These days, you often hear about criminal trials in which genetic predispositions to violence are invoked as factors mitigating moral culpability. Strictly speaking, though, isn't all our behavior -- good and bad -- dictated by an interaction of our genes and environment? If genes direct us in any case and at all times, does it really make sense to cite genetic determination in the instance of bad acts, as if these were exceptional cases?

You are quite right. There seems no good reason why genetic causes should absolve us from moral responsibility any more that other causes of our behaviour. This is a point that has often been made by Richard Dawkins. If there is a threat to free will and moral responsibility, it is determinism per se, not genetic determinism in particular.

Of course, there remains the question of whether determinism does undermine free will and moral responsibility. Compatibilists say no--they say you are free as long as your actions issue from your own conscious choices, even if those choices themselves are determined by your genes and environment. Incompatibilists say yes--if your actions are ultimately determined by causes beyond your control, then you aren't free, even if the determination proceeds via your conscious choices.

But, either way, genetic causes have no special status. Compatibilists will say that genetic causes, like other causes, don't undermine your freedom when they influence your behaviour by influencing your choices. And incompatibilists will say that non-genetic causes beyond your control, like your early upbringing, do undermine your freedom just as much as genetic causes.

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