Common Ancestry and Relatedness

Most of you reading this blog post must be wondering why I titled my blog this way. I decided that the discussion of common ancestry and relatedness is a commonly misused concept; people often refer to relatedness as a characteristic that occurs just because two species have many similar physical characteristics, or refer to our own most recent common ancestor as the chimpanzees. People constantly refer to some organisms as more advanced than others just because they have more genes in their genome or more appendages that connect their legs, or in the instance of argument that humans are more complex than other animals, we are apparently more complex just because we can solve complicated math problems, write poetry, and play music. This is not the case, and quite frankly, now understanding this concept much better, this irks me every time, and I think it is critical that people understand the errors in these statements so as to see the true pattern of evolution and relatedness between all species - that we are all interconnected in so many ways.

Common ancestry, unlike common belief and the belief of systematists in the early 1700’s, is determined not by the most physiological similarities between species, but by the most recent common ancestor shared by the two species. This could be analogous to a family pedigree: you would not say that you are more closely related to your cousin than to your brother just because both of you have blue eyes, whereas your brother has brown eyes. Instead you would intuitively say that you are more closely related to your brother because both of you share a more recent common ancestor (your parents) than you and your cousin (your grandparents). The same idea applies when determining the relatedness between two species. In the above image, species A and B are more closely related than A and C because A and B share a more recent common ancestor than A and C. A and B share a common ancestor at 3, whereas A and C share a common ancestor at 1, which is much more ancient than the ancestor at 3.

Thus, this model allows us to see that only common ancestry can explain why similar structures in distantly related species occur. Similar structures appear because all species share a common ancestor, and during gene mixing and recombination, some of the genes are transferred to the new population of the species (off topic, but a reason why I do not support genetically choosing favorable traits in a child: it disturbs natural selection and gene recombination), and over time, the traits change along the branches of the tree, and accumulate changes. Hopefully this cleared up the common misconception of relatedness and allowed you to see just how different evolution really is, and how all species are actually interconnected to one another. Once I understood this, my view on the species around me changed drastically! I hope the same happened for all of you as well.

~Valeria