Because of a prediction, a very strong prediction, I made on another thread, I’ve had reason to look into just what has been happening to Darwin’s finches way off on the Galapagos Islands.
Here is a paper published last year in Science Magazine by the Grants, experts in Darwin’s finches. I looked at their paper, looked at their data, and have come to the conclusion that what I predicted as the ultimate explanation to changed beak sizes is the more reasonable interpretation of the data they present.
But before we even get to the data, here’s a remark from a National Geographic website review of the article that supports my basic position:
“ Researchers from New Jersey’s Princeton University have observed a species of finch in Ecuador’s Galápagos Islands that evolved to have a smaller beak within a mere two decades.
Surprisingly, most of the shift happened within just one generation, the scientists say.”
The shift happened in ONE year? What kind of population genetics are at play here?
Well, to the data:
The most important information that we get from the article (only 3 pages in pdf) are contained in Table 1 and Figure 2.
The Grants’ paper is concerned with how Geospiza fortis and Geospiza magnarostris compete. Their conclusion is that during the drought years of 2003-2004, when the population numbers of both species fell drastically, that the “competition” from G. magnarostris, due to the numbers of both species being almost the same for the first time since G. magnarostris came over from the mainland, caused “character displacement” (beak size change) of G. fortis to a smaller size.
Table 1 gives the number of observed feedings of the three main seed types (small, medium, large) by each of the species. Figure 2 gives the beak size mean of G. fortis over the last 33 years, beginning in 1973-74.
The Grant’s give four ‘lines of support’ for their conclusion. Their fourth ‘line of support’, I believe, becomes the very reason for re-interpreting their results. The fourth ‘line of support’ is that in the drought year 1977, when G. magnarostris were few in numbers, and hence, not able to compete with G. fortis, the beak size of G. fortis actually increased so as to be able to take advantage of the Tribulus cistoides seeds (the large ones), whereas in 2004, with a similar drought taking place, but, however, with G. magnarostris now able to compete with G. fortis, the beak size of G. fortis decreased.
Let’s first notice all of Figure 2. For most of the 33 years that it records beak size, the beak size hardly fluctuates from its mean; there are only two noticeable/significant exemptions: the two drought periods, when, in BOTH instances, beak size changed almost ‘instantaneously’. The title of the National Geographic review had “instant” in its title.
Now to my prediction: my prediction is that changes in the morphology of species is driven mostly, if not completely, by environmental ‘triggers’. Table 1 now becomes important. Notice the difference between the observed feedings of G. fortis between 1977 and 2004. While both were small, the number of feedings on T. cistoides for G. fortis dropped from one sixth for 1977-1989, to one twelfth for 2004—half as much! But that’s not all of the story. In the paper, the Grants indicate that when examing these lowered ‘feedings’, whereas in normal years an average ‘feeding’ on T. cistoides was 9 to 23 mericarps, in 2004 it was never on more than 2 mericarps. That’s a factor of somewhere between 5 and 12. Taken altogether, then, this means that the amount of T. cistoides consumed by G. fortis fell in 2004 to somewhere between one tenth, and one twenty-fourth, of its normal consumption.
Let’s also notice that while both G. fortis and G. magnarostris were decimated, G. magnarostris did not change its beak size to a smaller one. If we look at ‘feeding’ observations for G. magnarostris we see that while they ate a larger proportion of the medium sized seeds than normal, nonetheless, their main intake continued to be T. cistoides.
The more reasonable interpretation of the Grants data is this: there is some protein(s) found in T. cistoides that cause beak size (and other (6) correlated characteristics, see Table 2) to increase, and that in the absence of these protein(s) beak size will diminish. The most likely method of this change is, I believe, through a changed developmental pattern in the next generation. (One possibility is that RNA is involved here, and that somehow the presence of protein(s) that come(s) from the ‘large’ seeds is able to transmit the fact of its presence, or absence, to the subsequent generation).
This thesis, though controversial perhaps, renders what we see—over a 33 year history—sensible, because: (1) It explains why G. magnarostris, despite being decimated by the drought, still does not change—since it is still principally ‘feeding’ on T. cistoides; (2) It explains why G. fortis changes beak size in ONE generation (“Instant” evolution); and (3) most importantly, it explains why in 1977, at a time when G. magnarostirs was very small in numbers, G. fortis INCREASED its beak size in ONE generation; that is, since there were no G. magnarostris to compete with, the G. fortis had all the T. cistoides to themselves. In the next generation beak size “popped-up” in size to the same degree that it decreased in size during the 2004 drought when their consumption of T. cistoides dropped drastically.
As a follow-up to this study, here is what the Grant’s propose: “Our findings should prove useful in designing realistic experiments, by identifying ecological context (high densities at the start of an environmental stress) and by estimating the magnitude of natural selection.”
Here is what I consider to be another important point in all of this. From an ID perspective, this kind of an experiment is a complete waste of time. What would be valuable, OTOH, is an experiment wherein native Galapagos seeds are fed to controlled populations of G. magnarostris and G. fortis while observing changes to beak size (and other traits that are correlated). You see, ID really is “science”!
Finally, let’s remember that Kettlewell’s experiment and the Galapagos Finches are the Modern Synthesis’ great claims to fame. Well, I think they got it completely wrong. What do you think?