The subtitle of Olson’s book gives the plot away: Olson holds that psychological properties and abilities are not relevant to our continued existence through time. In contrast to the received opinion in analytic philosophy, Olson is one of the growing number of philosophers who argue that we can survive the loss of memory, consciousness, and any other of our psychological states and abilities. According to Olson we are animals, members of the species Homo sapiens, and our continued existence involves only the continuity of a (biological) life. While the continuity and stability of our mental life might be awfully important to us, we can — and as fetuses did — survive without it.

The Human Animal is both clear and engaging. Olson does a fine job of unearthing those common-sense intuitions that support the biological approach and showing how deep they run. In a chapter entitled ‘Was I ever a Fetus?’ Olson answers that of course he was, and that psychological approaches to personal identity are unable to account for this fact, for, at least prior to six months, a fetus does not have any interesting psychological properties. As Olson points out, there really is something quite counter-intuitive about the thought that we come into existence only when a human being attains a certain degree of psychological sophistication. “If your five-year-old daughter finds her baby brother disgusting, and you remind her that she, too, was once an infant, you do not mean merely that she developed from an infant. You mean that she herself, not some other thing, once weighed ten pounds, nursed at her mother’s breast, cried at night, and did everything else that babies do.” (78) Olson claims that the problems for the psychological approach go beyond mere counter-intuitiveness. If a new entity – the person – comes into existence when an animal attains a certain level of psychological structure, what happens to the animal that develops that psychological structure? Are there two entities, both of whom can think, act, and communicate? Or does the animal go out of existence when the person comes into existence? (Surely not!) The psychological approach would seem to be committed to the view that there are two entities in your room – indeed, sitting in your very chair! – reading this page. There’s you, the person, and there’s the human animal. But, says Olson, this is perfectly absurd. Better to adopt the biological approach, and hold that we simply are animals. In response to objections of this kind proponents of the psychological approach often invoke the notion of coincident entities: the idea that there can be two things composed out of exactly the same stuff. There is much debate about the tenability of coincident entities: suffice it to say that although Olson seems to have common sense on his side – doesn’t it look as though there’s only one thing, a human being, that can attain, and then lose, psychological states and abilities? – much more needs to be said on this difficult issue.

There is a second reason to warm to the biological approach, although this is a theme that Olson is strangely silent on. Our therapeutic response to psychopathologies such as Dissociative Identity Disorder (DID, formerly Multiple Personality Disorder), involves taking the whole human being as the object of moral concern. Psychological accounts of personal identity seem to be committed to the claim that extreme cases of DID result in the formation of a number of persons, while biological accounts will say that in such cases we have one person with a severely fragmented psychological life. It is by no means obvious that ‘the’ problem of personal identity – assuming that there is one such problem – is a problem about the identity of the proper objects of moral concern, but if it is, then there is reason to think that our intuitive response to various pathologies provides some support for the biological approach.

Although Olson prosecutes the arguments for the biological approach with force, I was less impressed with his handling of objections to his position. (After all, there are reasons why the biological approach has been ignored.) Brain-transplant objections are often thought to be fatal to the biological approach. Suppose that Mary’s brain is transplanted into Jane’s body, and vice-versa. It is tempting to say that Mary has acquired a new body (the body that used to be Jane’s). But as Olson points out, whole-brain transplants fail to distinguish the psychological and biological approaches to personal identity, for the brain-stem is essential for the continuity of a life, and thus my continuity according to the biological approach. The crucial case is a cerebrum-only transplant: Mary keeps her brain-stem, but gets the cerebrum that used to be Jane’s. Or should we say that Mary goes with her cerebrum, and gets a new body and brain-stem? Olson admits that our intuitions support the latter description of the case, but claims that there are independent reasons – namely, those that support the biological approach – to accept this surprising conclusion. Olson does not deny that we might have prudential and moral reasons to say that Mary has received a new body and brain-stem – “the transplant intuition is based on practical concerns that may be perfectly valid” (44) – but he denies that the transplant intuition shows that any sort of psychological continuity is necessary for numerical identity over time. One might have qualms about this position. Suppose that Mary took out a loan before the transplant, but after the transplant she defaults on her loan repayments. But who does this “her” pick out? If it refers to Mary – the numerically identical individual over time – as it seems to, then it refers to the individual that has the body and brain-stem that, pre-transplant, we referred to as Mary’s, but the cerebrum that we referred to as Jane’s. As Olson concedes, it doesn’t seem right to hold that individual responsible for what Mary-pre-transplant did. But how can we hold the other individual – the one with the cerebrum that the pre-transplant-Mary had – responsible for defaulting on the loan repayments, given that she is a numerically different individual from the individual that took out the loan? The problems raised by Olson’s willingness to cut moral and prudential concern free from the constraint of numerical identity run very deep indeed.

Let me close with a general worry about the framework within which Olson’s discussion takes place. Like many philosophical discussions, the personal identity debate can take on an eerie glow after a certain point. One begins to wonder what, exactly, the question is. Olson says that the topics of his book is “our identity through time” (7). But why should we expect there to be a single, well-behaved account of ‘our’ identity. Perhaps our boundaries contract and expand according to the conversational norms currently in place. Of course, there must be a certain sort of stability to first-person reference, but the sort of stability necessary for practical cognition might fall short of that demanded by philosophers working on personal identity. Perhaps it is not reckless to suggest that one of the lessons of the personal identity literature is that our self-conception is composed of diverse, and competing, strands. Olson reminds us that we are animals and as such are the subjects of biological lives, but it is no less true that we are the subjects of experiential lives, and an account of our numerical identity needs to find ways to accommodate this fact as well.

Timothy Bayne was until recently a graduate student in the Ph.D. program in Philosophy at the University of Arizona. He is now an Assistant Professor in the Department of Philosophy at The University of Canterbury, Christchurch, New Zealand (his native country).

Categories: Philosophical