You may recall that a while back I mentioned how Jerry Coyne praised some work on bat evo-devo. I also said that I was going to have to write that paper up sometime. The bad news: I haven’t written it up for the blog. The good news: I did write it up for a future Seed column. The better news: Stephen Matheson has a summary right now, so you don’t have to wait for my column to come out.
You should still subscribe anyway. It’s pretty on shiny paper.
Finals week is upon me, and I should be working on piles of paper work right now, but I need a break … and I have to vent some frustration with the popular press coverage of an important scientific event this week, the publication of a draft of the platypus genome. Over and over again, the newspaper lead is that the platypus is “weird” or “odd” or worse, they imply that the animal is a chimera — “the egg-laying critter is a genetic potpourri — part bird, part reptile and part lactating mammal”. No, no, no, a thousand times no; this is the wrong message. The platypus is not part bird, as birds are an independent and (directly) unrelated lineage; you can say it is part reptile, but that is because it is a member of a great reptilian clade that includes prototherians, marsupials, birds, lizards and snakes, dinosaurs, and us eutherian mammals. We can say with equal justification that we are part reptile, too. What’s interesting about the platypus is that it belongs to a lineage that separated from ours approximately 166 million years ago, deep in the Mesozoic, and it has independently lost different elements of our last common ancestor, and by comparing bits, we can get a clearer picture of what the Jurassic mammals were like, and what we contemporary mammals have gained and lost genetically over the course of evolution.
We can see that the journalistic convention of emphasizing the platypus as an odd duck of a composite creature is missing the whole point if we just look at the title of the paper: “Genome analysis of the platypus reveals unique signatures of evolution.” This is work that is describing the evidence for evolution in a comparative analysis of the genomes of multiple organisms, with emphasis on the newly revealed data from the platypus.
As part of the Expelled Exposed site, there are a series of educational videos to counter creationist claims. They’re short, simple, and easy to understand.
My last Seed column is online, which reminds me (as if I weren’t uncomfortably aware already) that I have to finish up the next one today, which actually isn’t the next one, which is already done and submitted, but the one after that. These long leading deadlines force one to live a few months in the future…
You know, if you subscribed to the print magazine, you’d be halfway to my future already instead of living in my distant past.
I have to criticize the video below. It’s a beautiful piece of work, and the animal it shows is spectacularly well-adapted, but it does not demonstrate the fulfillment of a uniquely Darwinian prediction.
An orchid was found with a nectary that was only accessible by way of a long, narrow tube, and Darwin predicted the existence of an insect pollinator with an almost equivalently long tongue. However, an Owen or a Cuvier, scientists of that century who did not accept evolution, could have easily made the very same prediction, on the basis of created functionality: a god would not have made the flower that way unless he also, in his infallible foresight, also made a complementary pollinator. One could also make an argument based on an orchidized version of the anthropic principle: the flower is there, therefore it must have been produced by a parent flower that had been pollinated, therefore there must exist a long-tongued pollinator.
The special Darwinian character comes from the explanation of how such a phenomenon came to be; not by the fiat of some arbitrary creator, but by a set of processes that must still operate. It is to the advantage of the flower that the pollinator has to struggle a bit to reach the nectar reward, pressing itself against the flower and covering itself with pollen, while the pollinator would prefer to be able to reach in easily and without mess and fuss to get its dinner. This means that there is selection for flowers that have slightly longer nectary tubes than the insect tongues, while there is selection for insects that are able to reach all the pools of sweet nectar — but this is a race in which the insects will always be slightly behind.
What Darwin predicted was not a perfect match between nectary and proboscis, but that the insect proboscis would be slightly shorter than the nectary, and that’s what you find in his work On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects, and the Good Effects of Intercrossing. Another prediction that I haven’t found that he made explicitly is that there should be a range of heritable variation in nectary length — it could just be that that was so obvious in the collections he examined that it wasn’t necessary to state it.
Anyway, lovely as it is, a video of an insect with a remarkably long proboscis is not confirmation of Darwin’s theory. The key element of that theory is a description of a process which generates diversity over time in populations, which isn’t assessed by examining a single organism at a single moment in time.
(via Atheist Media Blog)
Maybe you think it’s spring — I don’t, I just looked out through ice-glazed windows at half a foot of new snow — and you’re thinking about the garden. Here’s an idea: you don’t need to take a trip to the Galapagos to study evolution, you can do it right in your backyard. The New York Botanical Garden is opening a new exhibit, called Darwin’s Garden.
In all, the tour is 33 stops, spread throughout about half of the garden’s 250 acres. Visitors who enter the exhibition through the Enid A. Haupt Conservatory will encounter a replica of a room in Darwin’s house, designed so they can look through the window, as he did, to a profusion of plants and bright flowers: hollyhocks, flax and of course primroses, what Todd Forrest, the garden’s vice president for horticulture, calls “a typical British garden.” On a table stands a tray holding quills, brushes, sealing wax and tweezers, the kinds of simple tools Darwin used to conduct his world-shaking research.
Brilliant! Evolution is not something that requires exotic, out of the way locales and weird, obscure organisms to study — it’s everywhere.
The title gets the principal objection of any creationist out of the way: yes, this population of Podarcis sicula is still made up of lizards, but they’re a different kind of lizard now. Evolution works.
