structural:expansion
Evolution

The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1.05 billion years old.

Biologists studying evolution propose several explanations for the development of sexual reproduction and its maintenance. These reasons include reducing the likelihood of the accumulation of deleterious mutations, increasing rate of adaptation to changing environments, dealing with competition, DNA repair, masking deleterious mutations, and reducing genetic variation on the genomic level. All of these ideas about why sexual reproduction has been maintained are generally supported, but ultimately the size of the population determines if sexual reproduction is entirely beneficial. Larger populations appear to respond more quickly to some of the benefits obtained through sexual reproduction than do smaller population sizes.

However, newer models presented in recent years suggest a basic advantage for sexual reproduction in slowly reproducing complex organisms.

Sexual reproduction allows these species to exhibit characteristics that depend on the specific environment that they inhabit, and the particular survival strategies that they employ.