The subject of relatives has been bouncing around my brain of late. The statements, ‘the gorilla, a relative of modern humans’ and ‘the salmon, a relative of modern humans’ are both true, but one is perhaps more true than the other. Obviously all things alive today are relatives at some very deep and very ancient level. As far as we know and can tell, life only originated once on Earth and if you go back far enough fungi, trees, people, dinosaurs, bacteria and viruses have some form of common ancestor somewhere, not to mention all the things in between. However, there are of course, relatives and then there are relatives – relativity is all relative.
It’s clear that humans are more closely related to gorillas than they are to deer, closer to deer than to salmon, and closer to salmon than spiders, but they are still all related. Move in though, or move to an unfamiliar group and that becomes trickier – are beetles closer to flies or mantids, are spiders closer to weevils or centipedes? Unless you have a pretty good grasp of the detailed phylogeny to hand or some clear qualifiers any statements about relationships rapidly, or even instantly, become fuzzy to the point of being irrelevant.
You do see this at its worst in the media (big surprise) but I am sympathetic here. When trying to communicate the idea that some groups or species are closely related to others, aimed at an uninformed audience and avoiding technicalities and illustrations it becomes very tricky very fast. =I’ve also seen a fair amount of tired internet discussions along the lines of ‘Velociraptor isn’t related to Tyrannosaurs at all’. OK the ‘at all’ we can allow as conversational hyperbole, and of course tyrannosaurs and dromaeosaurs (within the theropods) are quite well separated, but they are also related. Compared to say, Dilophosaurus, they are quite close, compared to a crocodile, very close, compared to Troodon, not close. That statement is as true as it is false.
But is it really so hard to use a qualifier or two? Something like ‘Linheraptor is not a particularly close relative of Velociraptor’ is potentially confusing and in a sense no more accurate than ‘Linheraptor is a particularly close relative of Velociraptor’ – just how ‘not close’ or ‘close’ is it? But add just a few extra words and the distinction is obvious, accurate, succinct and informative: ‘Linheraptor belongs to a small group of dinosaurs called dromaeosaurs that includes Velociraptor, but within the group the two are not especially close relatives”. There’s really quite a lot of information in that 20-odd word sentence. It puts the two in context with each other, and the wider group of dinosaurs or theropods as a whole (since this sentence should obviously not stand in isolation in an article). So stick in a few qualifiers and make things more clear, it really will help and it might stop a few discussions were both people are right but arguing pointlessly from different perspectives.