I already made two different questions about similar things, How could an efficient respiratory system evolve for giant arthropods? and How could an efficient circulatory and cardiovascular system evolve for giant arthropods?.

Those questions asked about the "how", but this is about the "why".

This is because I would like to have giant arthropods which require those adaptations in a potentially Earth similar enviroment, in possible convivence with vertebrates and other creatures inspired by questions in this site. This all without use of magic or genetic engineering, just natural adaptation and evolution.

So, what kind of enviroment pressures would drive arthropods to develop these adaptations?

Considering that a suitable environment is available for this, but what are the characteristics of this environment?


2 Answers 2


Low atmospheric pressure and higher oxygen concentration

Respiratory systems tend to get more efficient at high altitudes, with improved air flow in the lungs and more red blood cells. For arthropods that would mean adapting a more efficient respiratory system, with more active pumping of the air and more oxygen carrying molecules in their cells. However it should also be noted that there aren’t many insects at high altitudes, either because the wind would sweep them away of that it’s a little too cold for them. Either way have your world have a thinner atmosphere to force all bugs to adapt.

Also as we’ve seen in many documentaries, insects used to be larger when the earths atmosphere had more oxygen. Thus reducing the amount of oxygen is clearly not the way to go. Although small asthmatic bugs seems like a good comedic premise.

  • $\begingroup$ I like what you say about the great heights, but increasing the oxygen in the atmosphere is completely the opposite of what I want, that would not make arthropods improve their capabilities, it would only make their current characteristics work while conditions are like that. $\endgroup$
    – Drakio-X
    Aug 21, 2021 at 2:26

Lowering O2 levels would require either shrinking (which is what happened) or a more efficient cardiopulmonary system.

Shrinking is easier but it could have gone the other way if the right mutations were waiting to become useful.

I can't think if any pressures that wouldn't be more efficiently solved by getting smaller. So, random mutation at the right time is the most likely, IMO.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .