How long have we been human? (featuring Dr. Scott Solomon)

Daniel and Kelly chat with Dr. Scott Solomon about ancient hominid species, and how we learn about them.

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Episode Transcript

Speaker 1 (00:07):
If I could go back in time to witness any
historical moment, going back in time to observe ancient human
species would be near the top of my list. How
do they build their fires? How do they treat their children?
How do they solve problems? And how do they communicate
with each other? Do they dance?

Speaker 2 (00:25):
Do they sing?

Speaker 1 (00:26):
Do siblings argue with each other? But unfortunately Daniel hasn't
figured out time machines yet, so I'm kind of stuck
for now. In the absence of time machines. The best
we can do right now is search for fossils and
try to learn what we can from things like the
shape of these fossils in the DNA that's sometimes left behind.

(00:47):
And lucky for us, we have doctor Scott Solomon back
on the show to tell us about what we've learned
so far about ancient hominids, and that's almost as good
as a time machine. Welcome to Daniel and Kelly Extraordinary Universe.

Speaker 3 (01:14):
Hi.

Speaker 4 (01:15):
I'm Daniel. I'm a particle physicist, but I don't remember
the moment that I became human.

Speaker 1 (01:19):
Hello. I am Kelly Weiner Smith. I study parasites and space,
and thank goodness, we don't remember the moment we became
human that I'm guessing that that is a biologically, you know,
a private moment between your parents.

Speaker 4 (01:32):
Probably, Oh, I don't know. I don't feel like I
was human at birth. You know, I don't feel like
I was me at birth. I was just a screaming blob.
I think it's fascinating that what emerges from that is
a sense of self, a sense of who you are,
but you can't really trace it all the way back,
like its origins itself are sort of lost to your

(01:53):
own memory. I feel like that's similar to how like,
as a species, we have some historical memory and some writing,
but our own own history is lost. But we were
there right like in principle, we saw all this stuff happen,
and if we just like kept better records or told
each other about it, we would know the answers to
all these questions.

Speaker 2 (02:11):
Yeah.

Speaker 1 (02:12):
Yeah, And I think this is an interesting thread that
sort of wove itself throughout our conversation with Scott Solomon,
where I think your definition of human encompasses a lot
of the things that modern humans do today, Whereas I
think a lot of us would be comfortable thinking of
humans as you know, like not too many steps beyond
when our you know, most common ancestor with chimpanzees came

(02:34):
down from the trees or something like that.

Speaker 4 (02:36):
No, I'd love to hold like a one million year
old stone tool and think about, like, who was the
person who made this, because there was a person and
they made it, and they like had lives and loves
and argued with their siblings and had betrayals and all
sorts of stuff and maybe even hummed music to themselves.
Who knows, but you know, what was it like to

(02:57):
be that person. It feels like a real connection with
our past. Yeah, But because we were sloppy in our citations,
we don't know who invented the stone tool and who
came up with these early ideas, and who first invented
music and stuff, and so unfortunately we can't give those
people credit.

Speaker 1 (03:12):
Shame on the early humans they why didn't they develop
copyright and patent law much earlier? Clearly that's the peak
of humanity.

Speaker 4 (03:21):
Lab notebooks, man, it's all about lab notebooks. They had
taken better notes, we would know. But don't you find
it frustrating? Like some of the mysteries in the universe,
like what's inside a black hole? Like nobody knows. But
these questions like where did we come from? How did
this all work? People were there literally m and so
somebody knew we just forgot. Yeah, that's like what what

(03:41):
are we even doing?

Speaker 1 (03:42):
That is frustrated, And you know, with black holes, I
feel like that's the kind of thing where through equations
and good equipment, maybe one day we'll get answers to
some of these, but things like did our hominid ancestors
argue with their siblings? Like gosh, that would be really
hard to get an answer for. You know, some of
these like social things, we're never gonna know, and that

(04:03):
that is a little devastating.

Speaker 4 (04:04):
Well, the other thing that's frustrating about this whole field
is that there are probably answers waiting for us buried
in the earth, Like what fraction of human fossils have
we found that exist? You know, some tiny, tiny fraction
And if you just knew where to go, like, oh,
go dig here, go dig there, the answers are waiting
for you. That's incredibly frustrating. In the same way, like

(04:26):
the answers are there, if we could just get them
out from the earth. If somebody told me that, like
the answer to what's inside a black hole? I buried
it in a treasure chest somewhere on the planet, like
I even go figure it out, Like I would be
on the hunt, you know.

Speaker 1 (04:38):
Right the rest of your life, you would be spending
trying to find that.

Speaker 4 (04:42):
Yeah, exactly, And so that it's so frustrating. These questions
are so important and so meaningful, and the evidence is
right there in front of us, maybe, but we just
can't get to it. Anyway, It's fascinating and wonderful to
think about.

Speaker 1 (04:54):
Well, and I think it's fascinating and wonderful to be
the kind of scientists who are searching for those things,
because if once in a while you do find some
amazing piece of information that suggests, you know, this is
probably when we started using fire or something like that.
And so we are bringing Scott Solomon back on the show.
He did an amazing episode in the past about like
current and continuing human evolution, and now we're bringing him

(05:17):
here to look to the past. And he's been to
a lot of the archaeological sites where we look at
ancient humans. He've researched ancient humans a lot for his
upcoming book where he looks forward to what evolution might
look like on Mars. And we had an absolutely fantastic
conversation with Scott today.

Speaker 4 (05:32):
Yes we did, Thank you, Scott.

Speaker 1 (05:34):
And Scott suggested to me that we ask our extraordinaries
the philosophical question that Daniel and I have essentially just
been discussing, which is when did we become human? So
let's see what the extraordinaries had to say about that.

Speaker 5 (05:48):
I think we became human when we started talking technically
with the emergence of Homo sapiens, but more likely a
couple hundred thousand years later, with the development of culture, symbolism.

Speaker 4 (05:58):
Art, and language eighty two one hundred thousand years ago,
roughly when we developed chins.

Speaker 5 (06:04):
Evolution continually progresses. There is no specific enduring definition. By
way of example, a person with a substantial set of
mutations could be defined as a different species at this
particular moment. We cannot truly define when a proto human
became a human and when we change in a way
that a particular specimen is no longer a human being

(06:24):
by the standard of today.

Speaker 2 (06:26):
When we got opposable thumbs. I think we became human
when we came down out of the trees began to
weave leaves for clothing, learned to use fire to cook
our foods, lived in communities, and buried our dead chins
and thumbs.

Speaker 4 (06:39):
Amazing.

Speaker 1 (06:39):
Yes, we got some fantastic answers, and let's go ahead
and see what our expert, Scott Solomon says, and so.
Doctor Scott Solomon is a teaching professor in the Department
of Biophysics at Rice University. He's the author of Future
Humans Inside the Science of Our Continuing Evolution, and his
upcoming book, Becoming Martian, How Living in Space Will Change

(07:00):
Our Bodies and Minds, is coming out through MIT Press
in early twenty twenty six. He hosts the podcast Wild
World with Scott Solomon, Taught What Darwin Didn't Know, the
Modern Science of Evolution for the Great Courses, and you
can check out his streaming series Becoming Martian on Curiosity Stream.
Welcome to the show, Scott.

