Portal was the first Valve-developed game to be added to the OS X-compatible list of games available on the launch of the Steam client for Mac on May 12, 2010, supporting Steam Play, in which players that had bought the game either on a Macintosh or Windows computer could also play it on the alternate system.
1 Eurasian Pleistocene megafauna became extinct in roughly same time period despite having a much longer time to adapt to hunting pressure by humans. 2  However, the extinction of the Eurasian megafauna can be viewed as a result of a different process than that of the American megafauna.
See Image 1. Humans can also cause extinction by over-hunting. If sufficient numbers of an animal are killed, their populations can drop to a level from which they cannot recover. An example of this kind of extinction is the Steller's Sea Cow, a marine mammal that was hunted into extinction a few centuries ago.