Does reductive scientific enquiry into human behaviour destroy free will?

When I was 17 my physics teacher told me that all biology was chemistry, all chemistry was physics and all physics was maths. “And maths?” I asked. “Ask the philosophers” was her reply.

This is an excellent example of the reductionism inherent in much of scientific enquiry. Broadly speaking, reductionism supposes that there are causal mechanisms underlying all phenomena, with further causes underlying these mechanisms, which can be detected if we only know where and how to search for them. Logically elegant, it appeals to a part of us that wants to connect together the sum total of our knowledge into a set of universal concepts. But when we apply this system of thought to human behaviour, as geneticists, neuroscientists and evolutionary biologists (to name a few) do, it can raise some interesting challenges to our intuitive beliefs about free will, morality and self.

Portrait of David Hume in 1766 by Allan Ramsey

Portrait of David Hume in 1766 by Allan Ramsey.
Public domain image from Wikimedia Commons.

In 1748, the Scottish philosopher David Hume wrote that the connections that we form between concepts or events are based on observations of cause and effect lying in a linear sequence i.e. cause leads to effect and not the other way around. According to Hume, for us to have freedom of action (and by extension, responsibility for action) our choice to perform a given action must be the cause of that action in this sequence. But what if choice, at least conscious choice, can be shown to occur after the action itself?

In 19991 the neuroscientist Benjamin Libet conducted a classic experiment to investigate just this. He asked participants to flex the fingers of their right hand, and measured the electrical activity, called readiness potential (RP), in the regions of their brain controlling those actions.

Simultaneously, participants watched an oscilloscope clock, where a spot of light moves around the perimeter every 2.56 seconds. For each movement, the participant was asked to note the position of this spot on the clock when they were first aware of their intention to act. The experiments showed that brain activity increased about half a second before conscious awareness of the intention to act. Experiments in subsequent years have demonstrated even longer gaps, of up to 10 seconds. Can moral responsibility continue to exist in the face of this evidence?

Libet's classic experiment. Image used under a CC-BY-3.0 from Information Philosopher.

Libet’s classic experiment.
Image used under a CC-BY-3.0 from Information Philosopher.

Some believe it can. The philosopher John Locke presented an argument in 1690 that still leaves room for moral responsibility within this framework. In his analogy of the locked room, Locke presents us with a man, unaware that the room he is in is locked. Given that he has no idea that he is unable to leave the room, Locke reasons that we should still consider him responsible for his choice to stay there. In this case, despite intention having no effect on outcome, responsibility for the outcome is maintained by the mere existence of conscious deliberation before the outcome is known.

However, this still leaves room to question the decision-making process itself, and the forces that influence it. A large body of research exists that links human behaviours to hormonal activity in the brain, which is mediated at the level of the genome. For example, a study published last year2 showed that variation between Finnish twins in a gene controlling the expression of the hormone vasopressin in the brain explains around 50% of the difference in how many times they had cheated on their long-term partners.

Genetic Prison

Public domain image by Guiz from Topwallpapers.

Intuitively we like to believe that we are responsible for the choices we make, but the discovery of more and more genes influencing our behaviour may suggest, from a reductionist point of view, that our choices are in fact influenced by chemical forces outside of our control. We need to decide whether this genetic variation is a part of the ‘self’, and therefore encompassed within our sense of moral responsibility. Alternatively, we may consider ourselves exempt from physiological influences over which we have no conscious control.

These issues are already being debated in courts of law3. The MERMER test, which measures the unconscious reaction of the brain to a stimulus, such as a photograph or recording, in order to assess memory of a crime, has been used to incriminate and exonerate criminal suspects around the world. In Spain, the defence of Antonio Losilla, accused of murdering his wife in 2013, objected to the use of the MERMER test to establish his guilt, claiming that using evidence from his unconscious mind violated his fundamental right not to incriminate himself. This argument was rejected and Losilla was convicted.

In this case, the Spanish courts decided that evidence from Losilla’s unconscious mind was not subject to the same rights as evidence from his conscious mind. Losilla was granted no legal right to withhold this evidence, counter to the analogous right that he was granted not to consciously confess to the crime. It suggests that, legally, the Spanish courts do not consider the part of his unconscious mind that stores this information to be part of his ‘self’ and subject to his rights as an individual. Consider the implications in an alternative, hypothetical case, one where the same court was presented evidence that showed that the actions of a defendant were caused by influences within their unconscious mind. Would they similarly separate these unconscious influences from the individual, and acquit them of the crime?

Data from genomics and neuroscience cannot prove the existence of a deterministic universe; they can be used only in a predictive way. However the case of Losilla shows that advances in these fields are already having impacts on how society views our responsibility for our actions. If on-going success in the reductionist approach to science continues to reveal the mechanisms underlying our behaviour, we may have to prepare ourselves for serious challenges to some of the most fundamental ways in which we understand who we are and how we interact with the world around us.


1. Libet, B. (1999) Do we have free will? Journal of Consciousness Studies 6, No. 8-9, pp. 47-57
2. Zietsch, B. P., Westberg, L., Santtila, P. & Jern, P. (2015) Genetic analysis of human extrapair mating: heritability, between-sex correlation, and receptor genes for vasopressin and oxytocin. Evolution and Human Behavior 36: 130-136
3. Pallarés-Dominguez, D. & González Esteban, E. (2015) The ethical implications of considering neurolaw as a new power. Ethics & Behavior 00(00), 1-15

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