(A brief essay on predators, prey, and a species’ genetic health (Completed 1/22)
We’ve all seen those nature shows on television where excellent camera work reveals a predator bringing down some prey and the narrator, in order to soften the dose of what we viewers may perceive as violence, says something like: “nature is so wise; the predator culls the weak and sick animals from the herd thereby keeping the gene pool (of the herd) healthy and insuring the survival of the species!”
However well-intentioned a statement like that is to shield us from harsh reality I think it falls far from the truth …. do you really believe that predators are extra-sensory enough to target individuals that have genetic defects? Or altruistic enough to cull those genes for the benefit of the other species’ health? That’s a stretch far beyond my willingness to make!
Temporary illness, infancy, or temporary injury does NOT imply inferior or harmful genes! Often the target is a baby or young individual who hasn’t the size or the experience to defend itself – does youth necessarily imply weak genes or a tendency toward illness? Of course not! Let’s say another individual twisted its leg in a gopher hole and can’t run away from the predator – does physically caused lameness imply weak genes? Only sometimes at most. And how about the individual that ate a bad patch of grass or some hallucinogenic mushrooms by mistake and got sick, does that individual necessarily carry weak genes? Negative!
Sometimes if the hunger is great enough, predators will attack a physically strong individual but again that has nothing to do with being able to detect genetic weakness in the prey animal. It has everything to do with haphazard circumstances such as which individual was closest to the predator or got most separated from the herd!
What does keep a gene pool sustainable is more difficult to say but I think the major factors are:
- The balance between harmful microbial infiltrators and a herd’s immune system strength.
- The assumption that food sources in the environment remain sufficient to continue sustaining herds in the area.
- The assumption that predators’ numbers don’t swell enormously so that they wipe out the prey herd in question.
- If it exists (and I suspect it does), the individuals’ reluctance to mate with other individuals that are too closely related to it and would therefore yield a statistically genetically inferior offspring.
- In possible fifth place is “junk DNA” or DNA of unknown purpose that could allow for genetic variability and adaptability to environmental change.
In species that practice it, I claim that the jousting between physically robust males for the right to mate is of limited importance. In the short run it does ensure that the strongest physical specimens are selected to defend herd members against a tooth and claw attack, but in the long run it doesn’t defend against genetic illness or microbial aggression; nor does it enhance memory to be able to lead the herd to alternative food sources in time of drought or famine.
Likewise, the female’s ability to reject a male for mating purposes or actively choose one she likes better has little to do with long term herd genetic health and more to do with pregnancy timing or rank order within the herd. I suppose an exception to that claim is when a female refuses to mate with a male that is too closely related to her; but even in that case I have to believe that she knows him from historical and physical presence and not because she can sniff out his and her own genetic makeup and reach a chemical conclusion that they’re a bad statistical match.