The Loom

The Dawn of Brains and Bones

lancelet.jpgGo back far enough in our history–maybe about 650 million years–and you come to a time when our ancestors were still invertebrates. That is, they had no skulls, teeth, or other bones. They didn’t even have a brain.

How invertebrates became vertebrates is a fascinating question, made all the more fascinating because the answer tells us something about how we got to be the way we are. In order to reconstruct what happened, scientists can study several different kinds of evidence. They can look at the bodies of invertebrates to find the ones that share traits with vertebrates not found in other invertebrates. Those common traits may be signs of common ancestry. Scientists can look for signs of this ancestry by studying the DNA of vertebrates and invertebrates. They can also examine the fossil record, to discover transitional forms that offer clues to the transitions that can’t be found in living species.

When scientists consider this evidence, the answers don’t come pouring into their lap like coins from a slot machine. They have to put together hypotheses that do the best job of explaining vertebrate origins.They can then test those hypotheses against new evidence. Sometimes the old hypotheses hold up. Sometimes it turns out they were based on a misreading of the evidence. New hypotheses emerge to take the place of old ones. But those new hypotheses have to be better than the old ones. Scientists do not just suddenly declare that any explanation will do.

This is how science works. It occurred to me that this fact bears repeating when I read a recent comment to this blog. The comment emerged in a discussion about some observations from Randy Olson, a movie director, on how to communicate effectively about evolution. Some people agreed with Olson’s ideas on livening things up, while others worried that he just wanted to dumb science down. The differences were real, but the discussion was productive–at least until a couple creationists chimed in.

These creationists claimed to offer some helpful advice, but it’s pretty clear from their comments (and their links to creationist web sites) that they really had nothing of the sort in mind. They don’t actually want to help people understand evolution; they’re just exploiting some common misunderstandings about evolution, and about science in general.

They do provide one service, by showing which misundertsandings they think they can exploit most effectively. “Anonymous” writes:

“But you need to be honest about the scientific accuracy. How often does a new discovery come out that requires a rewrite of the evolutionary timelines and trees. If memory serves, I’ve read at least 2 posts on this blog in the last year with statements to that effect. How can you say Evolution is Science and Science is Truth and then in the next statement that Evolutionary scenarios must be rewritten. The public hears this.”

If only I could put words in the mouths of people I write about–life would be so much easier. Anonymous might as well have written, “You say that your cat can speak Mandarin. The public hears this.” Not from me.

Scientists learn new things about the world. They revise their theories. They do not pull away a curtain, to reveal Truth with a capital T, and walk away. And just because they do not deal in Truth with a capital T does not mean that they deal in pure nonsense. Their knowledge improves, although it never reaches perfection.

The origin of vertebrates is a case in point. Among living invertebrates, scientists have identified certain groups as being closer to us than to other invertebrates. The biggest group are echinoderms, which include starfish. They may not have skulls or brains like ours, but they do share some peculiar traits. In other invertebrates, for example, a hole in the early embryo called the blastopore becomes the mouth. In echinoderms and vertebrates, it becomes the anus.

Along with echinoderms, a few less familiar species have also shown strong links to vertebrates. One group is called the tunicates. These include the sea squirt, a truly bizarre animal. It begins life as a tiny tadpole. It swims with a tail made of a stiff rod called a notochord, along which runs a hollow nerve cord. It also has slits in its throat for swallowing food. These traits are not found in echinoderms or other invertebrates, suggesting a close link to vertebrates. Remarkably, most of its vertebrate-like traits disappear when it gets to be an adult. It lands on the sea floor on its head, rotates its organs ninety degrees, and eats its own nervous system. It then sits on the sea floor, filtering food and making new tadpoles.

Then there are the lancelets. These creatures (such as the one in the picture here) look like sardines with their heads cut off. They have a similar life cycle to sea squirts, swimming as larvae and then settling to the sea floor. But they have more traits in common with vertebrates. The tip of their nerve cord, for example, shows many striking similarities to the overall organization of the verebrate brain, even down to the genes that build each. It also has muscles arranged into blocks along its length–the same sort of blocks that you can get your fork into when you have fish for dinner. They don’t degenerate into a sac as adults. They just dig into the sediment and stick their heads out, so they can filter food passing by.