Speaker 3 (07:21):
Thank you. I'm excited to be back.

Speaker 4 (07:23):
Thanks for joining us to talk about humanity's do it.

Speaker 1 (07:26):
Yes, we're so glad you're back. We had so many
good comments from the last episode that you were on
talking about evolution. I think our community doesn't get enough
evolution and they're excited to hear about it. So let's
talk about Homo species. So did a lot of ancient
humans exist previously? And like, how do we know about
how many of them there were? Like do we think
there were a lot of them?

Speaker 3 (07:47):
Yeah, that's a really good question. So, you know, I
guess what we're talking about is, you know, species that
existed once upon a time that are not our species,
Homo sapiens, but that are also you know, close relatives,
maybe not in a direct line of descent to us necessarily.
That's kind of an interesting thing to talk about. But

(08:08):
we know, for example, that we shared a common ancestor
with chimpanzees. Chimpanzees are among all the species that are
still alive today, they are our closest living relatives, and
we know that because mostly of genetic data. So we
can look at the DNA of chimpanzees and all of
the other apes and primates and everything else that's alive,

(08:29):
compare it with our own DNA, and they're actually more
closely related to us than they are even to other
apes like gorillas, which that part alone kind of always
blows my mind. I think it's incredible, Right, you think
about chimps and gorillas as being kind of like similar
to each other, but chimps are closer to us than
to any other living ape other than us.

Speaker 4 (08:49):
And that's a measure where we just are looking at
our DNA and looking at their DNA and calculating some
sort of genetic distance.

Speaker 3 (08:54):
Is that right, that's part of it. It's actually even
more complex than that. It's kind of cool because you know,
you can just look at, like what percent similarity do
we have? And that's one measure of it.

Speaker 4 (09:04):
Though that measure is weird because we also have like
fifty percent DNA in common with bananas.

Speaker 3 (09:08):
Right exactly, that's right. Well, we do share a common
ancestor with bananas, but you have to go back pretty far.
So yeah, I mean that's telling us about common ancestry, right,
it's telling us about it's like you have some percent
of your DNA in common with your cousin and even
less in common with your like you know, fourth cousin
twice removed or whatever it is. Right, So yeah, if

(09:29):
you go back far enough, you can find DNA that
we have in common even with like bacteria, there's not much,
but there's a tiny bit. So the more that we
have in common the more closely related we are in general,
but even more specifically, it gets down to like, yeah,
but what DNA, what's the DNA doing? And that's when
it gets really interesting because then we can actually trace
the history of specific genes and see the way that

(09:52):
those genes have changed over time, and that allows us
to put together kind of a family tree of similarities
and track exactly how those parts of our genome have
changed over time. So we now know that if it
if you went back in time about six to seven
million years ago, you would find the common ancestor that

(10:12):
we shared with chimpanzees, right.

Speaker 4 (10:15):
Six or seven million.

Speaker 3 (10:16):
Nice, six or seven million. So you know, like, you know,
I have friends who are historians, and we always joke
about like to me, that's like yesterday, right, like six
to seven million years that's not so long ago. For
an evolutionary biologist or geologists also, you know, they would
kind of probably be on the same page with that, like, oh, yeah,
it's yesterday. And you know, in the history, you know,

(10:37):
if you're used to time scales on the order of
hundreds or thousands of years, that's that's a long time ago,
and that's and that's fair.

Speaker 4 (10:44):
Well, my experiments take ten of the minus twenty three seconds,
so six million years. It feels like a long time.

Speaker 3 (10:51):
But not in the history of the universe, right, I
mean that's like that's like a blink of an eye.

Speaker 4 (10:54):
Yeah. Absolutely. So you're saying that we have a common
ancestor with chimps and we know that because as we've
looked at the DNA and we can project back based
on the rate of change and the specific genes that
have changed. Have we found a fossil that confirms that
or is this just based on DNA?

Speaker 3 (11:11):
Right? That's great, great question. So, yeah, so we do
know a lot about the history of the lineage. Like
if you think about that split between so there was
a common ancestor of humans and chimpanzees, and then there
was some kind of a split that took place, and
there was one lineage that eventually led to chimpanzees and
another lineage that eventually led to us. And we can
talk all about what do we know about that? But

(11:33):
your question is like, do we have fossils to help
to fill in the picture of what was happening at
the time of the common ancestor and maybe right afterwards, right,
to help complement what we know from genetics, and the
answer is sort of, we do have fossils that go
back to around that time. It turns out that that

(11:53):
period of time in the part of the world where
this was happening, which was like tropical Africa, doesn't, unfortunately,
have a ton of great fossils preserved from exactly that time.
So that's one of those things where there are some
kind of missing little gaps in there. But we've filled
in more and more and more, and so we are
starting to get a really much more complete picture of

(12:17):
not only what was happening around that time, but particularly
of all the things that happened subsequently, Like if you
track the lineage that eventually led to us, turns out
it's way more complicated than people used to think. Right, So,
I mean, you can go back to Darwin's time, right.
Darwin he obviously, you know, gave us the first notion

(12:39):
that we have this evolutionary history, right, and he speculated
that we must be closely related to the great apes,
the chimpanzees, gorillas, orangutans, And that was based just on
like similar anatomy, like if you look at the skeleton
of a chimp and a gorilla and a human and

(12:59):
a museum or something like that. Like, you know, there's
a lot of similarities, there's some pretty clear differences too,
but he speculated that they must be our closest living relatives.
And then he also speculated that there must be some
fossil species that once existed that kind of span that
gap between us and the common ancestor that we shared

(13:20):
with those apes. And he even predicted that that common
ancestor probably lived somewhere in Africa, mainly because that's where
the majority of apes great apes, that's chimpanzees, gorillas, or rangutans.
So there's a rangutans in Asia, but gorillas and chimps
are only in Africa, so that kind of makes you think, Okay,
Africa might be where most of this history took place.

(13:42):
But at the time, none of those fossils were known,
so that was really just kind of like a kind
of a wild guess and it took a while, but
he turned out to be right.

Speaker 1 (13:54):
I'd like to talk about how how fossils are formed,
but right now, okay, so I'm thinking of a V
in my head, and the bottom of the v has
our common ancestor, one side has chimpanzees and one side
has Homo sapiens, which is us. And we've talked about
how there are other Homo species. Also, what's the right
way to think about where those lines belong on this
V that I have in my head.

Speaker 3 (14:15):
Yeah, so if you think about that V, you're right,
like the point where the two lines come together, that
was the common ancestor that we shared with chimpanzees. Something
happened and there was a split and then the lineage
that eventually led to Homo sapiens. This is where, like
I think a lot of people have in their mind
that like image of like a hunched over ape that
like then there's like slightly standing up a little taller,

(14:38):
and then a little taller and eventually like leads to us.

