Mainstream Christianity quickly came to terms with evolution, writes Prof. William Reville

We celebrated the 200th anniversary of the birth of Charles Darwin (1809-1882) on February 12, 2009. Darwin's discoveries had a more profound influence on the modern world than the work of any other scientist. His big discovery was natural selection which explains 'design' in the living world, the origin of species and is the driving force behind evolution. Darwin also explained that man is descended from an ape-like animal - an idea that made most people very uncomfortable at the time and that continues to bother many people to this day.

Darwin was the son of a wealthy physician. He studied medicine in Edinburgh for two years but wasn't interested and moved to Cambridge University to prepare for a career as a clergyman. He graduated with a B.A. in 1831 and, on impulse, he enrolled as naturalist on the voyage of HMS Beagle. On the five year voyage (1831-1836) around the world, Darwin collected evidence he later used in formulating his theory of evolution through natural selection.

Characteristics

Darwin didn't invent the concept of evolution. The principle of evolution - that living species change their characteristics considerably over long time spans - was widely accepted by naturalists at the time. For example, Jean-Baptiste de Monet, Chevalier de Lamarck (1744-1829) proposed a broad theory of evolution in which simpler forms of life developed into more advanced forms by inheritance of acquired characteristics - we now know that acquired characteristics are not inherited.

Most scientists in Darwin's day were Christians. A powerful argument for the existence of God, the argument from design, was perfected by the Protestant clergyman William Paley (1743-1805). Paley argued that a designed object implies a designer and since nature is full of wonderful biological designs, e.g. the eye, there must be a super-intelligent designer, viz. God. Darwin studied Paley as an undergraduate and was very impressed, but he later destroyed Paley's argument by showing how 'design' in nature arises naturally and unconsciously through natural selection.

Theory

Natural selection was Darwin's big discovery, and in the phrase 'The Theory of Evolution through Natural Selection', the word 'theory' refers mainly to natural selection and not to evolution. Natural selection works as follows. Variation naturally exists in any biological population. Some variations are better equipped to thrive and breed than others and will therefore leave more offspring than their fellows, thereby ensuring that their particular characteristics are passed on more effectively to the next generation. This 'natural selection' automatically proceeds generation after generation, selecting those varieties best suited to the environment - 'designed' to fit the environment. There is no need to invoke a supernatural designer.

The faithful inheritance of characteristics is central to natural selection. Darwin did not understand the mechanism of inheritance. This mechanism was worked out by the Augustinian monk Gregor Mendel (1822-1884) who showed that the expression of biological characteristics is controlled by 'factors' that we inherit from our parents and these factors independently sort and segregate as they pass from generation to generation. Today we call these factors genes. Chemically genes are made of DNA, long information-rich molecules composed of four different kinds of subunits (called nucleotides) termed A, T, G and C. The information content of DNA is encoded in this 4-letter alphabet, expressed as 3-letter words.

Chemistry

DNA controls the day-to-day chemistry of our cells and is also the hereditary material passed from one generation to the next. Errors (called mutations) naturally creep randomly into the information encoded in DNA and this new information is passed on to the next generation. Mutations are usually harmful to the organism and are weeded out by natural selection. However, sometimes a mutation confers a new characteristic on an organism that is beneficial, improving procreation prospects, and such mutations are preserved and spread by natural selection. The combination of this trickle of novelty into the genetic material through mutations, combined with natural selection, is sufficient to explain how organisms can change slowly, gradually achieving very significant changes over many generations and how new species arise. Evolution is often said to proceed through chance (random mutations) and necessity (natural selection - a lawful process). Life began on earth about 3.8 billion years ago, probably as a simple single form, and it has been evolving ever since, eventually producing the myriad life forms, including humans, that today colonise every environmental niche on earth. Humans are descended from an ape-like ancestor - the human line of descent branched off from the ape line several million years ago.

Implications

Darwin's theory had profound implications for religion. According to the Book of Genesis, universally and literally accepted throughout Christendom before Darwin's theory, God created all biological species individually about 6,000 years ago in pretty much the same form as we find them today. But Darwin's theory says that existing species, including humans, are descended with modification from a long line of previous quite different forms. Naturally, Darwin's proposal came as a big shock to Christians. When Darwin's ideas were explained to the wife of the Bishop of Worcester she exclaimed - ''Descended from the apes! My dear, let us hope that it is not true, but if it is, let us pray that it will not become generally known''.

However, mainline Christianity quickly came to terms with evolution.

The Catholic Church accepts the theory's explanation of the origin and development of species generally, including the human body, but holds that the supernatural 'soul' is inserted into the body by God. Today only a small minority of European Christians reject evolution, but a more significant Christian minority in America rejects and actively campaign against evolution.

The theory of evolution through natural selection rests on massive amounts of scientific evidence, including the fossil record, comparative anatomy, patterns of embryonic development, vestigial structures, and molecular biology. The theory is science's mature explanation of how life developed on earth and it is the central unifying theory in biology. I accept the theory of evolution, as do countless other Christian scientists. In common with other Christian scientists, I accept that, somehow, God sustains the world, and I also believe that science shows us how God's natural world works. There is no contradiction here. In the words of Theodosius Dobzhansky (1900-1975), the great evolutionary geneticist, and also a Christian, ''Nothing in biology makes sense except in the light of evolution''.

Dr William Reville is Professor of Biochemistry and Public Awareness of Science Officer at UCC - http://understandingscience.ucc.ie