In the eighteenth century, Lamark attempted to explain what had caused animals to evolve. He suggested that characteristics acquired by individuals during their existence were transmitted  to their descendants.  For example,  ancestors of the giraffe, running out of food, had tried to reach higher leaves in trees. They had stretched and elongated their necks during days. Then, they had passed to their offspring this feature of a slightly longer neck . The offspring had imitated their parents and little by little the entire species had retained the long neck as a permanent feature.

Lamark’s ideas were enticing. It meant that part of what was achieved during life was bestowed upon the progeny. Efforts were not wasted, they entered the cycle of generations. Direct physical heritage was the way for organisms to rise toward perfection. This in itself was be the principal reason for evolution, from amebas to humans.

This theory, however, could not explain how most characteristics had appeared in the first place. Flapping a limb in the air does not make it grow feathers. No effort to see brings a blind creature to develop an eye. Furthermore, Lamarkism could not offer any mechanism by which alterations of the body would impact the eggs or sperms of a parent. In fact, it was already quite clear that they do not. Children of  manual workers were not born with callous hands!

Searching for possible evidence in favor a Lamark, some scientists even cut off the tails of generations of mice. They found no variation in the tail size of the progeny. Eventually, most biologists rejected the concept of an evolution based on the transmission through heredity of acquired characteristics.