An Other Study Demands Discrimination Between Adaptation and Evolution

In addition to the discussion about evolution and adaptation that ensued after reading the Pod Mrcaru lizard article here another argument that I came across while reading John Alcock’s “Animal Behavior”[1], an interesting book that I read with enthusiasm. On page 18 Alcock describes a study conducted by P. Grant and R. Grant on Darwin’s finches [2].

The observation can be summarized as follows:

  1. drought years -> large seeds (Tribulus cicloides) -> large billed individuals are favored
    as a result of natural selection finches have larger-than-average beaks
  2. rainy years -> small seed predominate -> small bills are more favorable
    as a result of natural selection finches have smaller-than-average beaks

This can be illustrated by the following graph. In this picture the average beak size and the average amount of precipitation are normalized they equal 1 (y-value). The blue curve shows the amount of precipitation and green is the beak size. The illustration shows how beak size follows the average rainfall. This illustration is not taken from the publication is my model calculation made based on these data.


The axes don’t bear labels, intentionally, because the same set of curves can be applied to prey-predator relationship, the the adaptation of an eye to light intensity, and to almost every adaptation process. What makes the authors call this evolution?

  1. Is it because it involved genetic material? Is that the only reason? Then, for the sake of clarity, I’d prefer the term genetic adaptation and propose to reserve the term evolution to processes that involve progress.
  2. Is it because it involves natural selection? Well, according Fauceir Theory natural selection is subject to adaptation and evolution.

1.    Alcock, J., Animal behavior : an evolutionary approach. 9th ed. 2009, Sunderland, Mass.: Sinauer Associates. xvi, 606 p.
2.    Grant, P.R., Unpredictable Evolution in a 30-Year Study of Darwin’s Finches. Science, 2002. 296(5568): p. 707-711.


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