Young people from all over the world send me questions about the discovery of sediba and the science
behind the find. I wrote The Skull in the Rock to speak to those eager questioners. There are some
questions, though, I did not get to answer there. Here, calling on insights from my scientific colleagues, I
respond to the most frequently asked questions. If I also give that answer and accompanying photos in
Skull, I list the pages. You can see this FAQ as the book extended into digital space.



How was the site and the fossils discovered?

In the middle 1990’s,I had conducted an expedition across southern Africa, funded by the National
Geographic Society designed to map fossil sites using the then relatively new technology of GPS and to
discover new sites. While the expedition discovered many new caves and fossil bearing localities (over 100
caves and 4 new fossil sites in the Cradle of Humankind area alone), it was somewhat of a disappointment
in not yielding any significant discoveries. In addition, without him knowing it, the result were erroneous due
to deliberate error being placed in the GPS signal in the late 1990’s. In early 2008, using Google Earth to
spot caves in the Cradle of Humankind World and to correct the errors in these earlier maps, In that same
year I renewed the exploration programme in the area. With the assistance of these new technologies
available, I discovered, over a few months, more than 600 caves and more than three dozen new fossil sites
in one of the most explored areas on the planet! On the 1st of August 2008, while mapping with my dog Tau,
I discovered the fossil site of Malapa. On the 15th of August I returned to the site with Dr. Job Kibii, Tau and
my then 9 year old son Matthew. Within minutes Matthew had discovered the first piece of hominid,
belonging to the MH-1 skeleton. Two weeks later, I discovered the remains of the adult female skeleton MH-
2 and since then, the site has yielded one of the most remarkable records of early human origins of any site
on the planet. And no - I didn't give Matthew a raise in his allowance! It was a privilege enough for us to just
be involved with such an important discovery. FOR MORE SEE PAGES 30-35 IN THE SKULL IN THE ROCK

What does Australopithecus sediba mean?

Australopithecus means “southern ape,” after the genus of the Taung child, named by Prof. Raymond Dart,
also from the University of the Witwatersrand, Johannesburg. Sediba means natural spring, fountain or
wellspring in Sotho, an appropriate name for a species that might be the point from which the genus Homo
arises. As the hominids were also found preserved in an ancient underground lake or spring, the name also
relates to their place of discovery. Malapa is the name I gave to the site of the discovery after I found it. It
means "my home" in Sotho. The species was named in a paper in Science in 2010.

What is a hominid/hominin?

A hominid is a member of the  family that includes humans, chimpanzees, gorillas and their
extinct ancestors. Hominins are members of the human branch after the human lineage split from that of
chimpanzees, and thus include living humans and extinct human ancestors, such as the Australopiths.
Hominins are characterised by bipedal locomotion, although this may not have been the case for the very
earliest members of the group, and relatively small canine teeth. Later members of this group (those in the
genus, Homo) are characterised by larger brains than those of living apes like chimpanzees, bonobos,
gorillas, orangutans and gibbons. For an article I wrote discussing this matter go to National Geographic's
Viewpoint: Is It Time to Revise the System of Scientific Naming?.

T
his new date of 1.977 to 1.98 million years ago is one of the most accurate ever
achieved in the early hominin record. How were the fossils dated?

When the fossils were announced in 2010, the age of the fossils was announced as being between 1.78
and 1.95 million years old. At that time, however, our teams had not discovered the top of the deposit, which
was discovered in late 2010. The deposit is capped by a flowstone (a limestone layer), that was dated
using Uranium-Lead dating and found to be the same age as the flowstone at the base of the deposit. This
allowed us, using palaeomagnetic dating, to identify a very specific, well dated reversal of the Earth’s
magnetic poles that occurred between 1.977 and 1.98 million years ago. This is a remarkable 3000 years in
2 million, or an incredible 0.15 % error in the date! The work of the sediba team suggests that as the fossil
record for early human ancestors increases, the need for more accurate dates is becoming paramount.
Cosmogenic dating was also used to interpret the landscape formation and to determine the depth of the
cave at the time of deposition. This research appeared in two scientific papers in the journal Science. FOR
MORE ON THE DATING OF SEDIBA AND THE METHODS DISCUSSED BELOW SEE PAGES 40-46 IN THE
SKULL IN THE ROCK

Why can’t you date the fossil themselves?

