Final answer:
The modern synthesis in biology combines natural selection and genetics, explaining how natural selection affects a population's genetic makeup and leads to the evolution of populations and species.
Step-by-step explanation:
The modern synthesis in biology combines natural selection with genetics. The mechanisms of inheritance, or genetics, were not fully understood when Charles Darwin and Alfred Russel Wallace were developing their theory of natural selection. However, the integration of genetics and evolution in the modern synthesis describes how natural selection affects a population's genetic makeup and how this can result in the gradual evolution of populations and species.