The frog that does not stop croaking for weeks, the pigeon that is exhibited with its chest swollen to the impossible, the firefly that flits all night illuminating the darkness with its abdomen … What an enormous effort we make to attract the opposite sex !
How expensive sex is for us!
The energy that individuals of different animal species invest in sexual reproduction is established at various levels.
First, you have to make genitality attractive and attractive to the opposite sex.
To this initial plane of anatomical attraction it is joined by the invisible but irresistible physiological resources, led by the pheromones, which stun those who either do not see very well, or chemoreception motivates them more.
And if this display of charms is still not enough, some taxa such as birds and mammals have carried the nuptial and mating courtships to a point of absolute sublimation.
The result is that there is no individual in most species that can resist the fatal combination of overwhelming anatomy, enveloping physiology, and elaborate and sophisticated ethology (like the scorpion waltzes, which leave the dance of the seven veils at the height of a medium hair fan).
If to all this we add the variable “Time invested in getting mated” and, therefore, the fertilization of the ovules and the achievement of a new generation for the species, we confirm our starting hypothesis.
That is, the amount of ATP molecules (adenosine triphosphate, the energy currency of life) that is invested in the very varied mechanisms of sexual reproduction of animals is extraordinarily high.
Sexual reproduction, therefore, is not expensive but very expensive. Especially when compared to the simplicity of the fisipartition of an amoeba or the budding of a polyp, both, asexual reproduction mechanisms.
The “other costs” of sex
In addition to complex reproductive structures and long courtship activities (some would even qualify them as tiresome), organisms that reproduce sexually do so through eggs and sperm.
Both, remember, are haploid cells, that is, they have a single chromosomal endowment, unlike the rest of the body cells (somatic cells) that are double chromosome endowed.
In other words, organisms cut their genetic potential in half when they reproduce sexually.
In contrast, when an animal resorts to some of the various asexual reproduction mechanisms it does so without depriving itself of any of its genetic wealth.
In short: on the one hand, sexual animals invest an enormous amount of energy and, on the other, we waste half of our genetic potential.
Sex is therefore wasteful and restrictive. So, Why did it prosper from an evolutionary point of view?
The reason for the success of sex
There is no greater advantage for a species, evolutionarily speaking, than having a vast gene pool.
It is the way to have various options (genotypes) potentially adaptive in the face of the unpredictable changes in the environment that life on this planet entails.
Thus, in the face of alterations in external conditions, there would be more potential individuals that could survive and reproduce, thus guaranteeing the continuity of the species.
In other words, everything that generates diversity of genotypes will be a golden tool for the species, natural selection will consider it a good thing and will not eliminate it.
From this point of view, the appearance of sex was a bargain (a bargain), since it was an authentic factory of production of genetic variability. Let’s see how.
At a first level, as eggs and sperm are generated by a process of meiosis, they undergo the reduction of the chromosomal endowment and the recombination of genes between chromosomes from the paternal and maternal lines during their formation.
These gene crossovers (crossing over) occur randomly, both in number and in sections of affected chromosomes. The result is that eggs and sperm are all genetically different from each other.
On the other hand, chance again intervenes at a second level at the moment when it is a certain sperm (and not another) that fertilizes a certain egg (instead of another).
Result of all this is that sex brutally increases the chances of generation of individuals genetically different in species and with it, your chances of survival and diversification.
If we compare it with the accumulation of non-lethal mutations -the slow path of increasing diversity of species that only reproduce asexually-, sex supposed the rapid multiplication of the potential to generate genetically diverse descendants and the exponential expansion of the range of potentially adaptive options to different environments of the species.
In other words, sex him it gave march to evolution.
For those who are not yet sufficiently amazed at the benefits of sexual reproduction, it turns out that it offers some extra benefits.
Specifically, it allows to counteract the negative effects of many harmful mutations generated by chance.
The double genetic endowment enables the good allele to neutralize the deleterious allele of the homologous chromosome. For the same reason, the possibility is created that the rare advantageous mutations that arise in separate individuals, can be combined into a single being (homozygous for that character).
But there is still more. Sir Ronald Fisher suggested a century ago that sex could facilitate the spread of advantageous genes by allowing them to better escape their genetic environment if they arose on a chromosome with harmful genes.
A final argument is provided by the authors who suggest that sex would help individuals resist parasites.
In this new biological interpretation of Lewis Carroll’s Red Queen paradox, the sexed hosts would be continually running (adapting) to stay in one place (resisting parasites)
You see, sex is a real invention, evolutionarily speaking. And that I have not even made an evening allusion to all the details in which I have no doubt that all readers will be thinking …
*TO. Victoria de Andrés Fernández is a tenured professor in the Department of Animal Biology at the University of Malaga (Spain).
This article was originally published on The Conversation.
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