NYT Science Section - All Evolution

Every Tuesday the New York Times publishes a Science section called Science Times. It would be remiss of me to forget to mention this weeks Science Times. This week every article concerns genetics, evolution or development.

The first article to draw my eye is called "From a Few Genes, Lifes Myriad Shapes" by Carol Kaesuk Yoon. It's about evo-devo, evolution-development.

The development of an organism — how one end gets designated as the head or the tail, how feet are enticed to grow at the end of a leg rather than at the wrist — is controlled by a hierarchy of genes, with master genes at the top controlling a next tier of genes, controlling a next and so on. But the real interest for evolutionary biologists is that these hierarchies not only favor the evolution of certain forms but also disallow the growth of others, determining what can and cannot arise not only in the course of the growth of an embryo, but also over the history of life itself.

The field of biological development has been reinvigorated by molecular biology. It provides clues such as how genes of the same family (pax6) in fruit flies to man control eye development.

Dr. Cliff Tabin, a developmental biologist at Harvard Medical School, points out that the Galapagos finches studied by Darwin no longer exist. Natural selection has resulted in birds that look very different due to the availability of different foods that are now found on the islands.

For while the species are descendants of an original pioneering finch, they no longer bear its characteristic short, slender beak, which is excellent for hulling tiny seeds. In fact, the finches no longer look very finchlike at all. Adapting to the strange new foods of the islands, some have evolved taller, broader, more powerful nut-cracking beaks; the most impressive of the big-beaked finches is Geospiza magnirostris. Other finches have evolved longer bills that are ideal for drilling holes into cactus fruits to get at the seeds; Geospiza conirostris is one species with a particularly elongated beak.

The birds with the bigger, different beaks simply expressed a gene already present, bmp4 earlier in development.

“There aren’t new genes arising every time a new species arises,” said Dr. Brian K. Hall, a developmental biologist at Dalhousie University in Nova Scotia. “Basically you take existing genes and processes and modify them, and that’s why humans and chimps can be 99 percent similar at the genome level.”

Here is an important thing to remember in evo-devo.

“The genetic tools to build fingers and toes were in place for a long time,” Dr. Shubin wrote in an e-mail message. “Lacking were the environmental conditions where these structures would be useful.” He added, “Fingers arose when the right environments arose.”

And here is another of the main themes to emerge from evo-devo. Major events in evolution like the transition from life in the water to life on land are not necessarily set off by the arising of the genetic mutations that will build the required body parts, or even the appearance of the body parts themselves, as had long been assumed. Instead, it is theorized that the right ecological situation, the right habitat in which such bold, new forms will prove to be particularly advantageous, may be what is required to set these major transitions in motion.