Convergent Evolution Upends Honeyeaters' Taxonomy 186
grrlscientist writes in with a beautiful piece of science, beautifully explicated. The poignant bit is that the birds in question are all extinct. "Every once in awhile, I will read a scientific paper that astonishes and delights me so much that I can hardly wait to tell you all about it. Such is the situation with a newly published paper about the Hawai'ian Honeyeaters. In short, due to the remarkable power of convergent evolution, Hawai'ian Honeyeaters have thoroughly deceived taxonomists and ornithologists as to their true origin and identity for more than 200 years."
Nothing New (Score:5, Interesting)
There have been debates over the taxonomy of odd creatures (with similarities to other known creatures) forever. Sometimes simple physical resemblence just doesn't really tell the tale. Of course, evolution producing similar looking/behaving birds is nothing new either (just look at how similar African parrots [wikipedia.org] and South American parrots [parrotparrot.com] are to one another).
The really great debates come when zoologists get into trying to classify an animal that looks like (or behaves like) two DIFFERENT known creatures. One of my personal favorites is the Red Panda [wikipedia.org]. The bottom of its body and claws look like a bear's (you can see it clearly in this picture [wikimedia.org]) and it eats only bamboo, just like a Giant Panda. But the rest of it looks like a raccoon. This cute little furball finally had to be given its own unique family [wikipedia.org], because no one was quite sure where to put the little bastard. And it's still debatable if it truly deserves its own family.
Why still depend on observation? (Score:5, Interesting)
I realize that in this case (being dead for 200 years) it is more difficult, but why don't they _just_ use DNA sequencing to determine the classification of animals?
Observation (of both behaviour and appearance) is influenced by the observer and is variable. Two people never see the same thing the same way. Ask a man and wife what colour the living-room couch is and you will get two different answers! =)
The DNA sequence will never lie, and that sequence will tell us FAR more about common evolutionary traits then our eyeballs will.
Re:Why still depend on observation? (Score:5, Interesting)
The answer is two-fold: money, and existing taxonomies are mostly correct.
Biologists have limited resources, so comprehensive reassessment of the entire tree of life based on genetic analysis is going to get done bit by bit over a long time, and we know we're pretty safe going with what we've got in the meantime.
And while enough genetic analysis has been done to confirm traditional taxonomy on quite a few species, it is only the cases where there is a disagreement that it makes the news. In all the other cases they agree, so traditional taxonomy is left intact.
There are a few dramatic cases like this one, though. There are a couple of species of lizard in the Yucatan that have an extra cervical vertebrae that turn out to have independently evolved that way (I prefer the term "independent evolution" rather than "convergent evolution", as the latter may confuse laypeople into thinking that distinct species have somehow become one.)
In those cases, genetic taxonomy wins, but they are always going to be in the minority.
Re:Who is this grrlscientist? (Score:5, Interesting)
Re:Predictive power of evolution! (Score:2, Interesting)
In a shameless reply to myself, I'd like to also add that the OP of this thread has an interesting point - seemingly contradictory evidence is claimed as supporting the same theory. Much like global warming. When your theory is defined such that it includes both sides of interpretation of any given piece of data, it is hard to argue against. (e.g., I heard on the news that it was getting colder and certain ice caps or something were growing, not shrinking, and that that is "exactly what is expected with global warming, because with something like global warming, the unexpected is going to occur." In other words, even though it SEEMS to contradict global warming, it really supports it, because this person's ideas about global warming are defined such that he has included any possible interpretation... or, perhaps it'd be better to say he has accepted global warming first and is trying to interpret the data to fit it afterwards. IMO, much of the theory of evolution is similar.
