For one, without genetic variation, a species is more likely to face significant danger from disease. In humans there are some diseases that affect a few races more than others, but because of...
genetic variation happens because of meiosis. chromosomes are randomly in each sperm/egg cell, and so when they come together it's unlikely to get the same combination twice
Genetic variation occurs through random gene mutation all the time and espescially during meiosis where different allele combinations occur through the formations of chiasma in prophase and as part...