In effect, your DNA just provides the building block for proteins. When an mRNA is transcribed from DNA, it is translated into a polypeptide that eventually is folded and converted into a functional protein. Once folded, the protein can function in processes within the cell, or it can be displayed on the membrane.

Humans are different from each other because our bodies make different proteins, and this makes our bodies function in a unique manner. For instance, a nepalese sherpa has a different haemoglobin gene than me, and this means his respiratory system is able to function more efficiently at high altitudes. It all starts at the cellular level.

Because genes lead to different structure and subsequently different functions in cells, they can also affect our behaviour. However, it isn’t as simple as that. The body is incredibly complicated. There are often countless genes involved in the same behaviour. There is almost never one gene determining a characteristic or behaviour.

If you wanted to genetically engineer an organism to make him/her more aggressive, you would probably have to change thousands of genes. You’d have to have knowledge about every single gene related to aggressive behaviour and know how to replace them with the correct alleles. It would be a pain in the ass. Its much easier to use artificial selection. When a criminal decides he wants to fight dogs, he wants the most aggressive ones so he can win fights. They select only the most aggressive dogs and breed them. This is essentially low-level genetic engineering. You’re selecting certain genes, specifically aggressive ones. The result is that you have offspring that are more aggressive. But this process often takes many generations, and can involve thousands of different genes.

Our behaviour is largely (or entirely) determined by the function of our brains. As such, the expression of proteins within the brain will determine the function of an organism. The polymorphisms in brain structure, neurons, glial cells and neurotransmitter/hormone levels are what will change the behaviour of an organism. There are many possible areas where different genes can lead to different behaviours. For instance, if an organism has a genetically different amygdala from most organisms, he will probably respond to stimuli in a different manner. Perhaps he has less of a fear response. Or, perhaps the organism’s anterior pituitary produces different levels of stress hormones, and this makes him respond to stress more acutely than other organisms of the same species. The possibilities are absolutely endless. They most certainly involve many different genes.

There may also be genetic difference in the amount (and distribution) of receptor proteins translated for neurons. Also, some people have naturally higher levels of neurotransmitters at certain synapses. For instance, some individuals have naturally lower baseline levels of dopamine in the mesolimbic system, whereas other people have higher baseline levels. The people with higher levels will respond more acutely to cocaine because it blocks reuptake of dopamine. As such, they need less cocaine to get the same effect as low baseline level people. The person will respond different to stimuli (i.e the drug) based on the set of genes expressed by his neurons. Do you see what I’m getting at here? There are countless areas where people can be genetically different in their brains.

One must always remember that there are often hundreds (if not thousands) of genes involved in a specific behaviour. You can’t say there is one gene for aggression, or one gene for peacefulness. Biology is incredible complicated. At our current level of knowledge, it isn’t that helpful to list a bunch of genes involved in a behaviour. Its often more helpful for neuroscientists to look at whole brain structures, or polymorphisms in brain receptors. In my opinion, reducing behaviours to a list of genes is a mistake.

There is too much of an emphasis on genes in our society. Too many people blame their genes for their behaviour; I think that is quite foolish. Genes play a large role in human behaviour, but you cannot ignore the effects of experience on the brain, and neither can you ignore epigenetic factors. We are greater than the sum of our genes.