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Originally Posted by This_person  The answer given above answers how asexual reproduction could occur. The question being asked is how did single cell division reproduction turn into sexual reproduction. At some point, there had to become a male and female of an living thing. In a mutation/evolution environment, when the first male (or female) came to be, who did that mutated sexual creature reproduce with to survive that species? |
The answer covers both. The argument that there must be a distinct male and female of the species to sexually reproduce is incorrect and I used steps starting from asexual reproduction to show this.
The first sexual reproduction, as far as has been discovered, included the same types used by modern corals, tubes, plants and worms. Asexually these creatures can reproduce through budding, division, etc. Evolution in asexual reproduction is limited to genetic mutation and genetic drift but still present.
A species might exist in group environments so the species evolves to asexually reproduce AND transfer material within the group. Each individual has both male (transfer) and female (receiver) parts. Single organism transmission gains the species little, but if every member of the group has both sexes it provides the opportunity for cross transmission. Division of the sexes may evolve to save energy, since offspring will not have to develop the structures of both sexes. Boiled down, the first sexual reproduction was likely within the same organism, then across organisms.