How does natural selection produce changes in populations and not individuals?

Natural selection acts upon individuals within a population, but the changes resulting from natural selection are observed at the population level rather than in individual organisms. This occurs because natural selection operates over successive generations and influences the frequency of certain traits within a population, leading to evolutionary changes over time. Here's how natural selection produces changes in populations and not individuals:

1. Variation within Populations: Populations consist of individuals with varying traits due to genetic variation arising from mutations, genetic recombination, and other factors. Natural selection acts on this variation, favoring certain traits that confer advantages in a given environment.
2. Differential Reproductive Success: Individuals possessing traits that are better suited to their environment are more likely to survive, reproduce, and pass on their advantageous traits to their offspring. Over time, these advantageous traits become more common within the population because individuals with these traits are more successful in reproduction.
3. Change in Allele Frequencies: As certain traits provide a reproductive advantage, the alleles (gene variants) associated with those traits become more prevalent in the population. Conversely, alleles for less advantageous traits may decrease in frequency or eventually be eliminated from the population.
4. Accumulation of Adaptations: Over successive generations, the accumulation of favorable traits results in adaptations that enhance the population's fitness and its ability to survive and reproduce in its specific environment.
5. Population-Level Changes: While individual organisms undergo selective pressures, the changes resulting from natural selection, such as shifts in allele frequencies and the prevalence of certain traits, become evident when observed across the entire population rather than in individual organisms.

Natural selection is a gradual process that operates on the genetic variation within a population, leading to changes in the genetic composition of the population over time. It does not change individual organisms directly but acts on their heritable traits, influencing the frequency of those traits within the population.