In continuous variation, there is a variety of measurements that go from one extreme to another. Skin colour is an example of this.
The environment also affects continuous variation...
B Negative
O Positive
This is known as environmental variation and the environment one lives in has a significant affect on oneself.
For example: where a cow lives, the quality of its diet and the weather, can all determine the quality of milk it produces.
There is also discontinuous variation. This is where someone falls into a distinct category; meaning you either have the characteristic or you do not. Blood type is an example of this.