We have grown accustomed to the concept of nature vs nurture, it’s a debate that has been raging long before the discovery of genetic material in the early 20th century. How many of our traits are predetermined? How many are a result of our environment? Perhaps my favourite illustration of the obsession with this debate is the chopstick gene. Recent research is making the line between nurture and nature increasingly fuzzy and blurred.
The idea that we inherit genes from our parents and these genes are responsible for our traits is common knowledge. But, recent studies are asking, what are the effects of the genes our parents have that we don’t inherit. These genes may influence our characteristics, but you won’t find them in the nuclei of our cells. You’ll find them being expressed in the cells of our parents.
This concept, known as genetic nurture (or my personal favourite ‘the parentome’) is nothing new. It has been known especially in animal research for some time. It makes more sense with an example; the quality of a cow’s milk affects the survival of the offspring whether or not the offspring inherits the genes required to produce nutrient-rich milk. This environmental effect (on the offspring) cannot be separated from the mother’s genes.
Another example, human this time, is the height of the mother affecting the gestational age of the foetus at birth. Again, the genes responsible for the mother’s height may not be transmitted to the next generation but are still having an effect. This is not Mendelian inheritance, it isn’t even inheritance. Genes are still the culprit.
The examples I have used so far are relatively simple, the next one comes from a recent genome wide association study. These studies assess huge numbers of genes and their correlation with certain characteristics ranging from intelligence to cancer. Their results are summarised in Manhattan Plots where the single nucleotide polymorphisms (changes in one base pair in a particular gene, each dot is a single SNP) are plotted against their correlation with a certain characteristic – the SNPs with the greatest association are located further towards the top. Initially, it was found that 74 allelic variants – particular versions of genes- were significantly associated with how long the individuals stayed in school. So far so good, the genes in question were found to be differentially expressed in the developing brain (and other things that made sense). Yet, these variants accounted for only a few weeks of the total difference.
What this tells us is that these alleles alone can’t account for the difference between people. It must be the environment is the next assumption (this quick conclusion served me well in A-Level psychology essays). Well yes, it is the environment, but as we’ve seen above, the genes we don’t inherit can impact the environment…
Another study, published last week, looked at the effect that the non-transmitted genes of parents (those that weren’t passed on) had on the educational attainment of their children. The combined effect of the genes on educational attainment that the child didn’t inherit was around 30% of the effect of the genes the children did actually inherit. Just to clarify, it was possible to sequence the genomes of the parents and only look at genes the child did not inherit. The variation in those genes between different parents significantly affected how long each child stayed in school.
These effects are likely due to the parent’s genes influencing whether the child has a stimulating environment, future planning and a huge range of other tiny factors. Effectively, it is an extension of “The Extended Phenotype” concept taken up by Richard Dawkins (one of my favourite science writers) where he outlined that an organism’s genes were influencing the environment and changes in the environment could, therefore, be thought of as an effect of the genes at work. He called this, rather menacingly, the “long reach of the gene”.
What this work shows is that the usual dichotomy between nature and nurture is outdated and, as Ben Goldacre likes to say, it’s a bit more complicated than that.