What is a Last Common Ancestor?
“Last common ancestor” refers to the most recent possible shared ancestor between two individuals, species, or groups of life. For instance, the last common ancestor of all animals is thought to have existed about 610 million years ago, though it may be much older. We can infer some of its features by looking at commonalities held by all living animals. For instance, the fundamentals of cellular metabolism are held in common among all animals. There are two ways to figure out the last common ancestor of two subjects, and they’re both imperfect. The first is to dig up fossils and make guesses about their place in the evolutionary tree, based on morphology and other clues. This can fail because interpretations can be incorrect, and the vast majority of all species never left any fossils. The second is to look at the genomes of living animals and see how much information they have in common. The less shared genetic information, the more distantly related to two are, and the differences be
