The problem is that this famous image tells you as much about evolution as transformers does about robotics. Evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection.
We will use Chimpanzee instead of monkey for now, at the end I will explain you the concept of monkeys. This picture makes evolution look like a linear process in which one species evolves into another and this further continues. But, in this matter it's different, instead humans and chimps became different species in another way.
To understand it we need to we need dive into the past when the humans and chimps not existed. At that time, another species lived, which was around 6 million years ago. This species splited into two different species and each of them followed there own evolutionary path. So, humans did not evolved from chimps instead they shared a common ancestor with them.
Chimps are more like our evolutionary cousins rather than our evolutionary grandparents. This is an example which shows that evolution is a branching process which can give rise to two or more species.
I will explain it to you with an easy example that your grandparents had more than one child and they each went off and started their own families creating new branches of your own family tree. The same thing happens in evolutionary families. A species can split into two or more descendant species and they can split again and again across the generations.
Let's understand that monkey's concept too. If we extend the family tree it includes the rest of the primates too, as in the image above. Primates is larger group that consists all the apes, lemurs and also the monkeys, etc. Primates is one single biological group because they evolved from one single common ancestor.
So, the monkeys aren't one single biological group, we've got the old world monkeys and the new world monkeys. By grouping them together from an evolutionary point of view would be like putting the gorillas and orangutans together in their own special group and calling them gurangutans.
