Tempo (Rate) and Mode (Style) of Evolution Are Not Related – #365papers – 2017 – 56

#365papers for February 25, 2017

Voje, 2016, Tempo does not correlate with mode in the fossil record: Evolution, v. 70, p. 2678-2689.

What’s it about?

Tempo describes the rate of evolution. Is change happening quickly, or is it very very slow? This is distict from mode, which describes the pattern of evolution. Is there a direction to the change, all individuals growing bigger than their predecessors, for example? Is there no apparent change over time? Is there change, but it seems to be going back and forth, where sometimes descendants are bigger and sometimes they’re smaller?

This paper shows that there is no relationship between tempo and mode.

Why does it matter?

Macroevolution is the evolution and appearance of new species (or families, or classes, etc) in living organisms. Microevolution is the changes within a species – sometimes drastic – that can take place over just a few generations. Microevolution is observable, with antibiotic-resistant bacteria all the way to elephants with smaller tusks than their ancestors. Macroevolution cannot be observed except by inference from the fossil record.

This paper shows that while microeveolution and macroevolution appear different, the difference might be in what we can best observe. Tempo is directly measurable in microevolution because we’re looking at modern organisms. Evolution appears to be very fast in modern organisms. Tempo in the fossil record must be inferred, and because of time-averaging in the fossil record, evolution appears to be much slower. This paper does a good job of showing how one might be deceived into thinking rates were slower, when in actuality, they were probably comparable.

And thus, evolution works the same way (most likely) for both macro- and microevolution.

Why did I read this?

This paper was found when I did a quick search on the term “macroevolution” in preparation for my paleontology class. Tempo and mode are topics that I cover in class, so this piqued my interest, especially since I struggle to understand the distinction between the two.

So I read this, then did a little more research, and realized that what I had been teaching was not exactly correct. It’s good that I read this, then, so that I can improve my lecture later this semester.

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