User:Mcgheess.83/The Evolution of Altruistic Behavior

The evolution of life on Earth can be studied and observed through many different traits that life, itself, possess. Each living organism on this planet has a specific DNA make-up, or genome, which determines everything about that individual. From fur color, to the presence of a heritable disease, to how aggressive an individual is all coded for in DNA and expressed in nature to where natural selection can select for or against specific traits. In this particular paper, the evolution of the behavioral trait, altruism, is discussed. Altruism is defined by an individual performing an action at the cost of its own fitness for the benefit of another's fitness. Hamilton first showed this relationship through a mathematical equation defining the cost and benefit compared to the relatedness of the individuals involved in such transaction. The groundwork laid down by Hamilton in the 1960's sets the stage for many evolutionary biologists that will study how altruism evolved.

The equation c/b<r, which is defined by altruism will be favored whenever the ratio of the cost of the actor to the benefit of the recipient is greater than the relatedness of the two individuals, ←Stephanie, follow this template for citing references.

is the mathematical expression of Hamilton’s Rule. The papers that will be used to discuss the evolution of this behavioral trait approach the topic from different angles, using different aspects of ecology to observe how and why natural selection would select for the “cooperative trait” or what is known as altruistic genes. The implications of understanding how altruism evolved can help evolutionary biologists discover more links within evolutionary transitions as well as why the cost of working in groups overcomes the obvious choices to increase one's own fitness. The aspect of relatedness between individuals in a population serves as a staple in altruistic behavior given the cornerstone work done by Hamilton. Since this study, altruism has been studied from a black and white approach. This means that the behavior of one individual is quantified as either giving benefits to a relative as a cost of one’s own fitness or giving no benefits to any individual at no cost to oneself. In a study done William Engels approaches altruism as a continuum of behavioral options for an individual. To set up this experiment, Engles focuses on the cost benefit ratio as a phenotype, x, in the population. He sets the degree of relatedness, r, to be constant. This allows x, to be a continuous trait, so that the actor has a wide range of behavioral options from which to choose (Engles 1982). This continuum allows evolution to act in a way that will favor individuals that exhibit cooperative behavior to increase in a population overtime. This is so because when there are many options for behavior, equilibrium can be reached rather than just a perpetual increase or decrease of the altruistic trait. Additive genetic relatedness affects the heritability of the trait, such that the lower levels of heritability exhibited, the slower equilibrium will be reached. The paper argues that by viewing the c/b has a continuum Hamilton's rule can be applied here. Alternatively, when limited by a two-way observation (Engle 1982) Hamilton's rule is no longer applicable and therefore an inaccurate representation of the selection of altruistic traits is concluded. This is something that is worth mentioning given the differences in experiment types encountered in researching for this paper. There is a certain degree in which altruism happens within a population. As addressed before, individuals who are related to one another give up some fitness of their own to increase the fitness of another. This makes sense because the two individuals share some genes; by helping the relative, some of their own genes are being passed on to the next generation. In a study done by Peter Taylor and Andrew Irwin, overlapping generations in a population can promote altruistic behavior. They observed the benefits of increased fecundity and survival by way of altruistic acts. By using mathematical models of ecological statistics variables, they observed whether increased fecundity or increased survival was promoted by altruism and which one truly benefits the individual. One thing that is important in this study was the population was not spatially static. Actually, to observe, truly, whether fecundity or survival is promoted by altruism the population had to be “elastic” (Taylor et al 2000) meaning there had to be some degree of dispersal among these related individuals. This is relevant because for altruism to be selected for there needs to be a way to export some of those benefits and compete with other traits among members of less relatedness (2000). This idea is supported by the fact that survival cannot benefit the population more than fecundity because if offspring were simply surviving in the same space then there would be increased competition with each generation. However, by way of the idea of fecundity supporting altruistic acts, viable offspring then disperse to new areas spreading the genes of the original population. Overall, if a population has the genes for altruistic behavior and there is some generational overlap, then those reproducing individuals will provide offspring of the similar genes in which multiple individuals will help support those offspring so that they may disperse and spread those altruistic genes to other areas. Therefore, overlapping generations support altruistic behavior. In other words as observations in population ecology evolved to include multiple individuals representing different generations as a unit, rather than one individual reproducing an offspring that will then go on to live as one until it reproduces, so did altruism. This is so because if the populations were to extend its genes, support