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Home Alone
Two, one, or none. As NATURE's BABY TALES shows, different kinds of
newborn animals get different levels of help from their parents. Some
baby birds and mammals get plenty of attention from both mom and dad,
in part because they are virtually helpless, and sometimes blind, when
they are first born. They need plenty of tender loving care. Other offspring,
however, are raised by just a single parent. That hardworking mom or
dad often makes great sacrifices, such as going without food for long
periods of time, in order to provide supper and shelter for the kids.
Sea turtles never know their parents. |
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But some parents don't play any role in their kids' lives; their babies
are left home entirely alone. Newborn sea turtles, for instance, never
know their parents. As BABY TALES shows, they must fend for themselves
once they break out of their leathery eggs and scramble down the beach
to the sea.
What explains the variation in parenting styles? One answer is that
evolution has fine-tuned each species to maximize the survival of offspring.
For some organisms, such as many insects and fish, that means putting
the majority of parental energy into producing as many eggs as possible,
but not caring for the offspring once they hatch. By producing huge
numbers of young -- some fish and insects can lay millions of eggs --
the parents increase the odds that at least a few of the babies will
survive. And by foregoing care, they can channel that energy into making
more eggs in the next spawning season.
On the other hand, some animals, including elephants, many sharks,
and people, produce just a few offspring and spend a lot of time and
energy helping them survive. Baby elephants, for instance, may spend
years traveling with their mothers, learning the ways of the herd. The
tradeoff is that female elephants may produce just a handful of babies
in their lifetimes. So they work extra hard to make sure that their
few children survive to carry on their genes.
Similarly, compared to other fish, some sharks produce relatively few
pups during their lives. While some hatch out of eggs, others actually
hatch while still inside the mother, and then are born "alive" when
they are ready to fend for themselves.
Such arrangements have a dark side, however. Researchers have shown
that some baby sharks become cannibals, eating their brothers and sisters
to improve their own odds of survival. Similarly, baby birds may kick
nestmates out of the nest in a bid to monopolize food. In the end, however,
by weeding out weak and diseased individuals, such competition between
siblings probably helps the best adapted babies survive.
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