Darwin’s original tree of life sketch. Species A is a distant relative of
B, C, and D, which are more closely related. In the diagram, all the
species evolved from a single starting point, labelled (1)Darwin started by drawing evolutionary trees based on things like
physical traits. On his Beagle voyage, he categorised bird species by
features such as beak shape, tail length, and plumage.[2] This field
of research would eventually become known as ‘phylogenetics’, after
the Ancient Greek words for ‘species’ (phylo) and ‘origin’ (genesis).
Although early evolutionary analysis focused on the appearance
of different species, the rise of genetic sequencing has made it
possible to compare organisms in much more detail. If we have two
genomes, we can see how related they are based on the amount of
overlap in the lists of letters that make up their sequences. The more
overlap there is, the fewer mutations are required to get from one
sequence to the other. It’s a bit like waiting for tiles to appear in a
game of Scrabble. Going from a sequence ‘AACG’ to ‘AACC’, for
example, is easier than getting from ‘AACG’ to ‘TTGG’. And like
Scrabble, we can estimate how long the evolutionary process has
been running based on how much the letters have changed from
their original sequence.
Using this idea – and plenty of computational power – it’s possible
to arrange sequences into a phylogenetic tree, tracing out their
historical evolution. We can also estimate when important
evolutionary changes may have happened. This is useful if we want