Preserving the Laetoli Footprints The discovery of hominid footprints in East Africa reshaped the study of human origins. Now conservators have protected the fragile tracks from destruction by Neville Agnew and Martha Demas THREE EARLY HOMINIDS cross a landscape covered with volcanic ash 3.6 million years ago in an artist’s rendering of the Laetoli footprint makers. A large male leads the way, while a smaller female walks alongside and a medium-size male steps in the larg- er male’s footprints.Other Pliocene animals—includ- ing giraffes, elephants and an extinct horse called a hipparion—also leave their tracks in the ash. 44 Scientific American September 1998 Copyright 1998 Scientific American, Inc.
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Preserving the Laetoli FootprintsThe discovery of hominid footprints in East Africa reshaped the study of human origins. Now conservators have protected the fragile tracks from destruction
by Neville Agnew and Martha Demas
THREE EARLY HOMINIDS cross a landscape coveredwith volcanic ash 3.6 million years ago in an artist’srendering of the Laetoli footprint makers. A largemale leads the way, while a smaller female walksalongside and a medium-size male steps in the larg-er male’s footprints. Other Pliocene animals—includ-ing giraffes, elephants and an extinct horse called a hipparion—also leave their tracks in the ash.
44 Scientific American September 1998 Copyright 1998 Scientific American, Inc.
Copyright 1998 Scientific American, Inc.
One of the most remarkable events in the annals of anthropol-ogy occurred 20 years ago in an area of northern Tanzaniacalled Laetoli. A team led by famed archaeologist Mary D.
Leakey was searching for fossils of the early hominids that rangedthrough East Africa millions of years ago. In the summer of 1976, af-ter a long day in the field, three visitors to Leakey’s camp engaged insome horseplay, tossing chunks of dried elephant dung at one another.When paleontologist Andrew Hill dropped to the ground to avoid get-ting hit, he noticed what seemed to be animal tracks in a layer of ex-posed tuff—a sedimentary rock created by deposits of volcanic ash.On closer inspection of the area, the scientists found thousands of fos-silized tracks, including the footprints of elephants, giraffes, rhinocer-oses and several extinct mammal species. But the most extraordinaryfind came two years later, when Paul I. Abell, a geochemist who hadjoined Leakey’s team, found what appeared to be a human footprintat the edge of a gully eroded by the Ngarusi River.
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Excavations of the Footprint Tuff—as it came to be known—in 1978 and1979 revealed two parallel trails ofhominid footprints extending some27 meters (89 feet). The volcanic sed-iments were dated radiometrically tobe between 3.4 million and 3.8 mil-lion years old. The discovery settled along-standing scientific debate: theLaetoli footprints proved that early
hominids were fully bipedal—they hadan erect posture and walked on twofeet—long before the advent of stonetoolmaking or the expansion in size ofthe human brain. What is more, thetrackway provided information aboutthe soft tissue of the hominids’ feetand the length of their strides—infor-mation that cannot be ascertainedfrom fossil bones. For these reasons,the Laetoli footprints attracted a hugeamount of attention from scientistsand the general public. Leakey, whodied in 1996, regarded the discoveryas the crowning achievement of hersix decades of work in East Africa.
That the footprints have scientificvalue is obvious: they have answeredfundamental questions about human-ity’s past. But they also have a pro-found cultural symbolism. In a pow-erfully evocative way, the tracks ofthose early hominids represent thelong evolutionary history of human-kind. The footprints bear witness to adefining moment in the developmentof our species and speak to us directlyacross thousands of millennia.
For the past six years, the GettyConservation Institute—a Los Ange-les–based organization concernedwith the preservation of cultural her-itage—has worked with Tanzanianauthorities to ensure that the Laetolifootprints stay intact for years tocome. A team of conservators and
scientists recently completed a projectto protect the footprints from ero-sion, plant growth and other causesof deterioration that have threatenedthe trackway since its discovery.
A Pliocene Eruption
Skeletal remains stand a betterchance of survival in the fossil rec-
ord than impressions in mud or vol-canic ashfall. Yet traces of many ani-mals dating back to the Paleozoic era,some as old as 500 million years, areknown throughout the world. Becausean animal leaves many tracks duringits lifetime but only one set of boneswhen it dies, statistically it is not sosurprising that some of the tracks sur-vive as fossil imprints. The numberand variety of tracks preserved in theLaetoli exposures is nonetheless un-usual. At the largest of the 16 sites atLaetoli where tracks have been found,there are an estimated 18,000 prints,
CONTOUR MAP of hominid footprint G1-36 (right) was created by taking twooverlapping photographs of the print with a high-resolution camera. The deep im-pression at the bottom of the print indicates that the hominid walked like a modernhuman, placing its full weight on its heel. The length of the footprint is about 20centimeters (eight inches). On the next page, two views of footprint G1-25 showthat it suffered little damage between its discovery in 1979 and its reexcavation in1995. The reexcavated print (far right) is shown next to a photograph of the printtaken in 1979 by a member of Mary Leakey’s team.
