The fact that only a third of us accept that "natural processes such as natural selection" are behind our existence has had science thinking for some time.

Creationism is growing into a powerful political force. But the strength of their arguments and the forcefulness of their campaign does not entirely explain its growing success.

The debate has heated up in recent years as and a so-called "culture war" is being waged across a deepening partisan divide.

So why does the concept of evolution cause so much upset in an era overwhelmed with science - be it in medicine, transport, communication and calculation?

"Natural selection is like quantum physics ... we might intellectually grasp it, with considerable effort, but it will never feel right to us," writes the Yale psychologist Paul Bloom.

It's about the nature of our brain. It's an amazing device at finding new and successful ways to adapting to an ever-changing world - with the minimum of effort.

The brain has evolved, psychologists argue, to conserve its energy and speed up its processes through a series of "mental shortcuts".

This "unwillingness" to expend mental energy may be behind the difficulty of accepting complex ideas such as evolution.