Recipe for a human

© Ayse Kongur,

The Faraday Institute summer course is in full swing, and on Tuesday morning evolutionary biologist David Lahti presented some reflections about his own work on human behaviour. What he said was fascinating, and raises all sorts of questions regarding human personhood. The analogy that he used was the baking of bread. The ingredients he focused on were the ‘flour’ of genetics, the ‘water’ of the environment, the ‘yeast’ of agency and the heat of development. Not all of the ingredients are apparent in the finished product, but all are essential.

It would be easy to think that genetics is unimportant in the determination of behaviour. Over 90% of the prison population possesses a y chromosome, but being male is not considered a reasonable defence against criminal charges, and neither has anyone taken steps to prevent further violence by incarcerating all those in possession of such a chromosome (and perhaps that’s a good thing…)

Lahti spent the first part of his talk outlining some recent findings in the field of behavioural genetics, including alcoholism, trust, mate choice and political preferences. Amazingly (to me) there are indications of heritability for all of these traits, although because they are such broad categories it has proved difficult to find genes that play a major role in determining these characteristics.

I hear you cry, ‘I’m not determined by my genes!’, and that’s exactly what Lahti said when he gave us his top 10 guidelines for understanding the genetic control of human psychology and behaviour. It’s probably not the sort of top 10 you’re used to seeing, but here we go.

  1. Genes and the environment shape behaviour through development. The illustration for this was adapted from CH Waddington’s canalisation analogy. The ball of human behaviour rolls down the hill of development. The hill is structured into bumps and valleys by genetic variation, and the wind of the environment might blow the ball into one or other of these valleys. So all development is genetically, environmentally, and developmentally controlled, and to use these factors against each other in a ‘nature vs. nurture’ debate doesn’t make sense.
  2. There is genetic variation in all major behavioural traits. (i.e. at a general level – we’re not talking about your favourite colour or whether you like baking).
  3. Genetics is not just about explaining variation between individuals or populations. Embryonic development is genetically regulated. For some traits there is no variation: for example, the genetic control of head development is 100% – all of us have one!
  4. All genes are susceptible to evolution. There may be no lasting change in a gene if natural selection ‘purges’ organisms carrying mutations in that gene from a population because they are not viable, but every gene is nonetheless susceptible to mutation and natural selection.
  5. All genes are affected by their own environments. We are used to thinking about the environmental effects on whole organisms, but within your cells your genes are immersed in an environment that affects how they behave. They also interact with each other.
  6. Genes, their actions and mutations are diverse.
  7. All behavioural traits are controlled by complex networks of many genes. Multiple genes for each trait (polygenic traits), the activity of a gene being modified by other genes (epistasis), and a gene affecting several different traits (pleotropy) are not exceptions to the rule – intense interaction between many genes is the norm. The famous geneticist Dobzhansky predicted this a long time ago, but apparently much of scientific community didn’t take that too seriously and had to learn this lesson the hard way…
  8. The impact of genes and the environment greatly overlap. This is the reason why unexplained variation is often found in behavioural genetics studies. For example, research in the 1960s and 70s revealed that birds were acquiring innate traits – which sounds like an oxymoron unless you dig deeper and find that genetic potential is unlocked by environmental opportunity.
  9. The capacity for behaviour to be different in different environments or to respond to learning (plasticity), is itself a trait that has a genetic basis and evolves.
  10. There are multiple discrete levels of behavioural analysis. Four levels are commonly used: physiology (mechanical causation), function (adaptation), phylogeny (evolutionary history), and ontogeny (development). Lahti added a fifth level: agency (choice or morality), which cannot predicted by looking at the preceding levels. Purpose or religion could also be added, and this is also something that cannot be predicted by your genes – well not yet, and maybe never.

The bottom line regarding the question of genetic determinism is that your genes are not an external command that control you: they are part of what makes you, you. While we know that human will is not free from all influence we do, by and large, hold ourselves responsible for our own decisions. In our loaf of human personhood the yeast of agency cannot be located, but it was absolutely vital in the baking of the bread.

If you would like to listen to Lahti’s talk, you can to listen to the recording when it appears online in the next couple of months (it will take a while to get all 20 of the talks from the course online).

5 thoughts on “Recipe for a human

  1. Stephen Thompson July 13, 2012 / 7:21 am

    Thanks Ruth. From Waddington, it is interesting to contemplate the layers of ‘landscapes’ that we could consider to begin to understand origins and development, each one described by the interaction between variables in different modes and levels of organisation. Here you have genes and environment forming a landscape explored by behaviour. Simon Conway Morris has life exploring a genetics-environment landscape uncovering repeatable ‘threads’ that were not predicted. This idea is developing in fruitfulness!


    • Ruth Bancewicz July 13, 2012 / 11:32 am

      Thanks, an interesting thought. By development I meant the development from embryo to adult in an individual. That’s an interesting connection with Conway Morris’s work, though – but probably very tricky with something as complex as human behaviour!


  2. Richard Hosking July 16, 2012 / 9:50 pm

    Hi Ruth, Like the bread analogy!’s verse for Thursday was Matthew 4:4 (“Man shall not live by bread alone …”) which nicely complements David Lahti’s levels of behavioural analysis.

    MIT computational neuroscientist Sebastian Seung thinks we are defined as individuals by the unique set of relationships between our 100 billion brain cells – something he calls our ‘connectome’ – which contains a million times more connections than our genome has letters.

    Sebastian highlights our brain cells’ branching, tree-like structure and adaptable interconnections (synapses). He then uses the metaphor of a river and its riverbed to describe the dynamic relationship between the stream of consciousness and its neural substrate – i.e. our thoughts shape our brain which in turn shapes the flow of our thoughts*. (Psalm 1:2-3)
    (Includes a link to his *TED talk)


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