Animal Rights and the Wrongness of Killing

6. The Value of Human and Animal Life

We have now in our philosophical toolkit the essentials of a plausible utilitarian population comparator. However, before we are in a position to apply it to the problem of the morality of killing humans vis-à-vis animals, our maximizing principle requires further interpretation. What we need to know is the relative utilities of the life of a normal adult human being and the life of a normal sentient animal. More specifically, if we stipulate that the life of a very happy, normal human being is 10 units, on an arbitrary scale of happiness, and that a life that is neither worth living nor not worth living is zero units, what we need to know are the utilities of the normal lives of sentient members of other species. Furthermore, we need to ask: What are the average utilities of the lives of people living in developed and developing countries, those living at peace and in war-torn states, and so on? Answers to these questions will give us some indication of the relative values of the lives of normal human beings and normal animals.

These questions are extremely difficult to answer and, unfortunately, not much work has been done on them to date. I can only propose here a sketchy and tentative solution. The basic idea behind my answer is that, in general, normal human beings are happier than normal animals because they have more satisfied desires. Stated bluntly like this, this answer seems crude and naïve. However, I hope that a little reflection will reveal it to have a measure of plausibility.

Consider our own lives for a moment. Each of us has a vast number of desires, too numerous to count. Even though we cannot identify each and every one of them, it seems clear that for every desire of ours that is not based on false expectations and that comes to be satisfied, we feel happier (or, to put it more accurately, we feel more satisfied). How much happier we feel will, of course, depend on how important we considered our desire to be in our inventory of preferences. Let us ignore levels of importance for the moment.

Now, what happens when we develop a new desire, such as a taste for Beethoven, for philosophy or for wine, that we had not possessed before? If this new desire is satisfied periodically or at the appropriate time, it seems that we become happier for having cultivated this new desire. Our life has gained in richness and variety and, furthermore, in contemplating this added depth to our life, we can become even happier. The conclusion that we seem to be able to draw from this is that the more satisfied desires we have, the happier we are.

Now consider my dog. As dog's lives go, she is a happy dog, but her desires are very limited. I would suppose that she desires tasty food, absence of pain, shelter, companionship, outings in our car, walks and play. I think this just about sums up her basic preferences. Contrast this with her owner. I prefer all of the basic things that my dog prefers and considerably more. It is not that my dog can desire the number and types of things that I desire and that, as a matter of fact, she does not. The point is that my dog does not have the psychological capacities to desire what I desire. If I am right, then, there is an upper limit to how happy a member of the canine species can possibly be, just as there is, no doubt, a limit to how happy a member of homo sapiens can be. So, if my dog leads a reasonably satisfying life as far as dogs go and I lead a reasonably satisfying life as far as human beings go, then the amount of happiness in my dog's life must still be significantly lower than the amount of happiness in my life.

Book cover: Animal Liberation by Peter Singer

Consider, for a moment, a hypothetical example. Imagine two sentient creatures that are otherwise identical in their desires, except that the first has a desire for continued life while the second has a desire neither for life nor for death. Imagine further that the desires that are satisfied in the second being are exactly the same as those satisfied in the first, except that the first has their extra desire for continued life also satisfied and suspects no impending threat to their life. I suggest that the first creature is happier than the second because they have all of the satisfactions that the second has, in addition to the satisfaction of being alive. This additional satisfaction is akin to our own feeling when we feel happy to be alive.

I appreciate my example is purely hypothetical. The capacity to desire one's own future existence is dependent on the existence of a relatively complex central nervous system, and such a state of complexity brings with it the capacity to possess other complex preferences. Moving beyond the hypothetical, though, further bolsters my argument. For once a being can desire their future existence, they can also have many desires concerning what they are to do with their future life. If self-consciousness is the capacity to recognize oneself as a distinct entity with a past and a future, then there appears to be a sizable gap between the capacities for happiness of a merely conscious creature and those of a self-conscious creature. Just where self-consciousness first appears in the evolutionary continuum between simple vertebrates and the higher-order mammals is a matter in much dispute. I will leave that question to those best qualified to answer.

It may be objected that the capacity for a larger number of desires not only brings with it a larger number of satisfied desires, but also its opposite; a larger number of unsatisfied desires. So, with all things considered, the objection continues, it may be that my life is no happier than my dog's. If I did not have a desire for material possessions, the objector protests, I could not be dissatisfied with not having enough money; if I did not have a desire for music, I could not be dissatisfied with not having enough leisure time to listen to my favourite pieces; if I did not have a desire for knowledge, I could not be dissatisfied with my ignorance; if I did not desire my life, I could not be dissatisfied with its brevity, and so on.

I readily admit that an increased capacity to desire brings with it an increased potential for dissatisfaction. In this important respect, the more neurophysiologically complex the species, the greater is its members' capacity for suffering. However, I do think that once a desire is satisfied beyond a certain degree, this satisfaction will outweigh any remaining dissatisfaction. So, for example, the satisfaction that a normal person obtains from the material comforts that they do have far outweighs their dissatisfaction with not having more; the satisfaction that they gain from listening to their favourite music easily surpasses their frustration at not having more time to spend in this way; the satisfaction that they gain from living their life far outweighs their disappointment at the fact that it will be necessarily brief, and so on.

No doubt, there are some individuals who are miserable from obsessing over these unmet desires. These individuals become so focused on what they don't have that they miss out on enjoying what they do have.[12] I think these cases are more the exception than the norm and so do not appreciably impact the points I am making here.

The extra utility gained from the possession and satisfaction of desires not possessed by members of other species applies, I think, to most people living in peace in developed countries. For those living in dire poverty or in a war zone and at the borderline of existence, though, these extra desires go largely unsatisfied. In the struggle to scratch out a meagre existence and to just survive, the opportunity to develop such desires as a love of art, knowledge, fellowship, and so on, is largely missed. Sadly, it is not an exaggeration to say that many of these people live lives that are much less worthwhile than my dog's.[13]

We are now in a position to order roughly the utilities of the lives of members of different species, where those lives are reasonably satisfying. The lives of homo sapiens have the highest value, followed by the lives of the other higher-order mammals, such as whales, dolphins and chimpanzees. The value of life decreases as we descend the ladder of neurophysiological complexity to the level of reptiles and continue down through to the level of fish until we reach the borderline of sentience at the level of crustaceans.

Given our current state of scientific knowledge, it is extraordinarily difficult, perhaps impossible, to place a numerical value on the worth of individual lives from different species, where those lives are reasonably satisfying. One suggestion is that we simply count the number of types of desires that a creature of a particular species has and correlate this with a scale of values from 1 to 10. An ancillary or alternative suggestion is that we consider how impoverished our own lives would be if we no longer had the capacity to enjoy those things that are unable to be enjoyed by members of other species. Nevertheless, the fact that we do not have at our disposal such a metric will not substantially affect what I have to say. One thing that is clear from the foregoing discussion is that it is harder to justify the killing of a creature that lives a reasonably satisfying life for its kind the further up it is located on the scale of neurophysiological complexity. The taking of the life of a reasonably happy human being appears the most difficult of all to excuse.


  1. [12] This point was raised by Peter Singer in personal correspondence with me.
  2. [13] For an alternative utilitarian approach to this daunting problem of interspecific comparisons of utility, see Singer [1979c: 88–90].

Copyright © 2015

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