Wired that way: genes do shape behaviors but it’s complicated

Author: Kevin Mitchell / Source: Big Think

Many of our psychological traits are innate in origin. There is overwhelming evidence from twin, family and general population studies that all manner of personality traits, as well as things such as intelligence, sexuality and risk of psychiatric disorders, are highly heritable.

Put concretely, this means that a sizeable fraction of the population spread of values such as IQ scores or personality measures is attributable to genetic differences between people. The story of our lives most definitively does not start with a blank page.

But exactly how does our genetic heritage influence our psychological traits? Are there direct links from molecules to minds? Are there dedicated genetic and neural modules underlying various cognitive functions? What does it mean to say we have found ‘genes for intelligence’, or extraversion, or schizophrenia? This commonly used ‘gene for X’ construction is unfortunate in suggesting that such genes have a dedicated function: that it is their purpose to cause X. This is not the case at all. Interestingly, the confusion arises from a conflation of two very different meanings of the word ‘gene’.

From the perspective of molecular biology, a gene is a stretch of DNA that codes for a specific protein. So there is a gene for the protein haemoglobin, which carries oxygen around in the blood, and a gene for insulin, which regulates our blood sugar, and genes for metabolic enzymes and neurotransmitter receptors and antibodies, and so on; we have a total of about 20,000 genes defined in this way.

It is right to think of the purpose of these genes as encoding those proteins with those cellular or physiological functions.

But from the point of view of heredity, a gene is some physical unit that can be passed from parent to offspring that is associated with some trait or condition. There is a gene for sickle-cell anaemia, for example, that explains how the disease runs in families. The key idea linking these two different concepts of the gene is variation: the ‘gene’ for sickle-cell anaemia is really just a mutation or change in sequence in the stretch of DNA that codes for haemoglobin. That mutation does not have a purpose – it only has an effect.

So, when we talk about genes for intelligence, say, what we really mean is genetic variants that cause differences in intelligence. These might be having their effects in highly indirect ways. Though we all share a human genome, with a common plan for making a human body and a human brain, wired so as to confer our general human nature, genetic variation in that plan arises inevitably, as errors creep in each time DNA is copied to make new sperm and egg cells. The accumulated genetic variation leads to variation in how our brains develop and function, and ultimately to variation in our individual natures.

This is not metaphorical….

Click here to read more

The post Wired that way: genes do shape behaviors but it’s complicated appeared first on FeedBox.