A(n) is a category of the classification system of organisms that can include multiple kingdoms.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

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.

a symbiotic relationship with the mitochondria