I'm having trouble on this too :(
Other functions of the small intestine include absorption of nutrients and water, after they have passed through the stomach, using special structures called villi.
Because evolution itself is a very slow process. Having said that, the chance of having a continuum of various animals would mean that evolution would have progressed very fast. Because evolution is slow, different species establish themselves for different ecological niches and environments, this enables them to become better through time at a certain environment which then leads to eventual diversification in the number of species.