Many scientists argued that the ancestors of echinoderms branched off from our ancestors first. Then, after our ancestors acquired throat slits and a notochord, the ancestors of sea squirts branched off. Then our ancestors acquired rudiments of a brain, blocks of muscles, and other traits, after which the lancelet lineage branched off. At this point, the vertebrate body plan was still only partially built. Evolution had not yet produced skulls, spinal columns, eyes, and other features found in all living vertebrates. All that came later.

As I mentioned earlier, there are a couple ways to test this hypothesis. One is to look at the fossil record. Do the traits seen in echinoderms, sea squirts, lancelets, and vertebrates tend to turn up together in extinct animals, or do are they scattered all over the animal kingdom? Do paleontologists discover lobsters with skulls, earthworms with fish-like gills? No. They do find lancelet-like animals that have well-formed brains and even skulls–which is exactly what you’d expect as invertebrates evolved into vertebrates. They also find peculiar fossils that might be closely related to vertebrates or to the common ancestor of echinoderms and vertebrates. This sort of ambiguity is not surprising, because in the early days of these groups, you’d expect to find species that had not yet acquired the distinctive traits found in living groups. The same pattern turns up in the earliest hominids–they are so much like other apes that it can be hard to say whether they are ape-like hominids or hominid-like apes.

Another way to test an hypothesis about the origin of vertebrates is to look at DNA. In this week’s issue of Nature, a team of French scientists publish the results of just such a study–the biggest of its kind, both in terms of the range of animals studies and the mass of DNA analyzed in each one. They looked for the evolutionary tree that offered the best explanation for the differences and similarities in the DNA carried by each species. They put their results through a series of statistical tests to see if they were solid, or if they were just misleading illusions (removing one species from the study, for example, to see if a different tree emerged).

Their evolutionary tree has the overall shape of trees produced from other kinds of evidence. The French scientists find that humans and chickens are more closely related to each other than either is to frogs. Lampreys and hagfish are more distantly related to us, but closer than lancelets or echinoderms. Even among the invertebrates, patterns turn up that have been seen before. Insects are more closely related to us than jellyfish, for example, and jellyfish are more closely related to us than mushrooms.

The fact that studies based on anatomy, various genes, and fossils, all converge on these same patterns indicates that they’re onto something real. If someone shows you twwenty species and has you connect them with a family tree, there are over 200 billion billion different possible trees you could draw. But the trees that emerge from these studies only only minor variations on one another, not a random sample of all the possible trees. The odds of this happening by pure coincidence are incredibly tiny. But it’s exactly what you’d expect if they represented real evolutionary relationships.

The new tree does have a couple interesting surprises. One is that sea squirts–those weird nerve-eaters–are closer to us than lancelets. The other is that lancelets may actually be more closely related to echinoderms than to vertebrates and sea squirts.

If this conclusion is supported by more studies, lancelets may turn out to be a lot like the common ancestor we share with starfish. That lancelet-like ancestor then gave rise to some lineages in which some radical changes occurred. Once the echinoderm ancestors of starfish branched off, they must have lost some traits we still carry, such as a main nerve cord running along the back and throat slits. That conclusion would jive with some early fossils of echinoderms that appear to have slits.

The study suggests that sea squirts also changed a lot from a lancelet-like ancestor. They lost the muscle blocks of their ancestors and their nervous system must have become much simpler. Their odd sedentary filter-feeding evolved only after their ancestors branched off from our own. Rather than primitive, sea squirts may actually be highly specialized proto-vertebrates.

But as different as sea squirts may have become, scientists may still be able to learn a lot about our own origins by studying them. Much of what distinguishes us from invertebrates–eyes, teeth, and such–develops from a distinctive group of cells called neural crest cells. They first emerge along the back of the vertebrate embryos and then move through the body, giving rise to lots of different structures. Both lancelets and sea squirts have neural-crest-like cells. But only in sea squirts do they migrate as they do in our own bodies. By studying how these cells move, scientists may be able to understand a key step in vertebrate evolution.

