Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Thousands of years ago, several species of large mammals existed in North America. These species became extinct not long after the first human settlement of North America. Which human activity most likely contributed to the extinction of these mammals?
hunting
Overhunting.