Theory of Asynchronous Evolution

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The Evolutionary Theory of Sex: Variation of Sexes and Reaction Norm

A man marries a woman thinking she will never change
and a woman marries a man thinking he will change.
 And they are both wrong.

It was noted already that males are first who die from all damaging environmental factors. The male sex is a biologically weaker sex. If we draw a mortality curve for each sex separately, the male curve should contact with the front of the harmful environmental factor. Hence, either curves are shifted, so that the male curve is positioned between the front of the harmful factor and a female curve, or male’s curve should have a greater variation. The first decision is not satisfactory, because rescuing a female from the given harmful factor of environment (let’s say, cold) exposes them to an alternative factor (in this case, heat). This leaves us with the second decision—male’s curve should have greater phenotypic variation than female’s curve (Figure 1B). This is the corner stone of the new theory.

Figure 1

Distribution of male (- - -) and female (. . .)
genotypes (A) and phenotypes (B) in population.
β and γ—male and female reaction norms accordingly.

The hypothesis concerning wider phenotypic variation of males was proposed in 1965. It permitted an easy explanation of many earlier obscure phenomena, and first of all of the different mortality of sexes (Geodakian, 1974). Higher mortality of males is one of the puzzles of sexuality, a general biological phenomenon, which no theory could explain satisfactorily. In new theory it is interpreted as a “payment” for new ecological information, as a useful form for population to get new information from the environment. For example males have higher susceptibility to all “new” diseases of our century (infarction, arteriosclerosis, cancer, schizophrenia and others).

What are the causes and sources of this phenomenon? Why is the phenotypic variation of males broader than that of females?

Wider phenotypic variation of males can be a consequence of their wider genetic variation. It can also reflect wider reaction norm of females which allows them to leave zones of elimination and elimination discomfort. Wider genetic variation of males can be due to their higher mutation rate. More additive inheritance of parental characters by female offspring can decrease their variation compare to males.

Wider Reaction Norm of a Female

One more phenomenon may bring about different phenotypic variation of sexes—different reaction norm for males and females. The norm of reaction, or modificational variability, individuals of a female sex should be more than the appropriate reaction norm of males. In other words, a male’s phenotype is more “rigidly” related to genotype than a female’s. Therefore, in Ontogeny, the environment has more influence upon realization of a female genotype into a phenotype.

There is a certain zone of “ontogenetic discomfort” in which individuals do not perish, but experience inconveniences and difficulties, suffer from lack of adaptation (freezing, starving and so forth) (Figure 1B). The wide reaction norm allows female individuals to leave this zone and survive, while males stay in it and perish. Female individuals have bigger “space of abilities” due to their wide reaction norm compare to males. Therefore the sex differentiation can be treated also as a specialization on mutually additional qualities of perfection (female sex) and innovation, progressiveness (male one) in their relationship with the environment. The adaptation of female individuals to existing environmental conditions is more perfect, than males. On the contrary, the presence of various deviations (imperfections) from the norm (mode) of a population, give males more advantage in the adaptation to changed conditions of environment in the future.

The narrow reaction norm of males provides them wide phenotypic variation. Contrary, wide reaction norm of females narrows their phenotypic variation. At a first glance it seems that the wider reaction norm should result in wider phenotypic variation. However it is not so. It is actually the opposite: in a population where male phenotypic variation consists of individuals with narrow reaction norm, it will be wider, because it will be more close to their genotypic variation. A female’s phenotypic distribution consists of individuals with wide reaction norm. Therefore a female’s phenotypic variation curve will be narrower, since in conditions of stabilizing selection, the wide reaction norm will allow extreme genotypes to “escape” zones of “discomfort” and to come closer to phenotypic norm (mode) of a population. High ontogenetic plasticity of a female sex provides it’s high stability in Phylogeny. Hence, the male sex is more flexible in the phylogenetic plan, and the female sex is more flexible in the ontogenetic aspect. Such, at first sight paradoxal, role distribution in Phylogeny and Ontogeny actually is consecutive and logical. It realizes uniform idea of specialization of sexes on conservative and operative tasks of evolution. Slightly exaggerating, it is possible to tell, that informational relationship of a population with the environment is based upon the elimination of males and the “education” (ontogenetic shift) of females.

          Receiving the Ecological Information from the Environment                         High Male Mortality and Gamete Type  

High Male Mortality under extreme conditions leads to decrease in tertiary sex ratio. Simultaneously more males are required for selection.  See Sex Ratio 

 

 

 

Copyright 2005-2009 S. Geodakyan. All rights reserved.

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