There is one obvious way to test this scenario: sequence the genomes of other close vertebrate relatives. Previous studies have suggested that echinoderms share a close common ancestor with acorn worms, which have throat slits among other vaguely vertebrate-like traits. Including their DNA in a new study may support this current study, or pose a new challenge. That sort of result may disappoint those who would like science to deliver Truth in one perfect lump. But for scientists, it’s the sort of fresh challenge that gets them out of bed in the morning.

Update 2/23 8 am: Thanks to Dr. David Hone for giving me precise numbers for the possible trees.

Comments

  1. #1 donna
    February 22, 2006

    Sigh. You cannot explain a world full of colors to those people that see only in black and white. You can’t even explain to them why their eyes ought to be able to see black, white, and shades of grey, at least, if not the beautiful colors. They don’t want to know.

  2. #2 JDR
    February 22, 2006

    These creationists claimed to offer some helpful advice, but it’s pretty clear from their comments (and their links to creationist web sites) that they really had nothing of the sort in mind. They don’t actually want to help people understand evolution; they’re just exploiting some common misunderstandings about evolution, and about science in general.

    I would love people to understand evolution. I would love people to understand its shortcomings, as well as its attributes. I’d love people to understand and seperate fact from hypothesis. Most of all for the good of everyone on both sides, I’d like to see the debate take place, a debate of the best minds of both sides, in the public forum.

    I believe my advice was helpful to your side. The entire blog was filled with talk about needing to communicate more effectively with more engaging presentations. It was suggested that evolution needs more publicity to win its case. That’s ridiculous. Time magazine, National Geographic, Newsweek, USA Today, NY Times, etc., etc., etc., all publish frequent articles about evolution. Every blockbuster sci-fi movie since 2001: Space Odyssey has had an evolutionary slant. Every high school textbook in use in public schools has an evolutionary focus. Evolution holds a monopoly, and why shouldn’t it if every mainstream scientist believes it to be true. So why is the message not getting through to the majority of Americans? Do you really think its because it needs more publicity? Just make it more entertaining and it will take hold? Of course not a scientist should be able to figure that out.

    The debate is engaging, it evokes interest in science in general. You seem to see it as a destructive virus when it should be seen as an incredible opportunity to deliver science to engaged minds. Case in point: In the last 20 or so blog entries on the Loom, 2 have really taken on the subject of the debate (Cockroach and Dodos). The remaining 18 have a sum of probably 70 comments, while the 2 have nearly 280.

  3. #3 Stephen Uitti
    February 22, 2006

    Of course it isn’t Truth with a capital T. Science is about doing the best one can. It doesn’t promise truth, but it is credited with producing the best knowledge available – at least the best truth as testable with evidence. This is somewhat circular, since science is all about building up testable knowledge by testing it and using the ideas that work the best.

    The Bible has references to the wisdom of humans vs. the wisdom of God. And, if one considers what passed for wisdom 100 years ago, and extrapolate that back 2000+ years, it must have been obviously poor. As for checking the wisdom of God, one only has to say – “well this is wrong, and there must be a correct answer, which would be what God thinks”. One can also extrapolate forward, and expect that much of today’s wisdom will be considered folly 100 years from now.

    Then, for sure, people with edit with EMACS. (That’s a joke – pick your favorite religeous argument.)

    This idea of using the best ideas available is not confined to science. Most disciplines attempt to do this sort of thing. But consider art. How does one know when one idea is better than another when five people have seven opinions on which of two things is better? Science advances quickly because objective measures are available. One of the things scientists can communicate is that advancing knowledge is possible, and making even quite small contributions is very exciting.

  4. #4 John Hardy
    February 22, 2006

    What debate?

  5. #5 Melissa Bowlin
    February 22, 2006

    Interesting!

    I like the way you explained the re-writing of evolutionary trees, but I thought I’d try to expand on that a little bit. I pulled up space.com to see if I could find an article about recent astronomical discoveries–and found ‘A billion stars hiding in the Milky Way’ by Robert Roy Britt, http://www.space.com/scienceastronomy/060222_missing_stars.html. To quickly summarize the point of the article, astronomers think that a certain previously unexplained radiation is due to stars glowing very faintly rather than hot gases.