The fossils themselves are too old to be dated directly with something like radio-carbon dating. Radio-
carbon only goes back to around 50 000 years so we have to rely on dating the rocks that contain them to
achieve accurate dates. Also, the fossils themselves don’t contain materials suitable for dating, at least any
that have been identified by present scientific methods.

What is a flowstone/speleothem?

Inside caves we get a specific type of rock forming – the most common variations of this are stalagmites and
stalactites. A flowstone is the same type of material (calcium carbonate or lime) as a stalagmite but instead
of growing upwards and forming pillar like structures the flowstone flows out across the floor of the cave to
form a layer of calcium carbonate. These layers are usually a few CENTIMETERS thick but can be up to
several METERS thick. A speleothem, is a technical term used to describe any type of rock forming in a cave,
so stalagmites, stalactites and flowstones are all types of speleothems.

What is uranium-lead dating?

When the flowstone rocks are formed, uranium gets trapped in them, this uranium decays by natural
processes and forms lead. We know the rate at which uranium decays, and from measuring the amount of
uranium and lead present in the rocks today, we can calculate how old the rocks are. In this way the uranium
acts as a clock, which starts ticking once the rocks are formed. The amounts of uranium and lead we are
dealing with are extremely small, in the parts per million and even the parts per billion range. In order to
measure such small abundances of these elements we need large, powerful machines called mass-
spectrometers. The samples are prepared in a laboratory in Australia, the uranium and lead isotopes are
isolated and concentrated from the rocks and collected for measurements.

What is Palaeomag?

The Earth’s magnetic field currently runs from north to south, which is known as a NORMAL field state.
However, at various times throughout Earth’s history the field has reversed by 180 degrees in what is known
as a REVERSED field state. The timing of such major field changes is pretty well known for the last 7 million
years (Ma) based on studies of sea floor spreading zones, where these changes are recorded like a bar
code, as well as thedating of volcanic rocks. This bar code of field change is known as the
Geomagnetic Polarity Time-Scale or GPTS. All rocks contain some form of magnetic mineral. The direction
of the Earth’s field is preserved in cave sediments when water flushes these sediments into pools of water.
When the sediment settles out of suspension in water the magnetic minerals orient themselves to the
contemporary magnetic field. The sediments then become compacted and cemented, preserving the
magnetic field direction. By measuring sediments in caves and comparing the polarity with the GPTS, the
age of the sediments, and therefore the fossils within them, can then be determined.

What happens during a palaeo-magnetic reversal events like the one seen in the rocks of Malapa?
We don’t know, but scientists suspect there might be severe changes in weather patterns as well as
exposure to increased solar radiation as the Earth’s magnetic field fluctuates.


How were the individuals preserved?

The site where the fossils were discovered is technically the infill of a de-roofed cave that was about 30 to 50
metres underground just under two million years ago. The individuals appear to have fallen, along with other
animals, into a deep cave, landing up on the floor for a few days or weeks. The bodies were then washed
into an underground lake or pool probably pushed there by a large rainstorm. They did not travel far, maybe a
few METERS, where they were solidified into the rock, as if thrown into quick setting concrete. The rock they
are preserved in is called calcified clastic sediment. Over the past 2 million years the land has eroded to
expose the fossil bearing sediments. FOR A POSSIBLE RECONSTRUCTION OF THIS EVENT SEE THE
SKULL IN THE ROCK, PAGE 50

Did they die in a catastrophe?

The hominin skeletons were found with the bones either in partial articulation or in close anatomical
association, which suggests that the bodies were only partially decomposed at the time of deposition in the
lower chamber. This further suggests that they died very close in time to each other, either at the same time,
or hours, days or weeks apart. Other animals have been found with them - equally complete - including
sabre-toothed cats, hyenas, antelopes, mice, birds and even snails. There is also plant material that has
been found.

Is there organic preservation like plant remains or skin?

The preservation at Malapa is so good that there are certainly organic remains preserved like plant remains.
There are some indications that even soft tissues of animals are preserved, including possibly skin. This
material is presently under study by a world-wide based team of experts, who are attempting to prove or
disprove the existence of such important material, and develop ways to study things that have never been
found before in the early hominin record. Some scientific papers have been published on this.

What is so special about the brain scan?

The synchrotron scan of the brain used in this study is the most accurate ever produced for an early human
ancestor. At a resolution of around 90 microns (scan widths just below the size of a human hair), incredible
details of the anatomy of sediba’s brain are revealed that give the team an unprecedented look at the brain of
the MH-1 individual.