Speaker 1 (14:41):
And then like on the shirts, so it's true.

Speaker 3 (14:43):
Yeah exactly, or the bumper stickers or the memes, and
then like often you know, like the next step is
like you know, hunched over a computer or some or
you know, some insert joke here right like about the
downfall of humanity however you however you perceive it. But
that idea is like, Okay, we the common ancestor that
we share with chimpanzees, we think actually looked. It wasn't

(15:07):
a chimp, but we think it would have looked more
chimp like than human like. That's I think that's a
fair statement to make, Like, you know, getting back to
the question about do we have fossils, we have fossils
from very close to that time that do look much
more chimp like than human like. And what I mean
by that is if you look at the structure of
their bodies. You know, one of the big differences between

(15:28):
chimps and us is chimpanzees they don't walk on two feet.
They actually can walk on two feet. Technically, if you
give chimpanzees two very good pieces of food, like two
bananas or something like that, they will hold one in
one hand, one in the other hand, and then if
you want to get away from the other chimps, you
gotta move and you got to walk up right on
two So they'll do it. But they look super goofy.

(15:51):
And the reason is actually interesting. It's because they can't
balance on one foot. So like, you know, if you're sober,
you might be able to balance on one foot pretty effectively. Right.
That's because our hips and our leg bones and our
spine and and our foot. You know, all of that
is structured in such a way that enables us to
walk in a way that like, for a brief moment,

(16:14):
you are kind of balancing on just one foot while
the other foot is moving forward. And for a chimp,
they have to lean all the way to one side
in order to not fall over when they do that,
so they look really goofy because they're kind of bodies
move and left and right to not fall over. It's
not a very effective way of getting around. And so
you know, most of the time what they do is

(16:35):
that what's called knuckle walking. They walk on all fours,
but rather than like putting their hands palm down on
the ground, they put their knuckles down in a way
that looks super uncomfortable to me, like I would never
want to walk around, Like I don't think any toddlers
are crawling around with knuckle walking that I've seen, But
you know, it's it's an effective way for chimps and

(16:57):
gorillas to get around, all right.

Speaker 4 (16:59):
I have lots of questions about chimps and going bananas
and knuckle walking, but I want to hear the answer
to Kelly's question, which is about where those splits happen.
So after the split between the chimps and the proto humans,
are there lots more splits? How do we think about that?

Speaker 3 (17:13):
Yeah, so basically after the split with you know, the
chimp lineage. So those very first species that are on
the on our side, on the human side of that split,
they would have been walking on their knuckles just the
same way that chimpanzees and gorillas do. They weren't really
able to walk upright yet. But that starts to happen
in the fossil record, so you start to see species

(17:35):
that are around five to six million years old that
have some of the anatomical features that we use for
walking upright in their in their pelvis, their hips, and
their spine, in their their legs right. And there's a
lot of things that you don't necessarily think about that
are associated with walking upright, even like where your your
neck the bones in your neck attached to your skull.

(17:58):
For us, it's like the bottom of the skull, but
if you look at like a dog or another four
legged animal, it's behind the skull. So that has to change.
There's a lot of anatomical changes that take place to
be able to walk upright. And what's really cool in
the fossil record is we start to see some of
those individual components popping up in these species that are

(18:19):
from around that you know, five to six million year
old range. But then you get more splits, right, So
what's really I think one of the most fascinating aspects
of what we now know about human evolution is it
wasn't a straight line. You don't have this kind of like,
you know, one species that was hunched over leads to
one that was a little more upright, to another is

(18:40):
a little more upright. They kept having more and more
events where there was like one species that split into
two more of those v's, and so what we actually
see is a whole bunch of different species that are
on the human side of the split, but are not
necessarily species that ultimately left any descendants. They don't necessarily

(19:03):
lead directly to us, but they were more closely related
to us than they were to chimpanzees.

Speaker 4 (19:09):
And when we talk about these splits, it's a nice
sort of diagram to have in your head. There's a
solid line, it splits is another solid line, But in reality,
on the ground, you're talking about populations. Those populations are
drifting apart, and so that speciation event takes a little
bit of time. Right, You have like populations which starve
to differ and then diverge, and then at some point
they can't make babies together anymore, and that's when you

(19:30):
say they split. Right, it's a bit fuzzier than the
cartoon lines were drawing in our minds right.

Speaker 3 (19:35):
Now, That's exactly right. It is a process, and we
can only sort of see it as a process that
played out as one lineage that led to two only
after a lot of time has passed. And actually we
know that sometimes you can start to have a split,
but then they might come back together and sort of
like reform. So speciation started to happen, but doesn't actually
go all the way through to completion.

Speaker 4 (19:56):
They argued about bananas. Then they got together and decided
to share the bananas.

Speaker 3 (20:00):
That's right. There seems to have been a lot of
sharing of bananas in the history of our distant relatives.

Speaker 1 (20:08):
Bananas are showing up in the show more than I
would have guessed human evolution.

Speaker 4 (20:12):
Of course we're going to go bananas.

Speaker 1 (20:13):
H love it.

Speaker 4 (20:15):
So I love this conversation because we keep coming up
with more and more questions to ask, But I think
that finally gives us a chance to unwind back to
our original first question, which was, were there are lots
of other Homo species previously? How many do we need
to think about as we attracting the development of the
population that would eventually birth us.

Speaker 3 (20:32):
Yeah, so we now think that there were something like
twenty species, maybe more twenty that existed between the common
ancestor that we shared with chimpanzees and our species Homo sapiens.
Now the exact number is something that the scientists that
study human evolution like to argue about a lot. That's

(20:52):
a very kind of contentious. So exactly where to draw
those lines between species gets complicated, and partially that has
to do with what you were saying annual about, Like
the process of speciation isn't always clean. It can be
a messy process, and so sometimes it's like, well, is
that really a different species? Maybe that was like something
that started to become different but maybe didn't proceed all

(21:14):
the way to what we would normally consider to be
a new species. That could explain part of it, and
the other part of it is like any species you
look at, you know, there's always variation, Like these guys
over there look a little different. These ones over here
have an interesting, weird behavior that's different any species right
that you look at. So that always makes it a
little messier when you try to say, like where do

(21:35):
we draw the boundaries around the edge of what is
a species?

Speaker 4 (21:40):
And just to clarify, when you say twenty, do you
mean there's like twenty steps along that line between the
split between chimps and us or do you mean there
are twenty sort of parallel tracks there where different kinds
of Homo species split off.

Speaker 3 (21:53):
Yeah, exactly, it's it's the latter, So it's not it's
not the case that there was a step wise sequence
of A led to B, B, led to C, C
led to D and kind of them all up and
there's twenty. It's more of picturing like a bush, right,
So you've got like one stem and you can trace
that that stem branch is off and you get two
more leaves over there. But then on another branch just

(22:14):
over here, there's you know, there's three stems and they
each have three leaves. So some of these species we're
living actually at the same time, and that gets to
be really intriguing to think about.

