I'm interested in whether animals are sentient. David Deutsch's book The Beginning of Infinity (BoI*) has interesting things to say about this issue. Deutsch's view in my own words is that, as I've written previously in the context animal suffering specifically, animals are not sentient because "all they do is mindlessly execute inborn algorithms which are the result of biological evolution". He's confirmed to me in writing that he doesn't think animals are intelligent, which, for reasons you will soon learn as you read on, implies that they're not sentient. Elliot Temple, who used to be Deutsch's student, introduced me to Deutsch's view and has written about animal sentience as well. Among other things, Temple believes it's not "realistic to have serious opinions about animal rights without knowing how to code". I agree.

BoI has an index entry called "animal minds" with six references. The first reference is to chapter 7, which is about artificial intelligence. I've previously commented on the corresponding passage and am quoting my comment here:

In [chapter] 7, David Deutsch writes about how people over-attribute intelligence to animals that can recognize themselves in the mirror:

[S]ome abilities of humans that are commonly included in that constellation associated with general-purpose intelligence do not belong in it. One of them is self-awareness – as evidenced by such tests as recognizing oneself in a mirror. Some people are unaccountably impressed when various animals are shown to have that ability. But there is nothing mysterious about it: a simple pattern-recognition program would confer it on a computer.

[— p. 154]

(I personally wouldn’t call that awareness, but his argument stands.) I have written software that allows MacBook Pros and iPhones to recognize themselves in the mirror. You can try it out. Your MacBook Pro/iPhone does not suddenly become conscious upon visiting that website.

Deutsch then applies this argument to other areas which, in my terminology, are evidence of smarts but not intelligence:

The same is true of tool use, the use of language for signalling (though not for conversation in the Turing-test sense), and various emotional responses (though not the associated qualia). At the present state of the field, a useful rule of thumb is: if it can already be programmed, it has nothing to do with intelligence in Turing’s sense.

[— p. 154]

Basically everything animals do can already be programmed and simulated, so this last part applies to animals as well. Also, programs exist that far exceed animals' abilities, and those programs are not sentient, either. How do we know that? Because our best explanations of how such programs work make no mention of sentience, nor did we need to understand how to program sentience to write them.

Chapter 7 includes another passage which is relevant to animal sentience. It doesn't mention animals explicitly, which is presumably why it isn't referenced in the index:

There is a deeper issue too. AI abilities must have some sort of universality: special-purpose thinking would not count as thinking in the sense Turing intended. My guess is that every AI is a person: a general-purpose explainer. It is conceivable that there are other levels of universality between AI and ‘universal explainer/constructor’, and perhaps separate levels for those associated attributes like consciousness. But those attributes all seem to have arrived in one jump to universality in humans, and, although we have little explanation of any of them, I know of no plausible argument that they are at different levels or can be achieved independently of each other. So I tentatively assume that they cannot.

— p. 157

A few remarks about this passage. First, by "AI", Deutsch means what has come to be called 'AGI' – artificial general intelligence. It's basically a person's mind but simulated on a computer, so it would be intelligent and conscious just like humans are. It would not be qualitatively different from humans. Second, Deutsch's idea of the jump to universality is an important one because it cuts the world into two camps: everything that is a universal explainer (and, therefore, intelligent and conscious), and everything that isn't. This notion breaks with how most people think about intelligence and sentience, namely as a matter of degree. That's a fudge, and I've introduced, as mentioned above, the difference between smarts and intelligence to help clear things up. Third, Deutsch says it's conceivable that consciousness lives on some level of universality that's separate from the general-purpose-explainer one, but denies that this is the case. In other words, he thinks that only universal explainers are conscious. What Deutsch describes as a universal explainer is an intelligent or, in other words, creative being. He unifies those concepts into one – again, he thinks they arise on the same level of universality – which is why I use them synonymously. And it's why I wrote above that his believing that animals are not intelligent implies that he believes they're not sentient.

