Friday, 14 November 2014

How Selfish Genes Can Make Large Testes

Infanticide drives female promiscuity and big balls - life - 13 November 2014 - New Scientist

Infanticide by a dominant male is frequent in many species, having been observed in some 200 species of mammal alone. It is, of course, easily explained by gene theory of Darwinian evolution by natural selection; it is, like so much else in biology, completely nonsensical in terms of intelligent design by a benevolent designer.

It is especially common in species where a single dominant male has a harem of females but can be displaced by a new, younger male, and especially when the young are slow to mature. A male lion, for example, will normally kill all the cubs in the pride soon after he displaces an old or sick alpha male. This is also seen in chimpanzees and gorillas. I have even seen film of a male swallow removing newly-hatched chicks from a nest having, apparently, replaced his new mate's partner, possibly because he had been killed.

The males don't manage to stay dominant for very long, so when they can mate with the females, they need to do it as quickly as possible," explains Huchard. "It's not in their interest to wait for the females to finish rearing infants.

Elise Huchard,
Centre for Functional and Evolutionary Ecology, University of Montpellier, Montpellier, France
The advantage to males in this situation is that the female comes into season much more quickly so he gets his genes into the next generation earlier and this may be important where his period of top male may be a short and precarious one. For females, however, although mating with a dominant male helps ensure her offspring inherit his ability to dominate, it means she often wastes the considerable investment she has made in here relatively few germ cells or eggs, compared to a male's millions or billions of sperms. So, an evolutionary tension is present - the classic conditions for an evolutionary arms race.

One way females can mitigate the effects of male infanticide is by being promiscuous. Female promiscuity produces a situation where an infanticidal male may also be killing his own offspring, so reducing any advantage his genes may have had from his infanticide of the young of other males. The finely-balanced scales of adaptive evolution are tilted against infanticide due to the adaptive advantage of female promiscuity.

Now the evolutionary tension has increased again and the successful male will be the one which can either mitigate female promiscuity or turn it to its advantage. So, how do males 'retaliate' in this evolutionary arms race? Well, they produce more sperm, so improving the chances of promiscuous females bearing their children, and to do this, they evolve larger testes.

Note that there is no planning or purpose in this, it's just that the result looks like the result of strategic thinking and planning. Natural selection ensures that those females which are promiscuous have more successful young in the presence of infanticidal males, so the tendency to infanticide in males is reduced while the tendency to bigger testes and more sperm is selected for because that, again, produces more offspring carrying the males' genes in the presence of promiscuous females.

This was confirmed in a paper published today in Science. Dieter Lukas of the Large Animal Research Group, Department of Zoology, University of Cambridge, Cambridge, UK, and Elise Huchard of the Centre for Functional and Evolutionary Ecology, University of Montpellier, Montpellier, France, compiled a database of behaviour in over 200 mammals and mapped this onto the mammalian evolutionary tree. This showed that male infanticide is most common in species that live in groups with a dominant male whose period in office tends to be relatively short and insecure. The study also showed hints of a link between an evolutionary history of male infanticide and large testes.

Male mammals often kill conspecific offspring. The benefits of such infanticide to males, and its costs to females, probably vary across mammalian social and mating systems. We used comparative analyses to show that infanticide primarily evolves in social mammals in which reproduction is monopolized by a minority of males. It has not promoted social counterstrategies such as female gregariousness, pair living, or changes in group size and sex ratio, but is successfully prevented by female sexual promiscuity, a paternity dilution strategy. These findings indicate that infanticide is a consequence, rather than a cause, of contrasts in mammalian social systems affecting the intensity of sexual conflict.

Dieter Lukas and Elise Huchard; The evolution of infanticide by males in mammalian societies.
Science 14 November 2014: 346 (6211), 841-844. [DOI:10.1126/science.1257226]

The study also showed that male infanticide was probably practiced by the common ancestor of the great apes. It is still present in chimpanzees and gorillas but not in bonobos or humans. It's interesting to speculate here whether the invention by human males of religions, with their almost universal obsession with sex and associating it with sin and guilt, was an adaptive strategy against increasingly promiscuous females as we diverged from the other chimpanzees. Certainly, although chimpanzees and bonobos are thought to have diverged after chimpanzees and Australopithecines went their separate ways, bonobos have evolved comparatively larger testes than human males.

This is entirely consistent with the theory that gods are a memetic cultural fossil from the time when our ancestors lived in small bands with an alpha male who was at the same time the tribe's protector and an object of fear. Could religion be a cause of small testes?

So there we are, the apparent paradox of a species frequently killing its own young being an evolutionary adaptation, and yet fully rational with the application of selfish gene theory and what we know about evolutionary arms races and sexual reproduction giving rise to different competing strategies between the sexes. Not intelligent; not benevolent; not compassionate or moral; just utilitarian. The strategy which produces most descendants in the long term is the one which becomes the norm.

And totally at odds with any notion of intelligent design or even guided evolution by an intelligence with a plan. Any plan there is indistinguishable from no plan at all, unless the intelligence is a particularly nasty, malevolent piece of work with the character defects of a psychopath.

Any creationist with the courage of their convictions prepared to point out the error in my logic there? If not, why are you a creationist when the real world is so full of similar examples of where there could not have been an intelligent creator involved and none at all where one had to be?

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