Figure 12.18: Many animals, like this polar bear, have special body features that help them
live in a certain environment. ( 20 )
Adaptations and Evolution
The characteristics of an organism that help it survive in a given environment are called
adaptations. Adaptations develop when certain variations in a population help some mem-
bers survive better than others (Figure12.19). Often the variation comes from a mutation,
or a random change in an organism’s genes. The ones that survive pass favorable traits on
to theiroffspring.
To help you understand adaptation, think about a population of oak trees. Imagine that
most of the trees are easily killed by a certain fungus but that every now and then, there is
one tree that has a natural ability to survive the fungus. That one tree displays a variation
that gives it a better chance of surviving its environment. It also has a better chance of
living to produce seeds and have offspring. It will reproduce and carry on the species, while
the other trees will die off. The tree with the natural ability to resist the fungus will pass
that trait on to its offspring. The other trees will not live and have offspring. Eventually
the population will change so that most of the individual trees have the trait to survive the
fungus. This is an adaptation. Adaptations are inherited traits that an organism gets from
its parents. Over time traits that help an organism survive become more common. Traits
that hinder survival eventually disappear.
Changes and adaptations in a species accumulate over time. Eventually the descendants