The Proof Is in the Proteins

    On today's addition of Darwin, Freud, and the Pope Walk Into a Bar...We will be discussing Darwin's idea that there is interconnectedness between species as they descended from common ancestors.

   Over time there has been an overwhelming amount of circumstantial evidence that supports the existence of the universal common ancestor of all extant life on Earth, it is still an open question whether the universal common ancestor existed or not. Most recently, Douglas Theobald, challenged this problem and came up with a few conservative assumptions to show that the probability that all living species descended from a universal common ancestor is infinitely higher than any other hypothesis, including those of multiple origins of the kingdoms (bacteria, eukarya, archaea) or of rampant horizontal gene transfer between species that would, by mixing genomes, make life look as though it had a single origin when it didn't. Douglas is able to provide evidence; proteins of existing species showing a pattern of similarity and divergence reflecting the branching bush of evolution. 

    Whether or not you have an extensive background in biology, it's safe to say, we all have a pretty basic knowledge. But for some of us the only take away from biology is "mitochondria is the powerhouse of the cell". With this in mind, I will try to simply layout some of the general concepts involved in Douglas Theobald's research to help everyone better understand! 

    First, let's break down what genetic code is. DNA is composed of four different nucleotide units [(A) adenine, (G) guanine, (C) cystine, (T) thymine], these bases are strung together in a way that our bodies cellular machinery is able to read and turn them into a protein, which is virtually identical across all species.  These nucleotide units are read in sets of three that encode a certain amino acid. There are 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from these four nucleotides. Of the 64 codons, 61 represent amino acids, and three are stop signals. What was found was the correspondence between the code and the amino acid is nearly identical across animals, plants, and bacteria. There are a few exceptions to this, but they are minor: no species deviates from the code by more than a few amino acids (though some mitochondrial DNA deviates by as many 8 codons). So what does all of this mean? That there are simply too many genes involved in producing the code and turning it into proteins to think that the code's universality merely reflects evolutionary convergence in lineages that originated independently. As I referenced before, the universality results from ancestry, not coincidence. 

   No matter the definition you choose to claim, evolution is the change in genetic composition of a population over time. Meaning populations evolve..not individuals. So, does this in turn mean that life on earth arose just once? While many scientists have previously examined common ancestry more narrowly, as in, among only vertebrates, Theobald is the first to formally test Darwin's theory across all three domains of life. What we know from billions of years of evolution, humans share genes with all living organisms. But, relatedness among species is a concept that depends on genetics as well as history, and there is ample evidence that even distantly diverged lineages have, at times, experienced significant gene sharing (a process known as lateral or horizontal gene transfer, in contrast to the more typical "vertical" transmission of genes from parent down to offspring). Living organisms do have a history, and this does include universal relatedness of one sort or another, be it analogous to a simple tree, a more complex web, or something else. Phylogeny that accurately depicts the historical patterns of ancestry connecting eukaryote branches to their common root, but the shape of the tree is far from resolved. There are some cases that scientist have reconstructed phylogenetic trees within their laboratories and observed it directly as it occurs but as science advances further testing and revision will be done to their analysis'. 

    As scientists continue to divulge more evidence, two points are abundantly clear when it comes to studying common ancestry: evolution biology and phylogenetic literacy. There are many points of controversy that continue to be debated around the idea of common descent. But identifying, confronting, and clarifying misconceptions is how concepts become better understood. So, in this case, there is more relevant information out there to help prove the work of Darwin's theory of interconnectedness.