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I am thinking of evolution of human beings as a species. If we were to stablish a colony on, for example, Mars, how would the lower gravity affect future generations of humans living there? Is there any possibility that the lower gravity caused biological changes that would lead us to separate into two different species? (given the sufficient time)

I'm not asking what would happen if Martians went back to Earth, or how life would be different in a low gravity planet, I'm asking if we could split into two different species after enough time in a planet with lower gravity.

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    $\begingroup$ Possible duplicate of How does gravity affect evolution of life? $\endgroup$
    – Peregrine Rook
    Mar 18, 2018 at 18:53
  • $\begingroup$ Possible duplicate of What would happen if the people on Mars evolve to become incompatible (can’t live on Earth )? $\endgroup$
    – RonJohn
    Mar 18, 2018 at 18:55
  • $\begingroup$ Then this is a speciation question, which all depends on #1 how many colonists go to Mars, and #2 how much effort they put into make the colony as much like Earth as possible (eating the same foods, simulating Earth levels of sunlight, protection against cosmic rays, etc. Not that this is ever going to happen, since Mars is a dead planet, and there's less purpose colonizing it than there is colonizing the Atacama desert. $\endgroup$
    – RonJohn
    Mar 18, 2018 at 19:21
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    $\begingroup$ There are three questions that need answering. #1 How does lower gravity affect the chemistry of DNA replication? #2 How does it affect reproduction and growth of the fetus? #3 Since evolution is all about genes that get changed and survive, what genetic changes would be beneficial on a low-gravity Earth? #4 How many of those changes would have to accumulate to turn the Martians into an incompatible species? (I don't know...) $\endgroup$
    – RonJohn
    Mar 18, 2018 at 19:53
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    $\begingroup$ You need to be more specific about what you define as "different species". Please refer to this Wikipedia page on the subject of the species problem to see why defining this difference is non-trivial. Also note that some extremists would even define different skin color as a different species in humans. So this is a very difficult issue. $\endgroup$
    – StephenG - Help Ukraine
    Mar 18, 2018 at 21:58

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Humans would become taller, the decreased gravity would not compress their spines as it does on earth.

Assuming the planet has the same atmospheric composition as Earth, the pressure would likely be decreased, making harder to breathe.

The gravity itself would not cause evolution, however, mutations would occur in genes, e.g. more surface area of lungs. Natural selection could allow different lungs to become predominant.

Lungs with larger surface areas are quite likely to evolve, allowing humans to intake oxygen to the same extent as on earth, another evolution could likely be is increased numbers of red blood cells. This is probably the type of genotypical evolution you're looking for.

Purely based on the information given, not much can be determined. It would be beneficial if you went supplied more info regarding the planets atmosphere and the type of civilization that was formed.

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  • $\begingroup$ Gravity and atmospheric pressure are not directly related. On the ISS, the air pressure is the same as on Earth despite the micro gravity environment. $\endgroup$
    – 299 Neandertal Variants
    Apr 19, 2019 at 23:58
  • $\begingroup$ @299NeandertalVariants isn't that because the ISS is an artificially pressurized environment? I think all Lutro is saying is that if you took Earth's entire atmosphere and chucked it over to Mars, for instance, the surface pressure would be decreased. $\endgroup$
    – ben
    Apr 20, 2019 at 17:39
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STATURE

The heart would atrophy or not develop properly under low gravity so tall stature would be an advantage. This is because the heart has to pump hard to circulate more blood around a longer series of veins and arteries, helping to keep it strong.

SKELETON

The skeleton would be significantly weaker due to the lack of stimuli caused by the low gravity. Individuals with naturally high bone density and robust skeletons would be less likely to suffer injuries.

Joints would become smaller, especially the ankle, knee, and hip, because there would be less need to support heavy weight.

The pelvis would be a problem. It is put under a great deal of stress during child birth so pelvises that are wider and more robust would be selected for. This could result in more sexually dimorphic humans. Babies heads might also shrink to make birth easier (note that brain size has nothing to do with intelligence in modern humans).

SKELETAL MUSCLES

The majority of skeletal muscles would be severely weakened because of the lack of strain in everyday moment. This would result in a skinny, frail appearance. People that are able to easily gain muscles would be at lower risk of injury and would generally be in better health all around. (A diet high in protein might help with this problem as well)

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In the almost entirely artificial conditions imposed by the necessary life support systems for humans to survive on Mars without extensive teraforming the selective pressures would be of an almost entirely sociological nature. Being taller tends to be attractive however if someone is too tall to stand up straight in the habitat being hunched over all the time may make them less attractive, it's hard to predict these things.

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For evolution to occur some trate lacking in humanity at the moment would have to be killing inhabitants of mars. Seeing as we have determined that lowered gravity wreaks all kind of havoc on various human systems, after enough time, and enough deaths of the beings with weaker circulatory system and other related processes, the creatures on mars would have become significantly different from earthlings.

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