To the extent that some "examples" of evolution are still used even though they are silly, or hoaxes. In addition to previous example of the human example (that's a lot of the word 'example' in one paragraph), the moth thing in England was brought up, even though I'm pretty certain everyone agrees that no evolution occurred there, it was just a shift in population ratios.
convergent evolution examples (Score:5, Interesting)
I was always impressed by the similarities between sharks, dolphins, and icthyosaurs. Similarly, there's a phenomenal similarity between the flying reptiles such as the pterodactyls and bats with finger bones modified with flaps of skin to make wings. There's also the similarities between various species of gliding tree mammals, the flying squirrels and lemurs and the like. One can also talk of amazing developments with marsupials which had armored herbivores similar to a rhino and carnivores like a leopard-form. (and let's not forget that a Triceratops is built awfully similar to a rhino down to the armored hide, horns, and heavy, stocky legs.) All of these from obviously unrelated lines of descent converging on similar forms to satisfy ecological niches. If I recall correctly, there's also a type of fish that developed a false-placenta for live-birthed young -- it's not a true placenta because it isn't a placental animal but it serves the same purpose. I believe this fish was in the extended shark family.
The other thing that really amazes me is how the theory of evolution makes certain predictions that you'll simply not see contradicted. For example, there's the general rule that animals will adapt existing limbs for various purposes so you might see a rodent develop forelimbs into wings but you will not see a rodent sprout brand new wings from its back while retaining the previous four limbs. Even the weirdest body parts you can find can be seen to be modifications, not wholly new structures sprung forth from nothing. You won't see a bird suddenly come with three eyes or an elephant with a cyclopean eye or a cat with eight legs like a spider (barring genetic defects that will be unable to reproduce).
What's also amazing is how the lines between species get blurry. The old definition is that two populations are split as a species when they cannot interbred and create viable offspring. But we've seen from zoos that populations that don't mix in the wild can produce viable offspring such as ligers, tygons, then there's the blonde grizzlies that are a hybrid of grizzly and polar bear that did occur in the wild... All of these animals come from common ancestors if you go back far enough and it makes you wonder just how freely genes could be traded back and forth with the right technology and a proper understanding of genetics.
Re:Predictive power of evolution! (Score:1, Interesting)
In other words, they have decided that no other explanation should be allowed. Furthermore, textbooks are full of errors, as are college science classes, etc. My sister recently took a college level biology course and when briefly going over the presumed evolution of humans, known hoaxes were mentioned as proof.
Well, I just finished teaching a college level biology course. Every college level biology instructor has their own style and, until we replace in-person lectures with a single set of instructional videos prepared by the federal government, that's just something you're going to have to deal with.
For example, my approach to "teaching evolution" was to emphasize three basic ideas.
First, "evolution" can refer to a lot of different (but slightly related) things. On one hand, evolution can refer to a general tendency for a population to adapt to its environment over successive generations. On the other hand, evolution can refer to the history of life on earth even including speculation about the earliest origins of self-replicating molecular systems.
Second, while "scientific proof" is fundamentally based on factual observation and certain forms of logical reasoning, the question of what it means to "prove" something scientifically is complex and may be a matter of degree. Consider, for example, the question of whether the earth is round or flat. In modern times, the "roundness" of the earth is a matter of direct observation (thanks to various space programs). In the time of Columbus, there was overwhelming indirect evidence that the earth was round (from navigation) but no space craft for direct observation. Finally, before navigation, it may have made the most sense to assume that the earth was round (despite personal experience that it was flat) but there wasn't even much indirect evidence. Putting it all together, the degree of scientific proof for "evolution" depends on which aspect of evolution is being referred to. For certain aspects of evolution there are still, most likely, entire "continents" of knowledge waiting to be discovered.
Third, it is populations rather than individuals that evolve and there are deep questions as whether an individual should try to "help" their population evolve and what, if anything, an individual who was so inclined could do to "help" their population evolve.
Basically, evolution is a huge complex topic that is still an active area of research and my goal as an instructor was to get my students to take a slightly more nuanced view of evolution than is portrayed in the popular media. In particular, I wanted to expose them to some of the deep questions in evolution: not as final answers but as actual questions - questions that they might even someday choose to investigate as scientists.
