TEDxLSU
Juliet Brophy: How a new species of ancestors is changing our theory of human evolution
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In 2013, a treasure trove of unusual fossils were uncovered in a cave in South Africa, and researchers soon realized: these were the remains of a new species of ancient humans. Paleoanthropologist Juliet Brophy takes us inside the discovery of Homo naledi, explaining how this mysterious ancestor is forcing us to rethink where we come from -- and what it means to be human.
Juliet Brophy - Paleoanthropologist
Juliet Brophy explores human evolution in southern Africa. Full bio
Juliet Brophy explores human evolution in southern Africa. Full bio
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Human origins.
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Who are we?
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Where do we come from,
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and how do we know?
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In my field, paleoanthropology,
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we explore human origins --
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the "who" and "where" questions --
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by analyzing fossils that date back
thousands and even millions of years.
thousands and even millions of years.
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In 2015, a team of colleagues and I
named a new species in the genus Homo --
named a new species in the genus Homo --
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our genus --
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Homo naledi.
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Let's take a step back
and put that into context.
and put that into context.
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The last common ancestors
between humans and chimps
between humans and chimps
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date somewhere between six
and eight million years.
and eight million years.
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The earliest hominins,
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or earliest human ancestors,
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evolved into a group
known as the australopithecines.
known as the australopithecines.
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The australopithecines
evolved into the genus Homo
evolved into the genus Homo
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and eventually modern humans -- us.
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With each new fossil discovery,
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we get a little bit closer
to better understanding who we are
to better understanding who we are
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and where we came from.
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With these new fossil finds,
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we realize we now have to make
changes to this tree.
changes to this tree.
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Until this discovery,
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we thought we had a pretty good idea
about the patterns of evolutionary change.
about the patterns of evolutionary change.
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Current fossil evidence suggests
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that the earliest populations
of the genus Homo evolved in Africa
of the genus Homo evolved in Africa
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somewhere between two
and three million years.
and three million years.
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Fast-forward to approximately
300,000 years to where we see the origins
300,000 years to where we see the origins
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of the first modern humans.
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While the fossil record
between these time frames in Africa
between these time frames in Africa
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is relatively sparse,
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the fossils nonetheless
demonstrated certain trends
demonstrated certain trends
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from our earliest ancestors
to modern humans.
to modern humans.
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For example, our brains
were becoming larger
were becoming larger
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relative the rest of our body.
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Our pelves were becoming more bowl-shaped,
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and our hand-wrist morphology, or form,
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suggested a change in our grip
as we began to make and use stone tools
as we began to make and use stone tools
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and spend less time in the trees.
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These new fossils disrupt everything
we thought we knew about these trends
we thought we knew about these trends
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and force us to change the way
that we think about human evolution.
that we think about human evolution.
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South Africa in general,
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but the Cradle of Humankind in particular,
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contains numerous sites where hundreds
of thousands of fossils have been found.
of thousands of fossils have been found.
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As an undergraduate student,
I fell in love with one of them ...
I fell in love with one of them ...
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Mrs. Ples.
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The skull of a 2.1-million-year-old
early human ancestor.
early human ancestor.
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From that point on,
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I was determined to go to South Africa
and study human evolution.
and study human evolution.
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I first traveled there in 2003,
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and I did get to see my beloved Mrs. Ples.
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(Laughter)
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But words can hardly convey my excitement
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when I was chosen
as an early career scientist
as an early career scientist
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by Lee Berger,
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a world-renowned paleoanthropologist,
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to be one of the primary analysts
of recently excavated unpublished fossils.
of recently excavated unpublished fossils.
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This treasure trove of fossils
was being recovered from a new site
was being recovered from a new site
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called the Dinaledi Chamber
in the Rising Star cave system.
in the Rising Star cave system.
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Species are often named
based on a skull, a lower jaw,
based on a skull, a lower jaw,
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or, very rarely,
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a handful of postcranial,
or below-the-neck, elements.
or below-the-neck, elements.
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The fossils from Dinaledi
were another story altogether.
were another story altogether.
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An unprecedented
approximately 1800 specimens --
approximately 1800 specimens --
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so far --
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have been excavated
from the Rising Star system,
from the Rising Star system,
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representing at least
15 individual skeletons.
15 individual skeletons.
