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    Evolution In Detail: The Grants' Study Of Darwin's Finches
    By Michael White | November 21st 2008 12:43 PM | 6 comments | Print | E-mail | Track Comments
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    Welcome to Adaptive Complexity, where I write about genomics, systems biology, evolution, and the connection between science and literature,

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    Yesterday our department hosted Peter and Rosemary Grant, who spoke about their 30+ years studying natural selection and finches in the Galapagos. (If you're interested in the book version of their work, check out Jonathan Weiner's Pulitzer Prize-winning The Beak of the Finch.)

    While the Grants give a great presentation, full of pictures the Galapagos finches in action, my first impression was that none of this was really groundbreaking. As the Grants mentioned multiple times in the talk, Darwin anticipated so much of what they observe in the Galapagos. In an age of molecular genetics, a long-term, non-molecular field study is bound to seem a little old fashioned, although the Grants have recently been taking DNA samples and incorporating the tools of molecular genetics into their work.

    In the end, I came away from the talk satisfied. This work may not be conceptually groundbreaking, but I find it important for at least one reason: this is evolution in detail, in the wild. People often unintentionally tend to think of natural selection as a steady pressure that gradually shapes one trait into a more adaptive one. Scientists have long known that evolutionary forces are much more complex than that out in the real world, but when you think about these issues in the abstract, it's easy to let a failure of imagination bury that complexity.

    The Grants' work makes it much easier to appreciate how complex the real environment is. Their most famous result, at least in the popular press, is that finches of a given species with bigger beaks that enable them to crack hard nuts tend to survive under drought conditions, while finches with smaller beaks make a comeback during wet years. Their data shows how the population average beak size changes in response to conditions.

    Yet this is only the tip of the iceberg: the Grants have observed so many other complex factors coming into play. If  the cyclic weather conditions were the only major factor, then natural selection on beak size is simple, and over the long haul the beak size doesn't actually change much. The Grants however found other influences. For example, a different finch species, with a really big beak, colonized one island and was able to out-compete the existing large-beaked finches even during dry years. This meant that, contrary to what had happened before the island was invaded by the new finches, those birds from the original species with the smallest beaks ended up doing better than their larger beaked relatives. A new environmental factor, in the form of the new island invaders, changed the evolutionary pressure on beak size.

    You can keep piling on more variables. Sometimes a member of one finch species will take over the nest of another finch species, cleaning house by dumping out the eggs of the hapless, displaced finch. But sometimes one egg will survive the purge, meaning that a hatchling of one species ends up getting raised by parents of another species. That hatchling learns the distinct, species-specific song of its foster parents.

    This is important, because song is one way that finches know to mate with the correct species. Sometimes a bird of one species, raised as a member of another species, ends up engaging in cross-species mating, resulting in hybrid finches. This hybridization is rare, but it happens often enough to make a significant impact on the genetics of the two main finch species on the island.

    In their talk yesterday, the Grants argued that this gene flow between two species is leading to more genetic convergence - meaning that these two species could be on their way to forming a new mixed species. This is exactly the opposite of what was happening for the last 2-3 million years: the various finch species of the Galapagos have been diverging from each other since they last shared a common ancestor. 2-3 million years of divergence has been enough to create 14 new finch species, but not enough to eliminate all cross-species mating - that kind of sexual isolation takes much, much longer.

    The result of the Grants' work is that we can see evolution in flux, not as a linear pathway. The course of evolution ebbs and flows, often reversing itself or, upon the introduction of a new environmental variable, taking a completely orthogonal path. The Grants found two species that hybridize often enough to lead to genetic convergence, but this trend could easily reverse itself, and those two species may never converge. The Grants may have found very little that was not anticipated by Darwin, but they have worked out one of the most detailed pictures we have of evolution in action in the wild, at least the evolution that occurs on the scale of a human lifetime.

    Comments

    ...as Ronald Reagan once famously stated to Jimmy Carter... "well...there you go again"... If you came away from their presentation satisfied, then your satisfaction threshold is desperately low. Have you and the Grants been keeping track of these finches for 2-3 million years?? Is there a progressive pathway of finch fossils confirming this "understood" evolutionary species that all these supposed Scientists agree upon? I would encourage both you and the Grants pay a visit to their/your local Pet Store and observe the Finches for sale there and how diverse these birds are raised in captivity much less going so far away to a place where visitation is carefully controlled and mostly prohibited. What does it all mean Michael??...it means that these little creatures can adapt or die or move on. Sounds like humans...almost.

    rholley
    This reminds me of the work of the ornithologist David Lack , who spent the better part of a year from 193809 in Galapagos studying the finches and went on to do valuable studies on natural selection.  His life was featured in a BBC Horizon programme "Wings of Angels".  If I construe the title correctly, after his return from the Galapagos and the outbreak of war, he did radar research in the British Army.  Strange reflections had been observed which some speculated were from angels helping to protect us against Hitler, but Lack worked out that intensity of radar reflections followed an inverse fourth power law, so that a flock of birds flying 10 times as close as a group of planes would register 10,000 times as strongly relative to their surface area.

