They are about the size of a     but they can sound as large as ahas long suspected that the monkeys’  play a role in attracting mates.  the sounds are like other   version of  pick-up  or  that’s say, hey, check me out.

And now we know the quality of the    depends on a bond near their throats, called the  . The bigger the  , the deeper the Males with deeper calls sound more attractive to females, which means that males with smaller  have to come up with another strategies.

When you     and when you look up the monkeys, you notice that the  the testis are huge, and they white, they are really obvious.

University of  She and her team found that H. monkeys faced a   trade off.

As species can either have a really big bond, or it can be very    but not both. That finding is on journal Those spices with bigger   live in a single male groups, so it makes sense to invest   researchers calledthat is,   strategy  of attracting female’s attention.

But when the spices grow and include more    the best way to multiple males,  passing on more genes is to make more sperm, by building bigger testis. The research say the finding is the first evidence for evolutionary trade-off between mating cause and sperm production. And they warn that while human women do tend to make prefer males with a deeper voice, we might advertise ourselves in many other ways as well. So    to a enlarge