Final answer:
Before Darwin, scientists in the early 19th century believed that selection operated among species or among groups, based on shared traits. They recognized that traits could change over time.
Step-by-step explanation:
Before Darwin, scientists in the early 19th century thought that selection operated among species or among groups, based on traits shared by all members of the group. They believed that natural selection would lead to the selection of certain traits that were advantageous for the survival and reproduction of a species or a group. They did not have a comprehensive understanding of the mechanism of natural selection, but they recognized that traits could change over time.