Large pandas are recognized as an endangered species and have a low birth rate. Chinese scientists from the panda research center in Chengdu concluded that the poor birth rate is due, among other things, to the fact that nature has poorly "designed" animals. The females of the big panda are ready to reproduce only once a year for 72 hours, and only from 12 to 24 hours during this period they can be successfully fertilized. The males have disproportionately small penis, because of which sexual intercourse is possible only in a strictly defined position, and this position the males know poorly.