While examining specimens from the Cambrian explosion Simon Conway Morrison is reported to have said “Oh fuck, not another phylum!” More recent analyses have tended to push against the most radical pictures of what the Cambrian explosion was, but it is still generally agreed that something like the Cambrian explosion took place and requires some sort of explanation. Stephen Jay Gould, an advocate of the position that evolution often progresses through sudden leaps and bounds, has cited it to support his position. Many of these creatures were extremely alien looking and difficult to classify in existing taxonomic groupings. It is called an ‘explosion’ because of the vast number of diverse animal body plans that seem to suddenly emerge out of nowhere. It occurred in the prehistoric oceans from Persia around 545 to 520 million years ago. The Cambrian explosion is a mystery of evolution. I will mostly be reasoning using the fossil driven model, because that is the one that I know better, and I believe the one that has been best developed in the literature, but be aware that this other evidence exists that calls it into question. The discovery of the Ediacaran biota fills in this to some extent and supports the claim that the Cambrian explosion is less of a break with previous evolutionary continuity then once believed. In keeping with this, another argument that has been put forward is that the Cambrian explosion may appear to be a greater break with evolutionary continuity than it appears to be only because we lack as many fossils from earlier periods. If these are to be believed then that pushes in favour of a conclusion that the Cambrian explosion is not exceptional and so does not need an exceptional explanation, such as being driven by the evolution of sentience. One factor that calls into question some of the reasoning in this post is some of the newer forms of genetic and molecular analysis on evolutionary history that push back the common ancestors of many taxonomic groups to much earlier than the standard fossil driven narrative would have it. I may follow this post up with another post that gets deeper into the issue. Much of the post is set up, and I don’t reach any firm conclusions. This post is quite speculative and preliminary. I'm not an expert on the subject I’m writing about in this post. Both of these potential conclusions are interesting and important. The latter option implies that at least some simple minds are conscious. This is because it indicates that consciousness is more easily multiply realizable then we would otherwise think.

The former option commits us to position that probably implies that alien life and to a lesser extent digital minds are more likely to be conscious then we otherwise would think. If we believe octopuses are sentient this leaves us with two main options: believe that sentience evolved at least twice, or believe that our common ancestor with them was sentient. They also likely evolved from quite simple animals possibly resembling snails. But cephalopods are very distantly evolutionarily related to us. There is some strong reasons to think that octopuses may be conscious. One example of how learning about the evolution of sentience may be relevant is the case of octopuses and other cephalopods. It can also inform us about how contingent sentience may be, which can be relevant in assessing how likely it is that different types of digita or alien minds are sentient. This can better inform decisions about helping animals.

It’s particularly useful for cases we are most uncertain about such as insects and other invertebrates.

It may enable us to say that most or all animals descending from a certain ancestor are sentient. Thinking about how and why sentience evolved is relevant for finding out which beings may be sentient. For more background on the research that I’ve been doing look at this post here. I have been researching invertebrate sentience for approximately the past year and I believe this post is relevant to that subject. I don’t have enough space in this post to fully flesh out my position on consciousness, but they are fairly similar to Luke Muehlhauser’s position as articulated in his Report on Consciousness and Moral Patienthood. I’m principally concerned with valenced sentience and as a simplifying assumption I write as though sentience implies valenced sentience even though they are probably separable. I use the term ‘sentience’ synonymously with ‘phenomenal consciousness.’ I use a definition by example – your experience of savouring a good meal or of stubbing your toe are examples of sentient experience. Thanks as well to Jason Schukraft and Daniela Waldhorn for feedback on the post. Many thanks to Kieran Greig for funding me to write this post and for feedback on it.

Sentience vs consciousness