Speaker 4 (22:25):
The banana politics were bananas.

Speaker 1 (22:29):
So you said we have maybe twenty species, which I'm
guessing that number must have arisen from a bunch of
fossils that we found. Do you think we'll be arguing
over these same twenty forever or do you think there's
a lot of additional Homo fossils out there that we
haven't found yet, and maybe we'll end up saying there's
like a hundred Homo species.

Speaker 3 (22:48):
Yeah, it's a good question. I mean, I think two
things have been happening in the last few decades, both
of which are super exciting. One is that, like we
keep finding new species of you know, I'm gonna say hominis.
Hominid is the term that we us to describe anything
on our side of the split from chimpanzees, right, So
they're not all in the genus Homo. We get to
the genus Homo at some point in that history, but

(23:10):
that's a relatively recent development. There are other types of
hominids that were in different genera, Like Astralopithecus is another one,
So folks might be familiar with Lucy. That was a
species known as Astralopithecus aphorensis, and that is another example
of a hominid, so more on our it's definitely on

(23:31):
our side of that split, but not in the genus Homo.
So of all of those, if you add them all up,
then you can get something like twenty. And so, like
I said, there's you know, new discoveries that keep happening
of new species, some of which are in the genus Homo,
some of which are in some of these other hominid genera.

(23:52):
So that keeps happening, and that's of course super exciting
because these are you know, helping fill in the full story.
But the other thing that keeps happening is we keep
finding more and more examples of things that we already
knew about. And one of the things that that has
been doing is helping us to recognize that sometimes these
two things that we thought were different, if you find
something kind of intermediate in between them, you start to

(24:14):
sort of get a fuller picture and recognize maybe this
is actually all one thing, and maybe we need to
you know, not be always splitting everything up, but maybe
sort of you know, we talk about lumpers and splitters
in the science of taxonomy, and people tend to you know,
be more along the lines of kind of Oh, every
difference I see, I'm going to call a new species

(24:35):
those or we call those splitters, and the lumpers are
those that say, well, there's variation within a species. We
can lump all these together into one and it's always
a back and forth and their reality is often somewhere
in between. But yeah, both of those things are happening
right now, and that, like I said, it's super exciting,
but it also means it's hard to predict where we're
going to end up in terms of like how many

(24:55):
species might there end up being. Yeah, I don't know.

Speaker 1 (24:59):
You're doing such a good job of explaining this stuff, Scott.
I love hearing you talk about humans. All Right, we're
gonna take a break and when we come back, we're
going to hear more about how we go ahead and
study hominids. And we're back. Scott was telling us that

(25:29):
there's maybe twenty hominids, but who knows where that number
is going to be in the next decades, So let's
go ahead and talk about how we study these. So,
first of all, you know, you mentioned that a lot
of these species are found in Africa, but that there's
not a lot of fossils like what kind of conditions
do you need to get a fossil in the first place.

Speaker 3 (25:48):
Yeah, I mean when you think about what has to
happen for a fossil to be not only formed but
also like found, it's kind of amazing that we have any.
I mean, first of all, like when something dies, right,
a lot of times what happens is it gets eaten,
It gets chewed up, it gets you know, broken down,
destroyed in some way, either immediately upon death. I mean

(26:09):
if something gets eaten, right, you know, if you go
to East Africa today and go on a safari and
you see the big animals, there's big predators and you know,
scavengers that live out there, it's amazing that any bones
have made it at all up until today. So first
of all, when that individual died, it had to not
have its bones destroyed. But then later something had to

(26:34):
preserve them. So one of the places that I've been
very fortunate to spend some time is a place in
Tanzania called Olduvai Gorge. And this is a very famous
site in the history of like our study of human
evolution because a lot of hominid fossils have been found
there and I co teach a field course there with

(26:56):
my colleague here at Rice University, Manuel Domingas Rodrigo, and
he oversees excavations of fossils at Olduvai Gorge. So we
take students there and you know, it's incredible because you
walk around and in this one particular gorge, it's like
a canyon, right, there's literally fossils just strewn about on

(27:17):
the ground. And so it's a perfect example of like
how if you get the ideal conditions, fossils can actually
be common. This is one of the few places in
the world where the conditions were really ideal. And what
I mean by that is, first of all, it was
a place where a lot of animals and hominids, it
turns out, gathered together. And the reason is that between

(27:40):
you know, about one point eight million years ago and
a million or so years ago, this area was a
it was a lake. It was a shallow lake, and
so of course like a water hole, we all know
that's a good place to go to find wildlife, and
you know, hominids would have gone there for water as well,
and maybe also for hunting. It turns out, so there's
a lot of speed there and then when those individuals died.

(28:03):
It turns out that the second thing that is ideal
about it is that there are these volcanoes nearby, and
these volcanoes will spew out ash periodically when they erupt,
and that ash can bury all of the things in
the area, including the bodies of anything that had recently died,

(28:24):
and that then can basically preserve them. And basically what
happens is they go through a process in which all
of the kind of organic all the carbon based you know,
chemicals in our body get gradually converted into minerals basically
into rock, right, I mean, that's what a fossil is.
It's a rock that has the same you know, shape

(28:46):
as bone or other structures. And so you had the
perfect conditions for preserving all of this there. And then
the third thing, which is really remarkable is that now
you have today are a river or running through that area,
and of course that caused erosion, and then the erosion
means that the layers that have the fossils are actually

(29:07):
exposed at the surface. Wow, So all of those things
kind of all have to take place in order for
a fossil to not only be formed but also to
be accessible.

Speaker 4 (29:17):
Why can't we develop some sort of technology that looks
into the ground to see if there's a fossil there.

Speaker 3 (29:22):
Yeah, I know, I was telling a semi colleague, Manuel
Domingas RODRIGUOI every time i'm in the field with him,
I'm just so amazed by how patient he and his
team are, because they're showing us all of the ways
that they do these excavations. They're so meticulous and careful,
documenting every millimeter literally, and then they're slowly chipping away

(29:45):
at the edge of this canyon, and we're looking at
the canyon. I'm going like, Manuel, what's in there? Like,
don't you aren't you dying to find out what's in there?
And he's like, I mean, yeah, of course. Like I
don't know how you avoid the temptation to just kind
of hack away at it, but we know that you
have to be careful when you do thesex.

Speaker 4 (30:00):
Well, actually, let's put a finer point on that, because
this is something that I see people misunderstanding online, you know,
when they're impatient about excavations all over the place. Why
do you have to be so careful? Why can't you
just take a bulldozer and find a bunch of cool fossils?

Speaker 3 (30:13):
Actually, It's a really good point to discuss because you know,
there have been times in the past when that is
what people have done, and there still are certain situations
in which people still do that today. The problem is,
sure you might find well, first of all, you might
destroy the fossils in the process of excavating. That's a
real risk.

Speaker 4 (30:29):
Yeah.