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LAETOLI AREA in northern Tanzanialies in the eastern branch of the GreatRift Valley, where many hominid fossilshave been found. Other well-knownhominid sites include Hadar and Omoin Ethiopia, Lake Turkana in Kenyaand Olduvai Gorge in Tanzania.
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representing 17 families of animals, inan area of about 800 square meters.
Laetoli lies in the eastern branch ofthe Great Rift Valley, a tectonicallyactive area. About 3.6 million yearsago, during the Pliocene epoch, theSadiman volcano—located 20 kilome-ters (12 miles) east of Laetoli—beganbelching clouds of ash, which settledin layers on the surrounding savanna.At one point in the volcano’s activephase, a series of eruptions coincidedwith the end of an African dry sea-son. After a light rainfall, the animalsthat lived in the area left their tracksin the moist ash. The material ejectedfrom Sadiman was rich in the mineralcarbonatite, which acts like cementwhen wet. The ash layers hardened,preserving the thousands of animalfootprints that covered the area. Short-ly afterward Sadiman erupted again,depositing additional layers of ash thatburied the footprints and fossilizedthem. Finally, erosion over millions of
years reexposed the Footprint Tuff.The two parallel trails contained a
total of 54 footprints that could beclearly identified as hominid tracks.The soil covering varied from a fewcentimeters at the northern end of thetrackway—the area where the foot-prints had first been discovered—to 27centimeters (11 inches) at the south-ern end. To the north, the footprintsended at the wide, deep gully cut bythe Ngarusi River; to the south, fault-ing and erosion precluded any chanceof picking up the trail. The trackwayitself shows faulting, too, with a gra-ben—a section that had dropped 20to 40 centimeters because of tectonicactivity—near the midpoint. Part of thetrackway is also heavily weathered: inthis section the tuff had changed todried mud and the footprints werepoorly preserved. But in the less weath-ered part of the trackway the preser-vation was good, allowing clear rec-ognition of soft-tissue anatomical fea-
tures such as heel, arch and big toe.As so often happens in the field of
paleoanthropology, disagreement soonbroke out regarding the interpretationof the evidence. One point in disputewas the species of the hominids thatmade the footprints. Leakey’s teamhad found fossilized hominid bones inthe Laetoli area that were the same ageas the trackway. Most scientists believethese hominids belonged to the speciesAustralopithecus afarensis, whichlived in East Africa between 3.0 mil-lion and 3.9 million years ago. In fact,one of the Laetoli hominid remains—
a mandible with nine teeth in place—
became the type specimen, or definingfossil, for A. afarensis. (The famoushominid skeleton known as “Lucy,”discovered in 1974 in Ethiopia, is an-other representative of this species.)But Leakey did not accept that theLaetoli hominids were specimens ofA. afarensis; she resisted assigningthem to any species. (Leakey was cau-tious about interpreting her discover-ies.) She did believe, however, that themakers of the Laetoli footprints stoodin the direct line of human ancestry.
Another dispute concerned the num-ber of hominids that made the twoparallel trails. In one trail, the foot-prints were small and well defined,
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but in the other the prints were largerand less clear. Some scientists specu-lated that the trails were made by twohominids—possibly a female and amale—walking abreast or close to eachother. [For artistic representations ofthis interpretation, see “The Foot-print Makers: An Early View,” by JayH. Matternes, on page 52, and “TheLaetoli Diorama,” by Ian Tattersall,on page 53.] Other scientists believedthe trails were made by three homi-nids. In this view—which most paleo-anthropologists now share—the trailof larger footprints was made by twoindividuals, with the second hominidpurposely stepping in the tracks ofthe first [see “A New Look at Lae-toli,” at right].
