A group of cells that performs a similar function is known as tissue.
When a man and a women come together it is called sexual reproduction.
(had to keep it pg for the kids)
its necessary to keep the generations of humans alive. if this doesn't happen the human race will be no more.
There are all kinds of people who have different kinds of kids(skin color and features)
I think this is what you are referring to.
Hope this helps.
