it's fun to think about humanity settling the galaxy outposts of familiar Homo sapiens spread among the stars but there may be nothing at all familiar about these distant future spacefarers human populations on other planets may quickly evolve into things that look nothing like humans as we know them and it will start with Mars we may or may not ever become an inter solar species it's likely however that will at least take a shot at becoming interplanetary unless we manage to self-destruct in the next little while humans will be around for a long time at some point perhaps soon perhaps in the far future we will try to colonize Mars that colony will face monumental challenges to its survival but if those challenges are met we may reach a time when many generations of humans have lived and died on the red planet those people will be very different to us how will they change will Martian humans or human Martians actually evolve will they eventually become a species distinct from Homo sapiens humans have never stopped evolving whenever a human population is isolated characteristic genotypes develop sets of genes defining skin pigmentation heightened build immunities even facial structure define the group the more isolated the population and the more extreme the environment the quicker this adaptation happens for example humans of Tibet developed genetically coded larger lung capacities faster breathing and higher hemoglobin production these traits developed soon after they moved from neighboring China to the high-altitude in the layers around 3,000 years ago Mars is quite a bit more isolated and extreme than the Himalayas how might we adapt there first let's think about this evolution thing it's important to remember that evolution doesn't just morph or species into the optimal form for its environment evolution is blind it's an emergent effect of mutation and natural selection mutations occur at a steady rate due to DNA copying errors and through chemical and radiation damage mutations that improve the function of a gene or a useful trait will be more likely to spread through a population those that reduce function get weeded out but natural selection also maintains what traits we have if a genetic trait is no longer useful then random mutations will gradually destroy it like site and pigmentation for a fish or tails and appendices for humans use it or lose it so what traits are likely to be enhanced or developed on Mars and which are likely to decay Mars is very different to earth but the differences that we adapt to will depend enormous ly on to what degree our technology addresses those differences let's start with the one that's hardest to fix low gravity Mars has a surface gravity 38 extent that of Earth this could have different effects lower gravity requires less bone and muscle strength to function normally strength may not be as strongly selected for as it is on earth perhaps over generations Martian humans would become intrinsically weaker but there's another effect to consider we know that the zero-g experienced in orbital or interplanetary space leads to decreased bone density and muscle mass in astronauts we see this in the first Martian colonists also over the years of a human life on Mars this could be a huge health issue so genetic adaptations that counter the risks may be very strongly selected for perhaps the initial selection will be for people with especially strong bones and high muscle mass people who can afford a little strength loss and still be healthy this is an especially compelling scenario when you consider that bone strength makes us more resistant to injury and a really important issue maybe childbirth a mothers pelvis needs to be able to withstand significant pressure that has nothing to do with the gravitational field extremely brittle bones may greatly increase both infant and maternal mortality that would be a huge selection pressure in any population without very consistent access to safe c-sections so will Martians become stockier or skinnier over time people are likely to develop a resistance to Logie wasting after which strength may go down until then we may expect strong selection for very robust individuals that same low gravity may also affect height it takes a lot of effort for our hearts to pump blood from our feet to our heads that's why I lying-down feel so good in low G the heart doesn't have to work so hard so it's less of a disadvantage to be very tall in fact it may be a real advantage after long zero-g missions astronauts lose significant muscle mass in their hearts a life on low G Mars could be a serious risk for early cardiac problems having a little extra height would keep the heart more active and healthy perhaps Martian humans will end up much taller than their earthling forebears ok gravity isn't the only difference between Mars and Earth what about this pesky lack of a decent atmosphere well that's not something we can easily evolve to deal with we'll always need some degree of technology both for a survivable air pressure and oxygen level and to protect us from space radiation but if these technologies aren't perfect or consistent we may see some adaptation this is especially true if we eventually terraform Mars because probably whatever atmosphere we build won't be as thick as Earth's there are many potential adaptations to low oxygen environments different mutations have arisen in Tibet versus the Chilean Andes versus Ethiopian highlands in all cases these humans are able to sustain more activity with less oxygen so we might expect future Martians to be incredible endurance athletes Martha thin atmosphere and lack of an ozone layer also means the surface is bombarded with hard UV radiation it's deadly and requires artificial protection but again assuming this isn't completely mitigated with technology or terraforming we may see rapid evolution of darker skin pigmentation on the other hand the less intense sunlight at Mars compared to earth means it'll be harder to produce vitamin D this factor is believed to result in the paler complexions found at high latitudes on earth so will Martians be dark or pale it depends which of these effects we better handle with technology perhaps we'll have lily-white Martians in underground cities and much darker Martians on the surface even more dangerous than the UV our high-energy cosmic rays and solar particles these bombard the surface due to the sparse atmosphere and the absence of a protective magnetic field unless humans stay underground or in well protected shelters pretty much all of the time they will see an increase in DNA damage from these that's going to mean increased mutation rates the most obvious thing that will result in is a lot more cancer perhaps Martians will evolve defenses we have natural DNA repair and cancer fighting mechanisms these may become enhanced most mutations are bad but sometimes they're beneficial and increased mutation rate may mean evolution proceeds faster on Mars than it does on earth the final really important issue is that Mars is sterile as far as we know it has no microbes whatsoever the human immune system is constantly being exercised by exposure to Earth's biosphere which contains countless bacteria and viruses this results in a massive selection pressure to keep our immune system up to date in an environment absent those pathogens the genes that code for immunity will gradually mutate into uselessness use-it-or-lose-it future Martians will be highly susceptible to earthly diseases and this effect may actually speed up their divergence from the humans of Earth so even if Martian colonies are extremely well resourced and have technologies to mitigate a lot of the challenges of Mars there will be an inevitable drift between the Martian and earth populations when populations at the same animal species are isolated from each other they drift apart genetically at first it's just cosmetic but eventually there's a drift in function and ultimately in their capacity to breed together at that point we consider the populations to be separate species speciation has occurred this effect will be amplified on Mars because the intermixing with earth populations will be minimal earth will quickly become a deadly place for Martians they'll find Earth's nearly three times higher gravity incredibly uncomfortable and any stray viral or bacterial infection could kill them this latter will also make them very wary about allowing earthling visitors to Mars the inevitable divergence between Earth and Mars will eventually lead to speciation but that's a very slow process Homo sapiens have been around for 200,000 years into pretty wildly different environments this has led to an incredible variety of physical appearance yet we're all still Homo sapiens our cousins Homo neanderthalensis Homo erectus Homo floresiensis and others evolved speciated from a common ancestor and they shared earth with us for millennia they've since gone extinct leaving us as the only species of the genus Homo but perhaps a new species of human is ahead give Martian colonies some tens of thousands of years and some rapid evolution and homo mocchi Ensis may enter the scene tall strong bones yet slender enduring yet disease pruned and cosmetically very different perhaps they'll be the first in a long line of Senden species that spread their way planet to planet then start to start