Speaker 3 (30:30):
But the second thing is, even if you find them,
a lot of what we can learn about a fossil
comes from the exact situation in which it was found.
So you can hand me a fossil bone and I
might be able to tell you some things about it,
or more to the point, I can hand it to
Menuel and he will tell you some things about it.
But you know that we can get a lot more
information by saying, oh, yeah, but this fossil was found

(30:53):
together with maybe this stone tool, or with these other fossils,
or maybe there were multiple individuals together in place. That
starts to tell us something about the social interactions among
these individuals. And they've literally found carcasses of animals with
stone tool cut marks on the bones and the stone
tools are still there, like it's just it's insane, right,

(31:15):
So you can learn so much about what people or
hominids were doing at the time by understanding the exact
context in which these were found. So if you destroy that,
you've lost the opportunity to learn anything that we can learn.

Speaker 4 (31:30):
And if you rush through your excavation, then you're sort
of using it up for future generations where people might
develop better technology, less invasive or understand there's questions that
they want to ask that we can no longer ask
because people excavated using technique X instead of technique why.

Speaker 3 (31:46):
Yeah, And that's actually something that you know, archaeologists and
paleontologists today recognize and part of their sort of standard
practice is to always keep a section that is not
excavated and think that might be really interesting, but to
preserve it for future generations under the assumption, as you said,
that like at some point in the future, people are
going to have other ways of studying this that we

(32:08):
don't have today, and we don't want to, you know,
cause them to miss out on that opportunity.

Speaker 4 (32:12):
So why can't we like put a thumper on the
surface and like gatherunce your data and feed it into
AI and have it tell us like here are all
the fossils.

Speaker 3 (32:20):
Yeah, So I think there have been some developments along
those lines. They can use things like ground penetrating radar
to like look underground and try to get some sense
of what's there, and you might be able to find
some large things that way, but to find you know,
some of the fossils that they pull out of these
sites are incredibly tiny, and so, you know, I think
part of it is is just the resolution of these technologies.

(32:43):
And the other thing I think is that you know,
keep in mind, the fossil is rock, yeah, and you're
looking for one rock embedded within a bunch of other rocks. So, like,
you know, I don't know much about the specifics of
how the technology works, but I'm guessing that just being
able to differentiate between those two types of things is
probably really hard.

Speaker 4 (33:00):
Yeah, you're looking for a needle in a needlestack.

Speaker 3 (33:02):
Basically.

Speaker 1 (33:03):
How many hamidid species has manuel found in there?

Speaker 3 (33:06):
Well, they have found a few, but you know, in
old of I Gorge generally there are three species that
are known from the fossil record from that particular site,
and it's actually the place where two of them were
first discovered. So the very first hominid fossil found at
old of I Gorge was found by Mary Leaky along
with her her husband Lewis Leaky. They were sort of

(33:26):
the pioneers of looking for human hominid fossils in that site,
and they found one that they called zinge z i
in j was the nickname. It was short for Zinganthropists
boisei as the species, and the genus name has been
revised since those days. It's now known as Paranthropist Boisey.

(33:47):
But that was a really big deal, and that's a
good example of a hominid that we think was on
a branch that didn't eventually lead to us. There's you know,
like I said, there's debate among folks in this field
about exactly what the the shape of that family tree
looked like and which species led to which other species,
et cetera. But they are pretty different from us. They
were more sort of like large bodied, very thick jaw.

(34:10):
They looked like they were eating like grasses or other
very like fibrous foods that are really hard to break down.
So their skull is quite different from the species that
we think are the ones that eventually led to us.
Another species that was first found in OLDEVII Gorge is
Homo habilis, so this is now in the genus Homo, right,

(34:34):
and so this is something that is certainly more close
to Homo sapiens, but still still pretty distinct from us.
And in part it's based on like the size of
the head, which of course is you know, an indication
of the size of the brain. So we talked before
about like walking upright being one of the big transitions
that took place. The other major one, I mean, there
were a lot that the other major one was the

(34:54):
expansion of the brain and therefore the expansion of the skull.
And so in part our genus Homo is defined by
the size of the skull, but we also see within
species of Homo kind of more and more expansion of
the brain, which you know, is at least correlated with intelligence.

(35:14):
Intelligence is famously hard to hard to define, hard to measure.
It's not, you know, brain size is a perfect measurement
of intelligence by any means. But at least in looking
at the history of human evolution, we do think that
with a larger brain, you know, generally speaking, you start
to see more intelligence and more sophisticated types of behaviors.

Speaker 4 (35:34):
It is amazing that we have any fossils, given how
hard it is to arrange all of those things to
happen just the right way. Don't you worry that you're
looking at an unusual, unrepresentative sample of the ancient population
because you know that it doesn't happen evenly everywhere. For example,
if future humans only studied like current physics professors, I

(35:55):
wouldn't want them to extrapolate, you know, the whole population
based on a few of us. Don't you worry about that?
And how big a sample are we talking about? Like
how many different individuals have we found fossils of?

Speaker 3 (36:05):
Yeah, that's a really good point. So you've got the
small sample size problem. Anytime you're dealing with fossils, right,
you're gonna, like I said, it's so hard to you know,
even have them be preserved, much less find them. So
what often happens is, you know, somebody finds something and
it's the first of that kind, right, and then that
makes it hard to draw too many conclusions because we

(36:26):
don't know, you know, how representative it was. But what
has fortunately happened in the last I would say, you know,
sort of fifty years or so, especially in the last
few decades, is we've found more and more examples of
the same what people generally accept as being the same species,
And like I said, there's some debate about it. Is
this the same? Is this not where to draw the line.

(36:48):
But there's some exceptions, some of the earliest species that
are only known from a few specimens. But as you
get more and more recent, as you get to something like,
for example, homoerectus. That's a really interesting species because we
know that the earliest Homo Erectus were found in Africa,
but then you start to see Homo Erectus popping up

(37:08):
in the Middle East, in parts of Europe, and in
parts of Asia and Southeast Asia. In fact, the first
one was found on the island of Java in what
is today Indonesia. So that was the very first member
of our lineage, the very first hominid to leave Africa
and spread out across a lot of the world. So
there's a lot now of fossils of homoerectus.

Speaker 4 (37:29):
Is that like one hundred or a thousand? A million?
How many are we talking about?

Speaker 3 (37:31):
Not a million? I don't know the exact count, but
I would hazard a guess that we're talking about you know,
hundreds something like that. Yeah, And you know, some of
these are very fragmentary, so you might only have one bone, right,
and in other cases you have part of a skull,
but kind of putting it all together, we have a
very good sense of what the entire body looked like.

(37:54):
That's the other thing, right, is like you might only
have a tiny piece of something, and you have to
figure out how much information can you get about the
entire individual, much less the entire species from that one
little fragment. In some cases we can learn a lot,
but you know, it certainly helps to have more and
more pieces of that puzzle.

Speaker 1 (38:12):
Can we talk about timeframe a little? So I think
you said that the split between chimpanzees and humans was
like six to seven million years ago, and then you
were talking about Manuel study site, and I never remember
the name of the place, so I'm just going to
say Manuel Study site that was one million to one
point eight million years ago.

