Re: Why Sex ?

CurtAdams (
Wed, 17 Dec 1997 18:40:38 EST

"Berrie Staring" <> writes:

> Why (leave just pure coincidence out for now)
> do we need sex to spread our genes?
> Wouldn't it be easier if we could all make a child?
> without the sex. I mean why didn't the two
> chemicals to trigger this stay together..........
> From the selfish gene point of view, it would double
> the "people" who w(c)ould spread the code.

Generally speaking, sex probably exists because it
allows reassortment of the genome. This can be useful

a) Changes where change *per se* can be a benefit, as
in host/parasite races

b) Combining useful genes/mutations from what otherwise
would be separate lines of descent. Say gene A and gene
B are both beneficial compared to a and b, and you have a
population with both sexual and non-sexual lines:

Non-sexual Ab
Non-sexual aB
Sexual Ab
Sexual aB

Sometime sexual Ab will mate with sexual aB, producing some of each:

Sexual ab
Sexual Ab
Sexual aB
Sexual AB

The sexual AB members will have an advantage over all other
sexual members of the population, and if it's large enough, it will
exceed the disadvantages of sexuality and they will replace
*all* other groups, leaving a solely sexual population. (This
analysis is grossly oversimplified but you get the idea.)

Sex isn't always a win; some species reproduce by selfing and some
of those seem to have been around for quite a while.