Evolution is a change in the frequency of genes in a population over time. Evolutionary psychologists try to explain universal behaviors. They study how natural selection has encouraged certain behavior patterns to develop.
Charles Darwin (1809–1882) was a British naturalist who is best known for his contributions to evolutionary theory. Although others had noted that species evolved over time, Darwin first put forward the theory of natural selection to explain the process of evolution.
According to this theory, certain inherited characteristics give an organism a survival or reproductive advantage. Organisms pass on these characteristics more often than they pass on other inherited traits.
Example: The species of primates called mandrills have evolved to have bright blue rear ends, because brightly colored rumps help them attract mates and give them a reproductive advantage. Porcupines evolved to have quills, because quills help them to avoid predators and reproduce. This gives porcupines a survival advantage.
A characteristic that gives a reproductive advantage helps an organism to mate successfully and pass on its genes to the next generation. A characteristic that gives a survival advantage helps an organism to live long enough to reproduce and pass on its genes.
People often use the phrase “survival of the fittest” instead of “reproduction of the fittest,” but according to evolutionary theory, survival alone isn’t enough. Creatures need to survive long enough to reproduce. Reproductive success is measured by how many offspring a creature produces.
Another concept related to reproductive success is inclusive fitness, described by W. D. Hamilton in the 1960s. Inclusive fitness is the reproductive fitness of an individual organism plus any effect the organism has on increasing reproductive fitness in related organisms. Some researchers believe that the concept of inclusive fitness explains why certain organisms sacrifice themselves to save others in the species. According to this theory, people might risk their lives to save their children or close relatives, but not to save distant relatives or unrelated people. Because people share more genes with close relatives, saving them has more payoff in terms of passing on genes to the next generation.
An adaptation is an inherited characteristic that becomes prevalent in a population because it provides a survival or reproductive advantage. Because evolution occurs over a long period, an adaptation can remain in a population even after it has stopped being useful.
Example: Human beings have a genetic preference for fatty foods, which explains why fried chicken, french fries, and buttery popcorn are so popular. Evolutionary psychologists say that the preference for fatty foods derives from the days when people hunted and gathered and food was scarce. Eating high-fat foods was important because fat gave people the calories they needed. In other words, the preference for fat was adaptive. Today, in wealthy countries with abundant food and sedentary lifestyles, the preference for fat remains, despite the fact that it no longer has beneficial effects. In fact, consuming fatty foods can lead to health problems.
Evolution relies on mutations, or small changes in genes. Mutations happen because of two events that can occur during the formation of egg and sperm cells:
Sometimes, a mutation results in a new trait. If the individual with the mutation reproduces successfully, the mutation will be passed on. If the new trait proves advantageous, the mutated gene that caused the trait will increase in the population over a long period and thus propel evolution.