Perhaps the answer is "physical characteristics". I am simply making an educated guess, however I do know early philosophers classified organisms into two groups, Plants and Animals, and identified them based on physical characteristics.
Answer:
Homologous structures provide evidence for common ancestry analogous structures show that similar selective pressures can produce similar adaptations beneficial features Similarities and differences among biological molecules in the DNA sequence of genes can be used to determine species relatedness
Answer:
Genetic variation is caused by:
mutation
random mating between organisms
random fertilization
crossing over (or recombination) between
chromatids of homologous chromosomes during
meiosis
