Assuming that a person can survive on a world that's super-habitable, with it's 1,5 atm atmosphere consisting in 38,4% of oxygen, with increased concentration of (~0,5%) hydrogen and (1,2%) carbon dioxide, and it's surface gravity of 1,24g, how would a human body evolve and adapt over generations to this environment?
We're taking a baselane human, colony and we're supposed to see how would human body change over generations, to adapt to those new conditions and use them for own advantage.
Maybe let's try to predict changes after a century, half a millenia and five millenias.
Everything below is just my guess, if you know the answer, you can stop reading now and answer.
After a century, we might be seeing slight alteration of the hemoglobin, to try and adapt to those high concentrations of oxygen, which would cause the cells to live and multiply much more rapidly, possibly increasing a chance of cancer and a shorter lifespan, but also a lifespan "much more lively" - higher and more efficient metabolism releasing much more energy for our disposal. We'd probably also see more stoutier people, with bone and muscle mass growing, to hold off against the gravity, and with the height decreased, to not waste so much energy pumping blood high up.
After half a millenia, I think we could start observing changes inside the ribcage, with lungs slowly shrinking with generations (there's already plenty of oxygen, no need for lungs that big), to make place for a stronger and bigger heart, that could allow the blood to be pumped higher up the body, possibly allowing the humans to preserve their "default" height and opening up room for further growth.
After 5 millenias, and that's going to be probably the least accurate guess, an average person would have a heart size of their head, making it an easy job to not only be over 2 metres in height, but to also maintain the muscle and bone structure needed to withstand the higher gravity.