The footprints prompted other in-triguing questions: Where were thehominids going? What caused themto break stride—which is indicated bythe position of four footprints in thenorthern section of the trackway—asthough to look back on where theyhad come from? Were they a familygroup? Were they carrying anything?And how did they communicate?These tantalizing questions will neverbe answered, but scientists can use theevidence gleaned from the Laetoli siteto attempt to re-create the moment
when the hominid tracks were made.Much of the controversy over the
footprints arose because few scientistshad the opportunity to study the printsfirsthand. At the end of each field sea-son, Leakey’s team reburied the track-way for its protection. But the teammembers made casts of the best-pre-served sections of the trails and docu-mented the site fully. Researchers cre-ated three-dimensional contour mapsof some of the footprints by photo-
graphing them from two perspec-tives—a process called photogramme-try. Leakey later published her workwith several co-authors in a monu-mental monograph that dealt not onlywith the hominid prints but also withthe many animal tracks and the geol-ogy of the Laetoli area. The evidencecollected by Leakey’s group—whichalso included fossilized pollen andimpressions of vegetation—providesan unparalleled record of the African
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A New Look at Laetoli
The artist’s rendering of the Laetoli footprint makers on pages 44 through46 reflects the widely accepted interpretation that the trackway was
made by three hominids.Many of the larger tracks at the site have features in-dicating that they may be double footprints.The evidence suggests that a rel-atively large hominid—about five feet tall,based on the size of its footprints—walked first,and a hominid four and a half feet tall deliberately stepped in theleader’s footsteps, perhaps to make it easier to cross the slick, ash-coveredground.A smaller hominid—about four feet tall—apparently made the paral-lel trail of well-defined footprints.The trackway indicates that this hominid ad-justed its stride to keep up with one or both of the other hominids.
The illustration shows the two larger hominids as males and the smaller in-dividual as a female, but this was not necessarily the case: the smallest mem-ber of the trio could have been a child.The female is shown walking slightlybehind the lead male because the two could not have walked abreast with-out jostling each other. —The Editors
made by two hominids walking in tandem. The two northern-most tracks (far left) were destroyed by erosion between theirdiscovery in 1978 and reexcavation in 1996. Four other tracks
in the northern section—G1-6, G1-7, G1-8 and G2/3-5—markthe point where the hominids apparently broke stride. Also pres-ent are the tracks of a hipparion.
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savanna during Pliocene times and acontext in which to understand betterthe hominid trackway.
The Root Problem
Fieldwork on the Laetoli footprintsended with the 1979 season, and
Leakey’s team used local river sand torebury the site. Because the tuff is softand easily damaged, the mound of sandwas covered with volcanic boulders toarmor it against erosion and the animalsthat sometimes roam across the site—
particularly elephants and the cattle ofthe Masai people living in the area. Wenow know that seeds of Acacia seyal, alarge, vigorously growing tree species,were inadvertently introduced with thereburial fill. The loose fill and the phys-ical protection and moisture retentionprovided by the boulders created a mi-croenvironment conducive to germina-tion and rapid plant growth. Over thefollowing decade, the acacias and othertrees grew to heights of over two me-ters. Scientists who occasionally visitedthe Laetoli site began to voice concernthat the roots from these trees wouldpenetrate and eventually destroy thehominid footprints.
In 1992 the Antiquities Department ofthe Tanzanian government approachedthe Getty Conservation Institute, whichhas extensive experience in preservingarchaeological sites, to consider how thetrackway might be saved. The followingyear a joint team from the institute andthe Antiquities Department excavated asample trench in the reburial mound toassess the condition of the hominidfootprints. The assessment revealed thattree roots had indeed penetrated someof the tracks. But in the areas where noroot damage had occurred, the preser-vation of the prints was excellent. Lea-key’s intuitive decision to rebury the sitehad been the right one. With hindsightwe can now say that perhaps greatercare should have been taken in how thesite was buried. Also, periodic monitor-ing and maintenance—including the re-moval of tree seedlings before they be-came established—would have avoidedthe need for a long and costly conserva-tion effort.
The Getty Conservation Institute andthe Tanzanian government agreed tocollaborate on the project, but beforefieldwork could begin, various optionshad to be considered. Fossil bones areroutinely brought into the laboratoryfor study and permanent safekeeping.
Preserving the Laetoli Footprints50 Scientific American September 1998
REEXCAVATION began in 1995with the southern section of thetrackway (top right). Conservatorsextracted the acacia tree roots thathad penetrated the Footprint Tuff(middle right), then removed thefill from the footprints (top left).The reexcavated trackway (bot-tom left) was photographed with aPolaroid camera (bottom right) torecord conditions.N
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Indeed, to leave them in the field wouldbe irresponsible: they would certainly belost or damaged. But could the entirehominid trackway be lifted and movedto a museum in Tanzania? Was it tech-nically possible to do this without dam-aging the footprints? Some scientistswere vehement in their belief that thiswas the only way to save the tracks.
