Abortion is a great example of a topic where the two sides argue from completely different perspectives. One side—pro-choice—argues that abortion is a private matter, and hence it is up to the woman to decide. The other—pro-file—claims that a fetus is a human life, and hence abortion is akin to murder. Is it possible to have a discussion about abortion that overcomes these positions? I would argue that there is. But, also, I would argue that this issue combines two moral biases, or bugs, that we face: our need for categorical answers and the role of purity.

The issue at hand is to identify when a human life starts. And here we run into the first problem: this question makes no sense. A human life gradually appears from the moment the egg is fertilised. We seek a discrete function, but it is continuous. Therefore, we have to define an arbitrary threshold—and that is OK. Notice that the two extremes of this debate have defined a threshold as well: one at conception (week 0) and the other one at delivery (week 40 or when the baby is born). In fairness, the pro-choice stance is generally against late-stage abortions absent medical reasons; yet slogans such as my body my choice are not so nuanced.

We need to define a threshold so that it can be written into law. But the difficulty on defining this threshold comes from our flawed moral intuitions. A key insight from The Moral Landscape is to view morality as one views health. Our moral intuitions, as our health intuitions, can be, and often are, wrong. These moral intuitions are an evolutionary trait. As is our desire for sweet food. Yet this desire can be bad for our health. In this case, a usual reaction for any given abortion threshold X would be to argue that someone whose pregnancy is at X + 1 is basically the same as someone at X. Sure, but we still need the X.

An arbitrary threshold needs to be defined, and we need to be comfortable even if X + 1 is almost the same as X. But some people would not accept this, as they see abortion as a sin. The concept of purity—sin can be seen as the destruction of this purity—is ingrained in the psychology of an important part of the population. The figure below, from Haidt and Graham (2007), shows that liberals and conservatives differ substantially in this point.

This, again, appears to be a failure of our moral intuition. Some people might argue that purity appeared as a way to enforce social norms. For instance, stealing is probably bad for the survival of a tribe. Hence, as years pass, and as the tribe punishes these actions, those with strong moral intuitions against stealing are more likely to succeed. This could be an explanation, but as mentioned earlier it is no different than our desire for sweet food. Put it differently, one could also use an evolutionary rationale for racism. Yet we (well, most of us at least) understand that it is morally wrong.

I find the topic of abortion to be a showcase of many of the failures of our moral intuitions, and a clear example of how much more we need to think about morality from an objective perspective. Or, at least, how much more we need to reduce the presence of religious concepts—purity, sin, commandments—when discussing about it.