Altruism: The Evolution Of Altruism In Human

Question 1:

Altruism is a behavior that benefits another individual despite the cost to oneself (Sparrow and Spaniol, 2018). Consequently, altruism in humans may have evolved as a result of either kin selection, group/multilevel selection or reciprocal altruism. By definition, kin selection involves the tendency to assist those of close relation compared to those more distantly related to oneself (Chaung and Wu, 2017). Secondly, multilevel selection theory involves group led benefits where the fitness of the group outweighs the costs to the individual (Ogorman et al., 2008). Thirdly, reciprocal altruism comprises cooperation between individuals where one helps another with the expectation that the other individual will help them out in return at a later date (Takano et al., 2016). Of the three types of altruism, I hypothesize that kin selection best explains and fits with the evolution of altruism in humans.

The kin selection hypothesis, also called the inclusive fitness theory, predicts altruistic tendencies will be higher towards another individual when the benefit to the individual and relatedness are greater than the cost to the actor (Foster et al., 2005).

Inclusive fitness theory supports the evolution of altruism in species, stating individuals will work towards increasing their fitness through the increased production of offspring or by aiding in the reproduction of relatives who hold similar genes to oneself (Chaung and Wu, 2017). The thought is if one were to partake in altruistic behaviors that benefit another individual, such as a close relative one would increase the fitness of that individual and, thus, increase the number of offspring being created that are of close relation to the altruistic individual. Furthermore, inclusive fitness theory presumes that altruism evolved to increase the percentage of the actor’s genes in a population, with research indicating that these mechanisms of altruistic behavior in humans follow with inclusive theory in the relatedness of the individual as well as being based on emotional closeness to an individual (Korchmaros and Kenny, 2001). However, when looking at it from the perspective of emotional closeness a major limitation in the theory of kin selection can be seen. The one limitation of the kin altruism theory is the presence of emotional closeness within a population, where individuals will tend to help others who they find emotionally close to themselves, such as friends than non-emotionally close kin (Korchmaros and Kenny, 2001).
Looking further into the evolutionary mechanisms responsible for kin altruism in humans, parental investment should be investigated, especially since male parenting in mammals are found in less than 5% of species, however with humans, this number is greatly increased (Geary, 2015). The principle of parental care involves the ratio of the cost to the individual and improved offspring survivorship. The concept of parental investment has indirect and direct benefits on the offspring, where offspring survival is increased directly through resource acquisition from the parents, and the indirect benefit of increasing the ability of the individual to pass on its genetic material (Geary, 2015). This principle closely follows the principle of kin selection where they both work towards increasing genetic inheritance through the population.
Additionally, Parental investment has the potential to expand to grandparents, as shown by kin altruism, whereby the grandparents will depict parental care towards grandchildren due to the genetic relationship between the two (Jeon and Buss, 2007). Jeon and Buss theorize that kin altruism should follow through to cousins as well as grandchildren who hold a direct line of relation. For this study, Jeon and Buss (2007) created a mathematical model to determine which cousins an individual would be more likely to show kin altruistic tendencies towards based on relatedness and compared these computer-generated numbers to the observed findings, showing that individuals will have cousin-specific behaviors towards those they sense more genetic relation too. A limitation of this study would detail the inability to without a doubt distinguish an individual's ability to recognize the variability in the genetic relation of non-identified cousins in the family. An improvement on this study to distinguish emotional relatedness to actual genetic relatedness would be to use individuals who are not already aware of the family ties between cousins to show the degree of altruism towards these individuals.
Overall, kin selection best explains the evolution of altruism in humans with the factors of parental investment, relatedness, emotional closeness towards family members, and increasing fitness through the aiding of relatives who hold similar genes to oneself. Furthermore, kin selection follows with the concept in altruism, where a behavior benefits another individual despite the costs to oneself, however, with kin selection the altruistic behavior ultimately benefits the fitness of the individual from purely a stance of increasing one's genes in the population. As such, I think kin selection best explains and fits with the evolution of altruism in humans.

