Yeah, they can. There's two ways; the cheat way and the normal way.
1. The Cheat Way- on the neighbourhood screen, hit [Shift]+[Ctrl]+[C], then type in:
boolprop testingcheatsenabled true
then load the female Sim's house. Hold [Shift] and left click on her, then select 'Spawn', then 'Tombstone of L and D'. When the tombstone is placed, click on it, select 'More', then 'Get Pregnant With...' and select the second Sim's name. As far as I know, she can get pregnant with herself. If you want, click on the tombstone again and select 'More', then 'Speed up my Pregnancy'. *ta daa*
2. Normal Way- Have a male and a female sim. Build up a relationship between the two, so they fall in love and have a crush on each other. Then, if the friendship bar is pretty high up, select either sim and click on a bed, hot tub, or car and tell them to get in. Once they are in the car, find the other sim and 'Ask to join'. If they are in the bed or hot tub, tell them to 'Cuddle' the other sim, then 'Try For Baby'. If it works, you'll hear a sort of nursery lullaby music, if not, make them try again and again over some days- some male sims are infertile >.< *ta dah*
umm... good luck??