Evolution and the reason for two sexes

[Willo89]

Why, from an evolutionary standpoint, are there only two sexes?

My thoughts regarding the question �

Sexual reproduction is used to spread successful genes throughout the gene pool, so the question is asking, from an evolutionary perspective, why there are not three, four or more sexes and what benefit is provided to evolution by only having two sexes? (because having three sexes appears to me to spread those genes more quickly)

My thoughts regarding the answer �

Is there some mathematical optimisation by having two sexes, in which case evolution has gravitated towards that 'best' solution, or has evolution been constrained by the physics of the double helix (which has only two strands and is hence constrained to two sexes)

The direction of this line of thought is this: If evolution were not constrained by physics, and existed in a 'virtual' environment, then could it have resulted in life forms that existed with more than 2 sexes?

If you decide to answer this question, then please can you answer with respect to the thoughts outlined above and not take this thread into alternate directions, because they do not help me resolve the issues I need to resolve.

Many thanks

Willo89

[Symmetryigr8]

If you had four sexes, would all four be required for reproduction, or just any two or three of the sexes.
If you needed all four then the odds of four creatures finding each other and being able to reproduce and having the right mix of sexes is smaller than with two creatures. Also imagine trying to work out dominance and picking the best possible mate out of three different types

[rov1200]

The basic threads of life are pure simplicity. The binary system is well known in the computer sphere with '0' and '1'
The genetic code is made up of only 4 letters, A,T,C,G , giving a maximum of 64 permutations. Just 3 of these letters together perform the start code of any gene ATG.
Therefore in the basic building blocks of lfe everything can reduced to a very small alphabet. The complexity only comes with the length of the DNA which extends into billions of characters long. So why introduce a third constant to muddy the waters.

[Symmetryigr8]

You seem to be anthropomorphizing DNA, it doesn't care how complex it is, its job isn't to be understood. You wouldn't ask particles why they added a neutron to muddy the waters. Evolution does what works best regardless of difficulty to comprehend as we don't need to comprehend reproduction to do it.

[rov1200]

Don't be too concerned symmetry judging by other posts 3 stars are reserved only for the question.

[WaldoMcFroog]

There are not just two sexes. There are also hermaphodites.

[Willo89]

Hi all,

I have tried to respond to your comments but the website keeps collapsing with an ASP scripting error in response to my reply (perhaps a portent that I am talking rubbish -:))).

I will try again later.

To everyone who has posted � thanks - any considered response is really appreciated.

Willo89

[Willo89]

Rov � I haven�t given 3 stars because I haven�t received responses that answer my question but then perhaps I didn�t express myself clearly enough :-))

Symmetry�s initial answer was the best, and in answer to his/her question regarding multiple sexes in reproduction - I was assuming that all sexes are required for reproduction. Symmetry, however, takes the standpoint that dominance and best possible mate selection is required. (an eminently reasonably comment given our experience of evolution)

This and your initial answer appear to be looking at evolution �as is� and not looking at how evolution �could be�. Ie the fact that life contains DNA and current 4 building blocks, or the fact that sexual reproduction requires mate selection, dominance etc.

Although I said �If evolution were not constrained by physics, and existed in a 'virtual' environment, then could it have resulted in life forms that existed with more than 2 sexes?�- I suspect that I did not emphasise this point sufficiently.

I am asking whether evolution, as we understand it, might have developed completely differently under different physical environments, where the basic building blocks were not based on a double stranded helix, which I presume (possibly falsely) is constrained by our local physical environment.

My reasons for this line of thought are because I am interested in building a computerised model of evolution , and so it is vital to understand the facets of evolution that exist because of the early structures that were built in earth based life, and those that are generic within any possible environment.

Waldo � I agree, and cases such as this and asexual reproduction also raise lots of questions (which I may raise in future) but were not the subject of this post.

Please continue the debate with reactions to my thoughts outlined above.

Willo89