    His Wikipedia biography contains this gem:

    he once claimed to have single-handedly caused the renaming of a group of birds through the submission of a scientific paper, his 1935 publication, "Territory and polygamy in a bishop bird, Euplectes hordeacea hordeacea (Linn.)" in the journal Ibis. Up to that point birds in the genus Euplectes been referred to simply as bishops, but the journal editor felt that with that form the title might cause misunderstanding.
    Robert H. Olley / Quondam Physics Department / University of Reading / England
    ....I would be willing to bet that there are those still living in the UK that are yet convinced that the good Lord did indeed give charge to His angels to protect the "mother land"...as you see the Germans also had radar so while Mr. Lack may have ultimately given credit to birds flying closely within the radar field the Germans may have for a time recognized a large contingent of airplanes coming their way and kept their planes close to home for defense purposes. Which I would credit not to a happenstance of wandering birds but to a Creator who gives direction to his creation. I doubt these would have been Finches though, probably Crows... ;-)

    ok....just happen to be cruising by and I admit my ignornace up front, so forgive me. But I have read that finch beaks were not formed from genetic mutations, but instead via tweaks in the bmp4 protein.....these tweaks may very well be caused by way of hormones released by the mother bird, who was aware (on some level) of her environment. If this is true, that the embryos developed their adaptive beaks during development, where exactly is the natural selection? Darwin's theory was that natural selection selected from random variants....but this doesn't appear to be random. Thanks for any help.

    adaptivecomplexity
    I'm sorry my reply to you is so delayed. There are several points to keep in mind about the Grants' study:
    - They're looking at more than just beak morphology. Their study includes coloration, song, bird size, cross-species hybridization, etc., and their observations bear on a variety of elements of evolutionary theory. Beak size changes during drought is their most famous result, but it's not the only one.

    - The differences in beak morphology between species are genetic - you can't put a mother bird of a thick-beaked species under a different set of conditions and get a hatchling with the thin beak type of another species. Those genetic changes probably involve Bmp proteins, as well as other regulatory proteins which are being tested by the Grants' collaborators. 

    As for beak differences within species, some of that could very well be environmental, as you say, but the Grants also have evidence for a genetic component. Part of this  evidence is the fact that there is variation in beak morphology even when bird mothers are in the same environment -  there is variation that is not determined by the environment. Furthermore, it would be really, really surprising if there were no genetic variation at all affecting beak morphology, since such genetic variation is what is seen every time such traits are looked at in detailed genetic studies, and we now have studies of hundreds of traits in many different species. There is almost always random genetic variation affecting traits that natural selection can act upon.

    The genetic component of beak size variation won't be thoroughly established until some more DNA analysis is done to look more closely at the underlying genetic variation, but recently the Grants have been taking DNA samples and their collaborators have been analyzing it. That analysis will make this study much more complete.
    Mike
    I'm not sure there's a "progressive pathway" of any fossils that CONFIRM anything about evolution. They do, however, provide strong evidence which supports the overarching theory. Were you around for Julius Caesar's death? Can you confirm it? Are you there to witness the Earth orbiting our sun? Can you confirm that? Negative... I'll not lend much more an argument to the "Creator giving direction to His creation" other than to say he may have been asleep when it came to the moral misguidance which occurred throughout the war (ask the Jews) and perhaps concentrated more on radar. On to the real business of the Grants and their 30+ years in the field. I understand their work to be quite important. Their work supports the theory of natural selection, whereby selective environmental pressures lead to a change in a species population. These environmental pressures may not be as simple as rain-no rain, but may in some cases may be due to a new competitor, etc. Evolution as the genetic level, is the change in the frequency of alleles in a population. I suspect the DNA studies will confirm that, but as Mr. White clearly points out in his reply... "The genetic component of beak size variation won't be thoroughly established until some more DNA analysis is done to look more closely at the underlying genetic variation". Furthermore, one cannot go to the farm and study artificial selection and suggest that this would be sufficient to account for the 30+ years of study in the WILD where nature provides the driving forces, where life is somewhat removed from man's influence....which would have been the case (I assume) 2-3 million years ago. So, your point is what about the pet store? All of these difference species are actually the same species, just variants? Interestingly, I would like to point out that conclusions which support (never prove) of refute the theory of how these "tiny creatures" came to inhabit a myriad of niches are constantly being scrutinized. New evidence, such as the DNA, is being analyzed, scrutinized, and synthesized by the experts in the field and that will, I'm quite certain, be peer reviewed. The Grants have dedicated their lives to investigating the mechanisms of change which cause species to change. It's important because, while seemingly mundane and boring, it has supported Darwin's "little" theory. Pet stores versus The Galapagos? You can't be serious...