Why are Siberian tigers so big?

This one is an easy question to answer. It is to do with evolution. So, you have to believe in Darwin's theory of evolution to believe the answer. Siberian tigers live in colder climates than Bengal and Sumatran tigers. They live in the far north, in fact, the far east of Russia near Vladivostok. They live in the snow and birch tree forests. 

Siberian tiger. Image: MikeB

They need to be able to protect themselves against the extreme cold which is why through natural selection they have evolved to be bigger because this gives them a smaller surface area-to-volume ratio which helps to reduce heat loss from the body of the animal. As more body heat is conserved, they are warmer which helps them to survive. Evolution is an act of survival.

It is known as Bergmann's Rule.

So, animals living in the North of the planet where temperatures are considerably lower will generally be larger. Conversely, animals living near the equator will be smaller and this applies to the Sumatran tiger which lives on the island of Sumatra in East Asia. The Sumatran tiger is the smallest of the tiger subspecies. Sumatra is one of the Sunda Islands of western Indonesia.

RELATED: How many types of tigers are there?

Below, I publish a map showing where the Siberian tiger lives. You can click on it to see a larger version. There are flags embedded in it which you can also click on.