Final answer:
Genetic drift is a random process affecting allele frequencies and can lead to allele fixation in small populations, whereas natural selection is a non-random process that acts on advantageous traits and is not as reliant on population size.
Step-by-step explanation:
Comparing and contrasting genetic drift and natural selection involves examining several aspects of these evolutionary mechanisms. Genetic drift is a random process that can influence allele frequencies within a population's gene pool, usually more significantly in small populations or after events like natural disasters, known as the bottleneck effect.
It acts on the population by chance, not discriminating between helpful and harmful alleles, and can lead to allele fixation, especially in small populations, decreasing genetic variation and potentially increasing differences between populations.
This is in contrast to natural selection, which is a non-random process that selectively acts on phenotypes and alleles that confer an advantage in a given environment, thus discriminating between helpful and harmful alleles. Natural selection can also lead to allele fixation when advantageous alleles become universal due to reproductive success.
The effect of genetic drift is more pronounced in smaller populations, whereas the impact of natural selection is related to environmental pressures and is less dependent on population size.