Infant Mortality and the Argument from Life History

by ozymandias2 min read4th Oct 20174 comments


Animal WelfareEthics & MoralityUtilitarianism

Many people argue that suffering predominates in nature. A really simple form of the argument, supported by people like Brian Tomasik, is what one might call the argument from life history. In general, in most species, females produce many more offspring than can survive to adulthood; in some cases, a female may produce thousands or millions of offspring in a single reproductive season. Therefore, one can assume that most animals die before they are able to reproduce. In many cases, the offspring die before they can reasonably be considered conscious (for instance, an egg is eaten shortly after laying). However, even if half of animals die unconscious, the other half are a large source of disutility. Since death is generally quite painful, they may not have had enough positive experiences to outweigh the extraordinarily negative experience of death. It can therefore be assumed that there is more suffering than happiness in nature.

While this argument is intuitively compelling, I am not sure that it accurately reflects most people’s opinions about how happiness works, so I have decided to write up three thought experiments that might help people think about it. These thought experiments are quite preliminary; I hope to spark a discussion so that people who are concerned about wild-animal suffering can debate.

1. The Human History Thought Experiment

Although the human population has been growing for thousands of years, for most of history the growth was fairly slow, suggesting the argument from life history applies to us as well. In part, that was because many humans died in childhood: for example, in 1800 four-tenths of humans died before they were five years old, a quarter of humans before their first birthday. (Note that 1800 is fairly late, and the statistics may have been even more stark in, say, 1 CE.)

I do not mean to deny that pre-modern human life was miserable in many ways: people were hungry, diseased, and poor. And I certainly don’t mean to claim that high child mortality rates weren’t a tragedy. However, my intuition is that-- whether or not human lives were worth living before modernity-- the high child mortality rate does not single-handedly prove that human lives were not worth living. Other information must be gathered to prove that. I suspect many other people’s intuitions will agree.

To the extent the human history argument is misleading or anthropomorphizing, it strengthens my point: for instance, humans grieve their infants, while fish do not, so high infant mortality rates are worse for humans than for fish.

2. The Babykillers Thought Experiment

Humans have relatively few children and are growing (albeit slowly), perhaps suggesting that they are misleading as a thought experiment. Consider, therefore, a sapient species of aliens, the Babykillers. This species lays a thousand live young at a time. The young devour each other and only the single strongest offspring survives. All of the non-surviving thousand have miserable lives: they are tremendously hungry until they are eaten alive. The Babykillers have no way of modifying themselves to lay only a single offspring. To set aside issues of the Babykillers being replaced by humans, assume that Babykillers are not aware of any other species. Would it be ethically required to have a Voluntary Babykiller Extinction Movement?

Personally, I put some weight on the argument that diversity is intrinsically valuable and therefore it is harmful to eliminate a sapient species. Otherwise, my moral intuitions are conflicted about whether Babykillers are net-negative and should be extinct.

3. The Long-Lived Babykillers Thought Experiment

The Babykillers are a species as specified above, except that the Babykillers are also extraordinarily long-lived: the average Babykiller who survives infancy lives for a thousand years. The average Babykiller who is eaten lives for only an hour. Babykillers are also a happy and fulfilled species. Therefore, while 999/1000 Babykillers experience a short life of great hunger followed by a painful death, only about one in ten thousand hours experienced by a Babykiller consists of great hunger and a painful death. The rest are quite happy.

The Long-Lived Babykiller thought experiment is supposed to get at an alternate method of assessing well-being. Instead of thinking about whether the average member of a species has a life worth living, we instead think about whether the average hour experienced by a member of a species is worth experiencing. For species with high juvenile mortality and/or long lives, these may be very different metrics.

Intuitively, I think the Long-Lived Babykillers should not go extinct. I think that also goes along with my intuitions about the human case. Since humans are fairly long-lived, a relatively small percentage of human hours are spent being a sick infant. I’m also tempted by the practical benefits. You could, in theory, figure out whether an animal species’s existence is net positive simply by randomly sampling animals (although of course seasonal changes such as winter starvation or mating seasons would make this more complicated). However, many people have prioritarian intuitions. In that case, the experiences of animals who die young and painfully should be given more weight than the experiences of happy animals.

To be clear, I’m not necessarily satisfied by the “average hour” criterion. I do think we haven’t put enough philosophical work into understanding what makes a species’s existence net positive or net negative, and I hope my thought experiments will prompt some thought about the issue.


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Compelling arguments. I'm updating about how complex this topic is.

I also think that the 'zero line' we intuitively use to divided negative experience from positive experience is a little bit arbitrary. In planetary science, the sea level of a planet may vary over time, or the planet might have no seas. Because of this, scientists chose an arbitrary height ('datum') and consider that to be the geological zero altitude. I suspect that some disagreements about wild animal suffering might stem from people using different 'zero altitudes' for animal suffering. Some people think of animals as happy most of the time and some people think of animals as hungry and stressed most of the time.

I agree. I think that for humans a good approximation for the "zero line" is whether the human in questions wants to live, or wants to kill emself. It's an interesting question to what extent this criterion is applicable to animals. I think that in some sense it should be applicable, but one might argue that most animals are incapable of understanding the possibility of suicide or how to carry it out.

Personally, I put some weight on the argument that diversity is intrinsically valuable and therefore it is harmful to eliminate a sapient species.

If you don't mind me asking, why do you believe this?

Another factor that affects the thought experiment is whether we posit that the given state of affairs is entirely stationary, or can develop into something different in the future. Because even if we assume that in the past humanity was producing net negative utility, it might have still been better for it to endure in order to create a net positive future.