Okay, so this is unrelated to every question I've made so far except a select one. I want to see how a race of sapient, flying humanoids that are essentially humans, but with wings and tails.

Here are the Traits of these humanoids:

  1. Flight, but really more of Stunt Flight than Lazy Soaring.
  2. Capable of Running like a Human can.
  3. Lay Eggs.
  4. Thick Tail, as long as the Humanoid is Tall.
  5. As tall as a Human, and weigh as much as a Human when on Earth.

Some Things I hope will Help:

  1. I said WHEN ON EARTH. You can place them anywhere.

  2. Low gravity is known to lead to flight.

  3. This race doesn't have to be advanced, just Sapient (Human Intelligence), Humanoid (Bipedal, Can Run for a Long Time, Two Hands) but with a Thick, 4-6 foot long Tail, and Capable of Flight.

In what Environment would these Humanoids Evolve?

  • $\begingroup$ "How would these Humanoids Evolve?" They would evolve by common descent with modifications under natural selection, sexual selection, and genetic drift, just like any other life form. What other answer would you expect? $\endgroup$
    – AlexP
    Dec 7, 2020 at 19:37
  • $\begingroup$ @AlexP I meant what factors in environment would lead to them being like this? $\endgroup$ Dec 7, 2020 at 20:02
  • $\begingroup$ I recently addressed this basic problem on Meta. We barely understand how humanity evolved and you're asking us how fictional creatures could evolve. How will you judge a best answer? If you can't explain that, the question is opinion-based. It might help if we understood why this matters? Worlds change over evolutionarily long periods of time. The world of a sapient species is very, very different from the world of their fish-out-of-water progenitors. $\endgroup$
    – JBH
    Dec 7, 2020 at 22:01
  • $\begingroup$ Also, how do you know that low gravity is known to lead to flight? We have exactly one data point: Earth. On average, Earth's gravity has never changed significantly (maybe when the hypothetical Theia hit it). So other than scientific speculation... what proof is there that lower gravity would suggests a higher likelihood of flight? $\endgroup$
    – JBH
    Dec 7, 2020 at 22:05

1 Answer 1


Okay, there are four forces to put into consideration: Lift, weight, drag and thrust. The mass of a human is 70 kg, and Earth's gravity is 9.81 N/kg, so an average human would have a weight of 687 N under Earthlike gravity. We will assume that the wings and tail add some extra weight, but that is partially counterbalanced by hollow bones that sacrifice defense for mobility, and air sacs to further reduce density. The tail can be thin, but wide, and act as an airfoil to help with flight. We will put the weight of the humanoid at 75 kg, so their weight is 736 N. Lift will need to be a minimum of 736 N, and we will assume that air density is 1.225 kg/m^3.

Let's put the lift coefficient at .6, and the wings and tail will increase the body surface area. Let's put area at 4 m^2, so minimum flight speed is 22.4 m/s. Now, we need to solve for drag. I know a shortcut to find the frontal area of an object, and that is to divide volume by height. We will assume that density is 1000 kg/m^3, so volume is about .075 m^3, which puts the frontal area at .0221 m^2. We will assume an drag coefficient of .9, due to evolving to reduce drag. Thus, the drag force is equivalent to 6.09 N, on a windless day, and thrust can be just light, occasional flaps to provide enough force to push ahead. For a planet where such beings would evolve, it would probably have a lower gravity and thicker atmosphere than Earth.

Both of these factors are helpful to flying organisms, and a planet with both would definitely have more airborne species than Earth. And on their home planet, they'd be even better at flying.

  • $\begingroup$ Worth noting that to have both lower gravity and a thicker atmosphere, you need a different atmospheric composition, because lower gravity tends to result in planets losing their atmosphere. $\endgroup$
    – jdunlop
    Dec 8, 2020 at 1:03
  • $\begingroup$ Sure, it can be different, but they should still be able to breathe Earth's. And maybe a stronger magnetic field prevents that atmosphere from being lost. $\endgroup$ Dec 8, 2020 at 5:08
  • $\begingroup$ A magnetic field isn't sufficient (nor necessary) to keep an atmosphere from being lost. A stronger magnetic field would certainly reduce the rate of loss, but escape velocity is the larger concern. Venus' magnetic field is a 10th that of Earth's, yet it has a thicker atmosphere; Mercury's is strong, but it has less atmosphere than Mars, which has none. Jean's escape and hydrodynamic escape are equal considerations to stripping via solar wind, so a stronger magnetosphere won't allow a low-G world to retain an atmosphere. $\endgroup$
    – jdunlop
    Dec 8, 2020 at 5:44

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