Ironically, that is a message that most parents probably do not want to hear, but they should be the first to agree with Harris. Any parent should be able to confirm that no matter how much they try to treat their various children equally, they end up very different. In fact, when the proper measurements are done, two siblings raised in the same household are not much more similar than two randomly selected individuals of roughly the same age plucked from the same population. Despite what most parents want to believe and parenting manuals promote, the home environment plays a relatively minor role in shaping the development of children.
If it isn’t the home environment and it cannot all be the genes, then what explains individuality? Harris argues that the major determinant of a child’s intellect and personality is the influence of their peer group – other children. While the child may behave according to their parents’ expectations in the home, they put on a different face in the playground and shopping mall. Children act and respond to others differently in different situations. This is why children of immigrants do not learn their parents’ accents when learning English, but adopt the local dialects and accents of the neighbourhood kids.
Harris’s thesis is highly controversial as it goes against the modern trend for parenting expertise. It is also leaves out the extreme environments of Romanian orphanages and depressed mothers who have been shown to affect long-term development. Moreover, parents indirectly influence which peer groups children are exposed to because they choose the neighbourhoods and schools that their children end up in. That said, the goalposts are likely to shift again when one considers the pervasive role that social networking sites such as Facebook and Twitter now play in teenagers’ lives. However, even if today’s extensive networks outside the home play a greater role in shaping children, this cannot explain why Daisy and Violet, who shared the same genes, the same environment and the same peers, were still different. Perhaps it’s because people treat identical twins, even those conjoined at the waist, differently so as to distinguish them. That seems plausible, but a more likely explanation is in itself unlikely – and that is the role of random events in development: an area of research known as epigenetics.
Epigenetics
What do the sex of a clownfish and the spread of the common cold have in common? A strange question maybe, but both are examples of epigenetic phenomena that are triggered by social behaviour. They both depend on the interaction of biology and the influence of others. Epigenetics is the study of the mechanisms of interaction between the environment and genes – the way that nature and nurture work together.
Epigenetics provides answers to the sorts of common questions we all ask ourselves. Are we born mad, bad or sad, or is our personality determined by events in our lives? Why are our children so different when we try to treat them equally? These questions are at the heart of how best to create the societies we wish to live in; often shaped and controlled by government policies and laws. The answers people prefer to give to these questions come from deep personal opinions and reflect their political persuasion about the role of the individual in society. However, epigenetics offers a new perspective to understand human development that combines our biology with our experiences.
As we noted earlier, genes are the strings of DNA molecules, found in every living cell, that instruct the cell what to become. They do this by building proteins from amino acids, which in turn are made from combinations of atoms of carbon, hydrogen, oxygen and nitrogen. Every cell in the body has thousands of proteins and DNA determines what type a cell is and how it operates by regulating the production of proteins. Genes are like books in a library that contain information that needs to be read or transcribed in order to build the proteins. The proteins instruct the cell to become something, such as hair follicles, while others can turn them into neurons. This is a very simplistic account and there is considerably more to the story of the mechanism of genes, but for the level of discussion here, it is sufficient to know that genes are like sequences of computer code within the cell that control its operation.
Genes build humans and humans are very complex animals. Each body is made up of trillions of cells and the initial speculation was that humans must have a considerable number of genes to code for all the different arrangements of cells in our bodies. In 1990, scientists working on the human genome project began to map the entire sequence of genes for our species, using sophisticated technology that enabled computers to read off the sequences as strings of code. Very soon, it appeared that initial estimates of over 100,000 genes had been way off. Although the project is still continuing, at the last count it would appear that humans have only 20,500 different genes. That may still sound like quite a few but when you consider that the humble fruit fly, drosophila, has 15,000 genes, humans look decidedly puny in the genetic endowment department. In fact, much simpler living things like the banana or the rather revolting roundworm have more genes than humans and, as if that were not enough, the organisms that have the highest and lowest numbers of genes are both sexually transmitted diseases, trichomonas vaginalis with 60,000 and mycoplasma genitalium with 517.
So the number of genes does not reflect the complexity of the animal. The reason we initially overestimated the number of genes for humans was because the role of epigenetics was not yet fully appreciated. Moreover, it turns out that there is more information encoded in the few genes we have than is ever actually used. Only 2 per cent of genes appear to be related to building proteins. This information is only activated when the gene becomes expressed and geneticists now understand that only a fraction of genes are expressed. In fact, gene expression is the exception and not the rule. The reason is that genes are sets of IF–THEN instructions that are activated by experiences. These experiences operate through a number of mechanisms, but genetic methylation is typically one that silences a gene and is believed to play a major role in long-term changes that shape our development. If you think about genes like books in a library and the library is the full genome, then each gene can be read to build proteins. Methylation acts a bit like moving a book out of reach so the information to build proteins cannot be read, or blocking access to it by placing some furniture in front of the book.
DNA may instruct cells how to form and organize themselves to build our bodies but these instructions unfold within environments that modulate their instructions. For example, the African butterfly bicyclus anyana comes in two different varieties, either colourful or drab, depending on whether the larvae hatch in the wet or the dry season. The genes do not know in advance, so are simply switched on by the environment.
Sometimes those switches are social in nature. For many fish, the social environment can play a fundamental role in shaping how genes operate, even to the extent of switching sex. Clownfish live in social groups that are headed up by the top female. What Pixar’s film Finding Nemo did not tell the audience is that clownfish have the potential for transsexuality. When the dominant female in a school of clownfish dies, the most dominant male changes into a female and takes over. Or consider the humble grasshopper. When the population of grasshoppers becomes overcrowded, they change colour, increase in size and become gregarious and socially sensitive to other locusts. This transformation from a solitary grasshopper within a swarm is triggered simply by the amount of physical contact they have with others.40