Question 2:
A phylogenetic tree based on a single gene will not accurately represent the evolutionary history of species due to both lateral gene transfer, and the lack of DNA fragments to determine gene changes in long-extinct species resulting in a tree of life that will reflect only known species. Accordingly, lateral gene transfer refers to the transfer of genes between organisms and contributes to around 20-30% of the variation in genes between species (Bapteste et al., 2004). This poses an issue with phylogenetic tree reconstruction due to the sharing of genes between related and unrelated species causing certain species to appear more closely related when looking at a single gene. In contrast, the inability to use genes from extinct species causes large holes in the phylogenetic tree being constructed from known genes. This is because genes cannot be taken from ancient fossils or that only phenotypes can be inferred from a fossil, while genotypes are indeterminable in most fossil types.
Firstly, lateral gene transfer is the transfer of genes between organisms and can occur on account of viruses, transposons or from natural processes in most bacteria and archaea (Khan et al., 2016).

These naturally occurring processes allow for lateral gene transfer between prokaryotes. For instances, prokaryotes are capable of taking up DNA from their environment in a process called transformation, transfer genes through transduction with phage particles, and many other gene transfer processes (Ku and Martin, 2016). The transfer of genes may increase the mutation rate in the genomes of these organisms with the insertion of new DNA segments into their own genome with deleterious, beneficial or silent effects with the potential to increase the rate of change in organisms and thus the rate of

evolution.
The mechanisms of lateral gene transfer have contributed to the spread of antibiotic-resistant genes, with antibiotics installing strong selective pressures for resistance and the uptake of naked DNA elements in the environment contributing to the acquirement of antibiotic resistance genes through lateral gene transfer (Sieber et al., 2017). Furthermore, Sieber and associates (2017) identified a lateral gene transfer occurrence between humans and bacteria with a 685 base pair fragment of human DNA found. This highlights the issue of constructing a tree of life from a single gene as, if one were to use the single gene found in humans and certain bacteria, the tree of life would have the potential to depict humans as more closely related to a species of bacteria than that bacteria is to other bacteria. A further example showing the effects of lateral gene transfer on the construction of a tree using a single gene is seen in a study by Kanhere and Vingron (2009) who found that out of 171 different gene transfer incidences between Archaea and Bacteria, 118 of them were responsible for metabolic genes and 53 of them involved translation genes occurring between bacteria phyla resulting in dramatically different phylogenetic trees when these genes were compared to other genes. Due to the prevalence of lateral gene transfer, it is difficult to determine which genes are a result of the transfer and which represent gene losses and gains in a phylogenetic tree.
Secondly, the inability to use genes from long-extinct species causes large holes in the phylogenetic tree and difficulty in its construction from known genes. According to Moret and Warnow (2002), phylogenetic trees are constructed using DNA, RNA or amino acids for genes, yet a key challenge in constructing a tree from genes is inferring relation from ancient species where DNA fragments are not available. Much of the tree of life is comprised of species that are no longer around with multiple mass extinction events in our history. This causes large gaps and the tree to represent only extant organism. The fossils of extinct species may be made through the replacement of organic material with new material to create casts or per-mineralized bones (Freeman and Herron, 2001). Due to the organic material being replaced by minerals in most fossils, there are no traces of DNA to compare genes to extant species. However, some fossils are of remains suspended in amber or preserved in ice. The remains may contain trace amounts of DNA, unfortunately, the half-life of DNA does not allow for the preservation of ancient genes. For instance when extracting DNA from ancient papyri, researcher found the half-life of DNA to be between 19 and 24 years, resulting in the total loss of any DNA fragments in the papyri sheets made from ancient papyrus trees to be within 532 and 672 years (Marota et al., 2002). The half-life of DNA in this organic material does not leave much hope for the extraction of preserved DNA fragments from fossils. Nevertheless, in another study on DNA half-life, it was determined that small fragments of DNA can survive at temperatures below 5 degrees Celsius for 800-450 thousand years (Allentroft et al., 2012). Despite this increase in the lifespan of a fragment of DNA when subjected to extremely cold temperatures, the lack of DNA in remains older than 450,000 years leaves significant gaps in the evolutionary tree when using genes for comparison.
Ultimately in regard to the lack of DNA fragments and the abundance of lateral gene transfers, a phylogenetic tree made from a single known gene does not accurately represent the evolutionary history of species. The lack of DNA fragments from ancient species and thus the inability to determine the genes responsible for many species in our history generates far too many unknown variables and gaps in the evolutionary tree for an accurate representation. Additionally, the myriad of instances of lateral gene transfer between both closely and distantly related species causes discrepancies in the branching of species on the phylogenetic tree when comparing a single gene. In conclusion, a single gene should not be relied on to create the tree of life.