    I quote the following passage directly because I want to point out the similarites between the language used and the language often used when evolutionary trees are revised: “The discovery, if confirmed, “would have a profound impact on our understanding of the history of our galaxy, from star-formation and supernova rates to stellar evolution,” according to a statement released by NASA.”

    Discoveries purported to have ‘profound impacts’ on our understanding of astronomy are made with relative frequency; just keep an eye on the science portion of any newspaper or news website. And yet, this doesn’t mean that the planets in our solar system don’t revolve around the sun. It doesn’t mean that scientists have suddenly discovered evidence that will require us to re-write the basic tenents of how gravity works. In fact, what it usually means is that our ability to measure things has gotten better, as in the recent discovery of two moons around Pluto.

    The re-writing of evolutionary trees is similar. Phylogenies–hypotheses as to the relationships between groups of organisms, often depicted as evolutionary trees–were often based on morphological measurements or observations before the advent of molecular techniques. Thus, when people looked at tunicates (sea squirts) and saw no muscles in blocks like the lancets had, the most parsimonious (simple) explanation was that the common ancestor of lancets + vertebrates evolved those muscles after it had diverged from the ancestor of tunicates and thus lancets were more closely related to vertebrates. The problem is, evolution does not always work by the simplest route–if the new study is right, the tunicates lost the muscles somewhere along their evolutionary trajectory. However, we couldn’t have known that by looking at the morphology; there’s just not enough information. Instead, biologists had to use new tools just like the astronomers who discovered the moons around Pluto did–and when they did begin to look at DNA sequences, they found evidence that the most parsimonious explanation might not be the correct one.

    Just because a branch in an evolutionary tree is shifted slightly by a new study does not mean that evolution itself is being re-written or that evolutionary biologists don’t know what they’re talking about. Generally, these changes are relatively small compared to the structure of the overall tree as Carl pointed out above and involve times when either morphology just wasn’t a good character to use or when non-parsimonious evolutionary changes occurred.

    I think in scientific articles there’s often a need to imply–often incorrectly–that discoveries will have far-reaching consequences or are drastic deviations from current knowledge. Whether that comes from the journalists trying to make the science more interesting and important to the reader (and the editor!) or from the scientists speaking to reporters in the language they usually reserve for grant proposals, I don’t know, but I do think that it’s an unfortunate tendency. As such, I really appreciate the way the topic today was placed into context in the article.

  6. #6 kink
    February 23, 2006

    Wow, lancelets and sea urchins are brothers!!
    Surprise and also fascinating!

    >Both lancelets and sea squirts have neural-crest-like cells. But only in sea squirts do they migrate as they do in our own bodies.

    Yeah, and I suppose that only in some sea squirts do they migrate.
    Famous model sea squirts such as Ciona or Halocynthia do not have (at least, not discovered at present) such migratory neural-crest-like cells, though they do have non-migratory neural-crest-like cells.
    So, it is possible that those cells independently acquired migratory ability in some lineages of sea squirts.

    >By studying how these cells move, scientists may be able to understand a key step in vertebrate evolution.

    I fully agree to the importance of such studies.

    Anyway, it is apparent that the long quest for the origin of vertebrates entered a new era.

  7. #7 Dan S.
    February 23, 2006

    Carl – sweet post – discussing what science is, why we should listen to it, and what it tells us. A trifecta!

    JDR “It was suggested that evolution needs more publicity to win its case. That’s ridiculous. . . . Every high school textbook in use in public schools has an evolutionary focus.”
    Given a) the state of science ed – esp. regarding evolution and b) the level of general awareness about evolution, clearly it is not ridiculous. Much of this information is not getting out or being preached to the choir.

    “The debate is engaging, it evokes interest in science in general.”
    I have seen almost no evidence of this. The debate is a really sort of conceptual parasite – it burrows in and uses the poor raddled body of evolution to spawn out more of itself.

    ” Case in point: In the last 20 or so blog entries on the Loom, 2 have really taken on the subject of the debate (Cockroach and Dodos). The remaining 18 have a sum of probably 70 comments, while the 2 have nearly 280. ”
    Go look at the zombie cockroach thread. Pages of meaningless, pointless repetition, much of it empty theologizing (guilty as charged). Look at the difference when it manages to get back on track. Fewer comments? Sure, you don’t have people flooding it with pointless comments, and endless versions of the exact same questions and answers.

