Adaptations Are Inherited, Not Earned in a Lifetime

0:00Giraffes have very long necks. How did they get them?

0:04A long neck is an adaptation: an inherited trait that helps survival and reproduction.

0:11The wrong idea: a giraffe stretches up to high leaves, and its neck grows longer.

0:17Then its offspring are born with that longer neck.

0:21But traits are inherited through genes, DNA instructions passed on in sperm and egg cells, and stretching does not change them.

0:30Likewise, a weightlifter's muscles are gained in life, so they are not inherited.

0:36The right idea: in a population, a group of one species in one area, neck length varies, partly because genes differ.

0:46Suppose the environment changes: the climate dries, and only high leaves are left.

0:52Now longer necks are an advantage: they reach more food, so those giraffes are more likely to survive.

1:00They leave more offspring and pass on their genes for longer necks.

1:04This is natural selection: individuals with traits that suit the environment better leave more offspring.

1:12Over many generations, long necks become more common.

1:16This is microevolution: a change in how common alleles, versions of genes, are in a population.

1:25No individual giraffe evolved. The population did.

1:29Adaptations are inherited through genes and spread by natural selection, not earned in a lifetime.