Nature or nurture?

One of the hardest, but perhaps most interesting tasks for researchers is to understand links between our DNA and the environment we grow up and live in.

This used to be known as the nature vs nurture debate; nowadays people acknowledge both play a significant role. The focus has shifted towards trying to understand the complex interactions that take place between our DNA and the environment. It is these interactions that make us all who we are, but they are difficult to reliably identify and measure.

Genetic factors are your ancestry and inheritance. You inherit these from your parents, half from your mother and half from your father. Environmental factors include everything that affects you as you grow, develop and live your life. They can include diet, medicine, exercise, radiation, standard of living and chemicals in the environment. They may change the DNA directly, or have more subtle effects throughout life.

Currently there is little data on specific genetic – environment interactions, however there are two main types of research which collect the data needed to begin the research.

Population studies

If you study a large number of people over a long period of time and take regular measurements from them and their environments that you can compare with their DNA, you can try build up a picture of how their genes and environment interact.

The Bristol-based Children of the 90s population study has been collecting this type of data since 1990. They have been taking measurements and recording information on over 14,000 participants from before birth! They have been taking measurements and recording information on over 14,000 participants before they were even born!

Here are two examples of their studies that have identified environmental influences on development:

Diet
Participants use diet diaries to accurately record their eating habits, so that things don’t get missed off and forgotten. This has posed a fishy question; Should pregnant women eat fish?

In the United States, pregnant women were advised against eating fish due to levels of heavy metals. However, the UK-based Children of the 90s study found that eating fish during pregnancy resulted in important benefits to the child’s development.

The children of mothers who ate fish at least once a week during pregnancy were found to score higher on language, comprehension and social skills tests. Most notably, their understanding of words was higher than those whose mothers had not eaten fish at all.

They found no evidence that eating fish caused damage to the children.

Physical Activity
Children of the 90s use special activity monitors to measure the activity levels of participants as it is so hard to remember everything about how active you’ve been. Participants wear one for up to seven days at a time. They have found that a little can go a long way.

Their study showed that just 15 minutes of exercise a day could make a major difference to a child’s chance of becoming obese.

The study measured each participant’s body fat and used monitors to measure their activity levels accurately. They found that just 15 minutes of moderate exercise – enough to get a little out of breath – lowered the chance of becoming obese by 50%.

The researchers are now looking at whether the pattern of exercise can make a difference, and at the association between exercise and obesity over time.

Twin studies



Identical (Monozygotic) twins provide a unique opportunity to examine the interactions of our genes and our surrounding environment. Because twins arise from a single cell and start out sharing 100% of their genes, the role of genetics can be separated from the effects of our environment.

If the differences between us were only down to genetics then we would expect identical twins to become identical personalities with identical life histories. However, this is not the case. Although identical twins look very similar we know that they can have extremely different personalities and their lives can take very different courses. If their genetic code is identical, any differences between identical twins can, in theory, be attributed to differences in environment.

Non-identical (Dizygotic) twins provide a useful control in twin studies. They are no more related than other siblings and so share around 50% of their genes but as they are twins, they have shared a womb and so can help account for any effects the womb environment might have on individual differences. By comparing identical and non identical twins it is hoped that we can start to disentangle the role of genetics and that of the environments we grow up in.

Professor Robert Plomin is a leading expert and advocate of twin studies. He directs the huge Twins Early Development Study (TEDS) examining over 15,000 pairs of twins born in the UK between 1994-96.



By comparing identical and non-identical twins the study is investigating the genetic and environmental influences on learning, communication and behaviour.



Studies of children who have been separated from their biological parents and raised in adoptive families also provide valuable data on the interactions of genetic and environmental influences.

In a similar way to twin studies, such techniques help to disentangle the complex relationship between genes and the environment.

Since adopted children are not reared by their biological parents, it's easier to compare similarities and differences to the birth family than it is when children are reared by their biological parents and the impact of heredity and environment is far murkier.

Any similarities between the adoptive parents and the children are not inherited genetically, but clearly our primary carers heavily influence us and so we would expect some traits to be inherited via environmental means.

Adoption study designs have been applied to several areas of study including intelligence, obesity and depression.