Giraffes

Giraffes have often been used in history in an attempt to explain inheritence and genetics.

In the 19th century Lamark proposed a theory that living things changed by inheriting acquired characteristics. e.g. giraffes stretched their necks to reach food, and their offspring inherited stretched necks. This is now known to be wrong, since many experiments (and experience) have shown that acquired characteristics are not inherited, but nevertheless Lamark's theory was the first to admit that species changed, and to try to explain it.

Darwin explained the giraffe's long neck as follows. In a population of horse-like animals there would be random genetic variation in neck length. In an environment where there were trees and bushes, the longer-necked animals were better adapted and so competed well compared to their shorter-necked relatives. These animals lived longer, through more breeding seasons, and so had more offspring. So in the next generation there were more long-neck genes than short-neck genes in the population. If this continued over very many generations, then in time the average neck length would increase.

Today it is thought more likely that the selection was for long legs to run away from predators faster, and if you have long legs you need a long neck to be able to drink, but the process of selection is just the same.