It's been a while since I've seen the movie, but considering how the civilization of Mars is set up, where the males are thrown down the garbage chutes and left to fend amongst themselves in the trash...How do they reproduce and have kids?
They pop out of the dirt.
If I remember right, the baby Martians hatch out what I guess to be eggs (they are said to be "hatchlings"). Perhaps, they inseminate themselves artificially?
Not how eggs work - egg is a female reproductive cell, which has to be inseminated by a male to develop and hatch. Eggs with shells are, if memory serves, inseminated internally (two birds have sex, then the female lays an egg). So no, males can't produce eggs by themselves. Females might catch themselves a couple of males every now and again for artificial insemination (bet you thought this movie couldn't be any more creepy than it is, huh?). OR they're actually a motile form of some weird organism that spreads underneath the surface, strobilising every twenty five years. OR the eggs have a long dormancy period and the ones hatching now have been laid hundreds of years back, which means no eggs are being laid right now and the Martians are heading for extinction. Possibilities are endless.
When Gribble is explaining the birthing process to Milo, he confirms that the Martian hatchlings simply pop out of the ground like potatoes, if I recall correctly. He never mentions any sort of a fertilization or insemination process, and given the analogy he makes, there more than likely isn't one. Maybe the Martians are partially vegetative or fungal beings who don't individually birth their young. It would explain why the Supervisor thinks they don't need to be raised by their own kind, and why the males were initially confined to the trash heaps down below; if they were needed for reproduction, you'd think the females would keep them more conveniently close by, like in the cells they eventually lock them in later.
