Wednesday, March 24, 2004

More Than Words for Snow (3): Birth Control and Selfish Genes

In some ways, I'm not very happy with the writing in this post, and some of the problems I've had writing it I'll put down to the awful problems I'm having with my back, which make it so hard to think clearly when I'm sitting down at the computer....

I've talked before (here and here) about how the structure of our language and thought can easily mislead our thinking; here's another example, derived from Richard Dawkin's excellent book The Selfish Gene.

It's known that most birds regulate their clutch size -- the number of eggs they lay -- and it seems as if they do it for the good of the species, so they don't overtax the available resources. Dawkins argues, however, that this seemingly altruistic behaviour is in fact better explained as the result of the workings of selfish genes.

How could this behaviour arise from selfish genes? If the selfish gene view is correct, shouldn't we be expecting the birds to be wanting to have as many eggs as they can, so their genes are propagated as much as possible? Why then would these birds be limiting the number of eggs they are having - why would they be practising birth control? It's hard to imagine!

Actually, it's not that hard to imagine if we frame the problem in a more appropriate way. It's hard to imagine because of the way I've put things. I don't mean to say I've used some sort of special language-trick, however; what I mean is that we can, if we are not careful, be subtly mislead by the language we are using. To see what I mean you'll have to read on and see the details.

So what have I done to misleadingly frame the issue? What I've done is exemplified by the use of the term birth control. But what is wrong with that? If birds are laying less eggs than they could, are they not practicing a form of birth control? Would we not say that if people were limiting the number of children they have they are not practicing a form of birth control?

Perhaps we can clarify the problem by considering what we mean by 'birth control'. I think the essence the term's meaning can be captured by the following: birth control is limiting the number of children born; birth control controls (limits) the population; if you want to go about limiting the population you need to practicse birth control. It's hard to think how this meaning for birth control could be wrong, but it is -- in fact, as Dawkins explains, birth control can have exactly the opposite effect!

Dawkins says (pg 116):

[Each] selfish individual [chooses] the clutch size that maximizes the number of children she rears. If three is the optimum clutch size for swifts, what this means [is] that any individual who tries to rear four will probably end up with fewer children than rivial, more cautious individuals who only try to rear three. The obvious reason for this would be that food is so thinly spread between the four babies that few of them survive to adulthood.
That is, birds are practicing birth control in order to increase the number of children they have!

Lets now consider how and why the language has been getting us confused. How can birth control limit the number of children and also increase the number of children? The answer: it depends on the context. In the case of humans, at least in countries with a high-standard of living, birth control will limit the number of children. This is because baies have a high chance of surviving into adulthood, so any child born will increase the population and any child that isn't won't. In the case of the birds, and no doubt many other creatures, however, child mortality may be high, with the chances of a child surviving being dependent upon how much time and effort the parent(s) can devote to it. And thus having more children may, because you can't care for any of them adequately, mean you end up with less surviving children.

That's an explanation of how it's possible for birth control to either limit or expand the number of children, but how was it that we got confused in the first place? It was because the problem was framed in terms of number of children born, that this was simply the causal factor that effected population size, and that an increase in births meant an increase in population size (or, put the other way around, that an increase in population size comes from an increase in births). If we'd been careful about what we were thinking, we would have realised that we aren't really interested in the number of births but the number of children that survive. We'd assumed that the two meant the same thing.

We assumed the two meant the same thing because we didn't really think about the relationship between number of children born and population size. If we give the issue a quick think over in terms of the concepts such as 'giving birth to children' and 'population size', it's seems quite natural that there's a direct causal relationship between them, and if you take this answer it's hard to look at it and see why it is wrong. But there's a big difference about thinking about the concepts and really thinking about what the situation could be like (thinking 'what if the mother had twenty eggs rather than three?'). If we'd really thought it through, it ought to have been easy to see that having more children born could mean less children surviving.

I was originally planning to have a second part to this post, where I would discuss where our thinking had been going wrong, in terms of some vocabulary I've been developing for talking about this kind of stuff. But now I'm going to do that in a separate post which I'm going to start writing next.

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