I joined mander.xyz because it has a central theme around the natural sciences. It could possibly include STEM content as well; there is an ongoing discussion about it. The admin(s) are present and very responsive.
For anyone with a love of science and/or nature I recommend it highly as a home instance of Lemmy.
I’m not sure about this particular paper, but usually you can compare the number of mutations in a common protein and use that to estimate how long ago a common ancestor existed. As an example here is a graph of the number of mutations in mitochondrial DNA for the protein Cytochrome C. The more mutations you accumulate in a genome the larger amount of time since they split from a common ancestor.