Where is the synchrotron scanner that was used?

The synchrotron scanner is a multi-billion Euro device located in Grenoble France. It is called the European
Synchrotron Radiation Facility (ESRF) and sediba travelled there as diplomatic baggage under heavy
security escort. FOR MORE ON THE SYNCHROTRON AND BRAIN SCAN SEE THE SKULL IN THE ROCK,
PAGES 48-49

How does a brain endocast form?

With every heartbeat, the brain pounds out its shape on the developing skull of a child, eventually leaving a
beautiful impression of the external shape and form of the brain on the inside of the skull. By mapping the
contours of this surface, we can produce a clear image of the original brain that sat in the skull. Because
this resolution changes through time, the endocasts of children tend to be clearer than those of adults.

What does the study of the brain show?

This study of the brain shows a surprising mix of characters. The overall shape of the MH 1 endocast groups
closely with all humans. Given how small the brain of sediba is (around 420cc’s or the size of a medium-
sized grapefruit), these results are consistent with a model of gradual neural (brain) reorganization in the
front part of the brain. However, one of the major discoveries announced in the paper LISTED BELOW is that
the shape and form of sediba’s brain is not consistent with a model of gradual brain enlargement, which is
what has been hypothesized previously for the transition from
Australopithecus to Homo. This was published
in a paper in Science in 2011.

Is this the first, and most complete hand?

The right hand of the female MH2 published in these papers is the most complete hand of an early hominin
ever described. It is missing only a few bones (the tips of four fingers and a wrist bone). We have, however,
high hopes of eventually finding even these bones. FOR MORE ON THE HAND, SEE THE SKULL IN THE
ROCK, PAGE 53.

What is special about the hand?

The hand is one of the very special features of our lineage, as it is very different from the hand of the apes.
Apes have long fingers for grasping branches or for use in locomotion, and thus relatively short thumbs
making it very difficult for them to grasp like a human. Sediba has, in contrast, a more human like hand that
has shortened fingers and a very long thumb, although, at the same time it appears to have possessed very
powerful muscles for grasping. We have interpreted this as being a hand capable of tool manufacture and
use, but still in use for climbing and certainly capable of a human-like precision grip. However, the sediba
hand is still primitive in many ways compared to modern humans, and we do not suggest that
Au. sediba
was the only hominin around 2 million years ago capable of making tools. For example, Au. sediba hand
morphology is very different from the hand bones that were used to define the first tool-maker,
Homo habilis
or the “handy man.” This may suggest that there were many different hominins making tools with different
types of hand morphology around the same time period.

Compared to the hand of
Au. afarensis – Lucy’s species – sediba has fingers that are shorter (thus, a
proportionately longer thumb) and less curved, suggesting that
Au. sediba was not moving around in the
trees as much as Lucy. Sediba has broader finger tips, stronger muscles of the thumb and a more human-
like wrist that also suggest it had better manipulative abilities than Lucy and her kin. The hand was
published in the journal Science in 2011.

What is a precision grip?

A precision grip is a grip that involves the thumb and one or more fingers, but the palm is not actively
involved. There are several different types of precision grips, but the most common one people think of is the
ability touch the end of your thumb to the tip of your index finger. Other precision grips include a pad-to-side
grip between the thumb and the side of the index finger, such as when turning a key in a lock, or a pad-to-
pad “baseball” grip, like when gripping a ball with just your fingertips. Other primates are capable of some
precision grips but humans are unique in our ability to use these grips forcefully and for fine manoeuvring of
objects within the hand. Sediba would have, without a doubt, had an excellent precision grip.

Does Au. sediba imply that Homo habilis was not a tool-maker?

No, but the answer is a bit more complicated than that. The OH 7 hand bones were found in the early 1960s
in direct association with stone tools. Thus the OH 7 hand was assumed to be capable of making stone
tools, which was key to including these fossils within our own genus Homo and naming of the species
Homo habilis or the “handy man”. Since this time, few have questioned the tool-making ability of Homo
habilis.

