What makes some genetic mutations more likely to persist through generations? How does an organism’s environment influence which traits get passed down?
In Darwin’s Dangerous Idea, Daniel Dennett writes that natural selection shapes the development of species over time. The interplay between random mutations and environmental factors determines which traits become more prevalent in a population, leading to adaptations that help organisms survive.
Read more to understand how natural selection in evolution works and the surprising ways even tiny genetic changes can make a significant difference in species survival.
Natural Selection in Evolution
Dennett writes that natural selection in evolution is the second part of the algorithm (in addition to random mutation). Organisms with beneficial mutations have an increased chance of surviving long enough to reproduce and pass those same advantageous traits onto their offspring. Over generations, these beneficial traits become more common within the population.
(Shortform note: While Charles Darwin didn’t come up with the phrase “survival of the fittest,” he adopted it after other writers used it to describe his findings. Biologists have since tested how much of a difference in “fitness” between organisms of the same species is needed to trigger natural selection. Researchers made tiny detrimental adjustments to the genes in the microorganism salmonella. They found that reducing the bacterium’s fitness by just 0.01% was enough to create noticeable differences in rates of reproduction, suggesting that evolution will select for even the slightest variations over time.)
The Role of Environmental Pressure
According to Dennett, the environment in which organisms live largely determines which mutations are beneficial (and thus more likely to get passed on) and which aren’t. This is because different environments present different challenges and opportunities with respect to climate, food availability, predators, and competition for resources. Organisms with mutations that happen to be advantageous in their specific environment are more likely to survive and reproduce.
For example, imagine a population of wild, brown rabbits that evolves a mutation causing their fur to turn white in the winter. If these rabbits live in an area with snowy winters, this mutation will help them blend in during those months. Because it helps them survive, the mutation will be passed down to future generations. However, if this mutation appeared in a population of rabbits from a region where it doesn’t snow in the winter, it would not afford them the same survival advantage. Instead, it would make them more visible to predators during winter months and thus less likely to survive and pass the mutation on to subsequent generations.
(Shortform note: Research has largely supported the theory that organisms will evolve to suit their environment. For example, researchers have found that moving stick bugs from one environment to another creates selection pressure in favor of adaptive coloration. Biologists have also found that organisms at the edge of a habitat will adapt new traits to colonize and spread out into a greater range. Researchers built an artificial habitat to test this hypothesis with red flour beetles, a rapidly reproducing species. They found that trait selection at the boundaries of the artificial habitat allowed for a greater spread of beetles when compared to a control population.)
