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Interview
The
Latest Leakey Searches for Our Earliest Ancestors
A Conversation with Meave Leakey
Not long after Louis and Mary Leakey unearthed
"Zinjanthropus" in 1959 and reignited excitement about the human lineage,
their son, Richard, recruited a young zoology student from the University
of North Wales at Bangor to join the archeological team. Meave Epps married
her mentor and collaborated on many discoveries and reconstructions, including
"Nariokotome Boy," the most complete skeleton of Homo erectus found to
date. Richard later turned his attention toward bolstering a desperately
needed conservation movement in Kenya. After he lost his lower legs in
an airplane crash in 1993 and could no longer work in the field, Meave
turned her attention from fossil mammals to take charge of the family
paleoanthropological tradition. Meave Leakey now heads the paleontology
division at the National Museums of Kenya, and in 1994 she led a team
which discovered the earliest known hominid species, Australopithecus
anamensis. She was interviewed from her home in Nairobi by California
Wild editor Keith Howell.
Keith Howell: What is the earliest evidence
we have for hominid evolution?
Meave Leakey: The earliest hominids we
have are probably the ones from Ethiopia that Tim White [at the University
of California at Berkeley] found at Aramis [assigned to Ardipithecus
ramidus]. He hasn't published his material yet, so it's not quite
clear whether they are hominid or hominoid.
KH: What is the distinction between those
two?
ML: They are generally considered to be
hominids when they're bipedal, so that bipedality is the adaptation that
defines a hominid. Tim, in his original publication, said that he thought
that he had a hominid, but he didn't have terribly good evidence. I generally
say that the material from Kanapoi, at 4.1 million years, is the oldest
secure evidence of hominids.
The ancestors of apes and humans are hominoids.
So hominoids are found before the ancestral lines that led to modern African
apes and us diverged.
KH: Did bipedalism evolve before or after
hominids emerged from the forest?
ML: The evidence that we have from Kenya is that there was a major
change in vegetation around about seven million years ago, and at that
point we start getting herbivorous animals evolving adaptations for grazing
rather than browsing. And so there does seem to be a major change at that
time in vegetation, which may be related to climate. Now the hominids
didn't evolve till about five-and-a-half-million. I think their appearance
is associated with that change in the environment, although their evolution
is slightly later than we see it in other animals.
A lot of this work has been done with carbon isotopes.
By analyzing carbonates in soils we can detect changes in vegetation,
and by analyzing fossil tooth enamel we can tell whether the animals were
eating grass or leaves. You can see a major change in the vegetation about
seven million years ago from C3 photosynthesizing plants to C4 photosynthesizing
grasses.
The difference depends on temperature, the amount
of carbon dioxide in the atmosphere, and other parameters. For example,
C3 photosynthesizing plants are largely trees and shrubs and C3 grasses
are those that grow at high elevations, in forests and in places where
growing season temperatures are low. C4 photosynthesizers are the common
grasses found in the savannas and bushlands. They are tolerant to drought
and to lower carbon dioxide in the atmosphere. It is a bit complicated
actually. I have been working with Thure Cerling [University of Utah]
and John Harris [Los Angeles County Museum] on this and they have been
analyzing modern dental enamel and fossil dental enamel. It is very interesting
because the change that we see not only takes place in Africa, but also
in Asia and America. Thure believes that the change took place because
the carbon dioxide in the atmosphere, which has been slowly decreasing
over the last hundred million years, reached a threshold seven million
years ago when C4 plants, which are more tolerant to low carbon dioxide
levels, were at an advantage. The increase in C4 grasses was a global
phenomenon.
KH: You found Australopithecus anamensis
and felt it was earlier than A. afarensis. What was it about anamensis
that made you feel that way?
ML: We've got good dates now for the anamensis
sites. Anamensis mainly comes from Kanapoi, which is 4.1 million,
and from a second site, Allia Bay, which is 3.9 million. The differences
between anamensis and afarensis are mostly in the cranial
and the mandible morphology. The few pieces of crania that we have show
that it's much more primitive and more apelike than afarensis.
So if you look at the mandible, specifically the chin area, it has a distinct
morphology and the tooth rows are parallel. If you look at apes, the cheek
teeth align parallel to each other and there is no chin. Whereas if you
look at a human mandible the cheek teeth diverge: a "V" shape as opposed
to a "U" shape. If you look at afarensis it's "V" shaped, and if
you look at anamensis it's "U" shaped and there is no chin. The
canines are large and tend to be a slightly different shape as do the
premolars. So, some of the teeth seem to be much more apelike.
