Wednesday, August 11, 2021

Palaeontology Musings

It struck me a couple of days back that the field of paleontology and evolution has come up with some very evocative terms to describe phenomenon and name theories.

Take for instance the Red Queen Hypothesis. The term was coined by University of Chicago evolutionary biologist Leigh Van Valen in 1973. It is an explanation for his observations on patterns of extinction which came to be known as Van Valen's Law of Constant Extinction (itself a cool name). Van Valen did a broad survey of genus and family level extinction patterns of several different marine invertebrate groups and found out that the probability that a group could go extinct was independent of their age. The expectation might be that longer lived groups may have evolved more efficient adaptations and thus the likelihood that they could go extinct might decrease for older groups. 

Van Valen's finding was counterintuitive. A small clarification. The finding here is not that the rate of extinction is constant over time. It is not, obviously we just have to look at times of mass extinctions when rates of extinction increase enormously. What Van Valen found was that longer lived taxa were no better at avoiding extinction than newly appeared groups.

Why?...Enter the Red Queen. The inspiration for the name comes from Lewis Carroll's Through The Looking Glass. In it the Red Queen says to Alice; "Now, here, you see, it takes all the running you can do, to keep in the same place".

Van Valen reasoned that organisms are in a perpetual competition over resources. If one evolves a more efficient way of extracting resources, a cohabiting species will do so too. A sort of a metaphorical "arms race" results leaving both species at the same level of efficiency relative to each other. Besides, since evolution is changes in response to immediate challenges, already acquired adaptations cannot guarantee a fit to future environmental change. Longer existing taxa thus are likely to perish just as easily as newly emerged ones.

The Red Queen invited a lot of interest from evolutionary biologists and ecologists and has spawned rich directions of research since.

The other name I stumbled upon recently is Dead Clade Walking. This too concerns patterns of extinction and recovery. Paleontologist David Jablonski, also from the Chicago school of thought, in 2002, invented the term to describe his finding that many marine groups experience sudden drops in diversity spanning mass extinctions. Many don't go extinct but never quite recover fully either. It is not well understood why certain groups survive such global extinction events but then cannot rediversify. Some further work has shown that such drops in diversity without recovery need not be associated with mass extinctions but occur even during the background extinction that is going on. Understanding these patterns is another active area of research in paleontology. 

The type of research I've described readily invites a comment on how the field of paleontology has itself evolved. Besides the two scientists I mentioned, I will add David Raup, Jack Sepkoski, Elisabeth Vrba, Niles Eldridge and Stephen Jay Gould to name a few more. Beginning in the early 1970's these paleontologists collated large data sets of fossil groups, combing through literature and museum archives. They devised more expansive sampling strategies and subjected morphological measurements and life history attributes to rigorous statistical analysis. They used the emerging patterns to reconstruct broad histories of diversification and extinction and to test various evolutionary principles.  Their work reinvigorated paleontology from what was thought of as a descriptive field to one that began making significant contributions to evolutionary theory. This big picture approach inspired biologist John Maynard Smith to acknowledge that paleontology is ready to join the "high table of evolutionary theory". 

Do you know of a cool name for an earth science phenomenon or theory? Drop in a comment.

1 comment:

  1. A reader has sent this comment via email-

    Interesting! Through the Looking Glass is one of my all time favorite books. In school, my friend Maya and I had made a list of all the characters in the 2 Alice books and matched them with the girls and teachers we knew who most resembled them. The Red Queen was our Hindi teacher - whose 'Off with her head" attitude at the slightest mistake in grammar was legendary :)

    Did a quick Google search and found another Alice reference in evolutionary biology - The Cheshire Cat escape strategy where the diploid eukaryote, Emiliania huxleyi ( second part named after the Huxley who staunchly defended Darwin!) turns into non calcifying haploid cells when attacked by marine viruses, - they become invisible to them, like the Chesire cat did, slowly :)

    Check this out. :)

    Sushma Date