Psychogenetics
How genes affect our lives
Psychogeneticist Robert Plomin on the role of genes and upbringing in the formation of personality, the ability to foreign languages and gemini studies.
Psychogenetics is looking for genetic prerequisites for differences between people. 99% of our DNA is the same, people are almost identical, but the 1% by which we differ is of great importance. Many researchers are not interested in individual differences, they raise questions about the human species as a whole.
But psychogenetics raise questions about why some children have reading disorders and others do not, why some develop schizophrenia and others do not. This is what psychogenetics does ― it studies differences.
Nature versus Nurture
For a hundred years, psychologists have assumed that the only significant factor in explaining the differences between people is the environment, especially the environment created by parents in the first few years of a child's life. This opinion prevailed from Freud's works onwards. But with the help of psychogenetics, we found that the difference in people's DNA explains almost half of the differences between them. Genetics does not just "matter" ― it plays a huge role in almost all areas of psychology: human mental health, diseases, cognitive abilities, personality development or school achievements.
For a long time, people believed that our personality is completely conditioned by upbringing. Nature versus environment is an old debatable question in psychology. Psychogenetics have shown that nature (genes) is very important. The idea itself dates back to the beginning of the last century, when the first psychogenetic techniques were developed: the twin method and studies of families with foster children.
Twin Studies
About one percent of all babies born in the world are twins, and a third of them are identical twins. They are called monozygotic, since they develop from a single fertilized egg ― a zygote. They are like clones of each other, they have the same DNA. Another type of twins (two-thirds of the total number) are called dizygotic: they are similar to other brothers and sisters, but developed at the same time in the same womb. The twin method is to compare these two groups. If some trait, such as musical ability, is dictated by genetics, the assumption is inevitable that identical twins are more similar to each other than non-identical ones. This is a kind of biological experiment.
Diagram of the mechanism of formation of twins: on the left – monozygotic or identical (Eng. monozygotic), on the right – dizygotic or different (Eng. dizygotic). Designations on the diagram: Sperm – sperm, Egg – egg, Shared placenta – common placenta (the only one), Separate placentas – different placentas. / Trlkly // wikipedia.org
What did the twin method give us? A study of 15 million twins in four thousand papers showed that everything is inherited ― not only psychological traits, but also physiology (for example, bone length and density). All individual differences in biology and behavior are mainly due to differences in DNA.
The method of foster children
If the study of twins is a kind of biological experiment, then the study of families with foster children is a social experiment.
Both genes and upbringing are related to the family. For a long time, psychologists have known that schizophrenia is a family disease. Great, they said, it's all because of the environment, parents have developed schizophrenia in their children. But psychologists did not take into account the probability that genetics is also important. Genetic material is inherited: parents and children are 50% genetically similar.
Let's look at biological and foster parents. The children were adopted after birth, the biological parents passed on their genes to them, but did not participate in their upbringing. Children grow up in a foster family and are connected to foster parents through the environment. Such studies are a powerful tool for testing the importance of genetics. The method predicts that the similarity between biological parents and their children, with whom they do not live in the same environment, allows us to test the influence of genetics. Similarly, how similar children are to their adoptive parents is a test of how much parenting affects children.
The twin method and the method of foster children have shown the key role of genetics in the formation of a person. From the idea that nothing is inherited, we have moved on to the idea that everything is inherited. Now both methods are used to solve more interesting questions.
How early does the influence of genes manifest itself?
There is a constant interaction between genetics and the environment. Life events like financial crises, relationship problems, quarrels, job loss ― these are not events that passively happen to you (as if you have nothing to do with them). This is what you do with the environment. Genetics is connected here. Genes work through their correlation with the outside world.
For example, I study cognitive abilities. The most inherited of the hundreds of indicators of cognitive abilities is vocabulary. There are individual differences in mind: some people have a large vocabulary, some do not. You do not inherit words, they are not embedded in your DNA, including due to the fact that there are many different languages in the world, but the tendency to use language, to hear language subtleties, is inherited. My granddaughter always wants to know all the nuances: why does a word mean exactly that? And my grandson says: "What's the difference, you know what I mean!" ― and that's where the genes start to work. You start using the world around you, you communicate with people who think in a similar way to you. My granddaughter will communicate with other children who read books and who like intellectual conversations. This is a good example of how the view from the standpoint of genetics has changed our approach to how we interpret the concept of the environment.
Genetic prerequisites of language ability
The development of language skills is actively studied. Children vary greatly in how early they learn to speak, how their language skills develop over the course of life (how easy it is for them to speak fluently) and vocabulary. Einstein, for example, did not speak until the age of three.
The diagram shows the influence of genes on the psychological and emotional characteristics of a person. On the diagram: monozygotic twins (blue), dizygotic twins (red) and adopted siblings (gray) // wikipedia.org
Such studies often concern the study of the first language. An interesting question that psychogenetics began to address is related to the study of a second language. It turns out that many of the genes that regulated the acquisition of the first language are involved in this process: people with good indicators of mastering the first language are likely to have a pretty good command of the second. But there are also specific genetic factors. The research results are as follows: the success of mastering a second language is influenced by a third of the genes responsible for mastering the first, another third by another set of genes, and another third by the general level of intelligence.
What traits do we inherit?
There has been a real transformation in science: until now, people were only interested in the question of whether genes are important and, if so, how much. The answer to this question in all its aspects has already been found, although some people still do not accept it. Genetics is not just important, it is fundamental to almost all areas of psychology. It's no longer interesting to say, "This trait is inherited," because everything is inherited.
We go deeper and ask questions about development, about character traits. For example, in the field of psychopathology and mental illness, there are many different diagnoses. It turns out that their genetic effects are about the same, that is, the same genes cause many of the "different" disorders.
Another area of research is the interaction between genes and the environment. If both nature and nurture are important ― and this is so, because genetics does not explain all the differences, it usually explains about half ― many researchers are interested in finding out how they work together: they want to identify the mutual influence, correlation and interaction between genes and the outside world and how it affects human development.
The key idea is to go further and say, "Let's find the genes that are responsible for this." Everything is inherited, so let's find specific genes. If you can find the genes, you can do a lot more both in your field of research and in the field of solving specific problems. DNA is the best tool for predicting problems that we have, and forecasting will allow us to intervene in time to prevent them. This is the direction in which all medicine is moving.
For example, instead of waiting for a person to become an alcoholic and then trying to cure him (or waiting for someone to become obese and then trying to cure him), it might be possible to predict problems to prevent their occurrence. This is important both for individuals and for society as a whole.
We have already reached a turning point where we are beginning to link various features and specific genes. This will allow us to make individual predictions about genetic risks and resilience, vulnerabilities and benefits, which over time will allow us to predict problems and begin to prevent them.
About the author:
Robert Plomin – professor of Behavioural Genetics, King’s College London.
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10.07.2017