or lost certain traits during their lifetime. The use and disuse of organs was driven by the environment of the organism. The new traits were then passed on to their offspring, which led to a change in species over a period of time. This idea is also called the inheritance of acquired characteristics. For example, he said that present-day giraffes had longer necks because their ancestors had stretched to reach leaves higher up trees. This exertion caused their necks to grow longer, and that trait was inherited by their offspring. After many generations of neck stretching, the result was the present day long-necked giraffe.

Watch a video about heredity and family traits.


• The ancient Greek physician, Hippocrates, suggested that various body parts produced “seeds” that were transmitted to the offspring at the time of conception. • An ancient school of thought, called Ovism, held that women carried eggs containing male and female children and that the sperm just stimulated the growth of the egg.


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