Natural selection allows individuals with certain traits to survive based on the conditions of the environment. These traits give the offspring of individuals a greater advantage of survival, and those alleles continue on with greater abundance as long as that trait provides an advantage BASED ON CONDITIONS. If those conditions are to change, and the adaptive advantage is no longer a benefit, individuals with that trait may no longer have the "upper hand". There is no choices made on the part of the individual, or the entire group. The environment selects what is an advantage, and what is not.
Sexual selection is driven by what is perceived as being advantageous by the one making the choice. In female African Cichlids, females can select for color based only on female choice. Speciation of this species of fish has been a result of both natural selection (feeding advantages, and adaptations allowing fish to fill niches) and sexual selection (color patterns, size etc. that may not always influence survival. In sexual selection, there is a choice made by individuals and that choice may impact the group as a whole.
Darwin states that certain evolutionary traits can be explained by competition within a species. Darwin defined sexual selection as the effects of the "struggle between the individuals of one sex, generally the males, for the possession of the other sex" I'm sure had Darwin met my wife, he would have chosen his "possession" wording more carefully...but what we have seen in class is many times the female actually chooses who she will mate with based on the display or "fitness" of a male.
Fisher later tied female selection to genetic control and natural selection. He said that it is easy to see (and later based on mathematics) that every baby born inherits genes that made the father attractive to the mother and also inherits the genes that made the mother attracted to the male. So there is a female choice aspect, AND a natural selection aspect to sexual selection. The genes in males don't manifest the desire for a trait, and females don't manifest the trait being selected for. (I learned this from a lecture given by Dawkins himself...I will post the link).
More to come...I've got to get to teach class now.
Ok...I'm back.
Anyway, here is the link to the Dawkins lecture on Sex Ratio and Sexual Selection: http://richarddawkins.net/article,1354,Lecture-on-Sex-Ratio-Theory-and-Sexual-Selection,Richard-Dawkins
It is around 30 minutes long and it covers quite a bit of what we are talking about in class.
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I like the wording you gave, saying that the environment selects the advantage. But the advantage came before the selection takes place, right? that's the beauty of natural selection acting on those variations that came to be...what cames before, the mutation that turns up to be an advantace, or the environment selecting the genotype expresed in that advantageous phenotype?
ReplyDeleteJay
ReplyDeleteI agree with every aspect of your blog but I do believe that male organisms are in some cases choosy over what female he mates with. Not as much as "female choice", but I have many fish aquariums and I see some of my cichlids and guppies that are male will not mate with either a smaller than usual female or a sick one, too.
I like the way you tied everything together, specially at the beginning when you mentioned that the gain of advantage is based on conditions
ReplyDeleteSuzanne,
ReplyDeleteI was basing my comments about female selection based on experiments done with cichlids where males are separated into clear tubes they can't escape from (yet females that find them attractive can enter and mate). I'm arguing that females can have a huge impact on speciation based on personal choice. And I've seen some of that mating behavior you describe with humans at social gatherings...especially close to 2 a.m.!
Very good entry, however I would have liked to hear about Dawkins point of view through you're own words and what you thought about.
ReplyDeleteI really like your entry and the link that you put at the bottom!
ReplyDeleteI do also think that males can be choosy over their mates and that it is not just females, although it is the female that may be the more choosier one.