There’s no such thing as a free fly
[This is the pre-edited version of my latest article for muse@nature.com]

Neuroscience can’t show us the source of free will, because it’s not a scientific concept.

Gluing a fly’s head to a wire and watching it trying to fly sounds more like the sort of experiment a naughty schoolboy would conduct than one that turns out to have philosophical and legal implications.

But that’s the way it is for the work reported this week by a team of neurobiologists in the online journal PLoS One [1]. They say their study of the ‘flight’ of a tethered fly reveals that the fly’s brain has the ability to be spontaneous – to make decisions that aren’t predictable responses to environmental stimuli.

The researchers think this might be what underpins the notorious cussedness of laboratory animals, wryly satirized in the so-called Harvard Law of Animal Behavior: “Under carefully controlled experimental circumstances, an animal will behave as it damned well pleases.”

But in humans, this apparently volitional behaviour seems all but indistinguishable from what we have traditionally called free will. In other words, the work seems to imply that even fruit-fly brains are hard-wired to display something we might as well denote free will.

The flies are tethered inside a blank white cylinder, devoid of all environmental clues about which direction to take. If the fly is nothing but an automaton impelled hither and thither by external inputs, then it would in this circumstance be expected to fly in purely random directions. Although the wire stops the fly from actually moving, its attempts to do so create a measurable tug on the wire that reveals its ‘intentions’.

Björn Brembs of the Free University of Berlin and his colleagues found found that these efforts aren’t random. Instead, they reveal a pattern that, for an unhindered fly, would alternate localized buzzing around with occasional big hops.

This kind of behaviour has been seen in other animals (and in humans too), where it has been interpreted as a good foraging strategy: if a close search of one place doesn’t bring result, you’re better off moving far afield and starting afresh.

But this was thought to rely on feedback from the environment, and not to be intrinsic to the animals’ brains. Brembs and colleagues say that in contrast there exists a ‘spontaneity generator’ in the flies’ brains which does not depend on external information in a determinate way.

Is that really ‘free will’, though? No one is suggesting that the flies are making conscious choices; the idea is simply that this neural ‘spontaneity circuit’ is useful in evolutionary terms, and so has become hard-wired into the brain.

But it could, the researchers say, be a kind of precursor to the mental wiring of humans that would enable us to evade the prompts of our own environmentally conditioned responses and ‘make up our own minds’ – to exercise what is commonly interpreted as free will. “If such circuits exist in flies, it would be unlikely that they do not exist in humans, as this would entail that humans were more robot-like than flies”, Brembs says.

These neural circuits mean that you can know everything about an organism’s genes and environment yet still be unable to anticipate its caprices. If that’s so – and the researchers now intend to search for the neural machinery involved – this adds a new twist to the current debate that neuroscience has provoked about human free will.

Some neuroscientists have argued that, as we become increasingly informed about the way our behaviour is conditioned by the physical and chemical makeup of our brains, the notion of legal responsibility will be eroded. Criminals will be able to argue their clack of culpability on the grounds that “my brain made me do it”.

While right-wing and libertarian groups fulminate at the idea that this will hinder the law’s ability to punish and will strip the backbone from the penal system, some neuroscientists feel that it will merely change its rationale, making it concerned less with retribution and more with utilitarian prevention and social welfare. According to psychologists Joshua Greene and Jonathan Cohen of Princeton University, “Neuroscience will challenge and ultimately reshape our intuitive sense(s) of justice” [2].

If neuroscience indeed threatens free will, some of the concerns of the traditionalists are understandable. It’s hard to see how notions of morality could survive a purely deterministic view of human nature, in which our actions are simply automatic responses to external stimuli and free will is an illusion spun from our ignorance about cause and effect. And it is a short step from such determinism to the pre-emptive totalitarianism depicted in the movie Minority Report, where people are arrested for crimes they have yet to commit.

But while this ‘hard’ mechanical determinism may have made sense to political philosophers of the Enlightenment – it was the basis of Thomas Hobbes’ theory of government, for example – it is merely silly today, and for a number of reasons.

First, it places its trust in a linear, Cartesian mechanics of cogs and levers that clearly has nothing to do with the way the brain works. If nothing else, the results of Brembs and colleagues show that even the fly’s brain is highly nonlinear, like the weather system, and not susceptible to precise prediction.

Second, this discussion of ‘free will’ repeats the old canard, apparently still dear to the hearts of many neuroscientists, evolutionary biologists and psychologists, that our behaviour is governed by the way our minds work in isolation. But as neuroscientists Michael Gazzaniga and Megan Steven have pointed out [3], we act in a social context. “Responsibility is a social construct and exists in the rules of society”, they say. “It does not exist in the neuronal structures of the brain”.

This should be trivially obvious, but is routinely overlooked. Other things being equal, violent crime is frequently greater where there is socioeconomic deprivation. This doesn’t make it a valid defence to say ‘society made me do it’, but it shows that the interactions between environment, neurology and behaviour are complex and ill-served by either neurological determinism or a libertarian insistence on untrammelled ‘free will’ as the basis of responsibility and penal law.

The fact is that ‘free will’ is (like life and love) one of those culturally useful notions that turn into shackles when we try to make them ‘scientific’. That’s why it is unhelpful to imply that the brains of flies or humans might contain a ‘free will’ module simply because they have a capacity to scramble the link between cause and effect. Free will is a concept for poets and novelists, and, if it keeps them happy, for philosophers and moralists. In science and politics, it deserves no place.

Reference
1. Maye, A. et al. PLoS ONE May, e443 (2007).
2. Greene, J. & Cohen, J. Phil. Trans. R. Soc. Lond. B 359, 1775 - 1785 (2004).
3. Gazzaniga, M. S. & Steven, M. S. Sci. Am. MIND April 2005.


Philosophers, scientists and writers on free will

“The will cannot be called a free cause, but only necessary…. Things could have been produced by God in no other manner and in no other order than that in which they have been produced.”
Baruch Spinoza, Ethics

“Whatever concept one may hold, from a metaphysical point of view, concerning the freedom of the will, certainly its appearances, which are human actions, like every other natural event are determined by universal laws.”
Immanuel Kant, On History

“As a matter of fact, if ever there shall be discovered a formula which shall exactly express our wills and whims; if there ever shall be discovered a formula which shall make it absolutely clear what those wills depend upon, and what laws they are governed by, and what means of diffusion they possess, and what tendencies they follow under given circumstances; if ever there shall be discovered a formula which shall be mathematical in its precision, well, gentlemen, whenever such a formula shall be found, man will have ceased to have a will of his own—he will have ceased even to exist.”
Fyodor Dostoevsky, Notes from the Underground

“Free will is for history only an expression connoting what we do not know about the laws of human life.”
Leo Tolstoy, War and Peace

“There once was a man who said ‘Damn!’
It is borne in upon me I am
An engine that moves
In predestinate grooves
I’m not even a bus, I’m a tram.”
Maurice Evan Hare,1905

“We cannot prove… that human behaviour… is fully determined, but the position becomes more plausible as facts accumulate.”
B. F. Skinner, About Behaviorism

“Free will, as we ordinarily understand it, is an illusion. However, it does not follow… that there is no legitimate place for responsibility.”
Joshua Greene & Jonathan Cohen, 2004