Natural selection as tautology

From an old email exchange…

Here’s the brief summary of Darwin’s theory (from The Origin of Species – I believe).

1. If there are organisms that reproduce, and
2. If offspring inherit traits from their parents(s), and
3. If there is variability of traits, and
4. If the environment limits the size of natural populations,
5. Then those members of the population with maladaptive traits (as determined by the environment) will die out or reproduce less, and
6. Then those members with adaptive traits (as determined by the environment) will survive to reproduction or reproduce more.

To falsify this you have to assume that premises 1-4 are true and show that 5 or 6 are false. Take proposition 5, for instance. You would have to find members of the population with “maladaptive traits” (whatever those are) who don’t die out or reproduce less. From these definitions alone that seems impossible to me, since if the individuals don’t die or reduce their reproduction, then you can just say that they didn’t really have maladaptive traits. I suggested, therefore, that the theory gives names to things that are observed and that it doesn’t make predictions. You could also show that the theory doesn’t talk about reality as we know it, i.e. the premises (again propositions 1-4) aren’t true, but that seems as difficult.

Apparently Popper said something about how actually it’s not a tautology, or at worst is a useful tautology. I have no idea where. Obviously the interest comes from the likes of fossil records, phylogenetic trees, genetics, etc: perhaps that’s where the tautology disappears.

A short interlude on sex

Sex is interesting. Why can women have multiple orgasms; why is their refactory period shorter? What are the functions of the female orgasm (“it feels nice” is a good one to encourage sex, but why did humans not evolve so that penetration would bring a woman to orgasm more easily)? Why can many (most?) women not orgasm without clitoral stimulation? Why is it a particularly pleasing compliment to a man if he can ejaculate more than once during penetretative sex, i.e. overcome the refractory period problem and ejaculate again – not just bring his partner to orgasm by oral stimulation or whatever.

My vague take on the thing is a gang-bang theory of sex. Basic idea: perhaps in times past it was common for multiple men to engage in penetrative sex with one woman within a short space of time. This kind of behaviour leads to sperm competition, which would have allowed natural selection to improve the reliability of fertilization. Multiple male on one female action happens in other animals (and still in humans, but I guess no longer for the purpose of fertilization!), and to stop it males of various species do things like impose copulation costs (for instance males of some species have spikey bits on their genitals (!) to make encounters with other males before fertilization has occured less likely), guard their partners, punish females for their promiscuity, and so on. Another method for doing this would be the volumous production of semen.

Found an interesting paper on the human penis as a semen displacement device (Gallup et al 2003) where they got a fake vagina (a sex toy for males) and lots of models of erect penises, then used them to see – in effect – how the different penises could act as a sort of semen plunger.

So natural selection occurs both at the level of female choice (e.g. discarding sperm, reducing offspring number, selecting sperm by selecting mates) and sperm competition (e.g. semen flushing, having crap sperm). (See Snook 2005.)

Anyway, does anyone have any ideas for further reading? I don’t know this literature, but it’s all fascinating stuff.

Gallup, G. G. Jr., Burch, R. L., Zappieri, M. L., Parvez, R., Stockwell, M., and Davis, J. A. (2003). The human penis as a semen displacement device. Evolution and Human Behavior, 24, 277-289.

Snook, Rhonda R (2005). Sperm in competition: not playing by the numbers, Trends in Ecology & Evolution, Volume 20, Issue 1, Pages 46-53.