  8. #8 Dave Hone
    February 23, 2006

    Just a techie point from a cladist. Carl mentions that there are millions of possible trees for just a dozen taxa. Actually, its 654 729 075 possible trees (assuming no polytomies). At 13 taxa, its nearly 14 billion trees and by just 20 taxa, we hit the fantastic 221 0643 095 476 699 771 875 possible trees!

    This does not mean that our data is necessarily solid if we end up with a given tree from that number of possibilities, BUT as Carl says, if we a re running repeated analyses with independantly gained data sets and we continually converge on the same tree, we can have a lot of confidence on our methods and results.

    I have yet to see the Nature paper so I dont know how many taxa they used, but its fair to say that returning the same (or very similar tree) from over 200 billion billion possible trees gives us a damned good result.

  9. #9 Carl Zimmer
    February 23, 2006

    Thanks, David. I count 38 species in the Nature paper. I guess that would be more trees than in all the forests in North America.

  10. #10 Chris
    February 23, 2006

    So, does this revive Garstang’s hypothesis of vertebrate evolution via paedomorphosis?

  11. #11 DouglasG
    February 23, 2006

    As always, an excellent post. Thanks!

  12. #12 Dan S.
    February 23, 2006

    “I believe my advice was helpful to your side”
    Yes, it does, as Zimmer points out, highlight an important misconconception about how science works. The blame can be spread around quite a bit, with k-12 science ed getting most of it. It sounds like a bit of it can also stick to you (also the real/fake science distinction – no, that’s not how you put it, but that’s what it clearly meanss)

    So – you’re smart enough to understand why the validity of evolution doesn’t depend on some kind of absolute loyalty to one specific evolutionary tree (etc.), and that scientists aren’t insisting that is does. So, wanna help?

    “I would love people to understand evolution”

    Oh, you do! Great!

    “I would love people to understand its shortcomings, as well as its attributes. I’d love people to understand and seperate fact from hypothesis.”

    Uh-oh. Wait up . . . this sounds a bit like – ‘I would love people to understand global warming. I would love them to understand all flaws and assumptions and . . .”

    Anyway, re: communicating science, and threads teeming with creationist debate vs. much shorter serious science ones. Take this: “So, does this revive Garstang’s hypothesis of vertebrate evolution via paedomorphosis?” For meaningful on-topic comments – for a meaningful public conversation (live or via books, programs, etc. – it really helps for folks to have some mix of a) intellectual curiosity – especially active curiosity, b) interest, and c)a decent knowledge base* (although obviously not necessarily at this level!). People have noted that b varies wildly among the overall population, as if the case for numerous fields, but lots of folks who wouldn’t necessarily be interested in the above post might be interested in, say, pets, or whatever. And so on – all the points about presentation and education quality already made . . .
    —-
    Anyway, wouldn’t these findings seem to argue against that hypothesis? Annoying – it’s such a nice idea . . .

    *the only reason I have any clue what the quoted comment is talking about is that I have read large quantities of popular and quasi-technical science writing. But of course, the only reason I’ve done that was because of (b). (I have an appalling lack of curiosity, in the sense of asking questions).

    “So why is the message not getting through to the majority of Americans?”
    Why do you think, JDR?

  13. #13 Emily Sommer
    February 23, 2006

    I`m continually amazed at how many people are more inclined to believe in creationism or some variation therof, than in evolution.

    But then again, maybe it comes down to whats easier for the general population:

    Simply believing in something that doesn`t require or even need facts, or Knowing about something that is based on evidence, and which you have to actually learn about to understand (and which you can constantly learn more about).

    Afterall, if there is one thing that we as americans generally share, it is undoubtably lazyness.

  14. #14 bertnernie
    February 23, 2006

    I know its off topic, but:

    Might someone suggest a good and freely available article covering the current take on “embryonic recapitulation”?

