Evolution by natural selection brings change to every generation. Its four principles are overpopulation, variation, inheritance, and fitness.
Every generation has more born than able to survive. Random gene mutation allows for variation of genes in the population. The setup of the environment reduces the frequency of unfit variants and increases the frequency of relatively fit ones. A population can store many genetic variants at once to meet changing conditions. Natural selection works only on traits that are heritable. Fitness in evolutionary biology means the probability of surviving and reproducing in a given habitat. Only a tiny part of DNA mutations increases fitness, the rest is harmful. Fitness consists of survival, fertility, and success in raising children and grandchildren. Organisms of certain types survive better in certain conditions than others, and they tend to leave more offspring. Darwin predicted that the population would increase until it reaches the carrying capacity of the environment and the limiting resource runs out. The competition for survival would increase. Selective pressures of the environment will determine over time which genes serve for better adaptation. If conditions change, most adaptive characteristics will become predominant in the population. The same principles of natural selection apply to morphological and behavioral traits. If the genes of individuals can influence their behavior, provided the behavior increases fitness, then this behavior can evolve. Beneficial instincts should spread, and maladaptive ones should be weeded out of the population. Instincts are highly complicated, and humans have a choice to act on them (Miller 9/20/2022, Orr 2009).
Evolution by kin selection is based on the fact that relatives share genes. It is usually best for one’s fitness to cooperate with the close group and compete with others. We live in a world of shifting alliances, helping one over another. Instincts are getting misapplied. According to the kin selection theory, in which propagation of genes is seen as causal to altruistic behavior in kin over attachment and familiarity, there is a “selfish” motive behind helping kin members. A parent of a child has only half of her genes propagated. Rearing an own child, or a full sibling, or four cousins are equivalent in this regard. Family relationships set up selective pressures. Some species recognize kin (Miller 9/22/2022, Fellman 1992).
Evolution by sexual selection takes place when sex sets selective pressures and pushes individuals and further generations to adopt. The fitness goals are the same for females and males - to create a healthy independent child, but their parental investment is different - the amount of energy and time invested in children. As a minimum, females need to create an egg, perform a risky copulation, gestate during pregnancy, give birth, lactate, and carry the baby. Males only need to create smaller sperms and copulate. However, the competition determines enormous variation in male reproductive success. These differences cause sexual dimorphism. In general, females tend to be choosier, smaller, duller, and males more promiscuous, bigger, stronger, or flashier. Good genes are the only preference for females in societies where males do not provide any help with the young. Females want to have male offspring that are attractive to females to propagate their own genes with more likelihood, even though his genes might not be better for the son’s survival. Some females put more energy in raising sons of attractive males. Females determine the health of the male by his looks, which helps also avoid sexually transmittable diseases. With pair-bonding, parental investments of sexes even out, and the dimorphism decreases. Competency at fatherhood is the most desirable quality in males for females (Miller 9/22/2022, Sapolsky 2001).
References:
- Dr. Lynne Miller, lecture notes, September 2022.
- Allen Orr, Testing Natural Selection, 2009, Scientific American. Jan2009, Vol. 300 Issue 1.
- Bruce Fellman, Looking out for Number One, 1992. National Wildlife, World Edition, Vol. 30 Issue 1.
- Sapolsky 2002 - What Females Want