Removal would have been very risky,however, because the techniques for cut-ting out, lifting and transporting such alarge trackway had not been proved.The Footprint Tuff is far from being ahomogeneous stratum. It con-sists of many thin layers of vol-canic ash, each with differentweathering, hardness and cohe-sion. Without strengthening thetuff with resin—an interventionwith unknown long-term con-sequences—fracturing wouldprobably occur during removal.What is more, removing thetrackway or the individual foot-prints would separate them fromthe many animal tracks that hadbeen made at the same time.Part of the significance of thehominid trails—their setting inthe savanna landscape of EastAfrica together with the tracksof other Pliocene species—wouldbe lost.
An alternative proposal wasto shelter the trackway, erectinga protective building over it.The site could then be openedto the public, and the footprintscould be studied by visitingscholars. The Laetoli area, how-ever, is remote. There is no roadto the site and no water or pow-er lines nearby. Experience inTanzania has shown that with-out proper financing, trainedpersonnel and an adequate in-frastructure, sheltering the sitecould prove disastrous: it couldresult in the deterioration of thetrackway rather than its preservation.Even in countries where resources areplentiful, archaeological sites have beendamaged when planning has been inad-equate or when climate-controlled en-closures have not performed as expect-ed. Moreover, no shelter could fullyprotect the trackway from weathering:moisture from the ground below wouldrise to the surface seasonally throughcapillary action. Soluble salts in the wa-ter would crystallize on the surface,causing stress that would eventually
rupture the trackway. During the dryseason, dust accumulation in the printswould require frequent cleaning, whichwould inevitably lead to damage.
The third option was to reexcavatethe trackway, remove the vegetationthat had damaged it and then reburythe site more carefully, taking steps toprevent root growth that might harmthe footprints. Reburial is a proved pres-ervation method. The trackway sur-vived underground for thousands of mil-lennia; if reburied, it would be protect-ed from erosion, physical damage and
rapid fluctuations of moisture. Reburialis also readily reversible: the tuff can beuncovered in the future if the other op-tions become more feasible. For thesereasons, the Getty Conservation Insti-tute recommended reburial. In 1993Tanzania’s Antiquities Department de-cided to proceed with this recommen-dation, and a committee was set up toassist the implementation of the plan.Participating in the discussions wereLeakey and other eminent paleoanthro-pologists, Tanzanian officials and a re-
gional representative from the UnitedNations Educational, Scientific andCultural Organization.
Saving the Footprints
The conservation project began in1994. During that year’s field sea-
son, the trees and shrubs growing onand near the reburial mound were cutdown. To prevent regrowth, the conser-vation team applied the biodegradableherbicide Roundup to the tree stumps.In all, 150 trees and shrubs were killed,
69 of them directly on the re-burial mound.
Reexcavation of the trackwaytook place during the 1995 and1996 field seasons, beginningwith the southern section. Thissection was where the densestrevegetation had occurred and,coincidentally, where the bestpreserved footprints had beenfound in 1979. Archaeologistsand conservators used Leakey’sphotographs of the trackway tofind the exact positions of thehominid footprints. Also usefulwas the original cast of thetrackway, which was replicated,cut into conveniently short sec-tions and used as a guide for thefinal stages of reexcavation. Atemporary shelter erected overthe excavated area protected itfrom direct sunlight and shadedthose who were working on thetrackway.
In the southern section of thetrackway the trees had fortu-nately developed shallow, ad-ventitious roots rather than deeptaproots because of the hardnessof the tuff. As a consequence,there was far less damage thanhad been feared, and most ofthe footprints were generally ingood condition. In areas wherethe tuff was weathered, howev-
er, roots had penetrated the prints. Herethe conservation team surgically re-moved stumps and roots after strength-ening adjacent areas of disrupted tuffwith a water-based acrylic dispersion.Team members used miniature rotarysaws to trim the roots and routers toextract the parts that had penetratedthe surface of the trackway. The holescreated by root removal were filledwith a paste of acrylic and fumed silicato stabilize them against crumbling.
Recording the condition of a site is
Preserving the Laetoli Footprints Scientific American September 1998 51
LEAKEY’S CAST OF THE TRACKWAY was used toguide the final stages of the reexcavation of the footprints(top). Once the tracks were exposed and photographed,conservators recorded the condition of each print, notingany damage caused by root growth or erosion (bottom).