Speaker 2 (38:29):
What is the like.

Speaker 1 (38:31):
Earliest date when there were other hominids around? And this
question is going to lead into whether or not we
can get DNA out of any.

Speaker 3 (38:37):
Of these Yeah, yeah, that's really important questions. So yeah,
so yeah, you know, you start to see, let's see,
I think Lucy's species that's Astralopithecus e forensis is around
three and a half million years ago. So there you
have an example of a species that is definitely walking
upright on two feet, very much like us. We even

(38:58):
have footprints. This is a credible there's a site in
Tanzania near Oldevi Gorge where there are preserved footprints where yeah,
I mean it really is like basically like perfect conditions.
The volcano, one of those volcanoes erupted, there was ash
all over the ground and then it rained, so then
you have like a wet cement situation, and then some

(39:19):
of these individuals walked through that area and the ash
hardened and then that was preserved, so we could actually
retrace their exact gate. You know, the kind of like
if you go to get fitted for like running shoes
or something, they'll go and they'll like analyze your gait,
like how long are your strides, where are you kind
of putting pressure on your foot, and they'll give you

(39:39):
the right shoe to kind of help with your specific gate.
They can do those types of reconstructions on the gate
of Astralopithecus eforensus at three and a half million years ago.
Because of these tracks.

Speaker 4 (39:51):
Incredible, so cool can they tell if they had to
like drag a screaming toddler along or something.

Speaker 3 (39:56):
Well, actually, so there is a prehistoric There is an
indication of older individuals and younger individuals in some cases,
and we have now also found fossils of individuals of
different ages for some of these species. So we're starting
to fill in a little bit of what the kind
of you know, what does a childhood look like for
homoerectus and things like that. But you know, the other

(40:18):
thing I was going to say is so for that species,
for Lucy's species, as Trollopithecus e forensis they were walking
upright like us, but they didn't have a big brain
like us yet. So we're starting to sort of see
pieces that we know walking upright happened first. So by
three and a half million years ago, you had people
walking around in much the same way that we walk around,
but they didn't have a brain nearly the size of ours.

(40:38):
It was more of a chimpanzee sized brain. So we
assume that means most aspects of complex human behavior, language, art, social,
you know, dynamics wouldn't have yet been in place. Now
there's a lot of you know, guesswork that has to
be done, but that's that's the best guess for that,
So you don't get the you know, the very enlarged

(41:01):
brain happening until just the last couple of million years,
and it's it keeps increasing over the last two million years.
And this is super interesting because you also want to know, well,
why why did we become more intelligent at this particular time, right,
And one of the things that is fascinating is that

(41:22):
the time at which our brain started to really shoot
up in size coincides with the time in which the
climate in East Africa was very volatile, like it was,
you know, swinging wildly from you know, hot and wet
to cold and dry, and it kept changing in a
much faster way than it had previously. And so there's

(41:44):
this idea that those wild fluctuations in climate led to uncertainty, right,
and you had to kind of keep adapting, adjusting, but
maybe in a way that evolution itself can't keep up with, right,
So you can't adapt through natural selection when the environment
is constantly changing. Rather, maybe a better way to do
it is to develop intelligence that allows you to be

(42:08):
more adaptable yourself, to be able to use your intelligence
to work together as a cooperative society to try to
solve problems like finding food, finding water, protecting yourself from enemies.
So there's this idea that that climate being of going
through these wild changes might have driven the intelligence of

(42:28):
our ancestors.

Speaker 1 (42:29):
So that leads nicely into a question we have from
listener Jesse. And so here's the question, if there is
a physical and or sociological advantage to becoming an upright
tool using intelligent species, would the same advantages apply to
the rise of an intelligent alien species on another habitable planet.
And if physical characteristics are essential for becoming an intelligent species,

(42:51):
must they then be more human? Like surely we could
have limbs grown out of our heads or otherwise. Okay,
So I feel like that kind of ties into what
is needed to become an intelligent species. And this is
also a question for Daniel, who thinks a lot about aliens.

Speaker 3 (43:06):
Well, you know, I love this question for a lot
of reasons, one of which is I'm teaching a class
right now on astrobiology and we're asking exactly these kinds
of questions and talking about them with our students, like
how how much can we use the history of life
on Earth, to think about what might have already happened
on other planets, and to think about what could happen
in the future on other planets and other worlds and

(43:28):
different lineages of life. And so, you know, I think
there is this idea at least that some species on
Earth would have become as intelligent as we are. That's
one way of thinking about it that like, it happened
to be us because you know, the asteroid hit the
Earth and killed the dinosaurs and it ended up being mammals,

(43:49):
But maybe we could have had a super intelligent dinosaur
slash bird or something like that. That's like one argument
that has been made that like somebody was going to
become super smart and it happened to be us. There's
another argument that, like, it doesn't have to happen at all,
and the conditions had to really just be just right.
And in that way of thinking about it, you know,

(44:10):
we happen to be at the right place at the
right time and have the right kind of combination of
traits already in existence that allowed us to sort of
evolve through natural selection to be able to you know,
basically solve problems in one particular way, and that way

(44:30):
appears to have been through the use of language and
collective problem solving and social you know, complex social interactions
that we know how to manage. And that's kind of
a uniquely human way of solving the problems of of
you know, adjusting to this extreme environment. So, you know,
I tend to kind of lean more that way that

(44:51):
like we got lucky, you know, like it didn't have
to happen this way. And while you know that has
implications for understanding our origin, and I also do think
it has implications for thinking about what could happen elsewhere. Right,
So it doesn't necessarily mean that there has to be
intelligent life elsewhere, but maybe if the conditions are just right,

(45:13):
and there are species elsewhere that happen to have the
conditions that are necessary and be at the right place
in the right time, then that that might happen for
them too.

Speaker 4 (45:23):
I think it's really important to try to tell these
stories and try to understand our history. But something I
struggle with is knowing how to test these ideas, Like
it sounds compelling, but you know, there could be another
idea that explains that there could be another factor. Usually
in science, you don't just tell a compelling story that
describes you, dit you try to predict something that happens
and say, well, here's a prediction I can use to

(45:44):
test this theory versus that theory are aliens. The way
we can do that you build a model for how
intelligence develops, and then you can apply it to some
new data sete. You're like, I predict intelligence on this planet,
or I predict no intelligence on this planet, or is
this just an impossible standard because we're talking about in
the deep past and things that move very slowly.

Speaker 3 (46:02):
Yeah. No, I think it's a really good, really good point,
And you're right that we always want to be able
to back up our assertions with data and so otherwise
it's a nice story, but you know, there's no way
to know that that's the correct interpretation. So one of
the problems we have with the study of human evolution
is that, as far as we know, it only happened once.
And so you know, even if we could reconstruct the

(46:24):
exact sequence of events that led to us, it still
doesn't tell us how generalizable that is. It still doesn't
tell us how likely it was to We can say
that it did happen, but we can't necessarily know well,
if you change X, Y and Z, would it have
played out that same way again? So I mean there
are ways to do simulations, right, There are ways to

(46:45):
run experiments with other organisms, you know, that aren't humans,
that we can try to recreate certain conditions, but it's
not quite the same. So I think part of this
is the inherent problem we have of you know, human
evolution happened once. There's only one lineage of hominids, although
if there were multiple species living in the same place,

(47:06):
that does allow us to ask some questions about the
differences that existed between them, and you know, maybe someday
we'll know why our lineage is the one that survived
and not any of the others that very well could have.