Re:convergent evolution examples (Score:5, Interesting)
First of all, it's completely cold blooded. It cannot regulate its temperature at all. It's also blind and hairless. They have a queen that gives birth , and the others are workers in various castes, such as tunnel-maintainers, guards, or nurses.
So convergent evolution also happens in social structures, not just physiology.
Please clarify... (Score:3, Interesting)
Please clarify your definition of "natural", because your final point makes no sense.
scientific evidence that could point to a, shall we say, "supernatural" explanation (creation) is disregarded on the premise that the theory it supports (creation) is not a scientific theory.
This is a complete contradiction in terms. By "natural" in science, we are referring to that which can be observed and independently corroborated. By definition, any evidence must be natural and not supernatural, as supernatural indicates unobservable or unable to be corroborated.
Science deals only with the natural because the natural is the only thing that can be observed and measured. And, guess what... Science works. And guess what else, the scientific method that gave you the computer that you are typing this on is exactly the same as the scientific method that has (and continues to) worked out the theory of evolution.
One last little note:
And then, of course, we start arguing about what defines "micro" and "macro," what defines a "species," etc...
Not to get into an argument about it, but I just want to point out that WE define what species are, and our definitions are arbitrary. Nature doesn't really give a damn how we classify things. It will do its own thing independent of us. There is no difference, biologically speaking, between micro- and macro-evolution. The only real debate comes up when speaking about taxonomy.
Re:Predictive power of evolution! (Score:4, Interesting)
You're quite welcome for the post :)
To stick to true scientific terminology, a theory is never proven or disproven... proofs exist only in the world of mathematics. Theories are validated and invalidated. A prediction is made and a test is administered to a theory (an experiment), and this is what ultimately validates or invalidates a theory (or a portion of it). If the evidence invalidates, then the theory is revised to fit the evidence provided... rarely is the theory itself completely thrown away unless overwhelming evidence completely thrashes it to the point of it not being able to make any predictions whatsoever and it fails every test put forth to it.
This is what many cdesign proponentists fail to understand... our theories reflect all known knowledge on a subject and are being revised and updated damn near every single day. Our theories are not static, and they never will be. Textbooks will be outdated, new evidence will bring about change in our theories as well as reinforce them.
To put it simply, a theory is the logical framework built by all observed facts, data and research. To say something is "just a theory" is quite honestly an insult to the scientific community... one which many of us do not take lightly.
Re:Predictive power of evolution! (Score:3, Interesting)
As you no doubt know, that wasn't my point... as far as I know, there has not been any observed macro-evolution, thus the debate is less observation and more philosophy. And then, of course, we start arguing about what defines "micro" and "macro," what defines a "species," etc...
Have you seen an electron with your own eyes? No? And yet, I'll bet you would accept an explanation of electrical theory (especially if you were going to make a job out of it and your life depended on it)...
Where did that theory of electricity come from? Did it spring, fully-formed from the head of some scientist, who presented it to the Science Cabal to be accepted as holy writ?
Or maybe, it was built up over time, based on numerous observations by multiple people. My point, though, is that even though no one has seen an electron with their own eyes, it is accepted as fact that they exist with a certain set of characteristics. Why? Because it fits with the theory, and no one has found compelling evidence to the contrary.
Now, for Evolution, the original big idea came from Darwin (though I'm sure he must have been influenced by prior work) that species, isolated geographically, tend to diverge over time, creating new species. The mechanism by which this speciation seems to occur is called natural selection.
Darwin gets the credit for the whole idea, but the reality is that many people working over time have refined, and modified it. More importantly, many people have confirmed that the theory is the best explanation for what they are observing. No one has come up with a better explanation using the scientific method.
So, finally, to address your point that no one has observed "macro" evolution... This is silly. It is happening all around us, constantly. The fact that you don't live long enough to see it in anything other than bacteria is not a flaw in the theory, it's a flaw in your lifespan.
Re:Predictive power of evolution! (Score:3, Interesting)
Point is, it's not impossible, within the theory, to find a simpler descendant. But it's not as likely, since the natural environment seems to have a habit of encouraging biological complexity.