Good genes

= Good Genes Hypothesis =

The Good Genes Hypothesis is an evolutionary theory that elaborates on the motivations of female/male mate choice. It presumes that females and males of human and nonhuman animal species choose the mates that present “good genes” or “genetic quality.”

These are traits or qualities that have evolved through sexual selection; they are “signals of superior quality and condition." Species receive two resources that particularly affect their offspring: DNA, which is combined with the other mate's DNA in their offspring, and nongenetic material benefits, which are the result of adaptations in mates or as byproducts in mates. “Selection favors choice of mates that, all else equal, provide DNA that promotes offspring (and hence mate chooser's own) fitness." In other words, females and males are biologically designed to unconsciously choose the mates that outwardly show these qualities; some traits in men that indicate reproductive fitness are broad shoulders and an overall muscular body. Some examples of good genes in women are a .7 waist-hip ratio, and youthfulness. Symmetrical features in humans are considered to be representative of good genes in both sexes.

Examples of Use in Context
There are three different types of good genes that mates offer one another: intrinsic good genes, compatible genes, and diverse genes. Intrinsic good genes are associated with rates of very high fitness; the individuals who pass them down affect the mate chooser's offspring and their descendants.

Compatible or complementary genes of a mate possess alleles that work well in combination with the other mate's alleles, but not all of them.

Diverse genes are necessary to avoid lineage extinctions. Lineage extinctions occur when a species fails to reproduce. In environments where this may be the case, individuals diversify offspring to enhance fitness. This allows populations to successfully adapt to environmental changes. In times of this environmental uncertainty, individuals become either lucky or unlucky, meaning they either possess alleles that favor or disfavor the changing conditions. According to Thornhill and Gangestad, “an allele that predisposed an individual to genetically diversify offspring could be favored by selection over multiple generations of descendants.

According to Barash, sexual selection theories that weed out the mates with bad genes "is of greater concern to females than it is to males, simply because the male investment in each offspring need not be large, whereas a female is typically committing a large part of her reproductive future whenever she chooses a male." Males do exert some choice for females depending on the circumstances, although it is common that males compete, showing their dominance and good genes in action compared to other males for females to choose afterward. Inbreeding is an avoided practice because the gene combinations that result signal low fitness.

History
In a classic essay written by evolutionary biologist Robert Trivers in 1972, Parental Investment and Sexual Selection, he introduced the term “good genes” to the scientific discourse. It referred to individuals choosing those mates which possess the alleles that would benefit their offspring.

Debates
The good genes hypothesis poses many points for lively debate.

Richard Dawkins is an ethologist and evolutionary biologist. He wrote The Selfish Gene in 1976, sparking debates on the primary function of genes. The phrase, "selfish gene" was coined by Dawkins in this both critically contested and acclaimed book. The selfish gene theory states that genes, in colloquial terms, have a mind of their own, or that they are characterized as driving a human to successfully reproduce. This means that an individual's actions are not only motivated by their genes, but also by the desire to have offspring of genetic quality. In other words, Dawkin's publication has contextualized a biological or genetically determinist argument.

In recent years, more and more theories are challenging this viewpoint, such as the social selection theory posed by Joan's Roughgarden. Her book, "The Genial Gene," which alludes to the title of Dawkin's book, emphasizes examples of cooperation and altruism as evolutionary explanations for sex as opposed to a more selfish, sexually conflicting viewpoint that Dawkins presents as the inherent destiny of humanity because of our genes. The problems with The Selfish Gene theory are also problems of the good genes hypothesis, and the two can be linked together as conflicting in the science world on the grounds that they both rely too heavily on the agency and power of an individual's genes. Genetic determinism becomes an even bigger problem when it motivates biology. The overarching frameworks between The selfish gene and the good genes hypothesis reveal an ongoing, central debate in evolutionary biology.

Another issue with the good genes hypothesis is that it appears to be mistaking phenotype for genotype. In other words, our cultural conceptions of beauty are labeled as "signaling reproductive capacity," but a particular phenotypic ideal of beauty greatly discounts the necessity for genetic variation, which is crucial in promoting diversity among species as well as providing phenotypes that may respond to environmental changes in different ways and respond to disease more efficiently. The inherent evolutionary strategies behind the good genes hypothesis and the selfish gene hypothesis is debilitating to a more holistic understanding of biology because it attempts to seek perfection by rejecting genetic variation. In the words of Roughgarden, "'A major threat to the human rainbow is the misclassification of human diversity as disease....the absence of scientific definitions for normal and function opens the door for societal norms to take over - allowing social values to masquerade as science'" Although this quote can apply to a multitude of traits and actual genetic defects, it also applies to the idealization of beauty in relation to the good genes hypothesis, impacting the science through since it does not take into account diversity and instead is held up by social norms. Defective traits or merely "unattractive" traits are not always harmful to the individual, and may be neutral or even advantageous depending on the external environment.

It appears that there is a contradiction between the good genes hypothesis and the sexual selection paradigm. The good gene hypothesis suggests charactieristics like symmetry and waist-hip ratio as good genes in females, and males will be attracted to these traits; however, the sexual paradigm states that females are the coy choosers of the eager males so males are not the ones choosing, so why are females the ones that signal fecundity? This contradicts the notion that women are are more often the seekers than they are sought out by males. It proves difficult to reconcile sexual selection theory and the good genes hypothesis; however, in some situations males do become the choosers, and this directly challenging sexual selection theory. The good genes hypothesis is interestingly worded in terms of female mate choice moreso than male mate choice, and many recent studies have found dozens of problems with the sexual selection paradigm, challenging its validity.

For instance, the Encyclopedia Britannica explains the good genes hypothesis in relation to female mate choice. It states that the good genes hypothesis is "an explanation which suggests that the traits females choose when selection a mate are honest indicators of the male's ability to pass on genes that will increase the survival or reproductive success of her offspring." Wikipedia's definition also explains the hypothesis in relation to female mate choice. It states that "Females often prefer to mate with males with external ornaments." The information given by Thornhill and Gangestad in the chapter, "Good Genes and Mate Choice" from their book, The Evolutionary Biology of Human Female Sexuality (2008) states that males are attracted to the good genes of females, and this is contradictory to the sexual selection theory model.

There is little to no empirical evidence supporting the claims of the good genes hypothesis.

Author
Chelsea Faria