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Sex can't have evolved (Talk.Origins)

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Response Article
This article (Sex can't have evolved (Talk.Origins)) is a response to a rebuttal of a creationist claim published by Talk.Origins Archive under the title Index to Creationist Claims.

Claim CB350:

Sex is too complex for its origin to be explained by evolution. Males and females would have to evolve independently, and any incompatibility in any of the physical, chemical, or behavioral components would have caused extinction. Furthermore, evolutionary theory predicts that asexual reproduction would be favored because asexual species can reproduce faster.


CreationWiki response:

(Talk.Origins quotes in blue)

1. The variety of life cycles is very great. It is not simply a matter of being sexual or asexual. There are many intermediate stages. A gradual origin, with each step favored by natural selection, is possible.(Kondrashov 1997). The earliest steps involve single-celled organisms exchanging genetic information; they need not be distinct sexes.

As is so often the case, Talk Origins misses the point. The problem with an evolutionary origin of sexual reproduction is not so much the lack of a path, but that mutation and natural selection are incapable of doing the job. An evolutionary origin of sexual reproduction requires the development of two totally different but mutually compatible systems of organs; this multiplies the potential problems and increases the likelihood of failure.

Also, the Talk Origins article overstates what the Kondrashov article actually stated. Here is what the Kondrashov article abstract states:

The life cycles of cellular species are reviewed from the genetic perspective. Almost all life cycles include stages during which only one genome is transmitted from a parent to its offspring. This, together with interorganismal gene exchange, which occurs regularly in at least some prokaryotes and in the majority of eukaryotes, allows selection to evaluate different alleles more or less independently. Regular genetic changes due to intraorganismal ploidy cycles or recombination may also be important in life cycles of many unicellular forms. Eukaryotic amphimixis is generally similar in all taxa, but the current data on the phylogeny and reproduction of unicellular eukaryotes are insufficient to determine whether it evolved several times or just once. Theoretically , gradual origin of amphimixis from apomixis, with each step favored by natural selection, is feasible. However, we still do not know how this process occurred nor what selection caused it. For reasons not entirely clear, some properties of amphimictic life cycles are much less variable and more conservative than the others. Evolution of many aspects of reproduction requires more theoretical studies, while the existing data are insufficient to choose among the currently competing hypotheses. (emphasis added)[1]

(regarding the abstract quote above: "Amphimixis is another term for sexual reproduction, generally by the fusion of a male and female gamete and subsequent recombination. The opposite of amphimixis is apomixis: asexual (clonal) reproduction." [2] )

There is a difference between possible and theoretically feasible. Furthermore, the abstract at least adds some scholarly caution in that it states "we still do not know how this process occurred nor what selection caused it" and also adds that the evolutionists are currently choosing between competing hypothesis.

Males and females most emphatically would not evolve independently. Sex, by definition, depends on both male and female acting together. As sex evolved, there would have been some incompatibilities causing sterility (just as there are today), but these would affect individuals, not whole populations, and the genes that cause such incompatibility would rapidly be selected against.

  1. Brown did not say that “Males and females would have to evolve independently,” what he did say was that the “complementary reproductive systems of the male and female must have completely and independently evolved at each stage at about the same time and place.” The point is that both systems would have had to evolve without mutual influence.
  2. Talk Origins claim, that Males and females must have evolved together because sexual reproduction requires both, is circular reasoning. It is true that for them to evolve they would have to evolve together, but this is Brown’s point, since getting 2 complex but mutually compatible systems to evolve step by step and side by side is incredibly small.
  3. The fact that any incompatibility would be selected against, would also tend to prevent any significant change that could lead to sexual reproduction, unless it occurred nearly perfectly in both systems.

2. Many hypotheses have been proposed for the evolutionary advantage of sex. There is good experimental support for some of these, including resistance to deleterious mutation load and more rapid adaptation in a rapidly changing environment, especially to acquire resistance to parasites.

There are also plenty of reasons why sexual reproduction would be selected against.

  1. Asexual is faster than sexual reproduction.
  2. Sexual reproduction uses a lot of effort in finding and attracting a mate.
  3. Sexual reproduction can cause the loss of even the most beneficial of mutations, since only half of each parent’s DNA goes to a given offspring.
  4. Sexual reproduction can cause the loss of even the most beneficial of mutations though recombination.

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