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 One1.
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."
In
humans, this apparently volitional behaviour is traditionally ascribed
to our free will. Björn Brembs of the Free University of Berlin,
Germany, and his colleagues make the somewhat radical claim that their
experiment shows that even flies, although not making conscious
decisions, have a kind of primitive 'free will' circuit wired into
their brains.
That's
an intriguing idea, not least because it forces us to confront the
question of what on earth 'free will' could mean in a neuroscientific
context. My suspicion is that such a meaning doesn't exist.
Hardwired spontaneity
In
Brembs' experiment, a fly is tethered inside a blank white cylinder
devoid of any environmental triggers that might make it change
direction. If the fly is nothing but an automaton impelled hither and
thither by external inputs, then this lack of clues will leave it
choosing directions at random. But measuring the tugs that the fly
gives the tether reveals that it isn't trying to flit about randomly,
but instead attempting to alternate localized buzzing about with
occasional big hops.
This
kind of behaviour has been seen in other animals (including humans),
where it has been interpreted as a good foraging strategy: if a close
search of one place doesn't bring a 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
that does not depend on external information in a determinate way. This
seems to have proven useful in evolutionary terms, and so has become
hard-wired into the fly brain.
Such
a neural circuit could, the researchers say, be a kind of precursor to
the mental wiring of humans that enables us to ignore 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. The
researchers now intend to search for the neural machinery involved.
My brain made me do it
The
existence of such neural circuits would 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, 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
make-up of our brains, the notion of free will and therefore legal
responsibility will be eroded. Criminals will be able to argue their
lack of culpability on the grounds that "my brain made me do it".
While
right-wingers and libertarians feel this will hinder the law's ability
to punish and will strip the backbone from the penal system, others say
it will merely change the law's rationale, making it concerned less
with retribution and more with utilitarian prevention and social
welfare. According to psychologists Joshua Greene of Harvard
University, Massachusetts, and Jonathan Cohen of Princeton University,
New Jersey, "Neuroscience will challenge and ultimately reshape our
intuitive sense(s) of justice."2
If
neuroscience indeed threatens the notion of free will, some of the
concerns of the traditionalists are understandable. For if our actions
are simply automatic responses to external stimuli, it is then only a
short step to the pre-emptive totalitarianism depicted in the movie Minority Report, where people are arrested for crimes they have yet to commit.
But
the results of Brembs and colleagues suggest that, thanks to the
spontaneity circuit, even the fly's brain is highly nonlinear, like the
weather system, and not susceptible to precise prediction based on
known inputs.
Or maybe society made me do it?
In
any case, our behaviour is not governed by the way our minds work in
isolation — and so our responsibilities should not be evaluated that
way. As neuroscientists Michael Gazzaniga of Dartmouth College in New
Hampshire and Megan Steven of the Beth Israel Deaconess Medical Center
in Boson have pointed out, 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."3
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.
Brembs
and his colleagues have made a nice case for why the absolute
determinism advocated by some neuroscientists may not work. But it is a
mistake to think that the indeterminacy they highlight is the same
'free will' that philosophers discuss (see Box On free will), any more than talking about 'love' in terms of brain chemistry means we are analysing what Shakespeare wrote about.
