[MUSIC PLAYING] NARRATOR: This episode
is supported by 23andMe. 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 space farers. Human populations
on other planets may quickly evolve into
things that look nothing like humans as we know them. And it'll start with Mars. [MUSIC PLAYING] We may or may not ever become
an interstellar species. It's likely, however, that
we'll 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, height and 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 Himalayas 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 a 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 add in a useful trait
will be more likely to spread through a population. Those that reduce
function get weeded out. By natural selection also
maintains what traits we have. If a genetic trait
is no longer useful, then random mutations
will gradually destroy it, like sight and
pigmentation for cave 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 enormously 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% that of Earth. This could have
different effects. Low 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'd 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 may be childbirth. A mother's 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 low-G wasting, after
which strength may go down. But 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. And that's why lying
down feels 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 at 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 the 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. Mars's 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 are 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 this 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
are beneficial. An 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. See, 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 of
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 later 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 in some 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 martiansis
may enter the scene-- tall, strong-boned yet slender,
enduring yet disease-prone and cosmetically very different. Perhaps they'll be the
first in a long line of descendent species
that spread their way planet to planet, then star
to star across the reaches of space time. Thanks to 23andMe for
sponsoring this episode. The name 23andMe
comes from the fact that the human DNA is organized
into 23 pairs of chromosomes. 23andMe is a personal
genetic analysis company created to help people
understand their DNA. You'll be able to see which
regions around the world your ancestors come from,
learn how DNA impacts your health, facial features,
hair, sense of taste and smell, and sleep quality. Learning this information starts
with just spitting into a tube. As it happens, I just got
my 23andMe results back. I knew my heritage was
mostly Irish, some English, no doubt some other bits. The results did
pretty much confirm this with some surprises. One weird thing is that I'm not
entirely Homo sapien after all. Actually, none of us are. Anyone with European or
Middle Eastern ancestors has some Neanderthal DNA. People from other
parts of the world have traces of different
Homo genus cousins. I have a bit more
Neanderthal DNA than most. In fact, more than 89% of
other 23andMe participants. I should have guessed. I do have a rather
luxurious head of hair. It was really
interesting peering into my ancestry this way. I don't feel like it defines me. But it does represent a
long, fascinating story of human evolution and history
that ended in me, in us. But it doesn't stop here. Perhaps future Homo
martiansis will be amused by the fraction
of Homo sapien's DNA that they have. Go to 23andMe.com/spacetime to
support the show and learn more about your personal DNA story. As always, thanks so much to
all of patreon supporters. This week, a special huge
thanks to Samuel Dean Jacintho, whose contribution
at the big bang level is being used to fund a top
secret genetic engineering program. The first batch
of Homo martiansis will be shipped to Mars
as soon as that Musk guy finishes the spaceship. And I wanted to give a shout
out to a brand new PBS series, Above the Noise. It's a critical dive into
the science behind the news. You should check it out. Especially check out their great
interview with Adam Savage. He used one of the best
descriptions I've ever heard of what science actually
is and what it isn't. And now, your comment
on last week's episode on the great
American eclipse. Martin Ketling
asks whether a DIY of Arthur Ellington's
confirmation of general relativity
would be possible. Well, the answer is yes. But it ain't easy. Eddington measured
the very slight offset in the positions
of stars around the limb, the edge, of the sun due to the
powers of their light bending in the suns gravitational field. The difference in position is
something like 1.7 arcseconds. So you need a position precision
significantly better than that. The typical blurring
of Earth's atmosphere is one to two arcseconds,
which makes it tough. But with a clever
experiment, it's doable. You need to compare
the positions of stars on either side of the sun
during the eclipse and then several months later
when the sun has moved from that part of the sky. The stars should be a few
arcseconds further apart during the eclipse. You'll also need a
decent astroimaging camera and a relatively
high-end telescope. But it doesn't need to be
a research-grade scope. It's not an easy experiment. But with enough
preparation, it's possible. venkata asks why
the eclipse shadow moves from east to west
rather than west to east as you might expect due to
the rotation of the Earth. In fact, it's the moon's orbit
around the Earth that results in the shadow's movement. The moon orbits the
Earth once a month, which means it moves about
0.5 degrees per hour. That's its own angular
diameter on the sky. And it's also the
sun's angular diameter. So it takes one
hour for the moon to fully eclipse the sun and
another hour to move past it. And that's from one
position on the Earth. So the shadow actually
moves as the moon moves. Some of you objected to my
pronunciation of Oregon. I probably pronounced the O-- Or-ee-gone-- totally wrong. Sorry guys. Until I move to the
States, I've only ever read the name Oregon,
usually right before dying of dysentery.
Here are a few mostly related videos.
https://www.youtube.com/watch?v=ok8N2PkqCDs
https://www.youtube.com/watch?v=f2hbtj5Mh8k
https://www.youtube.com/watch?v=kKmdc2AuXec
It does not cover conscious manipulation of genes, and other technological interventions that are very close to the beings themselves. One might be nanobots that fight pathogens, which might include other nanobots.
In my opinion concious action is eventually needed to prevent Malthusian situations. Both for human genes and culture, but also AIs and simulations. Alas, currently humans are too awful to discus it.
Gahh, he's annoying.