essay by Philip Kitcher (and I wish I could remember who sent me there, but it was some time ago), which I shall respond to in detail at some point in the future (by which time he'll probably have forgotten he ever wrote it):

“A tale from the history of human biology brings out the point. John Arbuthnot, an eighteenth-century British physician, noted a fact that greatly surprised him. Studying the registry of births in London between 1629 and 1710, he found that all of the years he reviewed showed a preponderance of male births: in his terms, each year was a “male year.” If you were a mad devotee of mechanistic analysis, you might think of explaining this—“in principle”—by tracing the motions of individual cells, first sperm and eggs, then parts of growing embryos, and showing how the maleness of each year was produced. But there is a better explanation, one that shows the record to be no accident. Evolutionary theory predicts that for many, but not all, species, the equilibrium sex-ratio will be 1:1 at sexual maturity. If it deviates, natural selection will favor the underrepresented sex: if boys are less common, invest in sons and you are likely to have more grandchildren. This means that if one sex is more likely to die before reaching reproductive age, more of that sex will have to be produced to start with. Since human males are the weaker sex—that is, they are more likely to die between birth and puberty—reproduction is biased in their favor.”


This is the standard misunderstanding of how evolution works. It is very hard to avoid the language of teleology when talking of evolution. Even experts do it, and, although they at least only use the language, not the theoretical framework, it is very confusing to those who are trying to grasp the idea. The idea that ‘evolution’ holds a meeting with itself and says hold on chaps we need more boys in Bognor Regis this weekend, is nonsense, but it seems to be what people believe. In the ongoing debates between creationists and evolutionists that do so much to enliven the drudgery of existence in the southern USA, the evolutionist side is handicapped by the fact that most of its proponents are motivated by pure faith just as much as the creationists are. They ‘believe’ in evolution, but they don’t understand it.

Zebras did not evolve stripes to confuse lions. There are zebras because they evolved stripes which confuse lions. In the great game of life and evolution, being favoured means not dying young, and so getting the chance to reproduce. Less successful evolutionary pathways are truncated, not by some sentient ‘evolution’, but by the teeth of lions.

In most countries more boys are born than girls, but there is no obvious reason for this. The usual explanation is that, where there happen to be fewer males (for example) they will have a wider choice of females and so will produce more offspring (the males will have more offspring on average than the females). Thus those people who are genetically predisposed to have produce boys will have more grandchildren and the balance will be restored.

You may have noticed the hand-waving slipped in there. It assumes that there is such as thing as being ‘genetically predisposed to produce males’. This is not known to be true. It is known to be true that we are genetically predisposed to produce roughly the same number of boys as girls.

The real reason the balance is approximately maintained is that anything else, in a given population, would be unstable and would cause such a population to die out (or to seek to redress the imbalance socially, by mixing with neighbouring populations). This is observably true, because only approximately balanced populations exist, but we don’t know why it’s true. All we can do is wave out hands about and talk about restoring equilibrium. But a given population doesn’t restore its equilibrium. The unbalanced populations disappear. We only see the survivors.

We are, biologically, monogamous, and it is that that probably leads to there being an approximately equal number of males and females.

5 comments:

Vincent said...

Relating to your final paragraph,

1) What is the cause-effect relationship you suggest? How does monogamy lead to the same number of males and females?

2) Do you refer to equality of male and female births, as opposed to those who survive to a certain age?

Now to the "language of teleology". Before commencing my intended diatribe on this topic, I looked up the OED for a definition, and found the following in the list of illustrative quotations:

1893 H. Drummond in Barrows Parl. Relig. II. 1322 Darwin has not written a chapter that is not full of teleology.

One could look up further to see links between Darwin and teleology, but I'll just leave it there.

CIngram said...

I use the word teleogy when I'm argiung about this with myself, because of what I think I remember it means. I probably shouldn't have used it here. What I mean by it is the assumption that at some level evolution is directed and occurs in a certain way for a purpose. Many people use it as shorthand- the human pelvis narrowed so we could walk upright better, rabbits have a white fluffy tale to confuse foxes etc- but it makes it more difficult for others to understand.

In regard to the last paragraph, I'm not sure that the cause-effect relation is understood. It isn't by me, anyway. All we can do is observe that this balance is maintained, and speculate as to why it might be. By the way, Fisher, in his explanation, makes the assumption that some people are more likely to produce boys, and some girls. When I say that this is not known to be true, it's worth bearing in mind that Fisher knew his subject much better than I do.. I refer to approximate equality, because the relation of boys to girls born is about 105-100 around the world, but in adult populations this roughly reversed.

I would be interested to hear your diatribe on teleogy, if you still have the urge to produce one. But the reference you quote is more or less correct. There is a lot of of teleolgy (in the sense I use it)in Darwin, not only the language but clearly the assumptions. I don't know if it's a hangover from the thinking he grew up with, an attempt to 'save God' a la Kant (probably not), or whether he means it.

But it's worth remembering that Darwin knew nothing of genetics, not even the existence of the chromosome, and he knew almost nothing of the fossil record that is now available for study. What he did was to make a phenomenal number of highly detailed observations, and deduce from them that certain ideas about how they must have come about, and the relations between them.

Vincent said...

Yes, I feel that whatever dire accusations are fired by either side in this contentious topic, Darwin is invariably innocent.

As for my threatened diatribe, it may take a while. This goes into strange territory. I feel a blog post coming.

CIngram said...

I feel a blog post coming...

Oh, good!

Vincent said...

Now published with link to yours: http://perpetual-lab.blogspot.co.uk/2012/06/everything-desires.html