Why is it that most domesticated mammals and birds seem to have “personalities” and “emotions”, but fish and reptiles do not?

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Why is it that most domesticated mammals and birds seem to have “personalities” and “emotions”, but fish and reptiles do not?

In: Biology

Facial disparity.

You are around mammals more than birds, reptiles, and fish. They also share more common musculature in and around the face. So they make expressions you are familiar with.

Reptiles and birds we commonly encounter have their eyes farther to the side, and differently defined mouths.

Ask longtime fish owners (people who have only 1-5 in a tank) and they will say their fish have personalities. Ask anyone who has had a bird more than a year and they will as well. I haven’t spoken much with any reptile owners about their pets, but would wager it is the same case there. Once familiar with the animal, you begin to attribute emotion to various actions.

So, first we need to define what emotions are. Emotions are a trick of the mind, they’re a semi-reliable backbone and basically the extrapolated form of instincts. They’re evolved traits that act as basic programming to get animals to behave as is naturally beneficial for them to do so despite having higher brain functions that might normally interfere with this. To help understand this, think about example emotions – you shouldn’t be able to think of any emotion you can’t link to a direct and tangible purpose. Fear helps animals avoid dangerous situations. Hatred is a more complicated form of fear but serves basically the same purpose. Love encourages animals to reproduce and love (a different love, but English is a language woefully unequipped to talk about the different types of love) is the driving force behind altruism (which is in itself a curious concept). Boredom encourages play, a vital learning technique, while joy acts as the carrot of play and as a more general reward system for doing things that increase your chances of reproducing. Emotions all evolved at different points in evolutionary history, but are all just instinctual behaviours on some level. Personality is simply how humans perceive the accumulation of certain behaviours. Mammals and birds seem to have more personality only because they do more things.

Humans have a set of emotions best adapted to the life of nomadic foragers. Unfortunately, humans have so many emotions and rely on so much external data that we’re woefully under-equipped for dealing with the modern world, but that’s a whole other matter. Filial emotions evolved in the common ancestor of most if not all mammals. These emotions include things like a mother’s love for its own offspring. This would explain why mammals in general seem more humanlike. Social emotions evolved in social primates, which explains why despite being social animals, dogs are incapable of experiencing things like guilt.

Part of this is also that humans have bred pet species specifically to be more human-like. This is especially true of dogs and cats. Note how animals we don’t typically utilise as pets, like cows and sheep, we generally don’t consider to exhibit personality. This is because we assign no value to these animals outside of the meat, milk and materials they’re cultivated for, whereas we personify house pets. Humans are great at personifying things btw. Some cultures are so good at it they even personify completely inert objects regularly.

On the other hand, fish and reptiles are ectothermic – they gain their heat from external sources. This means their pace of life is much slower. Animals only evolve the intelligence levels that are significantly beneficial to their reproduction rate, and these animals simply don’t benefit enough from possessing more complex emotional structures than they already have. This isn’t to say that they’re stupid, because there’s growing evidence that reptiles are surprisingly smart, they just have lower metabolisms and are evolved to conserve energy, so they’re much less active in general. A lot of “personality” revolves around the play systems that animals use to learn. A lot of animals play, but the play done by fish, reptiles, amphibians and invertebrates are not what humans typically recognise as play, partially due to the fact that as ectotherms they’re slow as fuck to do anything.

I have fish and a tortoise. Both definitely have personalities. What are you basing your scientific research on?