It may not be long until an Australian court hears a claim about an offender with a 'crime gene'.
Australia would be a late starter to the field; the issue of a genetic propensity to aggression was first raised in the American courts in the 1990s. More recently, it has been considered by the Italian courts.
One way that genetics has been used overseas (and could be used in Australia) is in sentencing. To explain how it might be argued in Australia, I need to start with a case relating to an offender's social environment.
Australian law says that an offender who comes from very difficult family and social circumstances may be eligible for a lighter sentence. The High Court confirmed this in the case of William Bugmy, an Aboriginal man who had grown up in an environment of social disadvantage, alcohol abuse and violence.
The High Court's approach to difficult childhoods seems fair. It's not right to ignore the background of a man like William Bugmy because adverse formative environments make it harder to behave the way that the law expects.
But Bugmy's experience of violence and disadvantage has everything to do with nurture and nothing to with nature. So what's the relevance of this case to 'crime genes'?
The answer comes from research into a gene linked with the production of a substance in the brain called monoamine oxidase A (the MAOA gene). Some of the research suggests that some people may be particularly affected by the kind of environment that William Bugmy faced. Specifically, males with a low activity MAOA gene may be severely affected by a difficult childhood.
This issue wasn't raised in the High Court case. However, it may be possible for an Australian lawyer to argue that a client who had the double misfortune to have grown up in adversity, and to have a genetic vulnerability, is especially deserving of a lighter sentence.
According to this argument, nature made the offender vulnerable, and then nurture delivered the decisive blow. And now justice must take note of the double difficulty by way of a lighter sentence.
This kind of argument would apply to Indigenous and non-Indigenous offenders as both may have low-activity MAOA genes, and both may experience difficult childhoods.
But what would an Australian court do if presented with such an argument? It remains to be seen whether they would find the science credible. In any case, where it has been accepted in courts overseas, the reaction has been mixed. It is unclear what the Australian response would be.
Even if the offender is less blameworthy, perhaps their aggression leaves them a danger to the rest of us. Maybe society needs protection from such people through longer sentences. As Australian judges are supposed to consider both blameworthiness and community protection, this makes it difficult to predict how the law will respond.
The 'crime gene' (or put another way, genetic vulnerability) seems to raise issues about the aims of punishment. Do we aim to give offenders what they deserve, or do we just care about protecting the community? As Australian courts are supposed to do both, developments in science may make an already difficult job even more difficult.
We will have to wait to see how research into MAOA plays out in the future, as the link with aggression is far from certain. However, a picture is emerging of aggressive behavior being subject to many influences.
We might ask whether an offender was abused as a child, and whether they had a low activity MAOA gene. But why stop there? What about other genetic influences? Have they ever had a head injury? What were their peers like?
As we learn more about the way these things interact to affect behavior, we are getting close to one of the classical problems of philosophy; the free will problem.
There may still be scope for free will, responsibility and deserved punishment, even after all of these, and an increasing list of other factors, are considered. David Hodgson, a Judge of Appeal in the New South Wales Supreme Court and philosopher of some note, published a book defending the notion of free will shortly before he died in 2012.
But others have a different view. Early this year, in Scotland, the University of Aberdeen's Law School held a major conference which aimed to consider what a criminal justice system might look like if we stopped believing in free will.
This rejection of free will is a radical view, and one that is not widely shared, but it does seem that developments in science will insistently force hard questions about responsibility and punishment. It won't just be philosophers who need to come up with answers, lawyers will demand a response from the Australian courts.
This blog first appeared in August 2015.
Allan McCay is a senior researcher at Macquarie University's Centre for Agency, Values and Ethics. He also teaches at the University of Sydney's Law School, and Foundation Program.