Reptiles can change sex, but this is just a short term strategy.
(probably to be able to survive with just one female, who cant find a mate)
In the long run, it is required to combine 2 genoms from 2 differnt animals.
Else, the probability for unwanted mutations grows to big, wich is more severe
for large, slow reproducing lifeforms than for bacterias.

Also plants can reproduce with seperated plant parts, but
soon or later, a 2 sex reproduction must take place.