Vasco Grilo🔸 comments on Why planarians may hold the key to sentience: about primitive sentient organisms and immortality

[Vasco Grilo🔸]

Thanks for sharing your thoughts, Guillaume!

I would rank planarians lower than insects but higher than nematodes (their behaviors seem less chaotic, but I’m no nematode expert).

This is my intuition too considering planarians’ number of neurons, and that “number of neurons”^0.188 explains the welfare ranges in Bob’s book quite well. Bray et al. (2024) says planarians’ “number of neurons may fluctuate between ∼1,000 and ∼100,000 in a single animal during growth and degrowth”. Based on this, and the estimates below I collected, it looks like planarians have more neurons than nematodes, roughly as many as black soldier fly (BSF) larvae, mealworms, and soil springtails and mites, and up to as many as shrimps, and soil ants and termites.

I would be more interested in finding out if these animals somehow have a “lighter” form of sentience, as I’m not fully convinced sentience (as for current definitions) is either absent or present.

This reminded me of the article “All animals are conscious”: Shifting the null hypothesis in consciousness science by Kristin Andrews. I agree a greater focus on how instead of whether animals are conscious or sentient would be more helpful to assess their welfare.

I could not find any estimates for total numbers of individuals or colonies. Here again, instinctively, I would assume that they are still way less numerous than nematodes or even insects. Because they are very small (usually around 1-2 cm depending on the species)

Among farmed/​wild animals only (not considering farmed and wild animals together), smaller animals tend to be more numerous.