Lamarck thought that organisms came into being through spontaneous generation.
He thought they changed from simple organisms to more complex organisms because they had an innate drive to become more complex and "perfect."
Lamarck thought that when organisms changed their behaviors in response to a changing environment, their bodies changed. When they used a part of their bodies more, it changed accordingly. When they used a part of their bodies less, it shrank.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. ... The overwhelming majority of a species' offspring survive.
The population would increase drastically and we would run out of resources for food. then the birth rates would eventually equal out to number of death rates . we then wouldnt have anyone alive