Were our bodies especially designed for this planets gravitational field? For example, if we were born on the moon,

Question: Were our bodies especially designed for this planets gravitational field? For example, if we were born on the moon, and landed on Earth, would the gravity be equal to that of a place like...I don't know, Mercury? (Would our heads be harder to hold up, etc. )
- Keywords:
  body,
  evolution,
  gravity,
  moon
Asked by Christopher P. Bacon to Heather, Helen, Hugh, Jane, Julian on 11 Nov 2014.
- Julian Onions answered on 11 Nov 2014:
  
  Yes – our bodies are the result of millions of years of evolution such that the we fit the environment of this planet. Our muscles, bones and the size of our bodies are designed for Earth, partly because all those versions of humans and animals that were too big or badly adapted to the Earth tended to die out.
  Its often been suggested that if people went to live on Mars they would adapt somewhat to the gravity, and may have muscles too weak eventually to return to Earth.
  We see this with astronauts on the ISS, who have to exercise for more than two hours a day to stop their muscles and bones degenerating. Even so they are usually too weak to stand up when they land, and have to gradually recover.
- Jane MacArthur answered on 11 Nov 2014:
  
  Rather than thinking of them being ‘specially deliberately designed’, evolution is thought to be ‘survival of the fittest’. Eg if there were two early humans, a million years ago, one had 2 legs and one had one leg, the first would be more likely to survive. Similarly, one that had an ear on each side of his head would be able to tell the direction from which a predator or a warning was coming from, whereas one with two ears next to each other would not be able to tell the direction and be more likely to die.
  
  All kinds of mutations are possible and are seen in the world today. If conditions were different on the Earth then different mutations might have been favoured in preference to the ones that have been, and humans might look very different. It is more the ‘accident’ of mutation/new adaptations and ‘survival’ of favourable adaptations though, rather than any ‘design/selection’ process (which to me implies too much deliberate action or thought).
  
  As you say, a human born on the moon in 1/9th gravity might find it extremely hard to hold their head up on Earth (and potentially even to survive on Earth). However, if humans had evolved separately on the Moon, they would probably look entirely different to us, as gravity would favour different adaptations.
- Hugh Osborn answered on 11 Nov 2014:
  
  Great question! Yes, life on Earth is definitely limited by Earth’s gravity. All animals have to carry around their own body weight so the higher the gravity, the harder large bodies become to lift. That’s partly why land animals on Earth have never been bigger than house-sized dinosaurs.
  
  So if we evolved on a planet with the Moon’s gravity and came to Earth, our muscles and bones would struggle to support us. On a short term, however, humans might be able adapt to life in a high-gravity environment (up to a few times Earth’s gravity), just like we have adapted to living in zero-G environments like the International Space Station. Hope that helps!
- Helen Johnson answered on 13 Nov 2014:
  
  I think it’s all pretty much been covered, but can I just say I really like this question! If we were born on the moon I reckon we would be much larger, heavier creatures – if our muscles and bones stayed the same – or else have less muscle, because we wouldn’t need to try as hard to hold ourselves up against gravity. Apparently internal organs really aren’t affected by differences in gravity, apart from our inner ear.