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one of the most important and chal-lenging conservation activities. The teamconducted a full survey of the exposedtrackway to provide the baseline datathat will allow future investigators to as-sess changes. Using a Polaroid camera,team members made eight-by-10-inchcolor photographs of the footprints.They then laid acetate sheets over thephotographs and noted the places wherethere were fractures, loss of tuff and in-trusive root growth, as well as any oth-er salient information.
During the reexcavation, the conser-vators noted dark stains in and aroundeach hominid footprint. This darkeningwas the result of the application of Bed-acryl, an acrylic consolidant that Lea-key’s team had used to strengthen thefootprints before making molds of them.(Silicone rubber was applied to the track-way to create molds, which were thenpeeled off and used to make fiberglasscasts.) The staining was an unforeseenside effect: although the Bedacryl didnot damage the footprints, it impairedtheir legibility and thus their scientificvalue. The Bedacryl could be removedby gently poulticing the footprints withacetone and tissue paper, but becausethere was a risk of damage to the printswhere the underlying tuff was fragile,only two prints were cleaned.
In consideration of the fact that fewresearchers had ever seen the exposedfootprints—most of the scientific litera-ture is based on casts and photographs—Tanzania’s Antiquities Department in-vited a group of scientists to reexaminethe trackway while the conservation andrecording work was going on. BruceLatimer, curator of physical anthropol-ogy at the Cleveland Museum of Natu-ral History, Craig S. Feibel, a geologist atRutgers University, and Peter Schmid,curator of the anthropology museum atthe University of Zurich, were nomi-nated by specialists in the field of paleo-anthropology to come to Laetoli. Theirstudies included a formal description ofthe footprints, stature and gait of thehominids and an examination of thethin layers of the Footprint Tuff.
Once the footprints were uncoveredand the root damage repaired, a team ofphotogrammetrists recorded the track-way to make new contour maps of theprints. The new maps are accurate towithin half a millimeter, which is farbetter than the maps made by Leakey’steam in 1979. The Laetoli trackway maynow be one of the most thoroughly doc-umented paleontological sites. The new
Preserving the Laetoli Footprints
Iworked on my painting of the Laetoli footprint makers during the early fall of 1978,shortly after the discovery of the hominid trackway. As part of my research, I flew to
Africa to confer with Mary Leakey and her associates at their base camp in Tanzania’sOlduvai Gorge. When I boarded the plane, the only information I had on the projectconsisted of a few photographs of the footprints and the surrounding area, along witha report on the geology of the Laetoli site and a list of the animal tracks found there.
While at the base camp, I consulted with Leakey and made a number of drawings ofproposed layouts. She drove me to Laetoli so I could familiarize myself with the mainfeatures of the terrain. The analysis of the Laetoli sediments indicated that there hadbeen several types of volcanic ashfalls in the area—some settling undisturbed on theground, some redeposited by wind—but all the ash had come from the Sadiman vol-cano. Geologists believe the color of this ash was light gray, not very different from thecolor of the hardened tuff in which the footprints were discovered.
I based my reconstruction of the two walking figures on the descriptions of Australo-pithecus afarensis. Fossil specimens of this species had been found at Laetoli and theAfar Triangle of Ethiopia; the bone fragments and dental evidence indicated that thetwo hominid populations looked roughly the same and lived at the time the footprintswere made. I inferred the limb proportions of the adults from the skeleton of “Lucy,” thefemale Australopithecus whose fossil remains had been found in Ethiopia in 1974. I as-sumed these hominids would have been lean, energetic bipeds, capable of exploiting avariety of habitats. For this reason, they would have probably had relatively little bodyhair, to ensure rapid heat loss. They would have also developed a dark skin to counter-act the injurious effects of ultraviolet radiation.
At the time I worked on the painting, only a few fragments of A. afarensis skulls had been found. I had to base the facial features of the female figure on those of A.
africanus, a species I had earlier reconstructed. Leakey wanted me to emphasize thesmall stature of these hominids, so I painted several guinea fowl near the figures. Themale figure carries a digging stick, presumably the only tool of this species (the earlieststone tools did not appear until much later). The female carries her toddler on her hip,probably the most convenient position for a habitual biped. The theory that the trailshad been made by three hominids was not put forth until after I finished the painting.
The final depiction (below) accorded with the few facts of the Laetoli site that werethen known. The painting first appeared in the April 1979 issue of National Geographicmagazine to illustrate an article by Leakey about the trackway.
