Q. These animals could not breed together on their own?

More than that, actually, since they've probably bred on them halfway from here to there.

This would also explain why we have only been able to breed on Earth.

They are known to breed on land in the polar regions.

Perhaps you can show us how to breed the snakes on one of our worlds.

They breed on small islands, living in colonies of up to 50,000 individuals.

"If they're breeding them on the station," a security man said, "you'd think we'd have run across a few, at least."

They are the first generation of agency founders bred entirely on television.

A male has been recorded with four females breeding on his territory.

The nominate northern race may have bred on that island.