If you visit the human origins hall at the Smithsonian National Museum of Natural History, you'll see short films, interactive displays, and bronze sculptures of ancient humans. Near the end of the exhibition, you'll see a series of head-and-shoulder busts, not made of bronze but instead designed to look like actual human faces. The busts are placed at the approximate height of the ancient humans they represent, so the hobbit-sized Homo floresiensis peers up at you. If you're as short as I am, the head of Homo erectus is higher than your own (and if you have a shred of humility, you realize that, no matter your height or weight or workout routine, that hominin could snap you like a twig). In each case, no matter how ancient the human ancestor, you will believe there's a person inside looking back at you. The whites of the eyes aren't pristine; they're laced with visible blood vessels like our own. The eyes don't stare blankly; they see.
Those eyes are the hallmark of John Gurche, the same paleoartist responsible for the bronze sculptures. Gurche used to live in Denver and work at the Denver Museum of Nature and Science. While there, he taught a class on human origins, and I was one of his students. I still remember his introduction: "Of all the stories in the universe, maybe the most interesting is that a tiny corner of the universe became aware of itself."
Whether the human mind is divinely inspired is a spiritual question, not a scientific one, but our bodies consist of the same atoms that comprise the rest of the universe. Gurche is right. A part of the universe is aware of itself.
Humans are unique. True, we're not as unique as we used to think. Parrots can talk and do a little logic and a little math. Parrots and crows can solve problems. Squirrels are downright juvenile delinquents of urban ingenuity. Depending on how liberally you define "art," some elephants are artists. We probably haven't even begun to grasp the intelligence of most cetaceans. And yet, for all the ground other animals have gained on us in earning respect for smarts, we're still unique. With our upright stance and big brains and opposable thumbs, we have remade the world — for better or worse — to suit us. And so far as we know, we're the only species on Earth that ponders our origins.
Multiple lines of evidence, from the fossil record to physiology to DNA studies, show that we evolved from earlier life forms. And even though recent DNA studies have revealed slivers of Neanderthal or Denisovan DNA in some modern humans, most of our ancestry comes from one continent: Africa.
As 2015 drew to a close, I had been to Darwin's home outside London, and to the Galápagos Islands, thanks to the generous sponsorship of Somerville Anderson in Glasgow, Scotland. I'd also grown up in dinosaur-rich territory in Colorado, attended paleontology field school in Marmarth, North Dakota (hotbed of the end-Cretaceous extinction), even found a cool mammal tooth from the first million years after that extinction just minutes from my home. In August 2015, I ogled half-a-billion-year-old fossils from the Cambrian radiation. But if I wanted to look into the ancient eyes of humans in any meaningful way, I had to go to the continent of our origins. Somerville provided generous funding for another evolution adventure.
The Cradle of Humankind is a collection of limestone caves west of the South African cities of Johannesburg and Pretoria. Even better, the UNESCO World Heritage Site is home to a constellation of hominin fossils. Much of the research on these fossils occurs at the University of the Witwatersrand (Wits). Early in 2016, I reached out to Wits professor Francis Thackeray, and he kindly agreed to my request for a visit to the Evolutionary Studies Institute. I couldn't believe my luck, but Johannesburg's a grittier city than I'm used to, and getting around entails driving on the wrong side of the road like British people. Too 'fraidy-cat to go by myself, I invited a colleague, Ted Scambos of the Cooperative Institute for Research in Environmental Sciences, and his wife Kari to join me. We set off in mid-May 2016.
About the time I began planning my visit to the Cradle of Humankind, news broke of a new find, Homo naledi. The study was led by the Wits-based paleoanthropologist Lee Berger. Not only was this new hominin from the Cradle, but one of the researchers who studied the fossils lived and worked in Denver. His office was just a short light rail ride away from my home. Early in 2016, I contacted Charles Musiba and asked if I could talk to him about his research. He graciously agreed. I got to meet with him on March 3, 2016.
When you read as much about paleoanthropology as I do, you come across stories. Big egos, short tempers and so on. Dr. Musiba must have missed the self-absorption training because I couldn't have wished for a nicer guy. I showed up early for our appointment and tried to wait, quiet and bunny-like, outside his office, but he leaned back in his chair and beckoned me into his office with a big grin. Midway through our talk, one of his grad students appeared, and Musiba scooted over so the student could share the desk to work on his own project. We talked about Homo naledi, the Cradle, and above all, the famous hominin trackway at Laetoli, Tanzania.