JAY H. MATTERNES is an artist who specializes in the depiction of hominids and extinctmammals. His work has appeared in museums worldwide.
52 Scientific American September 1998
The Footprint Makers: An Early View
by Jay H. Matternes
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HOMINID FAMILY members leave their tracks in the ash from the Sadiman volcano.
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photography, mapping and detailed con-dition survey have added an enormousarchive of data to the base record com-piled during the Leakey field seasons.This material is being integrated into an electronic database developed in col-laboration with the department of geo-
matics at the University of Cape Town.When conservation and documenta-
tion were complete, the trackway wasreburied under multiple layers of sandand soil from the surrounding area andfrom the nearby Ngarusi and Kakesiorivers. The fill was sieved to remove
coarse material and acacia seeds. Theconservation team poured fine-grainedsand on the footprint surface, thenplaced sheets of geotextile—a water-per-meable polypropylene material—aboutfive centimeters above the surface toserve as a marker. Then the team mem-
Scientific American September 1998 53
Only very rarely does the fossil record provide evidence ofan actual event in human prehistory. So in the late 1980s,
when we were considering subjects for presentation in dioramaform in the American Museum of Natural History’s Hall of Hu-man Biology and Evolution, the making of the Laetoli footprintsseemed an obvious choice. Constructing lifelike sculptures ofextinct humans involves many tricky decisions [see “EvolutionComes to Life,” by Ian Tattersall; SCIENTIFIC AMERICAN, August1992]. The decisions involving the Laetoli hominids were partic-ularly difficult because the 3.6-million-year-old creatures are soremote from modern-day humans. Our Laetoli diorama posedan additional problem: it was designed to represent a specificevent—the journey of the hominids across a plain of volcanicash—but the evidence from that event is a little ambiguous.
Willard Whitson, the museum hall’s designer, and I visited theLaetoli site in Tanzania and discussed our plans for the dioramawith Peter Jones, an archaeologist who was part of Mary Lea-key’s team when the trackway was discovered in 1978. We alsoconsulted paleoanthropologist Ron Clarke, who excavated manyof the footprints. Nobody disputes that the two parallel trailswere made by beings who were walking bipedally (althoughthey may have been tree climbers as well). The footprints in thewesternmost trail were much smaller and more clearly definedthan the prints in the eastern trail, but Jones pointed out that thestride lengths were the same. Clearly, the hominids were walkingin step and accommodating each other’s stride—which meantthat the two trails were made at the same time. What is more,the trails are so close together that the hominids must havebeen in some kind of physical contact when they made them.
Some anthropologists concluded that the trails had beenmade by a group of three hominids. The western trail, they
claimed, was made by a relatively small individual, whereas theeastern trail was made by two larger hominids walking in tan-dem, with one individual deliberately stepping into the tracks ofthe other. But Clarke disagreed with this view. He claimed thatbecause the footprints in the eastern trail had so many consis-tent features, they must have been made by a single large ho-minid. The larger footprints were more poorly defined than thesmaller prints, Clarke argued, because the feet of the large ho-minid had slid more in the rain-slickened ash.
These facts and theories were our starting point. The rest hadto be conjecture. Individuals of different body sizes could havemeant a number of things: male and female, parent and child,older and younger siblings. And although we suspected thatthe two hominids were in physical contact, we had no idea howthey were supporting each other. Were they holding hands?Walking arm in arm? Carrying something between them?
The scene as we finally rendered it (above) shows two Aus-
tralopithecus afarensis, a large male and a smaller female, walk-ing side by side through a sparsely vegetated landscape. Weopted for a male and a female partly to maximize visual interestbut also to show the large sex difference in body size that is be-lieved to have existed in A. afarensis, the presumed maker of thetrails. The male’s arm is draped over the female’s shoulder. In theexplanatory text we emphasize that this scenario is consistentwith the few facts we have but is not the only one possible.
Feminists have excoriated us for the “paternalistic” nature ofthe scene, but in fact we decided to show the figures joined thisway because it seemed to carry the fewest unwanted implica-tions. Indeed, a look at the faces of these creatures, brilliantlysculpted by English artist John Holmes, shows that both areworried, the male as much asthe female. Here are two small,slow and rather defenseless individuals moving through
open country that almost certainly teemed with predators.These early hominids were clearly bipeds when they were onthe African savanna, but this dangerous and difficult environ-ment was probably not their preferred milieu. Plausibly, theywere crossing this hostile territory to get from one more conge-nial region to another. Their tracks were headed almost directlytoward the well-watered Olduvai basin, where the lakeside for-est and its fringes would have felt much more like home.