Speaker 1 (47:19):
All right, let's take a break, and when we get back,
we'll take a question from Alberto about whether or not
our hominid species has let's say, mixed our genetic information
with some of the other hominid species in our early history.

(47:50):
And we're back, and let's start with a question from Alberto.
All right, So Alberto asked, I recently learned about another
hominin branch called Demnis evans. Would you be willing to
share more information about them. Are there modern humans that
share their DNA? And I'll add I think Neanderthals we
also share some DNA with them, So yeah, tell us
about our species doing the hanky panky with some others.

Speaker 3 (48:12):
Yeah, I mean, this is one example of some of
the just absolutely incredible work that has happened in the
last few decades that's really kind of given us a
much much more complete picture of our ancestors and how
we got here, but also like a much much more
i would say, interesting, a much more complex version of
the story. So yeah, So what happened with the Denis Evans.

(48:34):
This is a discovery that took place in two thousand
and eight in a cave called Denis of a cave
in the Altai Mountains of Siberia, And what was found
was a part of a finger and a tooth, so
not much, not much to go by, but because this
cave is a place that is pretty cold and dry,

(48:55):
that turns out to be pretty good for preserving DNA,
And in this case they were able to to actually
extract and sequence the entire genome of the individual that
was found, just based on this tiny little fragment of
bone and teeth.

Speaker 4 (49:10):
So this is bone and teeth, not fossils, just to
be clear.

Speaker 3 (49:13):
So it was in a state that was I guess
partially fossilized, and so there was still organic material in there,
and so they were able to actually get enough of it.
And you know, part of what happens with looking at
ancient DNA is you can still have some DNA present,
but if it's broken up enough, if it's degraded enough,
then you can't necessarily make much sense out of it.

(49:35):
So this was both preserved and intact enough for them
to actually sequence the entire genome that was published in
twenty ten, and basically what they determined is that this
is a new type of hominid and they were similar
to Neanderthals because we also have DNA in fact complete

(49:57):
genomes from Neanderthals that had already been published, and so
this is basically a branch of our family tree that
is similar to Neanderthals and yet distinct enough that they're
kind of considered a separate, separate type of hominid. And
I'm not using the term species because there's debates about

(50:18):
is it actually different species, is it, you know, the
same species as us what we do know is by
looking at the DNA of these Denisovans, is that we
actually still have some of the DNA from Denisovans in
people living today. And so, yes, we know that our ancestors,
I say us as Homo sapiens modern humans, that at

(50:41):
some point in the past, and actually we now know
this happened multiple times in the past, that there were
episodes in which our ancestors, Homo sapiens, made it and
had children with Denisovans. And not only that, but that
that led to a child and that child was you know,
cared for and nurtured and survived itself to be an

(51:05):
adult and to go on and have its own kids.
So I think it's useful to point that out right.
It's not just people talk about, oh, we made it
with you know, Denisovans, yes, and had kids with them,
and those kids were you know, presumably loved, right. I mean,
we all know that that kids require a lot of care,
certainly when they're young, and so so somebody you know,

(51:27):
cared enough for those kids to nurture them, and they
survived and eventually some of their genes have ended up
in us. So it's not a lot of their genes,
So the highest percentages are like five percent Denisovans. So
you can have individuals alive today who like five percent
of their genes. So these are like the parts of
our genome that, like, you know, the DNA is coding

(51:49):
for a protein that does something in the body, about
five percent of that could be traced back to Denisovan DNA.

Speaker 4 (51:57):
Wow, I'm intrigued by your use of the word us
and denis Evans, Like, aren't we the Denisovans. Aren't we
all just descendants of all these people?

Speaker 3 (52:04):
Yeah? Exactly, And so I think we're starting to come
around to thinking about it exactly that way at least
I am.

Speaker 4 (52:11):
Right.

Speaker 3 (52:11):
So when we say that we you know, we made
it with them, we had kids with them, Like that
gives you a sense of like, how did people at
the time think about them? Right, Like, well, I'm fascinated
by by imagining what that world was like with that
interaction was like. And obviously we don't know any of
the details about how the interaction took place, you know,

(52:31):
was it consensual or not, who knows, But we do
know that a child was conceived and that child was
cared for, and that does I think tell us something.

Speaker 4 (52:39):
I mean, I've read Clan of the Cave there.

Speaker 3 (52:40):
Yeah, that's right, I mean that's exactly exactly.

Speaker 1 (52:44):
So there have been a lot of hominids. We argue
about how many species there have been, but now there's
only us. And so what happened to the rest of them?
Did they breed with us and they're still with us today?
Did they die off?

Speaker 5 (52:56):
What? What happened?

Speaker 1 (52:57):
Yeah?

Speaker 3 (52:58):
So I mean you can think in some sense that
like Denis Evans and Neanderthals, because we have some you know,
Neanderthal DNA in us today as well, in a sense
they're still here. And as Daniel said, they are us, right,
I mean, if we have their DNA, then why do
we say that they're extinct. I think the thing is that,
like now we have enough of fossil evidence, and we
found more fossil evidence by the way, for Denisovans. So

(53:19):
what I was talking about is the initial discovery. We
have now found more fossils, including a very intact skull
that has a fascinating backstory, and so we're starting to
know more about what physical features they had. We do
know a ton about the physical features of Neanderthals, which
lived more in Europe and Central Asia and Western Asia,

(53:41):
and so they had physical features that are different enough
from people living today that you know, for the most part,
what people say is, you know, wouldn't pass the subway test, right,
which is to say that, like, you know, if a
Neanderthal or Genisovan we're about to board a subway in
New York or any city for that matter, you know,

(54:01):
would would would someone look twice?

Speaker 4 (54:03):
That says a lot, because New York City has some
weird people on the subway.

Speaker 3 (54:07):
Well exactly, I guess you know. That's why the subway
test sort of rings true. It's like people are willing
to accept a whole wide diversity of humanity as just
being totally normal. But the Neanderthals, if a Neanderthal boarded
the subway, you might look twice, you know. So in
that sense, it's like, well, humans that look like that
aren't around today, but they did leave a legacy. I mean,

(54:29):
they left the legacy in our DNA. And there's interesting
examples of like particular genes, traits, things that you know,
happen in our bodies that we can actually trace back
to Neanderthals and Denisovans in some cases amazing.

Speaker 1 (54:45):
But what happens to the Okay, so forget Denisovans and Neanderthals,
the rest of them, Where did they go?

