ElI5 What were the very first sex organs?

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How did they begin? How did and egg develop to recieve DNA when that had never happened before and the male is independent of the female?

In: Biology
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Hey. Not an amazing answer to your question, but this is empty, so I figured it’s better than nothing.

Some bacteria have a mechanism where they can basically stab each other and share DNA around by injecting it in. Since bacteria don’t have nuclei, their DNA just sort of floats around, and just injecting new DNA works.

Considering sexual reproduction is actually more-or-less just single cells combining/exchanging DNA, I figure the first real sex was similar to how clams and that kind of animal do it, but mixed a bit with bacteria, as it was less sophisticated. Basically, they would just release cells into the ocean, and whenever the cells encountered others of the same species, they would stab and exchange DNA, then multiply and make new creatures.

Eventually, creatures who got close to each other before releasing their reproductive cells had more children, causing evolution to converge towards creatures being near each other for sex. This probably developed into direct insemination for some creatures, like mammals or whatever, since it’s more likely to cause a pregnancy, and so genitals evolved?

Again, everything after the bacteria fact is entirely my theory, so don’t take it as “the truth” or anything. I just figured I’d try to answer so these comments don’t stay completely empty.

It evolved in early prokaryotes, around two billion years ago. Single-celled organisms. Some basic form of a [Pilus](https://en.wikipedia.org/wiki/Pilus) (reachy-grabby arm) or a [Conjunction tube](https://en.wikipedia.org/wiki/Bacterial_conjugation), two cells together and their walls open up letting stuff flow between them.

There’s a handful of theories about how it started. Parasites and viruses using other’s, something happening with the process of splitting in two, using the DNA from the things consumed. Sexual recombination has a lot of benefit over asexual, from repairing DNA errors in the next generation to making evolution a team-effort.

[There’s more.](https://en.wikipedia.org/wiki/Evolution_of_sexual_reproduction) (There’s always more.)