Twins

When I studied zoology, too many years ago, Evo-Devo had not emerged as a separate field of investigation. At least I never heard about it. It's a cute abbreviation for Evolutionary-Developmental Biology. One of its recent stars is Professor Sean B. Carroll. He is doing exciting work and has written several books that can be understood by people who remember their high school biology. A question that comes up constantly is: How does a cell, or a part of an organism "decide" to become something different? Put in perhaps a better way: How does a branch of an oak tree "decide" to produce a leaf or an acorn in a particular spot? In animal development: How does an early embryo consisting of say 128 or 256 identical cells begin to differentiate, that is, develop a head here, an arm there, and perhaps a tail somewhere else? If I've aroused your curiosity, check out a book by Carroll whose title quotes a line from Darwin, "Endless Forms Most Beautiful." Meanwhile, when I'm not in the mood to digest the technically difficult stuff, I still get a great deal of pleasure from just looking at acorns and leaves on an oak tree. I hope you do, too.