Yeah, those guys were chimps. /s 
There is no doubt they hunted and killed mammoths with regularity. However, the claim that they hunted the mammoths to extinction is b.s. And those "early" men of 20,000 years ago had the same mental abilities that modern people do.
***However, the claim that they hunted the mammoths to extinction is b.s.***
Unless...they took less risk & killed too many small, young mammoths; thus diminishing the numbers of future breeders.
Have noticed how my dogs do not attack baby rabbits or squirrels....they just play with them and chase them away.
Which, in the wild, allows for breeders and future food.