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The research team
that I was invited to join
that I was invited to join
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was tasked with describing,
comparing and analyzing the fossils,
comparing and analyzing the fossils,
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with the difficult goal of identifying
to what species the fossils belonged.
to what species the fossils belonged.
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We were divided up
into our different areas of expertise.
into our different areas of expertise.
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We were divided up
in different areas of the lab, too.
in different areas of the lab, too.
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So there was "Hand Land,"
for the fossil hand people,
for the fossil hand people,
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"Hip Heaven" for the pelvis ...
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I was in the "Tooth Booth."
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(Laughter)
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And after long, intense days in the lab,
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the different teams would meet up at night
and discuss our findings,
and discuss our findings,
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still consumed by questions
from our analyses.
from our analyses.
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It was incredible how different
the interpretations were.
the interpretations were.
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Each body part seemed to come
from a different species,
from a different species,
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based on what we knew
from the fossil record.
from the fossil record.
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The suite of characteristics we were
seeing didn't match any known species.
seeing didn't match any known species.
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And if we had only recovered the skull,
we might have called it one thing;
we might have called it one thing;
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if we had only recovered the pelvis,
we might have called it another.
we might have called it another.
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The anatomy of the skeletons
didn't make sense
didn't make sense
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with the framework of what we thought
we knew of human evolution.
we knew of human evolution.
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Did it belong in the genus Homo?
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Should it be an australopithecine?
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Those bipedal, more apelike ancestors?
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Or perhaps it should be its own species.
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Ultimately, after much deliberation,
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we decided the Rising Star specimens
did indeed warrant a new species,
did indeed warrant a new species,
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which we called "Homo naledi."
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From the head to the feet,
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the fossils present a mosaic
of primitive, or ancestral,
of primitive, or ancestral,
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and derived or more modern-like features.
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The skull is quite derived,
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appearing most similar to early
representatives of the genus Homo,
representatives of the genus Homo,
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like Homo habilis and Homo erectus.
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However, the brain is scarcely
half the size of a modern human one.
half the size of a modern human one.
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One that is smaller than any other
early Homo that has ever been found.
early Homo that has ever been found.
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As someone who studies teeth,
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I might argue these are the coolest
fossils found at the site.
fossils found at the site.
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(Laughter)
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The assemblage consists of 190
whole or fragmentary teeth
whole or fragmentary teeth
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that range in age
from very old to very young.
from very old to very young.
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Like the skeletons,
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the teeth present a mix
of primitive and derived traits.
of primitive and derived traits.
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In modern humans,
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the third molar is typically the smallest,
while the first molar is the biggest,
while the first molar is the biggest,
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but Homo naledi
has the primitive condition
has the primitive condition
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where the third molar is the biggest
and the first molar is the smallest.
and the first molar is the smallest.
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The anterior teeth,
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or the incisors and canines,
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are small for the genus Homo,
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and the lower canine
has a cuspulid on it --
has a cuspulid on it --
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an extra cuspule that gives it
a distinct mitten-like shape
a distinct mitten-like shape
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that it shares with some specimens
of the early human, Homo erectus.
of the early human, Homo erectus.
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The overall shape of the teeth
looked odd to me,
looked odd to me,
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so I performed crown-shape analysis
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on the occlusal surfaces
of deciduous teeth, or baby teeth --
of deciduous teeth, or baby teeth --
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on your left --
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and the permanent premolars
and molars on your right.
and molars on your right.
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The deciduous teeth are especially narrow,
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and the premolars are unique
in their outline shape
in their outline shape
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compared to other hominids.
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In fact, when I compare the outlines,
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when I lay them on top of each other,
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they look very similar.
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We say they have
"low intraspecific variations,"
"low intraspecific variations,"
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so the variation
within the species is low.
within the species is low.
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When I compare this to groups
like the australopithecines,
like the australopithecines,
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the intraspecific variation
is much larger.
is much larger.
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Postcranially, the team concluded
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that the position of the shoulders
suggesting naledi was a climber;
suggesting naledi was a climber;
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the flared pelvis and curved fingers
are all primitive for the genus Homo.
are all primitive for the genus Homo.
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On the other hand,
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the humanlike wrist,
long slender legs and modern feet
long slender legs and modern feet
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are all consistent
with other members of the genus.
with other members of the genus.
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In 2017, we announced
more specimens of Homo naledi
more specimens of Homo naledi
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from the nearby Lesedi Chamber,
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also in the Rising Star cave system.