  15. #15 Bob
    February 23, 2006

    David Ignatius of WaPo wrote a column on 2/21 about how modern life produces more rage and less interest in understanding other people. He quoted a Charles McLean of Denver Research Group (never heard of him) who “argues that the Internet is a ‘rage enabler.’ By providing instant, persistent, real-time stimuli, the new technology takes anger to a higher level. ‘Rage needs to be fed or stimulated continually to build or maintain it,’ he explains. The Internet provides that instantaneous, persistent poke in the eye. What’s more, it provides an environment in which enraged people can gather at cause-centered Web sites and make themselves even angrier. The technology, McLean notes, ‘eliminates the opportunity for filtering or rage-dissipating communications to intrude.’ I (Ignatius) think McLean is right. And you don’t have to travel to Cairo to see how the Internet fuels rage and poisons reasoned debate. Just take a tour of the American blogosphere.â€�

    I think that Ignatius is half right. I think that the problem of the Internet is more anonymity and select posting of strong opinions than hostility and rage. If you could meet personally with JDR, there’s a good chance that you could have a discussion rewarding to both of you. Ignatius is wrong to imply that everything connected with blogs is sound and fury. Your blog and many others are constructive- it’s the comments that are the problem, especially if the site doesn’t screen out personal nastiness, which takes more work. Personal nastiness is catalytic and destructive.

    It’s very difficult to teach emotionally important issues by Internet; our media and culture which love controversy for its own sake have made it much harder to talk about evolution-creationism issues. I’m a physician who once debated a creationist in Mississippi. It was a hostile occasion. I was later asked if I wanted to debate in another forum. I suggested a round table discussion with several people at each pole of opinion and an artist who thought that both camps were wrong to moderate the discussion. However, those who contacted me simply wanted sound and fury.

    The teaching of evolution sinks of swims with high school science, which is often weak and test-oriented in this country. Why do students have to know who discovered the electron or the positron? Better that they know why those discoveries made sense and how other discoveries that made sense, like Hwang’s cloning experiments, were bogus. Those of us who believe in and love science must do more to help high school science teaching and teachers. Personal contact with the students in a respectful atmosphere can make all the difference in the world.

  16. #16 Michael Hopkins
    February 23, 2006

    It should be noted that one can find out how many evolutionary trees there are for x taxa at this table and calculator of 29+ Evidences for Macroevolution which also has a page on Statistics of Incongruent Phylogenetic Trees which discusses how many differences two trees can be and still be statistically significant.

  17. #17 ACW
    February 23, 2006

    Dr. Hone was correct in his counts for the number of possible binary phylogenetic trees with 12 and 13 species; however, he erred regarding the number of trees for 20 species.

    The number he quoted is correct for 18 species. For 20 species, the number is 319830 986772 877770 815625, or about 320 sextillion.

    And I cannot resist a challenge, however subtly stated, if it falls in my narrow domain of expertise. For 38 species, the number of trees is 13 114900 840751 548972 796135 496384 318234 575359 262373 046875, or about 13 septendecillion.

    Formulas and mathematical connections may be found at Neil Sloane’s peerless On-Line Encyclopedia of Integer Sequences; look for sequence number A001147.

  18. #18 john
    February 23, 2006

    Emily Sommer said, “I`m continually amazed at how many people are more inclined to believe in creationism or some variation therof, than in evolution.

    But then again, maybe it comes down to whats easier for the general population:

    Simply believing in something that doesn`t require or even need facts, or Knowing about something that is based on evidence, and which you have to actually learn about to understand (and which you can constantly learn more about)”.

    ———————————————

    Even for Charles Darwin it was a problem that was easier solved simply by “believing”. This snip from Janet Browne’s mezmerizing biography on Darwin:

    “Darwin always insisted that he believed in some form of God throughout the Beagle voyage and for some period beyond. In his Autobiography he says that he was in the end very unwilling to give up the last shreds of “my belief” and that this act took place some years after his return. But it is also clear that his kind of belief, though orthodox, was very loose, English-style orthodoxy in which it was far less trouble to believe than it was to disbelieve. Accepting the basic story of Christianity was much easier than grappling with doubt”.
    Janet Browne, “Voyaging”, 1995

  19. #19 john
    February 24, 2006

    Emily Sommer said, “I`m continually amazed at how many people are more inclined to believe in creationism or some variation therof, than in evolution.

    But then again, maybe it comes down to whats easier for the general population:

    Simply believing in something that doesn`t require or even need facts, or Knowing about something that is based on evidence, and which you have to actually learn about to understand (and which you can constantly learn more about)”.

