Under the Microscope: Evolution is in the news in the US. Some people, including a small minority of scientists, argue that life's complexity exceeds what the theory of evolution can explain. Their hypothesis, called Intelligent Design (ID), proposes that the design evident in biology points to the actions of an active intelligence.
President Bush has announced that he favours teaching ID in the schools. But mainstream science claims that ID is not a legitimate school of scientific thought.
ID advocates don't specify the nature of the intelligence they see working in the natural world, but it is no secret that they mean God. Most scientists believe that ID is simply the latest manifestation of creationism. Creationists interpret the Bible literally and conclude that earth was formed about 10,000 years ago containing the full range of biological species in more or less the same form as they appear today. Science shows that the earth was formed about five billion years ago and that life began in a simple form about four billion years ago, evolving since into the myriad forms that currently populate the globe.
Science bases its conclusions on a huge volume of evidence, including the fossil record showing the history of evolving life forms on earth. The traditional creationist contradicts science and, in order to explain the evidence for a very ancient earth, proposes that when God created the earth 10,000 years ago he adorned it with fake evidence of an ancient origin!
The US constitution forbids teaching religion in schools, so if creationism is to be taught it must establish scientific credentials. Realising this, the traditional creationists began a movement called Creation Science, which tried to discredit mainstream scientific evidence using "scientific" counter-arguments. This failed to convince, and in 1982 the federal court forbade the introduction of creationism into public schools because it would constitute the establishment of religion. In the meantime, ID has arisen and 19 US states are now debating its use in public education.
ID is a sophisticated version of the old argument from design, which reached its zenith in the writings of an Anglican clergyman William Paley (1743-1805). Paley argued that if you picked up a rock from the road you could explain its form and shape as the consequences of weathering, whereas if you picked up and examined a watch you would have to infer a designer. Paley then drew attention to the biological world filled with devices marvellously designed to fulfil their functions and inferred a Grand Designer - God.
Paley's argument was demolished by the theory of evolution introduced in 1858 by Darwin and Wallace. This demonstrated that biological design can arise unconsciously through natural selection. Natural variations crop up randomly in a biological species. Some of these variations enhance the capacity of their bearers to live in the environment and thereby to procreate. Genetic inheritance ensures that the numbers of individuals bearing these desirable characteristics increase and are thereby naturally selected. Thus, biological species and structures designed to work in the environment arise naturally as small random changes and are sequentially selected over time.
Darwin and Wallace knew nothing of the molecular mechanisms in cells that explain how evolution works. The chemical nature of the hereditary material was discovered in the 20th century - DNA - and hereditary information is encoded in the structure of DNA. Random changes arise in DNA, giving rise to mutations in the organism carrying the mutation. Sometimes these altered properties confer a reproductive advantage on the individual. Mutation trickles an ongoing stream of novelty into biological organisms and is the raw material on which natural selection works.
Proponents of ID claim that molecular investigations of the cell have discovered many vital structures of "irreducible complexity" that could not have arisen by the gradual mechanism of evolution and that must have been produced ab initio by an intelligent designer. To explain irreducible complexity, a leading ID proponent, Michael Behe, uses the example of the common mousetrap, which is made of several components - a baseboard on which the structure is assembled, a stout metal wire that fatally pounces on the unfortunate mouse, a spring that propels the wire on its deadly way, and a metal hook that precariously holds the wire against the tension of the spring until the unwary mouse releases it. The mousetrap is irreducibly complex because it would be useless as a mousetrap if any one of these components were missing.
Behe then points to several irreducibly complex biological systems, eg the flagellar apparatus relying on spinning motors that propels bacteria through liquid media. He claims that, since natural selection can only pick between systems that are already working, there is no way Darwinian mechanisms could have made the irreducibly complex systems found in living cells. If such systems could not have evolved, they must have been designed.
The ID argument is flawed because the components of irreducibly complex machines may have different but still useful functions. In the mousetrap example, remove the catch and you have a paperclip, take away the spring and you have a two-part key-chain. The catch can be used as a fishhook, and so on. Science has shown that evolution fashions the irreducibly complex by modifying and combining components previously used for other functions.
ID has yet to produce data that seriously confronts evolution and it certainly doesn't merit being taught as a scientific hypothesis. However, it does attempt to tackle science on scientific territory and cannot gain ground unless it produces genuine scientific evidence. So far, it has merely proved to be bad science.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC - http://understandingscience.ucc.ie