When we make a direct comparison between the bones preserved in
Au. sediba and the OH 7 “handy man”
hand bones, their anatomy is very different. The OH 7 hand appears to have a derived large, robust thumb
and very broad finger tips, while the
Au. sediba thumb is gracile and the fingers tips are not quite as broad.
In contrast, OH 7 still has fingers that are strongly curved and the wrist bones are more like those of African
apes, while
Au. sediba is more derived or human-like in these features. This difference in morphology
implies two (though not necessarily mutually exclusive) scenarios: (1) that both species are capable of
making tools but that they do this with different anatomy or (2) that the OH 7 hand does not in fact belong to
Homo habilis, but is instead the hand of another early hominin species. Either way, it is likely that many
hominin species were capable of making stone tools given that stone tools appear in the archaeological
record long before either
Au. sediba or Homo habilis are known to have lived. However, the paucity of
complete hand bones in the fossil record and our poor understanding of how the human hand functions and
what morphology is necessary to make tools has limited our ability to determine exactly which species made
tools and when and how tool-making first evolved. Sediba has shed new light on these questions.

Have you found tools?

Excavations have not been conducted yet, so it is premature to speculate whether we will find tools in direct
association with Au. sediba, although the hand and brain morphology suggest sediba may have had the
capacity to manufacture and use complex tools.

What is special about the pelvis?

The pelvis (hip bone) of sediba is a mix of earlier hominin shape and form and later human shape and
form. It is short and broad like our pelvis, creating more of a bowl shape than in australopiths like Lucy, but it
still retains some features of earlier hominins, particularly in the size of the joint that links the sacrum with
the vertebral column and the length of the front part of the pelvis. Parts of the pelvis are pretty much
indistinguishable from ours and it has what we call a sigmoid shape (s-shape) along the top of the blades. It
is surprising to see such an advanced pelvis in such a small-brained creature because of previous ideas as
to the origin of the shape of the human pelvis. The pelvis was published in a Science article in 2011.

What is the obstetric hypothesis and what does the pelvis of sediba have to tell us
about this?

The obstetric hypothesis is a scientific theory developed more than three decades ago that suggested that
the evolution of the larger brains of early Homo were the reason the human pelvis is shaped differently to
early hominins like Lucy, which are broader, flatter and more flaring. Sediba, with its small brain, proves that
at least in this lineage, the obstetric hypothesis for the origins of the human shaped pelvis is wrong, and it is
therefore probably a hypothesis that has been refuted in our entire lineage. The shape and form of the
sediba pelvis suggests that we must look to other explanations for the origins of modern pelvic shape.

What is so important about the foot?

The foot is very important in the evolution of the human lineage. Of all the evolutionary specializations that
define the human species, the foot is thought to be one of the most important and is pivotal in allowing the
evolution of arguably the most critical defining character of the hominins – habitual upright walking or
bipedalism.

What is special about the ankle of sediba?

Parts of both the child and adult’s ankles were found. The female MH2 ankle is one of the most complete
ankles ever found (only Little Foot’s ankle is nearly as complete), and it was found in articulation (the bones
connected, nearly in living anatomical position). The ankle joint is mostly human-like in form and inferred
function, and there is some evidence for a human-like arch and Achilles tendon. However, a surprising find
is that Au. sediba is ape-like in possessing a more gracile calcaneal (heel) body and more robust medial
malleolus (the lowest part of the tibia, or shin bone) than expected. This suggests that
Au. sediba may have
practiced a unique form of bipedalism, and almost certainly climbed trees. It is also surprising that with
parts of the heel being more primitive than earlier hominins like Lucy, it may mean that sediba did not
descend from this lineage. No ankle has ever been described with so many primitive and advanced
features in one complex, and if the bones had not been found stuck together, the team might have described
them as belonging to different species. The ankle was published in a Science paper in 2011.

With these ape like features, how do you know that Au. sediba was a habitual biped?

The distal tibia or leg bone contacts the ankle bone perpendicular to the shaft of the leg bone, like that of
modern humans. This is indirectly related to the position of the knee required for upright walking. In addition,
there is evidence of a longitudinal arch and strong Achilles tendon insertion at the back of the heel, both
being requirements of bipedalism. Sediba, however, practiced a unique form of upright walking, not exactly
like that of humans, with some degree of tree climbing.

How did you take the ankle bones apart?

The ankle bones were taken apart ‘virtually” using 3-D scanners, like CT scanners, and separating the
bones. These digital bones were then printed out so that they could be studied by scientists, thus the team
did not have to damage the articulated ankle.


How old are the children you have found?

