In 1809, French naturalist Jean-Baptiste Lamarck stated in “Philosophie Zoologique” that inheritable characteristics (soft inheritance) could be developed by the environment during an organisms life.

Lamarck believed that living things evolved in a continuously upward direction, from simple to more complex forms, toward human “perfection.” Lamarck believed that species didn’t die out in extinctions, rather they changed into other species. Since simple organisms exist alongside complex “advanced” animals today, Lamarck thought they must be continually created by spontaneous generation.