The choanoflagellate genome and metazoan evolution

Blogging on Peer-Reviewed Research

What are the key innovations that led to the evolution of multicellularity, and what were their precursors in the single-celled microbial life that existed before the metazoa? We can hypothesize at least two distinct kinds of features that had to have preceded true multicellularity.

  • The obvious feature is that cells must stick together; specific adhesion molecules must be present that link cells together, that aren’t generically sticky and bind the organism to everything. So we need molecules that link cell to cell. Another feature of multicellular animals is that they secrete extracellular matrix, a feltwork of molecules outside the cells to which they can also adhere.

  • A feature that distinguishes true multicellular animals from colonial organisms is division of labor — cells within the organism specialize and follow different functional roles. This requires cell signaling, in which information beyond simple stickiness is communicated to cells, and signal transduction mechanisms which translate the signals into different patterns of gene activity.

These are features that evolved over 600 million years ago, and we need to use a comparative approach to figure out how they arose. One strategy is to pursue breadth, cast the net wide, and examine divergent forms, for instance by
comparing multicellular plants and animals. This approach leads to an understanding of universal properties, of how general programs of multicellular development work. Another is to go deep and examine closer relatives to find the step by step details of our specific lineage, and that’s exactly what is being done in a new analysis of the choanoflagellate genome.

[Read more…]

Bad hackers! Bad, bad!

Hackers have replaced the Irish Catholic page with a cute video and a link to the Irish Atheists page. I really should scold such deplorable virtual vandalism, but, well, instead I grabbed a quick screen capture before it gets taken down.

i-b44a39bae2e360d336912d6ede5b393c-catholic_hack.jpg

I thought the video was pretty funny, too, mocking the silly costumery of the Catholic hierarchy. Alright, hackers, you were naughty, don’t do it again … but you did make me laugh.

Good news — it’s not a hack at all. Those clever Irish atheists merely beat the Irish Catholics to their domain name…so it should be up indefinitely.

Willfully obtuse

The principal of a high school in Texas (where else?) is censoring the school’s yearbook.

Senior Megan Estes, editor in chief of The Elk, said the point of the article, featuring two seniors who also are teen mothers, was to show fellow students how the girls are coping with motherhood and how their lives have changed. Estes said the principal told her he felt the article “glamorized” the teen mothers’ mistakes.

Principal Paul Cash said the topic of the article conflicts with the school’s abstinence-based curriculum. He also said he does not think the community would want that topic covered in the yearbook.

I think reality conflicts with the school’s abstinence-based curriculum. I wonder if he’s got an answer for that?

Probably something like “close your eyes real hard.”

Complexity isn’t magic

You should read John Allen Paulos’s latest column on complexity — it’s a central concept in the various debates that go on around here, and no one on the other side evinces any sign of actually understanding the subject. It’s always “complexity implies design” this, and “complexity only arises by intent” that. I’ll also second his recommendation of Stuart Kauffman’s At Home in the Universe: The Search for the Laws of Self-Organization and Complexity(amzn/b&n/abe/pwll) — it’s a very good book full of interesting ideas and empirical demonstrations of order arising out of randomness.

Another reason to read the column: the ABC news site gets a more diverse mix of commenters than we do here, and if you want to get a wider sample of the American mindset, they’re much more representative. And far more terrifying.

Lethal doses of stupid

There are limits to even my capacity to cope with The Stupid, and this video reaches them. It’s interesting in a historical sense, in that it seems to be an old recording — familiar faces look so young, and the whole thing has the clumsy style of a bad 1970s documentary—but it’s a whole half-hour of badly concatenated mish-mashes of creationist arguments. Who knew that Charles Darwin was responsible for the Big Bang theory, or that evolution was the foundation of astronomy? (Don’t tell Phil, his inferiority complex is bad enough.).

It’s rather weird to see old faces that most of you have forgotten or never knew, like Ian Taylor and Luther Sunderland and John Morris, all sitting there mired in the most awful ignorance and propagating lies about Lucy’s knee joint and Neandertal just being an arthritic old man and so forth, and realize that they or their successors are still spouting the same old lies today. Ignorance builds more ignorance, unfortunately.

The incoherence of the whole production is amazing, too. It starts of with this weird set of New Age rationalizations before wallowing in the reactionary pronouncements of fundamentalist kooks like D. James Kennedy … and then at the end it includes a five minute music video with Kurt Cobain of Nirvana.

There’s a brief discussion of the video here, brought up by a guy who thought it made good points and made him question his acceptance of evolution. Among the issues he had was that the movie claims that “cro-magnon and other pre-humans were determined to be transitional species from as little as a tooth or a rib,” which is actually an excellent example of an outright lie from the movie. Nope, not true. Cro-magnon refers to a variety of Homo sapiens, so calling them transitional is stretching the word. Transitional forms are far better established than as extrapolations from a single tooth — but the creationists sure milk their mangled story of Nebraska Man for all it is worth, and use it to falsely cast doubt on other explanations.

I’m not even going to try to address the details of that mess. It’s the Gish Gallop on video; if anyone has any specific questions, OK, but the shorter summary is that all the creationists in it are lying out of ignorance and all the scientists are taken out of context.

By the way, if the stupidity in that video doesn’t make your cortex disintegrate into slime, try this one — it’s the intellectual equivalent of huffing a hydrofluoric acid/osmium tetroxide cocktail.

And they call us arrogant

The premise of evangelical atheism is that you can introduce people to the importance of reason and they will come to a reasonable conclusion on their own. The premise of evangelical faith is that people must accept an arbitrary belief because an arbitrary judge, who the convert may not query, demands it. The former kind of proselytizer ought to be called a teacher, but is more often called an arrogant asshole; the latter ought to be considered a liar, a fraud, and an arrogant asshole in fact, but they actually believe they are humble servants of the lord.

Here’s a beautiful example of oblivious faith in a story of an encounter with a Mormon missionary.

His position was that there are NO righteous people absent baptism into the Mormon faith; that no one enters heaven without it.

Since it had recently come to public attention that Elie Wiesel’s name was on a list for future baptism, I asked him if Wiesel would qualify as a “righteous man”.

No, replied the Mormon, Wiesel would not qualify.

“But you would, being a Mormon?” I asked.

Yes, replied the Mormon.

Well, I told the kid, any belief system that makes you righteous over Elie Wiesel seems pretty obviously fucked.

But it does make the kid feel all noble and important for putting on a white polyester shirt and riding a bicycle, which I think is the point of the appeal of religion: all the righteousness, none of the sacrifice or hard work.