Muslim scholars, as part of their investigations into biology, resurrected the idea of evolutionary theory first hinted at by Anaximander. The most important contributor to Islamic evolutionary theory, and a leading scholar of zoology, was Al-Jaḥiẓ, (781– 869). He wrote a detailed treatise, Kitab al-Hayawan (Book of Animals), which became one of the most important works in the history of biology.

This book contained detailed descriptions of over 350 species of animal, interwoven with poetic descriptions and well-known proverbs. Al-Jahiz was the first scholar to realize the importance of the environment upon animals, and he understood that the environment would determine the likelihood of an animal surviving. As a result, he proposed a theory called the ‘Struggle for Existence,’ the forerunner of Charles Darwin’s ‘Survival of the Fittest.’

Brilliantly, he stated that animals struggled for existence, striving to find food, escape predation and survive long enough to breed. Thus, the most successful individuals would pass on their traits to their offspring, ensuring that they, in turn, would be more likely to survive everything that the environment could throw at them.

Al-Jahiz also related his ideas about food chains, noting that animals would seek food, but they would, in turn, be eaten by predators. The scholar also understood that chains were not one-dimensional and that animals had more than one food source. As each animal hunted, it was also hunted in turn, as part of the cycle of life.

Crucially, Al-Jahiz even applied his theories of inherited characteristics to humans, noting that humans also adapted to their environments; that is why darker skinned people generally lived in hotter and drier climates.