While we're on the topic of universal explainers, consider Deutsch's concept of people, which he defines in the glossary of chapter 3 as "entit[ies] which can create explanatory knowledge" (p. 75). In other words, universal explainers – which could also be described as entities that can, in principle, explain everything that is explicable, solve every soluble problem – but here that more directly includes non-human entities like AGIs and intelligent aliens. Note that Deutsch didn't call this class of entity 'mammals' or 'organisms' or something. That's not just because AGIs and aliens need not share our biology: he wasn't concerned about fitting animals other than humans into this category, and the term 'people' excludes non-human animals.

On that note, in my interview with him, he says (translated freely from German):

Ants, apes, rocks, planets – those are not people.

This shows that he does not consider animals to be people, and even considers them to be on the same level as rocks and planets in at least one regard, which is notable.

The second reference in the index to animal minds points to p. 268 in chapter 11. I believe this reference to be erroneous. That page is not about animal minds – it's about quantum physics generally and a concept called 'diversity within fungibility' specifically, and I'm not aware of either of them having any direct application to animal minds. I also checked pages 168, 368, 258, and 278, in case the given page number was off by 100 or 10, but those pages aren't about animal minds either.

The next reference is to chapter 12, which is about bad philosophy. Here's the relevant passage, with intermittent comments by me:

The behaviourist approach is equally futile when applied to the issue of whether an entity has a mind. I have already criticized it in Chapter 7, in regard to the Turing test. The same holds in regard to the controversy about animal minds – such as whether the hunting or farming of animals should be legal – which stems from philosophical disputes about whether animals experience qualia analogous to those of humans when in fear and pain, and, if so, which animals do.

— p. 320

Here, Deutsch creates an explicit link between what he said about intelligence and consciousness in chapter 7, as quoted above, and what he's about to say about animals. Deutsch continues:

Now, science has little to say on this matter at present, because there is as yet no explanatory theory of qualia, and hence no way of detecting them experimentally. But this does not stop governments from trying to pass the political hot potato to the supposedly objective jurisdiction of experimental science. So, for instance, in 1997 the zoologists Patrick Bateson and Elizabeth Bradshaw were commissioned by the National Trust to determine whether stags suffer when hunted. They reported that they do, because the hunt is ‘grossly stressful…exhausting and agonizing’. However, that assumes that the measurable quantities denoted there by the words ‘stress’ and ‘agony’ (such as enzyme levels in the bloodstream) signify the presence of qualia of the same names – which is precisely what the press and public assumed that the study was supposed to discover.

— pp. 320–321

When I first read the book, this was the clearest reference to animal minds to me. And it's the clearest indication that Deutsch does not just assume, like most people do, that animals are sentient. Back then I thought animals are sentient, and I remember thinking, 'wait, is Deutsch questioning whether animals are sentient?' But I came away from that passage not knowing either way. I think it would have been a good spot to explicitly state his view.

Deutsch continues:

The following year, the Countryside Alliance commissioned a study of the same issue, led by the veterinary physiologist Roger Harris, who concluded that the levels of those quantities are similar to those of a human who is not suffering but enjoying a sport such as football. Bateson responded – accurately – that nothing in Harris’s report contradicted his own. But that is because neither study had any bearing on the issue in question.

— p. 321

As an aside, I disagree that Bateson's response was accurate. I haven't read either study – no sources are given – but while Bateson and Bradshaw assumed that the "quantities" they measured were indicative of suffering, Harris showed that this assumption was wrong because they might just as well be indicative of someone enjoying a sport, and enjoyment is the 'opposite' of suffering.

The next reference points to a passage in chapter 14, which is about aesthetics.

An animal can be attracted towards another animal in order to mate with it, or to eat it. Once the predator has taken a bite, it is attracted to take another – unless the bite tastes bad, in which case it will be repelled. So there we have a literal matter of taste. And that matter of taste is indeed caused by the laws of physics in the form of the laws of chemistry and biochemistry. We can guess that there is no higher-level explanation of the resulting behaviour than the zoological level, because the behaviour is predictable. It is repetitive, and where it is not repetitive it is random.