A native of Tanzania, Musiba was fascinated by history as a little kid, reading every book he could about the ancient Greeks, Romans and Egyptians. In high school, his interests began to stretch further back in time, to prehistoric life. He wound up with a rock star of a mentor: Mary Leakey. From what I'd read about her, she had what you might euphemize as a strong personality, and I asked about that. "If you rubbed her the wrong way, she would let you know," Musiba admitted, "but she was gentle. Just no-nonsense."
Musiba volunteered for Leakey when he was in high school, and she convinced him to study archaeology. There were no university programs in archaeology in Tanzania at that time, so he went to Germany, and wound up studying biological anthropology. "That was fine since biology is pretty fascinating too." And he found he liked fieldwork.
The hominin fossil record so far indicates that our genus, Homo, arose sometime around 2 million years ago, and modern humans emerged about 200,000 years ago. So when a new hominin species is identified, paleoanthropologists need an estimate of its geologic age to fit the species into our evolutionary tree. When Musiba and his coauthors initially described Homo naledi, the species hadn't been dated, and that remained the case when I spoke to him in March. Musiba told me, "There are two things I can say about Homo naledi. One is, imagine if it is 2 million years old. That has big implications for the emergence of the genus Homo because it's evidence of species radiation. Two is, if it's younger — it could be as young as 60,000 years old — what are the chances to extract DNA? What would that DNA tell us?" Then we both agreed that it would be wonderful if scientists could extract DNA from Homo naledi and, for that matter, Homo floresiensis, the "hobbit" from Indonesia first described in 2004. Unfortunately, DNA degrades quickly in tropical regions, so we may be waiting for a long time.
Something I found remarkable in the initial description of Homo naledi was the hypothesis that the species might have intentionally discarded its dead. As tactfully as I could, I expressed my doubts to Musiba. He responded with a smile, asking, "Why do you find that hard to believe?" He pointed out well documented behaviors of elephants, who show apparent distress to the dead among their own species, and to behaviors of bereaved chimp mothers. Jane Goodall's studies aside, Musiba explained that no one has yet published a systematic study of how other primates deal with dead bodies today. And he explained that he didn't see Homo naledi behavior as akin to modern burial. "I don't see it as a ritualistic practice. They may have simply been clearing the bodies out of the way."
Most of my chat with Musiba was about a project close to his heart: preserving the hominin trackway at Laetoli, Tanzania. Members of Leakey's team stumbled across the trackway in the 1970s while engaging in a field camp pastime of Let's Throw Some Elephant Dung at Each Other. Initially described in 1979, the trackway was long interpreted as a diminutive australopithecine family walking away from a volcanic eruption, but Musiba has played a significant part in rethinking that interpretation. Further examination of the trackway surroundings found carbonates, hallmarks of fresh water, as well as the tracks of elephants, rhinos, hyenas, and different kinds of antelope. The trackway as probably near a water hole, and rather than belonging to a family walking through a wasteland, the tracks more likely belonged to unrelated individuals quenching their thirst at different times.
Regardless of the interpretation, the Laetoli tracks need protection. After being excavated by Leakey's team, the tracks were reburied for protection in the 1990s — an elaborate effort by the Getty Conservation Institute. Restudying the tracks in 2011, Musiba and his team found that the protocol the Getty had followed, including multiple layers and herbicide treatment of the soils placed over the tracks, hadn't been enough to prevent seeds from taking root. Even worse, the process of re-excavating the tracks added a little more damage. For real preservation, the tracks need to be freed of their soil, sand, tarp and rock covering, and placed in a climate-controlled facility. Musiba lobbied for such an effort for years, and by the time I talked to him, his work was paying off. Laetoli is now a World Heritage site, and funding had been secured to protect the footprints. Musiba showed me architectural plans for a museum and research complex at the site.