Here’s the story: in 1971, scientists started an experiment. They took 5 male lizards and 5 female lizards of the species Podarcis sicula from a tiny Adriatic island called Pod Kopiste, 0.09km2, and they placed them on an even tinier island, Pod Mrcaru, 0.03km2, which was also inhabited by another lizard species, Podarcis melisellensis. Then a war broke out, the Croatian War of Independence, which went on and on and meant the little islands were completely neglected for 36 years, and nature took its course. When scientists finally returned to the island and looked around, they discovered that something very interesting had happened.
There in the foaming welter of email constantly flooding my in-box was an actual, real, good, sincere question from someone who didn’t understand how chromosome numbers could change over time — and he also asked with enough detail that I could actually see where his thinking was going awry. This is great! How could I not take time to answer?
So here’s the question:
How did life evolve from one (I suspect) chromosome to… 64 in horses, or whatever organism you want to pick. How is it possible for a sexually reproducing population of organisms to change chromosome numbers over time?
Firstly: there would have to be some benefit to the replication probability of the organisms which carry the chromosomes. I don’t see how this would work. How is having more chromosomes of any extra benefit to an organism’s replicative success? Yes, perhaps if those chromosomes were full of useful information… but the chances of that happening are non existent and fly in the face of ‘small adaptations over time’.
Secondly, the extra chromosomes need to come from somewhere. I’m not sure about this, but I believe chromosome number are not determined by genes, are they? There isn’t a set of genes which determines the number of chromosomes an organism has. So the number is fixed, determined by the sexually reproducing parents. Which leads me to believe that if the number does change, and by chance the organism is still alive and capable of sexual reproduction, that the number will start swinging back and forward, by 1 or 2, every generation, and never stabilising. The chances of this happening are also very very slim.
Jay Hosler has a new book out, Optical Allusions(amzn/b&n/abe/pwll). If you’re familiar with his other books, Clan Apis(amzn/b&n/abe/pwll) and The Sandwalk Adventures(amzn/b&n/abe/pwll), you know what to expect: a comic book that takes its science seriously. Hosler has a fabulous knack for building serious content into a light and humorous medium, just the kind of approach we need to get wider distribution of science into the culture.
This one has a strange premise. Wrinkles the Wonder Brain is an animated, naked brain working for the Graeae Sisters, and he loses the one eye they share between them — so he has to go on a quest to recover it. I know, it sounds like a stretch, but it works in a weird sort of way, and once you start rolling with it, you’ll find it works. Using that scenario to frame a series of encounters, Wrinkles meets Charles Darwin and learns how evolution could produce something as complex as an eye; talks about the sub-optimal design of retinal circuitry with a cow superhero; discovers sexual dimorphism with a crew of stalk-eyed pirates; learns about development of the eye from cavefish and a cyclops; chats with Mr Sun about the physics of radiation; there are even zombie G proteins and were-opsins in a lesson about shape changing. This stuff is seriously weird, and kids ought to eat it up.
It isn’t all comic art, either. Each chapter is interleaved with a text section discussing the details — you can read the whole thing through, skipping the text (like I did…), and then go back and get more depth and directions for future reading in the science. This is a truly seditious strategy. Suck ’em in with the entertainment value, and then hand ’em enough substance that they might just start thinking like scientists.
It’s all good stuff, too. A colleague and I have been considering offering an interdisciplinary honors course in physics and biology with the theme of the eye, specifically for non-science majors, and this book has me thinking it might make for a good text. It’ll grab the English and art majors, and provide a gateway for some serious discussions that will satisfy us science geeks. I recommend it for you, too — if you have kids, you should grab all of Hosler’s books. Even if you don’t have kids, you’ll learn a lot.
Jay Hosler also explains the intent of the project, and you can read an excerpt.
[Since I had to fly away early this morning and missed all these talks, I had to rely on regular commenter DanioPhD to fill in the gaps … so here’s her summary:]
This morning’s final series of talks each focused on a different phylum, but the unifying theme was one of bridging the processes of microevolution and macroevolution. The first talk after breakfast (and a long night of Scotch-drinkin’ and story-swappin’ prior to that) was Bernie Degnan of the University of Queensland. He summarized his work on Amphimedon queenslandica, a sponge species developed as a model of a representative primitive metazoan. Sponges diverged from the metazoan lineage ca. 700 MYA and possess the most minimalist metazoan body plan–no nervous system, muscles, nor any discernible tissues in the adult body architecture. Their embryos, however, feature robust anterioposterior patterning, distinct cell types organized into tissues, and cell morphogenesis typical of more complex metazoans. These embryonic characteristics are achieved by a regulatory network of genes, which, while inactive in the adult sponge, strongly support the presence of similar molecules in the ancestral metazoan genome. A few million years after the divergence of porifera, metazoans were able to co-opt these molecular toolkits to build the diverse, molecularly and morphologically distinct tissues common to all bilaterians. PZ has previously written up one such sponge tale here describing the molecular precursors to a nervous system in the sponge genome. Precursors to pretty much every other developmental ‘big gun’, e.g, Hox genes, Pax genes, Wnts, Hedgehog, etc. are also present as a basic prototype, in the Amphimedon genome.
