Azara Blog: Genomic Conflict and the Divided Self

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Date published: 2005/01/29

The second lecture of the Darwin Lecture Series 2005 was by David Haig, about genetic conflicts and the "divided self". The first question he asked was why do we have a subjective experience of internal conflict, is it because:

On the first point he noted that natural selection is retrospective (i.e. organisms have adapted to cope with the past rather than the present environment). Evolutionary responses are limited by the pool of available genetic variability. And natural selection is not influenced by weak selective forces (random environmental variability providing more impact).

On the second point he noted that there could be different adaptive solutions determined, for example, by instinct, culture and reason. If so how does the individual decide between the different choices. Sometimes culture is more important a determining factor in some locations at some point in time than in other locations at other points in time (the example he mentioned was infidelity). It could be that the arbitration between the various choices is difficult because they are expressed in different "currencies" (for example, with infidelity how do you weigh the potential extra benefits of reproduction of your genes against the potential discovery of infidelity by your original partner).

Haig spent most of the lecture discussing the third point. There could, for example, be a conflict amongst memes (Richard Dawkins terminology) or between memes and genes or amongst genes.

He quoted one variant of a J.B.S. Haldane story that said that Haldane would be willing to give his life to save the life of more than two brothers or more than eight cousins. The argument is that each brother shares half of your genes and each cousin an eighth of your genes (on average). So if more than two brothers are saved then more than one copy of your genes (on average) are saved, versus only one lost if you die. And similarly with cousins. (This argument only makes sense if you believe that survival of one's genes is the driving force for humans.)

Unfortunately (or fortunately) it is not as simple as that. If instead of brothers you consider half-brothers then on average you share one quarter of your genes. So in theory if you save three half-brothers that is not enough to be worth sacrificing yourself, since on average only three quarters of your genes are saved versus one lost. This is true as it stands but ignores possible differences between genes inherited from your mother and genes inherited from your father. If the half-brothers have the same mother (and so a different father) then the three of them have one and a half copies (on average) of your maternal genes and zero copies (exactly) of your paternal genes.

It seems natural to believe that maternal genes and paternal genes are no different. After all the paternal genes might have come from the grandmother, not the grandfather, and similarly with the maternal genes. But it seems that these two sets of genes are different. (Ignoring the obvious X/Y differences.)

He quoted a paper by Barton, Surani and Norris (1984) which looked at mouse embryos with two fathers (so-called androgenetic embryos) and ones with two mothers (gynogenetic). None of these embryos came to term. Barton, et al. observed that in the androgenetic case the placental sacs were large and the embryos were small and in the gynogenetic case the placental sacs were small and the embryos were large.

Later on someone (else?) managed to get around the non-viability by producing so-called chimeric mice by joining two fertilised eggs, only one of which was androgenetic or gynogenetic. At birth the former had large bodies and small brains, and the latter small bodies and large brains. He quoted another study, by Keverne, et al. (1996), which showed that androgenetic mice had a larger hypothalamus and smaller neocortex, and vice versa for gynogenetic mice.

So past environment is important for genes. It seems that molecular biologists do still not understand the reasons for this (after the lecture Haig mentioned that DNA methylation might be one mechanism, but said it was known it could not be the only one).

He ended the lecture by talking about incest. Apparently some people believe that there is an innate biological aversion to incest. But apparently Freud already figured out that was probably a bogus belief, since if there is supposed to be such a natural aversion then why is there need for such a strong cultural taboo against incest.

Haig mentioned a simple model of incest where a father has no opportunity cost and the daughter's opportunity cost is the reduced fitness of the inbred offspring. (So this is isolating the biological from the cultural issues.) Without going into any detail he showed graphs which indicated that, not surprisingly given the model, the father's genes benefit in most cases and in two thirds of cases the daughter's genes do not. But in half of the cases (where the relative fitness of the inbred child was more than half a non-inbred child) the daughter's paternal genes benefited and always the daughter's maternal genes did not benefit. Haig suggested this asymmetry between the benefits for the paternal and maternal genes of the daughter might be one reason why there is so much psychological trauma for incest victims. But that sounds a step beyond the existing evidence.

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