Evolution is biology's core theme that ties together all the other themes. This is because evolution explains

The change in the inherited characteristics of organisms over successive generations.

Explanation:

Characteristics that defines a biological organisms are passed down from parent to offspring during sexual reproduction. These characteristic can change over time due to mutation of genes. The new characteristics can either become more dominant; if it enhances the organisms chances of survival, or can die away or even lead to the complete wipe out of the species, if it does not increase the odds of survival of the organism. The mechanism of the development, or eradication of these characteristics is through natural selection, and sexual selection.

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.

there's no big difference.

explanation:

the only little different between a rabbit and bunny is just that bunnies are much smaller than rabbits. bunnies are basically baby rabbits.