[inphusorian]

You forgot horizontal gene transfer.

[ch4s3]

This is very rare in eucaryotes, and especially in larger and more complex animals. Eucaryotes work really hard to keep foreign DNA out and their own DNA in the nucleus. Here’s a good article about the only known case in fish and why it’s so unlikely[1].

[1] https://www.cell.com/trends/genetics/fulltext/S0168-9525(21)...

[tiagod]

I think there's only one documented instance of horizontal gene transfer in fish and it increased fitness dramatically - https://www.quantamagazine.org/dna-jumps-between-animal-spec...