I am currently working on an alien planet which is inhabited by a race that looks "somewhat" humanoid. My question is, just because they have a similar strusture with humans, would they have a similar anatomy? (Respiratory system, digestive sytem, heart, brain etc.)

  • 1
    $\begingroup$ I'd like to say "No" but really it's entirely up to you. You could add the "Science Based" tag and try to narrow down the kind of answers you get, but unfortunately we've never met another alien so it's quite hard to say. Unless you can find a way to limit your question a little bit, it's likely to be closed for being "Primarily Opinion Based." $\endgroup$
    – bendl
    Commented Jul 11, 2018 at 17:55
  • $\begingroup$ Welcome to WorldBuilding John! You might be interested in some of our existing questions about similar topics, such as Would intelligent life evolve any other body plan than humanoid? If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Commented Jul 11, 2018 at 18:12
  • $\begingroup$ In the literature, some do and some don't. I think that makes this question opinion-based. $\endgroup$
    – user535733
    Commented Jul 11, 2018 at 18:33
  • $\begingroup$ You could rephrase this question: "How can I explain that a humanoid alien from a different world has the same basic physiology as humans"? $\endgroup$
    – Willk
    Commented Jul 11, 2018 at 18:43
  • $\begingroup$ What you're talking about is an interpretation of convergent evolution. Most theorists believe that convergent evolution between planets is highly unlikely. If your story doesn't need the detail, I recommend ignoring it. If your story can benefit from the detail, then your task as the writer is to supply a reasonable explanation for convergent evolution that allows the reader to suspend their disbelief. Bear in mind that we SciFi junkies have been happily chomping down convergent evolution withoug complaint for almost a century. $\endgroup$
    – JBH
    Commented Jul 11, 2018 at 19:13

1 Answer 1


This is a tough one. There is such a thing as convergent evolution - two creatures evolving to have similar attributes despite being unrelated. Think, dolphins - which evolved from deer - and sharks. Both evolved in the ocean. So if an alien evolved under similar circumstances, it could happen. First, you would need a vertebrate-type creature somewhere in the tree of life. Then you would need one with ganglia, then it would naturally evolve a cranium from there I think - some kind of casing to protect it. From there, sensory organs like eyes and ears would probably naturally evolve around the ganglia. Then the creature would need a way to breathe outside of water - but there's no reason it has to be in that order. They could already be breathing on land before they evolve ganglia. One thing is for sure - life would definitely have had to evolve in a substrate like water before it transitioned to land. Anyway, humans then evolved from tree climbing rodents that turned into tree-dwelling primates, and so on and so forth. So probably the alien species would evolve under similar circumstances, but their anatomy would probably come up with their own solutions to problems, such as breathing. Perhaps instead of lungs, they could continue to breathe through their skin - of course, that would come with its own challenges. This is all assuming they even need to respirate tho.

Anyway, in sum - similar environmental pressures, different anatomical solutions, will get you there.


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