Getting back home from a Thanksgiving journey full of turkey and queasy toddlers on airplanes, I just noticed that my visit-counter has rolled past the 500,000 mark. I never would have dreamed of such figures when I started this blog, and I just want to take a second to thank everyone who has ever clicked their way to the Loom.
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Natural selection is not natural perfection. Time and again, biologists have discovered traits that are both beneficial and harmful. Perhaps the most famous example is the devastating disorder known as sickle-cell anemia. To get sickle-cell anemia, you have to inherit two faulty copies of a gene that helps build hemoglobin, the molecule that traps oxygen in red blood cells. In this condition, hemoglobin can’t hold its shape if it’s not clamped around oxygen. Without it, the defective hemoglobin collapses into needle-shaped clumps, which then turn the cell itself into a sickle shape. The sickle cells snag in small capillaries, and the blood can no longer supply as much oxygen to the body. People who inherit only one copy of this defective gene can get by on the hemoglobin made by the remaining normal copy. But people who get two copies of the bad gene make nothing but defective hemoglobin, and they’re usually dead by the time they’re thirty. A person who dies of sickle cell anemia is less likely to pass on the defective gene, and that means that the disease should be exceedingly rare. But it’s not–one in 400 American blacks has sickle cell anemia, and one in ten carries a single copy of the defective gene.
Back in February I discovered the remarkable work of Australian biologist Bryan Grieg Fry, who has been tracing the evolution of venom. As I wrote in the New York Times, he searched the genomes of snakes for venom genes. He discovered that even non-venomous snakes produce venom. By drawing an evolutionary tree of the venom genes, Fry showed that the common ancestor of living snakes had several kinds of venom, which had evolved through accidental “borrowing” of proteins produced in other parts of the body. Later, these genes duplicated to create a sophisticated cocktail of venoms–a cocktail that varied from one lineage of snakes to another.
Continue reading “Which Came First, the Snake or the Venom?”
Following up on my earlier post, I wanted to relay one more piece of book news. I’ve been getting some emails over the past couple months inquiring about my book, Evolution: The Triumph of an Idea. I wrote it as a companion volume to the 2001 PBS television series, Evolution. Like the series, the book surveys the history and cutting edge of evolutionary biology, from the origin of new species to mass extinctions, from the rise of complex life to the emergence of humans. It also looks at ongoing evolutionary races, whether the competitors are hosts and parasites or members of the opposite sex. It puts evolution in a historical context, showing how Darwin’s theory emerged out of the science of his time and how social and political tensions have produced hostility to the notion of evolution today. (More details about the book can be found here.)
My latest book, Smithsonian Intimate Guide to Human Origins is now available on Amazon.com, and I think it’s getting put on the shelves at bookstores. I’ve only referred to the book here glancingly from time to time, and I wanted to take a minute now to give Loom readers a sense of the book (and perhaps inspire the sales of a few copies).