At the heart of the debate over intelligent design is this question: Can a scientific explanation of the history of life include the actions of an unseen higher being?
The proponents of intelligent design, a school of thought that some have argued should be taught alongside evolution in the nation’s schools, say that the complexity and diversity of life go beyond what evolution can explain.
Biological marvels like the optical precision of an eye, the little spinning motors that propel bacteria and the cascade of proteins that cause blood to clot, they say, point to the hand of a higher being at work in the world.
In one often-cited argument, Michael J. Behe, a professor of biochemistry at Lehigh University and a leading design theorist, compares complex biological phenomena like blood clotting to a mousetrap: Take away any one piece – the spring, the baseboard, the metal piece that snags the mouse – and the mousetrap stops being able to catch mice.
Similarly, Dr. Behe argues, if any one of the more than 20 proteins involved in blood clotting is missing or deficient, as happens in hemophilia, for instance, clots will not form properly.
Such all-or-none systems, Dr. Behe and other design proponents say, could not have arisen through the incremental changes that evolution says allowed life to progress to the big brains and the sophisticated abilities of humans from primitive bacteria.
These complex systems are “always associated with design,” Dr. Behe, the author of the 1996 book “Darwin’s Black Box,” said in an interview. “We find such systems in biology, and since we know of no other way that these things can be produced, Darwinian claims notwithstanding, then we are rational to conclude they were indeed designed.”
It is an argument that appeals to many Americans of faith.
But mainstream scientists say that the claims of intelligent design run counter to a century of research supporting the explanatory and predictive power of Darwinian evolution, and that the design approach suffers from fundamental problems that place it outside the realm of science. For one thing, these scientists say, invoking a higher being as an explanation is unscientific.
“One of the rules of science is, no miracles allowed,” said Douglas H. Erwin, a paleobiologist at the Smithsonian Institution. “That’s a fundamental presumption of what we do.”
That does not mean that scientists do not believe in God. Many do. But they see science as an effort to find out how the material world works, with nothing to say about why we are here or how we should live.