Question

what is natural selection?
every gene in a population
individuals leave and start a new population
survival of the fittest
new genes in a gene pool

Explanation:

Natural selection is a fundamental concept in biology. It refers to the process where organisms better adapted to their environment tend to survive and reproduce more successfully. This is often described as "survival of the fittest." The other options do not accurately define natural selection. "Every gene in a population" is too broad and not specific to the mechanism of natural selection. "Individuals leave and start a new population" describes a founder effect (a type of genetic drift), not natural selection. "New genes in a gene pool" could be due to mutations or gene flow, not natural selection itself.

Answer:

survival of the fittest