IAN TATTERSALL is a curator in the department of anthropologyat the American Museum of Natural History in New York City.
Preserving the Laetoli Footprints54 Scientific American September 1998
bers poured a layer of coarse-grainedsand and covered it with a special kindof geotextile called Biobarrier, which isdesigned to block root intrusion intothe burial fill.
Biobarrier is studded with nodulesthat slowly release the root inhibitor tri-fluralin, a low-toxicity, biodegradableherbicide. Trifluralin is not soluble inwater, so it is nonleaching and nonmi-grating: it inhibits root growth but doesnot kill the plants whose roots contactthe nodules. The effective life of Biobar-rier depends on the temperature of thesoil and the depth of burial. Based onthe manufacturer’s data, the materialwill have an effective life of about 20years at the Laetoli site. Above the Bio-barrier, the conservators added anotherlayer of coarse-grained sand, then laiddown a second covering of Biobarrierand a synthetic erosion-control matting.
The conservation team topped themound with a layer of local soil and abed of lava boulders to provide a physi-cal armor for the reburial fill. Themound, which is one meter high at itsapex, will be allowed to revegetate withgrasses; because they are shallow-root-ed, they will stabilize the reburial soilwithout posing any danger to the track-way surface. But the staff of the Antiq-uities Department will regularly moni-tor the site and remove any tree seed-lings that take root. The geotextiles are asecond line of defense should the main-tenance lapse. The shape of the mound,which has a slope of about 14 degreeson each side, will facilitate the runoff ofsurface water.
The entire process was repeated forthe northern section of the hominidtrackway during the 1996 field season.This section had suffered the most ero-sion because surface water from the sur-rounding area drains into the NgarusiRiver across the northern end of thetrackway. It was this drainage that ex-posed the first hominid footprint foundby Abell in 1978; unfortunately, the
same drainage resulted in the loss of thisprint and an adjacent one in the 18years between the burial of the track-way and its reexcavation. To preventfurther erosion, simple berms were con-structed from lava boulders around thetrackway to divert runoff from nearbyareas. Two gullies that were threateningthe northern end of the trackway werealso stabilized by placing lava bouldersand erosion-control matting on theirslopes.
Near the trackway, the team membersdug a monitoring trench, 2.5 meterssquare, which was reburied accordingto the same method used on the track-way. Parts of this trench will be period-ically reexcavated to assess the subter-ranean conditions and the continued ef-fectiveness of the Biobarrier. Acaciatrees have been permitted to survivearound the monitoring trench to seehow well the Biobarrier can block thetree roots. Although polypropylene ma-terials may be expected to last for manyyears underground, their use in tropicalenvironments such as Laetoli wherelarge numbers of termites live has notbeen properly evaluated. The monitor-ing trench will allow the AntiquitiesDepartment staff to check the perfor-mance of the geotextiles without dis-turbing the trackway itself.
A Sacred Ceremony
Experience has shown that successfulpreservation of remote sites requires
the cooperation of local people. If theyfeel excluded, there are frequently ad-verse results, from neglect to deliberateharm. Most of the people in the Laetoliarea are Masai. They have maintainedto a large degree their traditional way oflife, which centers on their herds of cat-tle. Cattle grazing on and around thetrackway site would cause erosion ofthe reburial mound and the destructionof the system of berms and drains fordiverting the surface runoff. While tend-
REBURIAL MOUND over thehominid trackway includes five lay-ers of sand and soil (diagram). Theconservation team poured fine-grained sand directly on the Foot-print Tuff (top photograph). Thereburial layers are separated bypolypropylene geotextiles and ero-sion-control matting (middle). Themound is capped with lava boul-ders to protect the trackway fromcattle and other animals (bottom).
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Copyright 1998 Scientific American, Inc.
ing the cattle, herders with time ontheir hands might also be tempt-ed to interfere with the reburialmound. Everyone in the regionknows of the intensive activity atthe site in recent years, and somelocal people have been curiousabout the Biobarrier and othermaterials used in the reburial.
Laetoli lies within the Ngoro-ngoro Conservation Area, a vasttract set aside by the governmentto preserve both the natural envi-ronment and the Masai commu-nity’s way of life. This extraordi-nary undertaking, perhaps uniquein Africa, has a good chance ofsucceeding under capable man-agement. We frequently consult-ed the conservation area’s region-al coordinator—who became amember of the advisory commit-tee for the Laetoli project—andthe chairmen of the two closestvillages, Endulen and Esere. Ontheir recommendation, a meetingat the site was called by the Lo-boini of the region, the tradition-al religious leader and healer.
