Charles Darwin created something of a stir when he wrote in the mid 1800s that we probably all evolved from apes.
His theories, published in The Origin of Species and latterly The Descent of Man, were denounced by the Anglican Church as blasphemy, before being embraced by academics across the world as the basis for future study of the life sciences. But 150 years on the controversy still rages.
In recent years, support for pre-Darwinian theories of creationism and its more recent offshoot, intelligent design, has grown. The clash has been brought into sharp focus in the United States, where attempts by some school boards - under pressure from the religious right - to allow students to "critically analyse aspects of evolutionary theory" have been challenged in the courts.
In December, a judge in Pennsylvania ruled that it was unconstitutional to compel teachers to introduce intelligent design in science classes.
In the UK, the debate between the two camps has been more subtle, but just as keenly fought. Attention has focused largely on the three secondary schools - two academies and one city technology college - in the North-east. They are controlled by the Emmanuel Foundation, a charitable trust established by Sir Peter Vardy, the evangelical Christian car dealer.
As semi-independent state schools, they can diverge from the national curriculum and, as such, have made no secret of their position that creationism deserves lesson time alongside evolutionary theories.
Indeed, Nigel McQuoid, director of schools at the Emmanuel Foundation, said this week that he believed the earth was created in six days (see right).
So what of the rest of the country? The official government stance, outlined last week by Jacqui Smith, schools minister, seems clear: "Neither creationism nor intelligent design is taught as a subject in schools."
However, Ms Smith, in a written answer to a parliamentary question, refuses to dismiss such theories from science lessons altogether. In her statement, she goes on to say that debates over evolution may emerge in key stage 4 biology, when pupils are asked to explain the existence of fossils.
"Pupils should however be taught about 'how scientific controversies can arise from different ways of interpreting empirical evidence'," she said.
"Also, the biblical view of creation can be taught in RE lessons, where pupils are taught to consider opposing theories and come to their own reasoned conclusions. Therefore, although creationism and intelligent design are not part of the national curriculum, they could be covered in these contexts."
Critics have seized upon this as legitimising creationism. Concerns have been fuelled recently by new science guidelines, published by the Qualifications and Curriculum Authority in a move to tackle the subject's declining popularity.
The QCA said that new syllabuses, being adopted from this September, are intended to allow a smaller number of topics to be tackled in greater depth, increasing the emphasis on experimental work and encouraging pupils to debate controversial issues such as nuclear power and human cloning.
Consequently, it has emerged that two of England's three exam boards - OCR and Edexcel - are encouraging teachers to use creationist theories to promote debate about how the existence of life has been interpreted over time. Critics fear the two should not be blurred. James Williams, science course leader at Sussex university school of education, said: "This opens a legitimate gate for the inclusion of creationism or intelligent design in science classes as if they were legitimate theories on a par with evolution fact and theory. I'm happy for religious theories to be considered in religious eduction, but not in science where consideration could lead to a false verification of their status as being equal to scientific theories."
Andrew Copson, education officer at the British Humanist Association, said:
"It seems inconceivable that the Government should give even tacit approval to the teaching of creationism as a scientific theory. That it should approve its teaching within the national curriculum for science is outrageous."
However, the religious right this week welcomed the move. A recent poll for BBC's Horizon programme found that more than half of Britons do not accept the theory of evolution and more than 40 per cent believe creationism or intelligent design should be taught in school science lessons.
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THREE SPECIES OF THOUGHT
Based on the concept that all life is the result of evolution over more than three billion years, through a process of mutation and natural selection.
A strict biblical interpretation of life, encompassing the belief that human beings and the universe were created by a supreme being or deity just 6,000 years ago.
Intelligent design theory
Recent creationist offshoot that there are tell-tale features of living systems and the universe that are best explained by a designing intelligence. It disputes Darwin's idea that the cause of biological change is wholly blind and undirected.