Scientists who classify living things are called taxonomists. It is their job to look at every kind of living thing and determine how they are similar and how they are different to other living things.
Here is where it gets a little tricky. A lifeform might be very similar to one living thing, but less similar to another, and even less similar to a third living thing. For example, a dog is very similar to a wolf, less similar to a horse, and very different from a lizard.