One of the challenges to doing research at Laetoli is that it's so remote. Musiba explained that Mary Leakey got a lot of work done by living in the area, and if the planned complex enables scientists to live at Laetoli full time, they will be able do more work. Musiba described the planned facility: three compounds with on-site living facilities and a research lab for the scientists, a training camp, an education facility for 40 kids and three teachers at a time, and an overall complex capacity of about 150 people. "The architect is based in Johannesburg and specializes in designs that are sustainable, energy-efficient, and blend into the background. The plan is that, when you fly over, you won't even see it." The completed complex will feature Masai-style buildings and solar power.
Musiba also discussed his plans to work with local women's groups at Laetoli. "The problem right now is that the local people are detached from the trackway," he said. "This is a way to make it benefit the people who live nearby."
Ted Scambos and I expected to fly from Denver to Atlanta and then from Atlanta to Johannesburg, arriving in Johannesburg on May 17, and starting our hominin adventure the next morning. Instead, we spent 24 hours cooling our heels in Atlanta while Ted got a new passport. Advice to potential South Africa visitors: You must have at least two blank visa pages in your passport for admission to the country.
At least Atlanta can offer same-day turnaround of passports. And Ted and I did get to hear a no-nonsense Atlanta airport shuttle lady, on the radio with one of her coworkers, characterize their mutual boss as "cra cra."
Back on track, we got through a 15-hour flight (not as bad as I feared it would be), passport control and baggage claim to meet Andre, the driver dispatched by our hotel, to meet us. I found our hotel in Johannesburg much more picturesque than our hotel near the Atlanta airport.
Ted and I met Francis Thackeray on our first morning in Johannesburg. When our cab pulled up to the entrance of the Evolutionary Studies Institute at the University of the Witwatersrand, Dr. Thackeray was there, smiling and waving the cab into a parking spot. Thackeray is like Musiba: nothing like the self-absorbed paleoanthropologists you read about, perfectly charming, and carrying fond memories of Mary Leakey.
After getting us some coffee and tea, he ushered us into his office, loaded with fossil casts, hominin busts, and pictures of luminaries who have preceded him at Wits, where he is the Phillip Tobias Chair in Palaeoanthropology. We sat down to chat around a small table, and he started off our conversation asking about creativity. He had just heard a TED talk about how to unlock it. When I asked for his own recommendations, he replied: (1) caffeine (it was morning), (2) curiosity, and (3) any kind of stimulation, even something as simple as "an interaction at the tea table."
Several months before I met him, Thackeray had an interesting interaction at Charles Darwin's dining room table. Thackeray participated in a field trip with a gaggle of fellow paleoanthropologists to Down House. Recounting the outing in A Most Interesting Problem, science writer Ann Gibbons points out that one of Thackeray's cousins was William Makepeace Thackeray, presumably a time or two removed. Like Darwin, William Makepeace Thackeray employed the very same industrious Victorian-era nurse, Jessie Brodie. Brodie reputedly chided Darwin that he should buckle down to his writing as her other charge did.
William Makepeace Thackeray was, of course, long gone when Francis Thackeray was born. Francis's father was the astronomer David Thackeray, who headed the Radcliffe Observatory in Pretoria. He fired his son's interest in science early on, and young Francis worked as his dad's night assistant, minding a giant telescope. Francis Thackeray's interests turned to early humans around the time he made a lucky find. Heavy equipment brought in to level the cricket field next to Thackeray's grade school turned up ancient stone artifacts, which he collected. Thackeray was lucky in another respect. He had a brave teacher named Andrew Swart, who wasn't afraid to talk about evolution.
Apartheid took effect in South Africa in 1948. "All the high offices were filled by Dutch Reformed Church politicians," Thackeray recalled. Apartheid institutionalized a strict racial hierarchy with white at the top, black at the bottom, and varying shades of brown in between. Any examination of common origins for all of humanity made apartheid apologists uncomfortable, so evolution was banned from public schools. Thackeray was pleasantly surprised when Swart gave a lecture on evolution. Swart emerged from that lecture unscathed, but when he continued discussing evolution at another school, he faced disciplinary action.
Thackeray enjoyed encouragement from other sources, too. He was allowed to collect stone artifacts from the gravels of Zambezi, and fossils from the dump at Sterkfontein. Looking at his Zambezi finds, the anthropologist Desmond Clark told him, "Well done, young lad," a pronouncement that left Thackeray feeling "chuffed." But when Robert Broom's assistant John T. Robinson looked over the same artifacts, he delivered bad news, saying the finds weren't tools at all. It was an early lesson for Thackeray that smart people can disagree. Decades later, the word on the artifacts is that the little ones were human-made and the big ones weren't. Thackeray also recounted that, as a teenager, he got to meet Raymond Dart, describer of the Taung Child, the first fossil hominin from Africa. "He was 80 years old, and his eyes still glistened."
