Spongeworthy genes


What are the key ingredients for making a multicellular animal, or metazoan? A couple of the fundamental elements are:

  • A mechanism to allow informative interactions between cells. You don’t want all the cells to be the same, you want them to communicate with one another and set up different fates. This is a process called cell signaling and the underlying process of turning a signal into a different pattern of gene or metabolic activity is called signal transduction.

  • Patterns of differing cell adhesion. But of course! The cells of your multicellular animal better stick together, or the whole creature will fall apart. This can also be an important component of morphogenesis: switching on a particular adhesion molecule (by way of cell signaling, naturally) can cause one subset of cells to stick to one another more strongly than to their neighbors, and mechanical forces will then sort them out into different tissues.

These are extremely basic functions, sort of a minimal set of cellular activities that we need to have in place in order to even begin to consider evolving a metazoan. Fortunately for our evolutionary history, these are also useful functions for a single celled organism, and while the metazoa may have elaborated upon them to a high degree, there’s nothing novel about the general processes in our make-up. The principles of signaling and transduction were first worked out in bacteria, and anyone who has a passing acquaintance with immunology will know about the adhesive properties of bacteria, and their propensity for modulating that adhesion to build complexes called biofilms.

So let’s take a look at the distribution of signaling and adhesion molecules in single-celled organisms, multicellular animals, and most interestingly, a group that is close to the division between the two (although more on the side of multicellularity), the sponges.

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What should a scientist think about religion?

In a thread that will not die at the Panda’s Thumb, the argument has settled into a more reasonable back-and-forth on the issue of the entanglement of atheism and science. There are a number of people, including many of the contributors to the Panda’s Thumb, who are adamant that evolution must maintain a plausible deniability from atheism—that atheism is not a necessary consequence of accepting good science (a point with which I agree), and that atheism is basically a scary thing that will alienate many potential supporters (a point with which I strongly disagree). One comment, though, highlights the problem with the atheist-averse strategy.

Distinguish between whether you are speaking as a scientist or as an atheist. If the two labels are not necessarily linked, then it helps to minimize the confusion by clearly stating on a particular matter, whether you are pissed off as a scientist, or as an atheist.

If you must say, “Religion is irrational,” I think a theist would like to know if you are speaking as a scientist or an atheist. Scientist: Is irrationality a scientific concept? On what quantitative measure do we evaluate irrationality? Atheist: Why do I reject God premises? Why is materialism a superior philosophy?

As I was puzzling over how to answer such an odd question, I realized why I thought it was odd. The scientist and atheist positions are the same. It doesn’t matter which hat I’m wearing, the answers won’t change.

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