for offspring over generations would have promoted and therefore evolved altruism. Empty sites within a habitat can promote altruistic behavior ( Alizon et al 2008). Given a population that occupies some given environment in which there are patches that are occupied and unoccupied. In the occupied patches, there will be competition between these individuals. It is important to mention that, for this study, there is a high degree of competition within occupied patches. If there are empty patches within the habitat, this could alleviate some of the competition among individuals in occupied patches. So by individuals dispersing, and spending some cost on the dispersal act, they are alleviating that competition of their neighbors (2008). This is benefitting non-dispersers by increasing their fecundity because fecundity of patch occupant’s was 75% of those who reproduced in a patch alone (2008). As well as, dispersing in what is known as budding dispersal can also promote altruism by kin selection. Small groups of related individuals occupying a new site will then have higher fecundity and decreased competition (Kümmerli et al 2009). In one study, the aspects of life history traits, population density within a habitat, fecundity and survivals’ effect on altruism are observed simultaneously. It is stated that there is a feedback between life history traits, demography, kin selection and the selective pressures on altruism (Lion 2009). This study suggests that survival is affected by both age structure and habitat saturation. Survivorship is a life history trait and this will affect the selective pressures on social traits which will then in turn affect the population dynamics, creating this feedback on altruism evolution (2009). Cooperative breeding comes into play here by individuals helping others to raise offspring thereby increasing fecundity which is known to support altruism behavior and the genes that code for such behaviors (2009). An observational study done by Robert Daniels, looks at the nest guard behavior of the Antarctic fish, Harpagifer bispins. H. bispins is a small fish that lives in the bottoms of shallow waters of the Antarctic Peninsula. They have the longest brooding period of any fish even among other Antarctic fish species which have on average longer brooding periods than non-Antarctic fish species. Daniels makes a point to define true altruism at the beginning of his publication. He defines a true altruistic act to be “an act performed that benefits an unrelated individual to the detriment...of the donor who can expect neither immediate nor futur repayment” (Daniels 1979). He observed H. bispins in its natural habitat, as well as in laboratory tanks, to observe the nest replacement behavior. There are two main threats to nests: predation and a fungal growth that when established nest mortality is certain. Nest guards are prevention measures for both of these and are usually unrelated males. To define whether or not the replacement of nest guards by unrelated males is truly altruistic or not, Daniels observed what, if any benefits do the male replacements receive when guarding the nest. Through observations in the field and in the lab, no substantial benefit is gained by the male nest guard. It is important to note here that this species of fish is social and that several unrelated fish can share the same area. If there were benefit to be gained from being a nest guard, it may include use of a protected site, increased social status, or experience in reproductive behavior (males). However, if these were the benefits to be gained, there are other ways that these can be gained with far less cost to the individual than nest guarding would provide. He also makes note of whether nest guard replacement is a parental act done by multiple fertilizers of the eggs. If this were the case then the nests taken from one area and placed in another should remain unguarded because those individuals would be unrelated. This does not hold up when observed in the lab. Nests that were transported to fish that were not there at the original site still guarded the nests. This study is interesting in thinking about how altruism evolved because of the harsh environment these seemingly true altruistic acts are taking place. Antarctic is the coldest continent in the world (amnh.org). Organisms adapting to the niches within harsh environments could have developed genes that express altruistic behavior to better survive in harsher environments. The evolution of altruism can also be observed from a resource perspective, not just fully on survival, reproduction, or spatial effects. Ecological constraints could be the strongest driver to evolve altruism (Van Dyken et al 2012). Altruistic traits such as “resource-efficiency” and “resource-enhancement” are easily observed through actions like provisioning, agriculture, and pack hunting. When there is local competition, these traits are strongly favored and can be observed in many social organisms (2012). Stemming from the previous discussion, increased survival and fecundity eventually will create more competition because more individuals are able to occupy a habitat. This will then put more strain on resources available to individuals. At this point in the evolutionary cycle, resource based traits will then become more selected for, promoting resourced based altruism (2012). This feedback loop will then continue to switch from favoring fecundity altruism to resource altruism and so on, always selecting for the altruistic traits that benefit the individual actors and recipients (2012). In conclusion, the evolution of altruism is somewhat of a new research topic. Substantial work in the field only being done in the last 60 years allots more questions to be asked. The more work done on what drives altruism to evolve will need to involve deeper understanding of ecology and population dynamics (Van Dyken 2012).