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Origin of sexual reproduction

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Sex has been called the "queen of problems in evolutionary biology". [1] Lower forms of life tend to reproduce asexually while higher forms tend to be male and female, but it has been difficult to identify any advantage that offsets the cost of the complicated system of meiosis. It is not a problem for creation because it is perfectly reasonable that God provide a harmonious, complex, and compatible system for reproduction

1 Sexual Dimorphism
2 Sexual Selection
3 Origin of Sex
4 Related References
5 External Links

Sexual Dimorphism

The evolutionary hypothesis is that life started by reproduction by fission. Later it developed asexual reproduction where each animal or plant had both eggs and sperm so it could fertilize itself. Later still, two physically distinct, male and female sexes developed along with a more complex system of reproduction. This third phase is called sexual dimorphism.

For evolution to develop two sexes, there must be an advantage in sexual reproduction that facilitates survival. Thus, beauty and sexual attraction must be seen to be adaptive. All the differences between the sexes in various species must be explained. Why in some birds, is the male or female much more highly colored than the other sex? How does competition for mates fit into evolution?

The two different kinds of females in ants and bees must also be explained, as well as why there are two sexes and not three or six.

Some researcher express the problem as being `Why are there males?`. And why are the number of males and females usually about equal in the animal world, when it would seem that a few males would be sufficient.

Sexual Selection

Evolution is thought to result at least partially from animals tending to select mates that they prefer in some way. Human beings would seem to be the creatures who are most fussy about physical features of their mates. However, there is no direct evidence that human features have changed by sexual selection in human history. If beards or large breasts are selected sexually why don't all men have beards, or all women have large breasts? Darwin's theory of sexual selection receives little consideration from recent biologists, because there are no clear examples in the wild that sexual selection has changed an animal.

There is some evidence that sexual selection helps to clear unfit or deformed animals from the reproduction of the species. This would show sexual selection to be more helpful for maintaining species of the same appearance and thus would tend to work against evolution. Animals that deviate significantly from the norm tend to be weeded out.

Why would a preference for hairless mates develop? Since chimpanzees are hairy and humans are not, it would seem that somewhere there was a preference for hairless mates that developed randomly and became associated with all the other different characteristics of humans over chimpanzees. But why should a preference for something different from the norm develop? and then spread to all the new race?

One researcher found that he could ruin a male swallow's chance of mating by making their tales less symmetric. Humans tend to find a computer averaged face as more attractive. How then does sexual selection help create a different species?

Origin of Sex

The origin of the X and Y chromosomes with their resultant differences in physical makeup and psychology are said to represent the most important challenge to the modern theory of evolution. Researchers say that the problems point to a very complex origin.

There is no evidence of any reproductive systems that are part way between asexual reproduction and sexual reproduction. It is hard to imagine how a partly formed reproductive system would be conserved because a non functioning reproductive system would certainly not be selected to reproduce. Some plants and simple animals reproduce both asexually and sexually, but that would seem to be an evolutionary advantage over animals that reproduce sexually. After all, a creature with both systems can reproduce whether there is a mate available or not. It would seem that having both systems would be selected over sexual reproduction, but sexual reproduction seems to have won.

For most sexual traits, a new mutation must occur in both the male form and the female form at the same time and in the same community for the mutation to have a chance to be conserved. Since the genetics that result in the physical change are often on separate chromosomes (like X and Y) this seems to be especially rare. How then would changes and development of sexually reproducing creatures occur?