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.
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.
Revere is thinking about how to grow meat without the animal. It’s a cool idea that’s been floating around in science fiction for a while now, but, well, of course it has problems, and Revere notes a couple.
The two biggest, as far as I can see from a quick perusal of the burgeoning literature, are finding a suitable nutrient to grow the cells in; and then growing tissue that has the proper texture for being a meat substitute. Animal meat is not just muscle cells but a complicated structure also containing connective tissue, blood and blood vessels, nerves and fat. Just growing up masses of identical cells isn’t sufficient. You have to reproduce an architecture.
I see those two problems as aspects of one much bigger problem. Muscle doesn’t grow in isolation: it’s always in a solid environmental context. It’s made up of cells that respond to activity in a way that enhances performance for the organism, and incidentally promotes flavor and texture and bulk for the delectation of the carnivore. So what do you need to make edible muscle mass, beyond a sheet of myocytes in a culture dish (which, I suspect, would have the texture of slime and would not sell well in test markets)?
An architecture is right. You need connective tissue to form a framework and you need a rigid but motile structure to do work and exercise the growing muscle. Then, because you want a piece of muscle larger than a drop, you need a delivery system for nutrients: a circulatory system, with a pump. This muscle in a vat is going to need a skeleton and a heart.
When I teach physiology, one of the organs I emphasize is the liver. It’s amazing how important a liver is to just about everything: growth, digestion, physical performance, reproduction, the whole shebang. Our cultured muscle will need a liver equivalent to support it. Even if we get rid of the digestive system entirely and feed this muscle mass on delivered supplies of pure glucose, amino acids, and various cofactors and enzymes, the liver is a primary regulatory agent for those substances.
Then we need an immune system. A huge lump of cells growing in a bath of sugar and amino acids is bacterial heaven — it’s going to need major antibacterial/antiviral support.
The more I think about it, the more I think people are going at it backwards. We shouldn’t be thinking about building muscle from the cells up, to create a purified system to produce meat for the market, we should be going the other way, starting with self-sustaining meat producers and genetically paring away the less commercially viable bits, like the brain. Instead of test-tube meat, we should be working on more efficient organisms that generate muscle tissue with the properties we want.
Guess what? Farmers have already been doing this! Look at the domestic cow and chicken and turkey: they’re far more brainless than their wild relatives, and have been reduced to as much stupidity and helplessness as possible, without compromising their ability to survive semi-autonomously and harvest nutrients from naturally occurring food sources. I don’t see all that much difference in the consequences between building up a functional meat producer from cells in a dish, and stripping down a functional meat producer from a line of domesticated animals. Both starting points are aiming at the same final result; I suspect that the top down procedure is more likely to achieve success in my lifetime.
I’m busy preparing my lecture for genetics this morning, in which I’m going to be talking about some chromosomal disorders … and I noticed that this summary of Fragile-X syndrome that was on the old site hadn’t made it over here yet. A lot of the science stuff here actually gets used in my lectures, so they represent a kind of scattered online notes, so I figured I’d better put this one where I can find it.
I haven’t even finished grading the last of the developmental biology papers, and already my brain is swiveling towards the genetics literature, as I get in the right frame of mind to teach our core genetics course in the spring. And, lo, here is a new paper in PNAS that addresses details of a topic I bring up every time.
There are a surprising number of heritable diseases that share a couple of common traits: they are neurodegenerative, causing progressive loss of neural control, and they also exhibit a phenomenon called genetic anticipation—they tend to get worse, with earlier onset and more severe affects with each generation. Some of these diseases may be rather obscure, for instance
Haw-River Syndrome (AKA Dentatorubral-pallidoluysian atrophy),
Friedreich Ataxia,
Machado-Joseph Disease, or
X-linked Spinal and Bulbar Atrophy Disease (AKA Kennedy Disease), but others you’ve probably heard of, like
Myotonic dystrophy and
Huntington Disease. These are dreadful diseases that are variable in their pattern of appearance, and have terrible symptoms, like loss of motor control, chorea, seizures, dementia, and eventually, death.
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.
Look: it’s possibly the world’s most annoying, boring video. Turn the sound down, it’s a car driving in traffic with a siren howling.
Of course, if you look a little bit more closely, you might notice…nobody is driving! This is an exercise in robotics and computer vision, and it’s one of the achievements that is winning the Franklin Institute Awards this week. Any lucky Philadelphians might want to make it a point to visit the Franklin Institute (which was one of our favorite museums when we lived in Philly) this week — they have a slate of events coming up associated with handing out these prestigious awards. It’s not just robotics, either: miRNAs are recognized, as well as the structure and origin of nucleic acids, and the ocean’s effect on climate change, ultra cold physics, and artificial intelligence.
There’s something for everybody, so it’s a good time to think about stopping by.
Check it out: it’s yet another transitional form, a 92 million year old snake with two hindlimbs. Cool! Just last week I was told that none of these things exist.
Since I was sent this photo from the evo-devo conference by Kevin Emerson, I couldn’t resist: this is the aftermath of two scientists duking it out in an intellectual arena.
Obviously, they had to wear different colored shirts so we could tell them apart in the maelstrom of the fray.
[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.
