Final answer:
Natural selection leads to changes in allele frequencies in a population by favoring traits that are beneficial for survival and reproduction, hence increasing their prevalence while decreasing detrimental alleles. This adaptive evolution is driven by environmental pressures and genetic variation within the population, but is limited by the existing genetic variance.
Step-by-step explanation:
Natural Selection and Changes in Populations
Natural selection is a core concept of evolutionary biology and it explains how specific traits increase or decrease within a population over time. This selective process impacts allele frequencies, which are the variations of a gene that may occur. When an allele offers an advantage, like better survival or reproductive success, it increases in frequency as the trait is passed on to subsequent generations. Conversely, alleles that confer a disadvantage may decrease in frequency or be completely eliminated over time, a process observed in population genetics.
A classic example of natural selection at work is the variation in wing coloration of the peppered moth, which changed from mottled white to dark with industrial soot and then back again as pollution levels decreased. Adaptive traits, like the longer neck of a giraffe, become more prevalent due to the increased survival and reproductive rates of those possessing the trait. This ongoing process is what leads to adaptive evolution, the tailoring of populations to their environments through the promotion of advantageous traits.
It's important to note that natural selection acts on the phenotype, not the genotype itself. The phenotype is the actual expressed traits that can give an advantage or disadvantage in survival. Changes in DNA lead to new alleles in a population's gene pool, and these changes can be beneficial, enabling adaptation and survival. However, natural selection can only act on existing variation and does not create new traits from scratch. Factors like nonrandom mating, polymorphisms, and genetic drift also play significant roles in shaping the gene pool of a population.