In a daylong meeting attendedby about 100 people, includingmen and women of all ages, theLoboini emphasized the signifi-cance of the trackway and explainedthe need for its protection. A sheep wassacrificed and a sacred ceremony heldto include the site among the placesrevered by the Masai people. In 1996,after the northern section of the track-way had been reexcavated, the ceremo-ny was repeated. Leakey herself attend-ed this meeting and was greeted bysome of the older people who recalledher work in the Laetoli area in the 1970s.
Ultimately, the survival of the site willdepend on the vigilance of the Tanzani-an authorities and the internationalcommunity. The Antiquities Department
has appointed two Masai men from thearea as full-time guards and instituted adetailed monitoring and maintenanceplan. The plan calls for regular photog-raphy from specified perspectives aroundthe site, periodic removal of all seed-lings—especially acacias—and repair tothe berms and drainage system.
Because the Laetoli site is not open tovisitors, we have installed a permanentdisplay at the Olduvai Museum, whichoverlooks the gorge where Leakey andher husband, Louis S. B. Leakey, madeso many of their famous discoveries.The museum is a short distance off the
dirt road that runs from the Ngo-rongoro caldera to the SerengetiPlain; it is accessible to both localpeople and international visitors.The room devoted to Laetoli con-tains the cast of the southern sec-tion of the trackway, along withtext and photographs that ex-plain why the site was reburiedand how it is being protected. Inthe past, the Olduvai Museumprimarily served internationaltourists en route to the SerengetiPlain. But the text of the Laetoliexhibit is in Swahili as well asEnglish, so it is hoped the localpeople—particularly Tanzanianschoolchildren—will come to themuseum to learn more about theLaetoli footprints and will be in-spired to care for the site.
Footprints are evocative. Whenastronaut Neil Armstrong trodon the surface of the moon, im-ages of his footprints were in-stantly recognized as symbols ofhumankind’s first steps into thecosmos. Between the Laetoli foot-prints and those on the moon liesa 3.6-million-year-long evolu-tionary journey. Looking at themyriad animal tracks at Laetoli,one has the sense that hominids
were not frequently encountered onthat landscape—their tracks are too fewin number compared with those of theother fauna. These creatures must havebelonged to an insignificant species thatsomehow escaped the inevitable extinc-tions in the harsh environment. Thewistful trail of three small figures care-fully making their way across the re-cently fallen ash from Sadiman is bothhumbling and stirring. These fragiletraces of humankind’s beginnings onthe plains of Africa deserve to be givenevery care and protection for their fu-ture survival.
Preserving the Laetoli Footprints Scientific American September 1998 55
The Authors
NEVILLE AGNEW and MARTHA DEMAS led the Getty Conserva-tion Institute’s project at Laetoli in Tanzania. Agnew received his Ph.D.in chemistry from the University of Natal in Durban, South Africa. Heheaded the conservation section of the Queensland Museum in Brisbane,Australia, before joining the Getty institute in 1988. He has undertakenconservation projects in China, Ecuador and the U.S. and is now the in-stitute’s group director for information and communications. Demasearned a doctorate in Aegean archaeology from the University of Cincin-nati and a master’s in historic preservation from Cornell University. Shejoined the Getty in 1990 and is currently involved in developing andmanaging conservation projects in the Mediterranean region and China.
Further Reading
The Fossil Footprints of Laetoli. Richard L. Hay andMary D. Leakey in Scientific American, Vol. 246, No. 2,pages 50–57; February 1982.
Disclosing the Past. Mary D. Leakey. Doubleday, 1984.Hominid Footprints at Laetoli: Facts and Interpreta-tions. Tim D. White and Gen Suwa in American Journal ofPhysical Anthropology, Vol. 72, No. 4, pages 485–514; 1987.
Laetoli: A Pliocene Site in Northern Tanzania. Editedby M. D. Leakey and J. M. Harris. Clarendon Press, 1987.
Missing Links: The Hunt for Earliest Man. John Reader.Penguin Books, 1988.
CEREMONIAL BLESSING OF THE TRACKWAYtook place in August 1996, when men and womenfrom the Masai community gathered at the Laetoli site(top). Leakey attended this event and reacquaintedherself with the local people (bottom). The great ar-chaeologist died just four months later.
