RUN-AWAY SEXUAL SELECTION
(A technical term intended to get round the problems with classical sexual selection)
Asked to 'explain
' the large ear
s, say, of some animal, Darwinism
gives us a choice of three (not a packet of three - that's something else) explanation categories
- The size of the ears is a consequence of natural selection.
- The size of the ears is a consequence of sexual selection.
- The size of the ears is a consequence of descent. The animal is descended from something with large ears. This is the reason given for a bat's wing being a distorted hand, for example. It cannot be the best way to make a wing from a 'let us design the most efficient possible wing' natural selection point of view.
We are given no clue as to which - 1, 2, or 3 - we should use.
Maud is looking particularly attractive this morning, so use sexual selection:
asked us to imagine
visiting a farmyard
and seeing a particularly attractive, and spectacular turkey cock
. We are impressed by this creature, remarking among ourselves upon its beauty
Might not a turkey hen
take the same attitude, share our inner lives
, regarding the cock
, asked Darwin, might she not choose to mate preferentially with him, forsaking the others? If so, he would leave more offspring
(other hens have no dislike for him) and future population
s would bare his weighted resemblance
Again, Darwin gave the example of an African tribe
who line their women up in a rank and then squint along the rank in order to decide which woman sticks out the furthest behind (he put this last bit in Latin
to serve Victorian
sensibility). This accounts for women's callipygousness
As to the animal's ears, perhaps females like big ears or perhaps the ears are a 'visual rank-dominance symbol' (advanced typically in the context of antlers) occasioning deference among other males.
Some of the Problems With Sexual Selection:
We must count this proposition true: 'Liking something implies
mating preferentially with it.' (Sporus's take on this is not to deny, or to affirm, its truth but to claim it is not 'scientific
'. This is because no 'algebra
' has been specified, no 'logic
', which supplies the implies. This is frequently a feature of Social Scientific
theories.) Many evolutionist
s feel this and related aspects of sexual selection, such as an apparent capacity for reading the mind of a Brussels sprout, require the re-jigging suplied by run away sexual selection.
Run-Away Sexual Selection:
- By chance a turkey hen is born which mates preferentially with males having extravagant plumage.
- Future populations bare a weighted resemblance to him.
- Their female offspring probably share their mother's appetite. So the process is reinforced.
- Their male offspring have extravagant plumage. So they get mated preferentially - since the female component of the population resembles the mother.
In short the process runs-away with itself and the population comes to consist in decorated males and in females lusting after decoration.
The simplest line to take is that the process can go in either direction. You could equally get Puritan
males with short feathers and naked areas.
With the large ears example, the process could give large ears - bigger than optimum hearing would require and natural selection would wish - or it could give undesirably, from a natural selection point of view, small ears.
If we look at the population at random times we will see large ears half, say, of the times and small ears the other half of the times. Neither condition is optimal for natural selection. The same will prevail for most of the animals' other attributes.
If run-away selection is real we are living in a world where almost all the characters of life show random deviations from what natural selection would lead us to expect. These deviations may well be large with a 'size' presumably in inverse proportion to the selective pressure
acting on the attribute. This is not the world we are normally told we inhabit.