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In addition, our geology team
managed to produce an age estimate.
managed to produce an age estimate.
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The date's a big deal
because, up until now,
because, up until now,
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we had based our analysis solely
on the morphology of the specimens,
on the morphology of the specimens,
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without previous knowledge
of how old something is --
of how old something is --
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something which could unconsciously
bias our interpretations.
bias our interpretations.
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With its small brain and flared pelvis,
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we would not have been surprised
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if the fossils turned out to be
two million years old.
two million years old.
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Instead, the fossils dated
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to 235 to 336 thousand years,
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an incredibly young date
for such a small-brained individual.
for such a small-brained individual.
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So think back to what I said earlier:
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we thought that our brains were becoming
larger relative to the rest of our body.
larger relative to the rest of our body.
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Now we have a small-brained,
young individual complicating this idea.
young individual complicating this idea.
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What does all this mean?
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Homo naledi has taught us
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that we need to reassess
what it means to be in the genus Homo.
what it means to be in the genus Homo.
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We need to rethink
what it means to be human.
what it means to be human.
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In fact, most of the characteristics
that we use to define the genus Homo,
that we use to define the genus Homo,
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such as brain size and hip morphology,
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are no longer valid.
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No other species exists with this mix
of primitive and derived traits.
of primitive and derived traits.
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Why is there so much morphological
variation in the genus Homo?
variation in the genus Homo?
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And what force is driving that variation?
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Another implication for these fossils
is that for the first time,
is that for the first time,
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we have concrete evidence
of a species coexisting in Africa,
of a species coexisting in Africa,
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at 300,000 years,
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with modern humans.
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Until this discovery,
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we only had large-brained
modern humans that existed in Africa.
modern humans that existed in Africa.
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Did they interbreed with each other?
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Did they compete with each other?
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Another implication
that these fossils have
that these fossils have
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is for the archaeologists
studying stone tools in South Africa.
studying stone tools in South Africa.
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Keep in mind that neither the Dinaledi
nor the Lesedi Chambers
nor the Lesedi Chambers
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have any artifacts in them.
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However, they do overlap in time
with several stone-tool industries,
with several stone-tool industries,
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the makers of which are considered
to be either modern humans
to be either modern humans
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or direct human ancestors.
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This begs the question:
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Who made the stone tools of South Africa?
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Brain size has historically
played a key role
played a key role
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in identifying a species as a tool user.
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The idea is that you need
to have a large brain
to have a large brain
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to have even the capacity
to make stone tools.
to make stone tools.
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But that notion has been questioned.
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Furthermore, Homo naledi,
even with its small brain size,
even with its small brain size,
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has a hand-wrist morphology
similar to other species
similar to other species
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that did make and use stone tools,
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suggesting it had the capability.
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With two species coexisting
in Africa at 300,000 years,
in Africa at 300,000 years,
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we can no longer assume
we know the maker of tools
we know the maker of tools
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at sites with no associated species.
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So where does Homo naledi fit
in our human evolutionary lineage?
in our human evolutionary lineage?
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Who is it most closely related to?
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Who did it evolve from?
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We're still trying to figure all that out.
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It's ironic, because
paleoanthropologists are renowned
paleoanthropologists are renowned
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for having small sample sizes.
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We now have a large sample size,
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and more questions than answers.
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Homo naledi has taught us,
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has brought us a little bit closer
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to better understanding
our evolutionary past.
our evolutionary past.
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So while Mrs. Ples will always hold
a special place in my heart,
a special place in my heart,
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she now shares that space
with several thousand others.
with several thousand others.
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(Laughter)
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Thank you.
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(Applause)
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ABOUT THE SPEAKER
Juliet Brophy - PaleoanthropologistJuliet Brophy explores human evolution in southern Africa.
Why you should listen
Juliet Brophy's research interests involve using morphometric analyses of fossil teeth to examine taxonomic differences among Plio-Pleistocene fossil human ancestors (hominins) and to evaluate their evolutionary relationships. Her most recent focus investigates the teeth of Australopithecus sediba and Homo naledi from South Africa. Her ongoing research helped establish the phylogenetic position of these fossils.
Brophy also documents the paleoenvironments associated with the South African hominins and assesses how changes in these environments might have influenced human evolution. She works as an assistant professor biological anthropologist with a specialization in paleoanthropology in the Department of Geography and Anthropology at Louisiana State University.
Juliet Brophy | Speaker | TED.com