Question

what role does a lice play in the existing of humans?

Answer 1

Lice have no beneficial role in the existence of humans. These small arthropods are bloodsucking parasites which dwell upon humans or other warm blooded creatures with no benefit at all to the host, only to their own gain.
Whilst they have no positive role in the existance of humans it is possible to view a theoretical link between their high presence on the primates from which we evolved and the development of social skills as many primates have grooming routines that involve interation with another of the species.
A negative role that these lice play is the ability to spread disease between humans by carrying of bacteria and viruses that they can exchange between members of the species.

Answer 2

Here is your answer.
I am a biologist and a teacher, so I hope this helps. Follow this link.
http://www.sciencedaily.com/releases/2011/01/110106164616.htm

Answer 3

one louse / many lice