Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because

Garrod hypothesized that individuals who could not metabolize protein could not produce the enzyme in their bodies. He was the first to identify the condition as a genetic disorder. Others thought it was caused by a bacterial infection. He came to this conclusion by noticing that the disease was more common in families where marriage between relatives was common. 

Accumulating more land so that your country can continue expanding without running into problems such as overpopulation