And the anamensis ear, the external, auditory
meatus, that's where the ear opening is, is small like a chimpanzee's
rather than large like that of afarensis and later hominids. And
then the palate is a different shape. The differences in all these things
are fairly subtle, but they're definitely there. That leads us to say
that the cranial morphology and the cranium itself is much more primitive
and more apelike than afarensis. But if you look at the postcranium,
the anamensis tibia that we have is very, very similar to afarensis.
We have a finger bone that is also similar, but we have a hand bone that
shows some differences. I think probably the hind limb was similar to
afarensis so that anamensis would have definitely been bipedal,
as bipedal as afarensis. But perhaps the forelimb was slightly
more primitive with less mobility of the hand. I am sure early hominids
would have climbed trees to escape predators and to forage.
KH: Do you feel there were many different
hominid species around that period?
ML: It's a difficult question to answer because, though we don't
have evidence to say that there were a lot of species around, I feel there
really should have been. If you look at any other mammalian group you
find that when there is a major adaptation, then immediately there's speciation
and you get a number of species experimenting with the adaptation and
just a few come through as being successful. So if you have a major adaptation
like bipedality you'd expect that you'd get a lot of experimentation,
you'd get a lot of different species. The fact that we haven't found them
probably reflects more on the fact that we don't have many sites of this
early age than that the species weren't there. If we had more sites, with
good fossil records, from between eight and four million years ago we
would probably have a very different picture. At the moment we're interpreting
anamensis as ancestral to afarensis. It seems to make a
very good ancestor. Because ramidus, the Ethiopian 4.4 million-year-old
species, hasn't been published, we really can't yet comment on that. I
believe that if we could find more sites then we might well see some things
happening in terms of speciation and the number of species.
KH: Are you currently working with anamensis?
ML: At the moment I'm not. I've moved to
a site called Lomekwi, which is just over three million years old, because
I want to know what hominids lived in the Turkana Basin at that time.
Lomekwi is contemporary with the afarensis site at Hadar. I want
to see if we find the same hominids or whether we're getting different
ones, and whether there was just one hominid lineage at that time or whether
there were more. So I'm working just further north from Kanapoi. It's
still in the Turkana Basin, on the west side of the lake.
KH: Why is there such a paucity of early
ape fossils while there are so many hominids and fossil monkeys?
ML: There isn't really. In Africa we have
many apes at many sites dated between 20 and 12 million, but don't have
a very good fossil record between about 12 million and 7 million. If you
go to Europe and Asia at that time then you do find a lot of apes around.
They have a lot of species and a good record. The fact that we don't have
them here, I think, has a lot to do with the sites. There are some sites,
but the specimens we're getting from them are not terribly good, with
a few exceptions. And I am puzzled, I have to say, at the exceptions.
I was working at a site called Lothagam that dated between five million
and nearly eight million and we didn't find any hominids before just over
five million. I found that really puzzling. I had expected that we would
find something, either apes or ancestral humans. So it may not just be
related to the fossil record. There may be something more to it than that.
It could be we're not sampling the right sites. Most of the sites we have
are in much more open countryside, and it could be, for example, that
at that point our ancestors were living in forests. But you definitely
do get a good record in Europe between about ten and seven million.
KH: Why do you think East Africa is so
productive for hominids?
ML: Because of the Rift Valley. We are
incredibly fortunate to have the Rift Valley because that system has been
forming over the last 20 million years. During the course of its formation,
water drained into the rift bringing with it lots of sediment, and the
sediments have buried the bones of any animals that were lying around.
So it was ideal for fossilization of carcasses and animal bones. And the
fact that the rift is continuing to form means you are now getting erosion
of those sediments, exposing the fossils. Which is just amazingly fortunate.
Also, many of the rift sites, like Turkana, are badlands, which cannot
be cultivated and are not threatened with buildings and concrete. There
are just an enormous number of sites in East Africa, but they're mainly
all in the Rift Valley.
KH: So after each rainstorm you go out
to inspect the site?
ML: Surprisingly, it actually takes longer
than that to expose the fossils, but yes we do. And with a significant
rainstorm there's always something that's come up. But I think it takes
decades to really weather out a significant number of fossils at a site.
KH: Are there any missing links still missing?
ML: Oh, yes, there are so many. They say "missing links" but it's
really like a chain with hundreds and hundreds of links, and everything's
missing until you find it. The more you find the more you need to know
and the more questions you have to ask and the more puzzled you are. If
you have just a few fossils of different ages you can draw a straight
line between them and say this is how it was and it all looks terribly
simple and easy, but the more specimens you get the more questions there
are, and it becomes much more complicated. And as we are increasing our
evidence we're finding we have more and more missing links if you like
to put it that way.
