Paleolithic Hunting and Gathering Groups Usually Numbered No More Than

Paleolithic hunting and gathering groups usually numbered no more than forty, because

A) hominids in larger groups usually ended up in fights over territory.
B) they instinctively wanted to mate so as to bring in new blood from other groups.
C) above that number, it was difficult to be sure of an adequate food and water supply.
D) that was the traditional way of doing things.
E) they could not provide tools and weapons for more than about forty.