Professors Mark Hanson and Peter Gluckman point out that the concept of developmental programming is often considered synonymous with the 'thrifty phenotype', where a fetus slows its growth or the growth of individual organs to cope with undernutrition in the womb. The adjustments are irreversible, and can lead to disease when life outside the womb involves abundant calories.
But, they say, there is more. Some adaptations have no survival advantage whatsoever at the time they are set in place: only later in life do their benefits show up.
For example, meadow voles have thick or sparse coats depending on the day length their mothers experience in early pregnancy. There is no immediate survival value when coat thickness is determined, but later on it matters a lot to the offspring. Many human traits are likely to operate in a similar manner.
Some programming traits are even passed onto subsequent generations – possibly by affecting genes, eggs within a developing female fetus, or her reproductive organs.
Many so-called programming effects probably operate by altering gene expression through "epigenetic processes". This can be induced during the embryonic period by environmental influences, which puts a twist on the traditional 'genes vs. environment' debate. Nutrition influences can mediate epigenetic change – for example the supply of folate can affect DNA methylation.
Mother's diets also come under Hanson's and Gluckman's scrutiny. People's protein intake has decreased since humans evolved, meaning that carbohydrate and fat intake must have increased to compensate. The resulting deficit of important amino acids as well as more starch and fat could lead to poorer health in offspring who develop under those conditions.
Notes for editors
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