Why do most living things have 2 sexes?

Although living things have different reproductive methods in nature, the vast majority are divided into two sexes: female and male. However, different methods such as asexual reproduction are also possible. So, why have most species in nature turned to the sexual reproduction system and divided sexes into two? How did this distinction emerge in the evolutionary process, and what are its biological advantages? Here are the reasons for having 2 sexes in living things.

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WHY AND HOW DID SEXUAL REPRODUCTION EVOLVE?

Approximately 1.2 billion years ago, living things transitioned from asexual reproduction to sexual reproduction. While asexual reproduction allows an individual to create its own genetic copy, sexual reproduction made it possible for genes from different individuals to mix.

Genetic diversity became one of the most important gains of sexual reproduction. The mixing of genes from different individuals allowed populations to become more resistant to environmental changes and diseases. In asexual reproduction, because individuals have the exact same genetic structure, the population was at great risk in the face of certain threats. Thanks to sexual reproduction, diversity increased and the natural selection process accelerated.

HOW DID THE EMERGENCE OF SEXES OCCUR?

Initially, organisms that reproduced sexually did so through a system called isogamy. In this system, all reproductive cells (gametes) looked alike. However, over time, gametes began to differentiate, and a process called anisogamy emerged.

As a result of this process, large and energy-rich egg cells became the gametes of females, while small and motile sperm cells became the gametes of males. This division of labor allowed the reproductive process to function more efficiently. While large gametes provided the nutrients necessary for the development of the embryo, small gametes facilitated the fertilization process by moving quickly.

WHAT IMPACT DID SEXUAL SELECTION HAVE ON SPECIES?

Sexual selection arises when individuals with certain traits increase their chances of mating. For example, a male peacock with colorful feathers attracts more attention from females and gains the chance to pass on its genes to subsequent generations more often. Competition between males and the selectivity of females form the basic dynamics of this process. For example, a strong male lion can earn the right to reproduce by protecting females. Females, on the other hand, try to guarantee the continuation of their lineage by choosing males with the healthiest and strongest genes.

HOW ARE SEXES DETERMINED?

Sex determination mechanisms in nature can vary. For example, the XY sex-determination system is common in mammals; males have XY chromosomes, and females have XX chromosomes.

The ZW system is seen in some birds and reptiles. Additionally, in some species, environmental factors can determine sex. For example, in turtles, the temperature at which the eggs develop can determine whether the individual will be female or male. Some species, such as snails, are hermaphroditic and possess both male and female reproductive organs.

WHY ARE THERE NOT THREE OR MORE SEXES?

Having three or more sexes would make the reproductive process complex. More sexes could reduce reproductive success by making it harder to find a suitable mate. Furthermore, a two-sex system is more advantageous for genetic recombination to occur in the most efficient way. However, there are exceptions in nature; a single-celled organism called Tetrahymena thermophila has seven different sexes.

News Source: 12punto