— pp. 358–359

Deutsch shouldn't be misunderstood to imply the presence of qualia when he uses words like 'taste'. When he says "there is no higher-level explanation of the resulting behaviour than the zoological level" he (I think) rejects any explanation on the level of universality he mentioned in chapter 7, which level consciousness inhabits in his (and my) opinion. In addition, predictability is a fatal blow to the idea that animals may be conscious: if they were creative, and, therefore, conscious, they would be unpredictable, just like people. Why? The Popperian argument is that the creation of knowledge – which is what creative entities engage in, by definition – is deeply unpredictable because if you could predict new knowledge you would have already created it and so it wouldn't be new. So there's a quick reductio ad absurdum showing the unpredictability of creative entities.

The last two references point to passages in chapter 16, which is about the evolution of creativity. The first passage goes:

Apes are capable of recognizing a much larger set of possible meanings [than parrots]. Some of them are so complex that aping has often been misinterpreted as evidence of human-like understanding.

— p. 407

The error Deutsch describes here is again that of fudging between smarts (here: complexity of behavior specifically) and intelligence. In this particular case, it's thinking that sufficient complexity implies explanatory universality, and with it, consciousness. The passage continues:

For example, when an ape learns a new method of cracking nuts by hitting them with rocks, it does not then play the movements back blindly in a fixed sequence like a parrot does. The movements required to crack the nut are never the same twice: the ape has to aim the rock at the nut; it may have to chase the nut and fetch it back if it rolls away; it has to keep hitting it until it cracks, rather than a fixed number of times; and so on. During some parts of the procedure the ape’s two hands must cooperate, each performing a different sub-task. Before it can even begin, it must be able to recognize a nut as being suitable for the procedure; it must look for a rock and, again, recognize a suitable one.
Such activities may seem to depend on explanation – on understanding how and why each action within the complex behaviour has to fit in with the other actions in order to achieve the overall purpose. But recent discoveries have revealed how apes are able to imitate such behaviours without ever creating any explanatory knowledge. In a remarkable series of observational and theoretical studies, the evolutionary psychologist and animal-behaviour researcher Richard Byrne has shown how they achieve this by a process that he calls behaviour parsing (which is analogous to the grammatical analysis or ‘parsing’ of human speech or computer programs).

— p. 407

Here, Deutsch explains how apes display sophisticated behavior without creating any explanatory knowledge – i.e., without being universal explainers. Recall once more that Deutsch thinks only universal explainers are conscious. He also contrasts aping to what people do:

Human beings acquiring human memes are doing something profoundly different. When an audience is watching a lecture, or a child is learning language, their problem is almost the opposite of that of parroting or aping [...]

— p. 409

And, later on, he contrasts again (this is the second of the two references):

Parrots copy distinctive sounds; apes copy purposeful movements of a certain limited class. But humans do not especially copy any behaviour. They use conjecture, criticism and experiment to create good explanations of the meaning of things [...]

— p. 410

Lastly, the New Yorker quotes Deutsch as saying:

If I were a biologist, I would be a theoretical biologist, because I don’t like the idea of cutting up frogs. Not for moral reasons but because it’s disgusting [emphasis added].

Perhaps the main reason people reject killing animals is that it's immoral because animals are sentient. Deutsch disagrees (as do I).

In short, I think Deutsch's view that animals are not sentient is in the book. It's not quite hidden away but it also isn't readily apparent and can easily be missed. One has to read the book multiple times and draw connections between passages that are spread over hundreds of pages. Readers would have benefited from an explicit statement of the view – something like: 'Only creative entities are sentient. All animals do is mindlessly execute inborn algorithms provided by biological evolution. Therefore, animals are not creative and, in turn, not sentient.' If I recall correctly, David Foster Wallace said in one of his books or lectures that one shouldn't assume readers will understand what's implied or follows logically from what's written – that one should write it explicitly and make it as easy as possible for readers to understand.

If you wish to learn more about animal sentience (or lack thereof) and related topics, read my posts 'Animal-Sentience FAQ', 'The ‘Animal-Rights’ Community Is Based on Fear and Intimidation', and 'Evidence Is Ambiguous'. The post 'Buggy Dogs' in particular and many of the comments underneath it provide lots of evidence for animals not being sentient. Also read my book.

* The edition of BoI I use is the American one from 2012, New York, Penguin Press.