Men, you can rest easy now.
The answer is yes. Yes, it is.
Darren Curnoe, associate professor at the University of New South Wales in Sydney, Australia, says that humans have the longest penis size amongst primates. He also says that variations in sizes is due to the evolutionary pressures of reproduction, the pressure differing from species to species.
For example, "sperm wars" are common amongst chimpanzees, where several male chimps try to impregnate a female chimp. Therefore, male chimps tend to have medium-sized penises and large testicles.
Meanwhile, amongst gorillas, only the dominant silverback gorilla gets to mate with the females, so the evolutionary pressure is much less than those of chimpanzees. Therefore, gorillas tend to have smaller penises.
Curmoe has two theories as to why male humans have bigger penises and medium-sized testicles.
One theory states that walking on two feet makes the appendage more noticeable, therefore giving females choices based on preferred size. Another theory is that the penis acts as a kind of radiator that releases heat to keep males cool while walking.
Check out the video below and be reassured that yes, your penis size is normal:
H/T: The Huffington Post