In biology, variation refers to the differences that exist between individuals within a population. These differences can be in their physical traits (morphology), physiology, or behavior. Variation is crucial for evolution because it provides the raw material for natural selection. Individuals with variations that make them better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to their offspring. Sources of variation include: Genetic variation*: This arises from mutations (changes in DNA sequence) and genetic recombination during sexual reproduction. Environmental variation*: This is due to differences in environmental factors that affect how genes are expressed. For example, identical twins can develop different traits if raised in different environments.