The juvenile MH-1 is around 10 – 13 years old in human developmental terms. He was probably a bit
younger in actual age (perhaps as young as eight or nine or so) as he is likely to have matured faster than
humans. The age estimate is based on modern human standards by which the eruption stages of the teeth
are evaluated and the degree of development of the growth centres of the bones. Studies are presently
being undertaken that will attempt to precisely give the age of this child at death. The other young hominins
found at the site are still under study and no exact, or even good estimates of their age have been made yet.

How old is the female skeleton?

Based on the extreme wear of her teeth, MH-2 is probably at least in her late twenties or early thirties but it is
very difficult to determine the age of an adult at death because their bones have completed growing.

Did she have children?

It is sometimes the case that females develop small pits on the back side of the pubic bone when they
deliver a baby (caused by stress on the ligaments crossing the front of the pelvis). These pits are known as
“scars of parturition,” and MH2 may have one such scar. However, these pits can also be produced by other
factors, and thus they do not always indicate that a female has given birth. It is likely that a female
Australopith of her age would have had children. Detailed studies are presently being undertaken that
should shed light on this intriguing question.

If she HAD, had children, would she have given birth to a large-brained or small-brained child?
The estimated adult brain size based on the MH1 juvenile is approximately 440 cm3, which is slightly below
the average for
Au. afarensis (Lucy’s species) and Au. africanus (Mrs. Ples’ species). This suggests that,
like australopiths, sediba gave birth to small-brained babies (based on the relationship of adult to neonatal
brain size in chimpanzees, australopiths are thought to have given birth to babies with brains on the order of
ca. 153 – 201 cm3).

How do you Karabo is a male?

There are features of the face that help us determine that the child is a male. The muscles of the child are
larger than that of the other skeleton, even though it is a child. There are also features of the pelvis that we
can use to determine that it is a male and with the new pelvis of MH2, we can now directly compare the
pelveses of a male and a female.

Are they related to each other?

At present we do not know for sure. But given the apparently very short time of between their deaths, and the
varying age of theindividuals, it is likely that they are related. Detailed studies are underway or are being
designed to address
this important question.


How does Australopithecus sediba relate to Lucy?

Australopithecus sediba is approximately a million years younger than Lucy. Some scientists feel that Lucy’s
species,
Au. afarensis, gave rise to Au. africanus.  My team suggeststhat Au. africanus or something earlier
than
Au. africanus, gave rise to Au. sediba. There is some evidence, based upon the both primitive and
advanced foot and ankle of sediba, that it does not descend from lucy’s species or maybe even africanus,
but comes from some as yet unidentified lineage of early hominin. Additionally, the very advanced nature of
sediba’s hand suggests it may not give rise to
Homo habilis, which although later in time, has a more
primitive hand, even though
Homo habilis is some 200,000 to 300,000 years
younger than sediba.

Has the new species named last year been accepted by the scientific community?

There is broad acceptance of the species Au. sediba among scientists as something previously unknown to
science. Very little debate has occurred around whether these bones represent a new species. The debate
has centered, largely, around whether the species should be placed in the genus
Homo.

So why is this not the genus Homo?

The fossils have an overall body plan that is like that of other Australopiths – they have small brains, relatively
small bodies and long and seemingly powerful arms. They do, however, have some features in the skull,
hand and pelvis that are found in later definitive members of the genus Homo but not in other Australopiths.
However, given the small brains and Australopith-like upper limbs, and features of the foot and ankle, the
team has felt that keeping this species in the genus Australopithecus was the conservative thing to do.
Nevertheless, sediba is turning out to be one of the most intriguing hominins yet discovered, and it certainly
shows a mosaic of features shared by both earlier and later hominins.

What about Homo habilis?

Our study indicates that Australopithecus sediba may be a better ancestor of Homo erectus and it may
certainly help to clear up some of this “muddle in the middle”.

Even after several years, why is there still rock attached to the child’s skull?

Due to the fragility of the base of the cranium of the specimen and to preserve part of the adhering matrix for
future research as technologies improve, the team has decided to leave the specimen partially in rock. The
team has been able to visualise this hidden part using some of the most sophisticated scanning technology
available.



Will there be more discoveries from Malapa?

Malapa is already one of the richest early hominin sites ever discovered but excavations have not
commenced yet. When they do, later this year, we expect to make even more remarkable finds at the site.
Frequently Asked Questions
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