Take a careful look at the image of two brains on this page. The picture is of the brains of two three-year-old children. It’s obvious that the brain on the left is much bigger than the one on the right. The image on the left also has fewer spots, and far fewer dark “fuzzy” areas.

To neurologists who study the brain, and who have worked out how to interpret the images, the difference between these two brains is both remarkable and shocking. The brain on the right lacks some of the most fundamental areas present in the image on the left.

Those deficits make it impossible for that child to develop capacities that the child on the left will have: the child on the right will grow into an adult who is less intelligent, less able to empathise with others, more likely to become addicted to drugs and involved in violent crime than the child on the left.

The child on the right is much more likely to be unemployed and to be dependent on welfare, and to develop mental and other serious health problems.

What could possibly cause so radical a divergence in brain development? The obvious answer is that it must have been some illness or terrible accident.