KH: What sort of expertise do you take
along on a paleontology dig?
ML: We always have a geologist. That's
the most important person we can take. Without a geologist nothing you
find means anything. We try to work out the geology before we actually
do any paleontology. And then, with the geology well understood, we can
put our fossils into context. We then take experts in dating, and looking
at fossil soils and things. And then, of course, we take along paleontologists.
But basically, and most importantly, my team is a field crew from the
National Museum. They have incredibly good eyesight and they know their
bones really, really well so that when they find something they know what
it is; they know exactly which animal it is, and which part of the body
it came from. These are the key people who find the fossils. If it wasn't
for them we really wouldn't have the record we have.
KH: When you find fossil skulls in hundreds
of pieces, how do you set them up and put them all together?
ML: Really, it's just a three-dimensional
jigsaw puzzle without the picture. If you know the anatomy of the skull
you can recognize where most pieces come from. With a jigsaw puzzle you
put all the blue pieces together and the green bits and edge bits, and
so on. With a skull, you put all the pieces of the face together and pieces
of the ear, and in the same way you try to fit those pieces that you know
come from one area together.
KH: What was the atmosphere like at Koobi
Fora 30 years ago when you were finding all those fossils?
ML: It was incredible. The area was unexplored,
with no roads and no people. It was a sort of no man's land as far as
the local tribes were concerned. When they came into the area they would
fight each other, so they tended to keep out. We were pretty much on our
own. And in terms of the paleontology, it was completely unexplored, too,
and everywhere we went we found completely new things. It was amazingly
exciting, and I love to be in remote places and be in the bush. It was
an experience I felt very privileged to be part of.
KH: How did you first get involved in human
origins?
ML: Well I did a zoology degree at the
University of North Wales in Bangor and for my Ph.D. I specialized in
modern monkey skeletons, and so when Richard [Leakey] asked me if I would
join the expedition and look at the fossil monkey skeletons, of course
I accepted. Which is how I first got up there. Then, after a very short
time, I was hooked. It was all so exciting and so much fun. But I had
originally intended to do marine zoology. I never intended to do paleontology,
but life takes different courses.
KH: According to Nina Jablonski, my colleague
here at the Academy, in spite of your busy life you never appear flustered.
I was wondering how you apportion your time between work in the field,
writing, traveling, and your family.
ML: I think basically we are a busy family
and we've all got lots to do and we're all busy doing what we all do.
When we do get together weekends and evenings, it's always very rewarding.
I think one just portions one's time as one can. Certainly the time goes
very fast and the years go very fast. But I try to do some traveling,
some field work, some lab work, and of course I have all the administration
at the museum, which takes a lot of time as well.
KH: I understand your daughter, Louise,
is following in your footsteps.
ML: Yes, that's the wonderful thing. We
now run joint expeditions and so she works with me in the field. She's
doing her Ph.D. on the area where we're working, only she's doing a later
time period so that she works in sediments that are aged 1.5 million to
three million and I work in sediments that are three million to four million.
We go off in our separate directions through the week and then come together
at weekends to compare notes and to catch up on the curating and packing
and cataloging problems. It works incredibly well. It's really lovely
to have her with me.
KH: Do you think your younger daughter,
Samira, will also follow in the family footsteps?
ML: No, no, no, she's at Princeton studying
quite a different field. She's more politically and development minded.
But she has many interests that coincide with Richard's, so that works
very well.
KH: What is Richard doing?
ML: He's busy running the Kenya Wildlife
Service. But he has recently been appointed Chairman of the Board of the
National Museums of Kenya, so he does give some direction to the museum
as well.
KH: Is this likely to bring him back into
the fossil world?
ML: I don't think so. It's hard for him
to walk in the field and without his own legs he gets extremely hot. But
he retains an interest in what we're doing, obviously.
KH: What are your plans in the field for
the next year or two?
ML: When we finish on the west side of
the lake, which I think might be this year or next year, then we're planning
to go back to the east side and rework some of the important sites at
Koobi Fora. Because we haven't worked there now since the late 1970s,
there should be a lot to do. Many new fossils must have eroded out. And
what we are basically trying to do is to systematically work sites that
have been worked before, but, this time, in much more detail and looking
much more carefully, so that we get a lot more information out of them.
Because there are many more techniques now that can be used to analyze
the data, we can learn more from each site than ever before.
Keith
K. Howell is Editor of California Wild.
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