Genetic drift and natural selection are two important ways that shape the diversity of living things in a population.

1. Genetic Drift:

   • This is a random process that changes how often different versions of genes, called alleles, appear in a population.
   • It’s more noticeable in small groups of organisms.
   • In small populations, random events can end up removing certain alleles, which means less variety.
   • For example, if you have a group of 50 animals, something random might happen and wipe out some genetic types, making the overall group less diverse.
   • You can use a simple formula to see how allele frequencies change in genetic drift: $p' = \frac{p + q/2N}{1 + 1/2N}$ Here, $N$ is the size of the population.

2. Natural Selection:

   • Unlike genetic drift, this is not random.
   • Natural selection helps certain individuals with helpful traits to live longer and have more babies.
   • This process works on traits that can be seen, like color or size, causing the helpful traits to show up more in the genes of future generations.
   • For example, if one allele helps animals be 10% better at surviving, it could become much more common over time.

3. Interaction Between Drift and Selection:

   • Sometimes genetic drift can undo the good effects of natural selection, especially in smaller populations.
   • While natural selection helps creatures adapt to their surroundings, genetic drift can cause some alleles to disappear or become the only ones left, no matter if they're helpful or not.
   • In steady environments, natural selection can help keep a variety of traits alive. But in changing environments, genetic drift might take over and lower the variety of genes present.