It was over a century and a half ago that Charles Darwin published his revolutionary book "On the Origin of Species". However, the genetic evidence that substantiate his theory of evolution was revealed many decades later. Nowadays, by virtue of their genetic analysis capabilities, scientists can calculate the genetic proximity between species and thereby place them on the evolutionary "tree of life". The following video depicts how life began on Earth and leads us through a journey from the first cells to human beings, all based on our current genetic knowledge.
The idea behind the tree of life is a rather simple one: life is dynamic and genetic deviations occur and accumulate constantly. Such deviations, which allowed for the development and diversification of species, left their footprints on the DNA of living organisms. In order to grasp this concept let's take one family as an example. A certain person has kids who resemble him as well as each other. As the years passed they had kids of their own. These grandchildren resemble their father, who resembles his father. However, there is a lower level of resemblance between the grandchildren and the grandfather. Were we to compare the DNA sequences of the three "species" (grandson, father, grandfather) we would learn that the grandson's DNA bears high similarity to the father's DNA, which is similar to the grandfather's DNA. The grandson's DNA bears less similarity to his grandfather's DNA, and in this manner we can place each of them in their genetic family tree.
Looking at cousins we can observe that their degree of similarity is smaller than that of siblings or parent and child. This principle is also true for species. When a species diversifies into two different species, the new species is more similar to its immediate predecessor ("father") than to its "grandfather". Analyzing the DNA sequences of different species can tell us how similar they are, which enables us to assign each species a similarity score. Using such scores for DNA segments can help us determine how close our species of interest are to each other and even estimate when diversification events occurred. Not surprisingly, analyses of the genetic evidence match quite remarkably to fossil dating. The trees of life, or in their scientific name phylogenetic trees, reveal that every two species have a common ancestor, or in other words that we all share a common origin.