We primates are a little slow on the sexual maturity scale—some of us reach 50 and still laugh at the word “penis.”

Joking aside, sexual maturity is the age at which an animal can reproduce, and many animals can do so surprisingly early in life. This week we investigated some especially precocious producers of young. (Read about babies that grow up without any parental help.)

Aphids, tiny insects found the world over, are “essentially born pregnant,” says Ed Spevak, curator of invertebrates at the St. Louis Zoo.

Aphids reproduce asexually, producing “miniature replicas of themselves,” Spevak says, “kind of like Tribbles from the old Star Trek series.” (Related: "5 Gross and Amazing Ways Animals Deliver Sperm.")

When that happens, a newly