Changes to humans within their lifetime were readily observable (such as the blacksmith example used in . To show that these characteristics were heritable, one piece of
necessary evidence would be to show that all of a blacksmith’s sons and daughters were strong simply because the blacksmith needed to be strong and not because the children
performed work similar to their father’s work as they grew up. Lamarck would have needed to show that the sons and daughters would be strong even if they became scholars
and spent most of their time reading.