Why is the number of sexes not 3 or more?
- a study on the distribution of the number of sexes
Yilong HAN
A working paper in Prof. Philippe Cluzel's biophysics course 491 PDF
Department of Physics, University of Chicago (2002)
There is little research about this topic. Although my paper mainly focused on
DNA-based lives, the heredity materials are not limited to DNA and most
conclusions should be applicable to most aliens on other planets. (Anyway, I
think natural selection is a logical truth which should not depend on
observation.)
Abstract
What is the best way of self-reproduction for life? 2-sex is much
superior than 1-sex because good mutations can propagate and meet in the
population instead of limited in some individuals. Similarly 3-sex is
much superior than 2-sex. For example, in our gene pool, say genes A, B,
C are good; AB, AC and BC are fatal combinations; while ABC is a
superman. Then it is almost impossible to get ABC from 2-sex
reproduction, but very easy from 3-sex reproduction. N-sex is much superior
to explore more DNA sequence space than (N-1)-sex. At equilibrium, N-sex
population should have 1 type of female (big gametes provider) and N-1
different types of male (small gametes provider) and each type occupies
1/N population. At very high natural selection pressure, I estimated that
the efficiency is mainly proportional to lnN/N, which reaches the maximum
at sex number N=3. Thus it appears that the natural selection pressure on
our planet was not extremely high so that 2-sex could wipe out 3-sex at its
baby stage; the selection pressure was not very low so that 2-sex were not
wiped out by 1-sex. Multi-sex is better for the
parent-competing-resource
mode than the offspring-competing mode.
"It should be possible by asexual means to produce an oak tree from a
bacterium, but not, probably, within the total lifetime of the
universe [5]." Fortunately the complexity of intelligence for
developing science is below the upper limit of the 2-sex complexity, so
that those 2-sex scientific organisms can shuffle DNA between many
parents or even engineer DNA in the lab to break the upper limit of
2-sex. "Human" with wings and chlorophyll is just a very conservative guess.
I think it would be the best to have flexible number of
sexes in one species. It has advantages of both low sex number and high sex
number. It is not clear why this did not happen.