Link: "Blood Is Thicker Than Water 🐬"
Ha ha, those Less Wrong guys sure love dolphins for whatever reason! (Alternative viewer.) Note that the "root of the causal graph" argument here for the relevance of phylogenetics is equivalent to the case that sex chromosomes are a good way to operationalize sex in humans—it's not that anyone directly sees chromosomes on a day-to-day basis; it's that chromosomes are the "switch" upstream of the development of all other sex differences. Talking about the setting of the switch (which you don't intrinsically care about) is a concise way to sum over the many, many high-dimensional details that you do care about.