Clade:
A clade (from Ancient Greek: κλάδος, klados, “branch”), also known as monophyletic group, is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single “branch” on the “tree of life“.[1]
The common ancestor may be an individual, a population, a species (extinct or extant), and so on right up to a kingdom and further. Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: “one clan”) groups. [Wikipedia]
I’ve been hearing about clades for decades, but don’t really know much about the concept. Noted in “Human or hybrid? The big debate over what a species really is,” (sheesh, ending a sentence with “is” seems ugly), Colin Barras, NewScientist (26 January 2019, paywall)
Perhaps, instead, the ultimate solution is simply to remove the word “species” from the scientific lexicon. In 2018, [Brent] Mishler [at UCB] and John Wilkins at the University of Melbourne, Australia, set out this argument. They suggested that we should focus on another division of life, the “clade”, a group sharing a common ancestor and so comprising a separate twig on the tree of life. They say we could classify organisms as the Smallest Named and Registered Clade, or SNaRC, rather than as species. So, for example, Neanderthals, Denisovans and living humans would be three distinct SNaRCs. There is nothing intrinsically special about SNaRCs, according to Mishler: they might interbreed or not, and the groups that fit the classification would vary across the tree of life, forcing us to accept that there is no common currency. By abandoning “species” and turning to “SNaRCs”, he argues, biologists would have a blank slate for thinking about biodiversity.
Which leads one to wonder, into just which SNaRC does a snark belong?
And just because it caught me by surprise, in the same article is this:
In the past century, scientists have redefined what a species is time and again, heaping confusion upon confusion (see “Parsing nature”). [Frank Zachos at the Natural History Museum Vienna, Austria] identifies no fewer than 32 competing definitions in his 2016 book on the subject, Species Concepts in Biology, and notes that two more have been added since then.
32?! No, 34!? Sometimes Nature doesn’t cooperate with our categorization schemes.
