When you take a look at the reproductive habits of some mammals, you'll find it is sometimes a little more interesting than the standard "birds and the bees."
The average female human is pregnant for about 280 days and its baby is completely helpless at birth. Human babies actually remain dependent on their parents longer than any other species--mainly because our unusually large brains take years to develop fully.
A female giraffe is pregnant for about 457 days--some six months longer than a human. And when the giraffe finally does give birth, the young are so fully developed that they can walk within hours. This adaptation is common among large, hoofed plant eaters that live in open spaces and must be able to flee from predators.
A small handful of mammals, the monotremes (such as the platypus), lay eggs. This is unusual for mammals but normal for most other vertebrates.
Marsupials give birth to tiny, hairless, and immature young who further develop in their mothers' pouch. There they continue to grow, getting nourishment by drinking milk.
For the more promiscuous side of mammals, look no further than these two: the Shaw's jird, a small African desert rodent that can mate 224 times in two hours; and Bonobos, who engage in sexual activity numerous times a day with almost every other member of their group, male and female alike. Bonobos, by the way are the closest living relatives of humans, along with chimpanzees.
- The Virginia opossum is pregnant for only 12.5 days (less than two weeks) before giving birth and the Indian elephant's gestation period is 646 days, or less than three months shy of two years!
- The nine-banded armadillo typically has four young at a time, all produced from a single egg cell. Because the babies are genetically identical, a single litter will always be all males or all females.
- Naked mole rats might have the most unusual social structure found in mammals. An entire colony of 20 to 300 is actually a single family led by a "queen" who is the only female that breeds. Some members of the colony serve as soldiers that protect the group while others are workers that dig tunnels and gather food. Such highly specialized colonies are much more common in insects than mammals.