Not sure why you're being downvoted. You're right of course that the male/female distinction of sexual reproduction is in itself is a clear case of 'biological division of reproductive labor'. Child-bearing itself is an even clearer example than breast-feeding. I'm not sure jly was really getting at the core aspects of eusociality there.

Humans aren't eusocial, but we certainly have division of reproductive labor. So do non-social sexual species.