Speaker 3 (54:51):
Yeah, So, in the case of other hominid species, partly
we don't know whether any of their DNA has survived
in modern humans because they lived long enough ago that
we haven't been able to get any intact DNA from
those fossils in order to be able to like understand
their genetics. So it's possible that some of those older ones,

(55:13):
like you know, homo Erectus for example, you know, there
might be homoerectus genes in us today and we just
don't know because we haven't been able to look at
a homo erectus genome. But in other cases, there's certainly
lineages of haman Is that we don't think left any
descendants that are still alive today. So yeah, there's a
big question of like why us and not them, right,

(55:34):
And there have been debates about did our ancestors kill them?
Did we just outcompete them? We were smarter, we were faster,
we were better at working together, you know, And so
you know, the short answer is, we don't know. That's
an ongoing debate. But I think the fascinating part that
we now do have a better insight into from looking

(55:55):
at Neanderthals and Denis Evans is that part of the
answer is we mixed with them, we enter with them,
and as you said, we are them in a sense
and they are us, and they're still with us in
some way, and maybe that was what happened further back
as well. And we won't know until we're able to
hopefully someday get some DNA or protein, some other kind

(56:16):
of you know, molecular evidence that would allow us to
answer some of those questions.

Speaker 4 (56:21):
And so as we look back in time, how far
back would you consider our ancestors to be modern humans
the kinds of people who would get on the subway
or could just like be plopped into modern society, grow
up in our schools and become a totally normal person.

Speaker 3 (56:36):
Yeah, so it's hard to say where we draw that line,
but I mean one way to do it is to
say our species Homo sapiens as we currently define it, right, So,
you know, paleor anthropologists who study human evolution, they give
a name, a species name to every fossil that they
find or every you know, piece of fossil that they
can get a genome from, and so only those that

(57:00):
are given the name Homo sapiens are technically our species
as we currently consider it. So the way you could
answer that is how old is our species, Homo sapiens,
And the answer is, yet again that people debate this,
but it's between two hundred thousand and three hundred thousand
years old. So that's kind of the brackets on when
are the earliest fossils that some people attribute to Homo sapiens,

(57:25):
So somewhere in the two hundred to three hundred thousand
year old range, which again I always say, like to me,
that's so recent, like our species is so new to
this planet. That's yesterday in the perspective of evolutionary biology.

Speaker 4 (57:41):
But just to underscore that, you're saying, if you took
a baby from a quarter million years ago and time
traveled them into the future and were raised by a
normal human family, they would be indistinguishable.

Speaker 3 (57:52):
Well, there are some ways in which anthropologists distinguish between
what they call archaic Homo sapiens and what they call
an atomically modern Homo sapiens. These are getting into like
what I would consider to be pretty like nuanced anatomical
differences in in you know, skull shape, in which features
are slightly larger, and these types of things. So this

(58:14):
is the sort of splitting hairs part of doing this
kind of science that you know, can be challenging when
you start to get into like reading the research papers.
But you know, it's still Homo sapiens. So as far
as I'm concerned, like, I think, you know, there's interesting
certainly questions to ask about, like well, what changes were
taking place? Certainly there, you know, must have been some differences,

(58:38):
even if it's cultural differences between the people living then
and the people living today, but anatomically physically right, Like
if you look at the skull of an early Homo
sapiens and the skull of somebody from today, they're very similar.
I mean, they're very very much like us. You'd have
a beer with them, I would. Yeah.

Speaker 1 (59:00):
I also feel like Daniel's question is like Laiden, with
his assumption about what makes people human? Could they survive
today in our modern era? And I think plenty of
people would argue that that's not the important thing about humans.
It's you know, maybe social behavior or language or chins.
One of our listeners said, chins, and I don't understand
the chin thing.

Speaker 3 (59:18):
The chin thing is super interesting because it's one of
the few physical features you can see in the fossils
that distinguish Homo sapiens from other species. We are the
only hominid that has a chin. So what did the
chin do for us? I don't think anybody really has
given a satisfying answer to that one. It seems to
be an example of a trait that comes about through evolution,

(59:40):
maybe just randomly and persists. It doesn't not all the
traits have to have an adaptive value, doesn't always have
to be useful for something. They can just come about.
But I do like my chin, so I'm glad we
have them.

Speaker 1 (59:52):
I like mine too. All Right, that was fantastic, Scott.
Thank you so much for telling us all about ancient humans.
But you're not just interested in ancient humans, interested in
like ancient human evolution and future human evolution. So tell
us about your upcoming book.

Speaker 3 (01:00:05):
Yeah, well, I you know, I've been interested in like
the idea that humans are still evolving for quite some time, right, So,
so my first book, published in twenty sixteen, was called
Future Humans Inside the Science of our Continuing evolution, and
that's all about the ways in which you know, natural
selection and other evolutionary processes have continued until today. But

(01:00:27):
then more recently, I've been exploring this one particular possibility
for our evolutionary future, and that is what would happen
if some of us left Earth and created settlements on
other planets, something that you have also thought quite a
bit about, Kelly. I know, we've had lots of conversations
about the idea of space settlement, and it's been super fun.

Speaker 1 (01:00:49):
I love our parallel careers. Your aunts and space and
I'm parasites and space, and we're both in like an
evolution in ecology sort of track and a space future
of humans in space track And anyway, it's always fun
talking to you.

Speaker 3 (01:01:01):
I guess that tells us that there's a lot of
ways to get to space. Huh, that's right, And so yeah,
I mean so basically, yeah, I've spent the last several
years doing a deep dive into this question of you know,
if at some point people are successful in creating space settlements,
what would that mean for the people living in those

(01:01:22):
space settlements, Like, what would happen to the descendants of
those first pioneers, those first settlers on you know, Mars
or anywhere else for that matter. You know, questions like
could a baby born on Mars come back to Earth,
and you know, would people gradually adapt to the conditions
on that planet, and would they eventually become a new

(01:01:46):
species of human. So yeah, So the book is called
Becoming Martian How living in Space will change our bodies
and minds And it comes out February seventeenth of twenty
twenty six. So super excited, and it's actually already available
for pre order if folks want to get a copy.

Speaker 1 (01:02:03):
And I got to read it, and I can say
that it's amazing. And it starts with a full word
by astronaut Scott Kelly, which is the wider Smiths didn't
snag an astronaut forward, So bravo. Not that the Wiener
Smiths are, you know, a bar against which anyone should
judge themselves. But I was pretty excited you got an
astronaut forward.

Speaker 3 (01:02:20):
Well, thank you, No, I was too. That was a
real wonderful thing that Scott Kelly agreed to contribute a forward.
But you and Zach actually helped tremendously with this book,
both in terms of sharing ideas and notes and reading
you know, draft copies and support all on the way.
So super appreciate it.

Speaker 1 (01:02:39):
Our pleasure. Yay Space and yeay Scott. Okay, so everyone
should pick up Becoming Martian and we'll see you on
the next episode.

Speaker 3 (01:02:46):
Thanks everyone, thanks for having me on again.

Speaker 1 (01:02:54):
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