    Even for Charles Darwin it was a problem that was easier solved simply by “believing”. This snip from Janet Browne’s mezmerizing biography on Darwin:

    “Darwin always insisted that he believed in some form of God throughout the Beagle voyage and for some period beyond. In his Autobiography he says that he was in the end very unwilling to give up the last shreds of “my belief” and that this act took place some years after his return. But it is also clear that his kind of belief, though orthodox, was very loose, English-style orthodoxy in which it was far less trouble to believe than it was to disbelieve. Accepting the basic story of Christianity was much easier than grappling with doubt”.
    Janet Browne, “Voyaging”, 1995

  20. #20 Dave Hone
    February 24, 2006

    I must confess I borrowed (stole) my data for trees based on given taxa numbers from the superb ‘Cladistics’ by Kitching et al.. I’m intrigued to see the numbers quoted by ACW and Michael Hopkins being so much higher.
    Is this an error on the part of one data set (mine or yours), or a result of using differing equations to generate the numbers for high numbers of taxa?

    Tree space is much understudied, despite the fact that cladistics froms an incredibly important part of modern biology. Few evolutionary studies get off the ground unless backed by strong systematic data of phylogenetic relationships.

    The numbers can be truly staggering: I have recently submitted a manuscript with an analysis of over 100 taxa, it comes to about 1.5×10 to 272 possible trees!!!!!!!. In one of these classic descriptions, I *think* (tenuous guess) that exceeds a number given for the number of atoms in the universe.

    So spare a thought for the lonely cladists stuck on the ‘Tree of Life’. Just 15 million or so extant taxa to start with………

  21. #21 Louis Simoneau
    February 24, 2006

    I think in scientific articles there’s often a need to imply–often incorrectly–that discoveries will have far-reaching consequences or are drastic deviations from current knowledge. Whether that comes from the journalists trying to make the science more interesting and important to the reader (and the editor!) or from the scientists speaking to reporters in the language they usually reserve for grant proposals, I don’t know, but I do think that it’s an unfortunate tendency. As such, I really appreciate the way the topic today was placed into context in the article.

    It had never occurred to me that the dramatization of routine scientific discoveries in the press could be having a negative impact on the public’s understanding of the way science works. Perhaps I’ve just become too blasé, too habituated to that kind of writing in scientific journals (and grant proposals.) On the other hand, a lot of these discoveries do have “profound implications” for our understanding of a given field, just not cataclysmic, start again from scrath implications. Either way, thanks for the enlightening comment.

    It brings us back to what seems to be a rather fundamental problem in science education and journalism: conveying the exciting and fascinating nature of the scientific endeavor and making it accessible and understandable to all, without compromising a clear, correct view of the underlying information and methodology.

  22. #22 JoXn S Costello
    February 24, 2006

    I have recently submitted a manuscript with an analysis of over 100 taxa, it comes to about 1.5×10 to 272 possible trees!!!!!!!. In one of these classic descriptions, I *think* (tenuous guess) that exceeds a number given for the number of atoms in the universe.

    Since the number of atoms in the universe is generally estimated to be around 10^80, that should be “far exceeds”.

  23. #23 CanuckRob
    February 24, 2006

    I wonder if people like JDR would also like to have people (like him/herself) teach people more about religion, its shortcomings as well as it’s attributes. Not bloody likely.

    Great post, thank you for sharing and illuminating the wonders of evolution.

  24. #24 mark
    February 25, 2006

    “there are over 200 billion billion different possible trees you could draw. But the trees that emerge from these studies only only minor variations on one another, not a random sample of all the possible trees. The odds of this happening by pure coincidence are incredibly tiny. But it’s exactly what you’d expect if they represented real evolutionary relationships.”
    What would Dembski have to say about this?

    Your essay also makes note of a common misunderstanding about evolution–there is no inexorable increase in complexity as a form evolves; sometimes some complexity is lost; sometimes new species are just different, neither more nor less complex.

    Where were you (and the Internet) when I was a student?

  25. #25 Alur
    February 25, 2006

    Thanks for a brief glimpse into our evolutionary surroundings. I am fascinated with your description of the sea squirts.

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