I want to have a species of intelligent coldblooded creatures. I don't need a hard-science explanation, but I don't want to handwave it alltogether. I want to know why they are how they are (and learn more about them for I search for their basic biology)

Traits that I am looking for but are negotiable

  • have hands
  • walk up right
  • be roughly human-sized
  • have sheds of greenish colour
  • live in village-like communities
  • they can communicate with each other (without technology)

I want them to be able to survive in both cold and warm environments. (Their movements (and perhaps their thoughts as well) will be slowed down in cold environment. Does ist affect their perceiving of time?)

  • What family of animals are they related to? What kind of traits do I have to hand wave, and for which can I get explanations?

  • How do they communicate with each other?

  • $\begingroup$ Poikilotherm animals cannot sustain doing effort for any length of time; being cold-blooded does not imply only an incapacity to generate enough internal heat to keep themselves warm, it also implies that they cannot shed heat efficiently enough to avoid overheating if they engage in continuous activity. So, no, you cannot have cold-blooded animals practicing agriculture (which is implied by living in villages). $\endgroup$
    – AlexP
    Dec 4 '21 at 21:53
  • $\begingroup$ In terms of brain to body size that may be true but not the whole truth, in fact most animals can ambush prey using camouflage or fend off predator by becoming bigger but for some like us we need to chase all day and flee all night in the savanna ;D $\endgroup$
    – user6760
    Dec 5 '21 at 4:41
  • $\begingroup$ Because an intelligent being's brain uses large amounts of energy, it generates large amounts of waste heat. So proportionately, your "cold-blooded" species is likely to be at least luke-warm. $\endgroup$
    – DWKraus
    Dec 5 '21 at 5:37

They have technology

And I mean stone age tech. Humans live in lots of places where it gets too cold for humans and too hot for humans. To compensate we have fire and we have clothes and we store food for times when there is no human food to be found. Your cold blooded people evolved in circumstances where the climate and ecosystem was good for them. Because of their intelligence they were able to leverage technology and cooperative culture to extend their range into more and more hostile environments.

Cold blooded creatures do generate some body heat through metabolic activity. Maybe these creatures adjust their diets to maximize that sort of heat generation. Cold blooded creatures can generate heat with muscles. Maybe they can purposefully shiver to warm up,or move around vigorously (warm up dance!), or otherwise heat up when needed. Clothing insulates all sorts of creatures. Your reptiles would bundle up in the cold.

@AlexP is right about keeping cool. In hot climates these creatures might be semiaquatic, shedding heat by staying in rice paddies and ponds. They might live underground where it is cool and sleep in the heat of the day.

The behavioral repertoire of humans can be used to keep your creatures functional in whatever sort of environment you want.

  • $\begingroup$ "Maybe they can purposefully shiver to warm up,or move around vigorously (warm up dance!)" — this brings up some potential for the cultural impact of being cold-blooded. Communal cooling baths in the summer, warming baths in the winter. This common aspect could make for some interesting plot points. $\endgroup$ Dec 5 '21 at 17:38


Hands are a no-brainer, most reptilians have something that can easily work like hands if an intelligence was behind their use. As for walking upright, while there are no alligators that can walk upright as far as I'm aware, they are capable of launching themselves straight up out of the water. This tells me they have at least a minimal ability to keep their spine straight in an upright position and could be improved upon if they were to go into a bipedal direction. By the way, in order for them to be pushed into this direction they're likely going to need pressures for longer arms and legs, so I'll leave it to you to determine exactly what made them require it(tree-climbing perhaps?). Their size category is already human-like if not larger so there's nothing to change there, and many species are greenish or brown so there's another thing you won't need to change about alligators.

Living in villages might come naturally to them since they tend to be grouped up anyway, at least when mating season comes. You won't have them do agriculture as most village-type communities do, but you can have them be fishing villages, which will tie in naturally with their swimming capabilities and even if they don't want to swim their ability and natural tendency to remain still and bake in the sun for long periods of time will aid in the proliferation of the use of fishing rods. Once they gain a greater understanding of fish in general they can perhaps build for themselves fish farms, which would aid in the formation of larger and more well fed villages. Feeding the fish would either be done naturally by having the farm be part of a river or from the produce that they'd have in abundance(since they won't eat any of it and won't need as much space for them) from farming plants. Them remaining full carnivores is more plausible as well since things would have had to be pretty dire for such a killing machine to gain traits to tolerate other kinds of foods.

As for communication, alligators can bellow. Now this is generally only for mating purposes as far as I'm aware, but it might be adapted for long range communication between two underwater individuals. The young ones can also do that cute squeak thing, whatever it's called, telling me they at least have the capability for the production of variable sounds. Intelligence + community living would drive them to develop more sophisticated forms of communication anyway, probably some form of speech via variable tone and length bellows if nothing else, so you don't need to think about this too much.

Just about the only thing you may have to handwave is the development of their higher intelligence. Alligators and crocs have been the way that they are for a long time and only severely drastic pressures will move them away from it, pressures severe enough that you're going to need to explain how it affected other creatures if it does ever come up in-setting.


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