How did gender evolve?

A distinctive feature of life:

They have to adapt to their surroundings and perpetuate their life forms. In order to adapt to changes in the environment, evolutionary algorithms are widely used in the biological world to achieve adaptive changes in living organisms.

The motivation for adaptive change comes from genetic mutation, which is a simple and effective way for living organisms to reproduce and replicate their original successful survival strategies in order to continue their own life forms. This is the initial reproduction situation of life, asexual reproduction, such as a wide variety of bacteria.

Hermaphroditism. The more complex the structure of the animal and the higher the evolutionary level, the more obvious the characteristics of its differentiation will be. Therefore, higher animals—vertebrate animals—mostly belong to the former; Animals with poor body structure, low evolution, or degeneration mostly belong to the latter.

It's a general rule. Because of this relationship, we must begin to look at the problems of the sexes first in the higher animals, and then in the lower animals. To the extreme, even in the higher animals, there is no trace of the origin of hermaphroditism, and human beings cannot be listed as exceptions.

The purpose of evolving sex was to have sexual reproduction.

Life begins with asexual reproduction, and only later evolved sexual reproduction.

Compared with asexual reproduction, broad variation in gene combinations in sexual reproduction increases the ability of offspring to adapt to natural selection and can also facilitate the spread of favorable mutations in populations.

For the above reasons, the emergence of sex accelerates the process of evolution. It can be said that the emergence of gender is a turning point in the evolution of life on Earth, which allows life to be more adaptable to the environment.

Broad variation in genetic combinations in sexual reproduction can increase the ability of offspring to adapt to natural selection. Randomly combined genes in the offspring produced by sexual reproduction may or may not be beneficial to the species, but at least increase the chances of a small number of individuals surviving in an unpredictable and changing environment, thus benefiting the species. Sexual reproduction can also promote the spread of favorable mutations in populations.

If there are two individuals in a species that have favorable mutations at different loci, within the asexual population, the two mutants will inevitably compete until one is eliminated, and it is impossible to retain both favorable mutations at the same time. However, in sexually reproducing populations, through mating and recombination, these two favorable mutations can enter the genome of the same individual at the same time and spread through the population at the same time. In addition, species that undergo sexual reproduction have diploid stages in their life cycles.

Diploid species have two copies of each gene, one of which is functionally in reserve. If this alternate gene is mutated and becomes a gene with a new function, the new function is still latent at this point. Through spontaneous repetition and genetic recombination in sexual reproduction, this new gene can be sequenced with the original gene, thus giving rise to a new gene.

Diploid species can enrich their genomes in this way. For these reasons, sexual reproduction accelerates the process of evolution. In the more than 3 billion years of biological evolution on the earth, life stayed in the stage of asexual reproduction in the first 2 billion years, and the evolution rate was slow, and the evolution rate accelerated significantly in the last 1 billion years or so.

In addition to changes in the Earth's environment (e.g., the emergence of an oxygenated atmosphere, etc.), the occurrence and development of sexual reproduction is also a major cause. This is illustrated by the fact that more than 98% of the more than 1.5 million species of living organisms, from bacteria to higher animals and plants, can reproduce sexually.