One of the important questions to address in the evolution of eukaryotes is the origin of multicellular forms of life. This process appears to have occurred at least four separate times in the evolution of eukaryotes, meaning that there may be more than one explanation for this process. We will ignore that problem and try to come up with general hypotheses that could explain multicellularity in several groups as opposed to being too specific. Any solution for the problem of multicellularity needs to explain this process in terms of our understanding of evolution. If we examine a multicellular organism, what we find is a group of cells working together, with different cells specialized for different jobs. This sort of cooperation seems intuitive, as it is a common part of human society, but from an evolutionary standpoint it presents important difficulties. The problem is that for such major changes to have occurred, it virtually requires that natural selection was involved in shaping the process at least some of the time. This means that being multicellular must have been successful at increasing the fitness of individuals who took part in it, compared to the fitness they would have received if they had remained as individual cells. If you examine a multicellular organism, you find that the vast majority of the cells are confined to a single generation, with any transfer of genes to the next generation taking place through the actions of a small number of reproductive cells (e.g., sperm and egg cells in most animals). This means that in terms of fitness, the majority of cells in a multicellular organisms have ZERO fitness while reproductive cells can have quite high fitness. This would seem to be an example of altruism, where one organism sacrifices fitness to help another individual increase its fitness. From an evolutionary standpoint, it seems that selection would be against an altruist because any genes that favored altruistic behavior should be removed by those individuals giving up their reproduction. This presents us with an evolutionary puzzle – altruistic behaviors seem to violate our understanding of evolution, but they do exist. This suggests that we need to modify our ideas so that evolution can encompass these sorts of behaviors. Three different hypotheses have been proposed to explain how altruistic traits such as multicellularity could have evolved. To test these explanations we would need to be able to see the process occurring in real time, which won’t be possible in most cases. However, if we can find organisms that are showing some aspects of a transition from single-celled to multicellular life styles, we might be able to test these hypotheses successfully. Research on multicellularity has examined a number of organisms, but one of the most commonly used are various species of slime molds. Slime molds are protists that can display both unicellular and multicellular life cycles under certain conditions. We will be examining these organisms as a way to test the different hypotheses for the evolution of multicellularity. Some information on slime molds is presented through links in D2L. When you are somewhat familiar with this case study, you will work together in your groups to discuss the answers to the questions, submitting one set of answers for each group. The document will be submitted to originality verification software, so your names should not be on it (put your names in the comments section where you upload the document to D2L). Your instructor will indicate the due date for the assignment in class.
Question: A second hypothesis for multicellularity is “kin selection”. What does the idea say and what is required for this hypothesis to explain altruistic behavior?