On the small table where we sat visiting there was a cast of a Homo habilis. The species was designated in 1964 by Louis Leakey, Phillip Tobias and J.R. Napier. I had heard from John Gurche in 2003 that the Homo habilis species definition had been problematic from the get-go, and asked Thackeray about it. He replied that John T. Robinson said it looked an awful lot like Australopithecus and "an argument played out in the pages of Nature." Just how to classify Handy Man is a question Thackeray is still trying to address, more than 50 years after the original species declaration.
Our conversation roamed over various adventures Thackeray had over the years, including a trip to the site of Sahelanthropus in Chad — one of the candidates for the title of earliest hominin yet discovered. Thackeray's Chad trip was a reciprocal visit after he had invited Sahelanthropus describer Michel Brunet to South Africa. "Picture 25 scientists strapped to the wall of a military plane, and after that, an airlift in a Russian helicopter." Thackeray didn't find any hominin fossils but few people have — only two hominins have so far been found in over 30 years of research at the site — but he was happy with his find of a 7-million-year-old fossil fish.
Thackeray also shared his thoughts on the guilty party behind the Piltdown hoax. For multiple reasons, including a letter to a friend with the injunction, "We must say nothing about this," and accounts of Jesuits' fondness for practical jokes, he thinks the real culprit was the Jesuit priest and paleontologist Pierre Teilhard de Chardin. In fact, Thackeray has heard from several Jesuits who share his suspicions.
And we talked about Thackeray's dream of a cast of Mrs. Ples in every school in South Africa.
"Mrs. Ples," who Thackeray suspects was actually male, was discovered in 1947 by the energetic, eccentric Robert Broom. Confident that Raymond Dart was onto something with his description of the Taung Child in the mid-1920s, Broom set out to find another example of a "man-ape" from southern Africa. As its name suggests, the Taung Child came from a quarry at Taung, roughly 200 miles from Johannesburg. In the 1930s, Broom worked with miners seeking lime (useful in gold mining) to find new fossils in Sterkfontein Cave, a fairly short drive west of Johannesburg. Unfortunately, the miners extracted lime by blasting it out, and hominin fossils could get blasted away with the lime. To extract fossils, Broom used explosives too. In 1947, he and his assistant John T. Robinson blew Mrs. Ples out of a Sterkfontein wall, cracking the skull in the process. Fortunately, most of the skull survived the incident. (Believe it or not, that blast wasn't actually the stupidest thing ever to happen at Sterkfontein; in 1960, Robinson took New Zealand clairvoyant Geoffrey Hodson to the cave complex and asked if the clairvoyant could see into fossil hominins' lives.)
Absent postcranial remains, paleoanthropologists must look for clues in the skull, and Thackeray thinks that the supersized cochlea — the auditory part of the inner ear — indicates maleness. (Women exasperated by men's listening particles might beg to differ.) The canine teeth aren't preserved, but the tooth sockets are. They're the size you'd expect for a female, but Thackeray suspects that preparation methods used decades ago may have obscured their true dimensions. He also thinks the skull may have belonged to a juvenile as the wisdom teeth had not yet erupted at the time of death. In early 2018, he backed up this assertion with a paper in the South African Journal of Science. He pointed to Broom's original measurements of the canine socket. Thackeray also pointed to the "indisputable evidence for open cranial sutures" (babies are born with unfused sutures, which close over time, and can be used to estimate an individual's age), and concluded that Mrs. Ples was really a small male.
In 1996, Thackeray gave an I-have-a-dream speech about his desire to provide a cast to every South African school within 20 years. By the time we talked, he had previously arranged for casts to be made of Mrs. Ples, but although the arrangement was working well, the cast-making contract was subsequently awarded to a different company, which soon went out of business. So Thackeray's goal of introducing Mrs. Ples to schoolchildren throughout South Africa is on hold for now.
But more on Mrs. Ples later.
After our introductory chat, Thackeray accompanied Ted and me to a room I won't soon forget. Shelves lined the walls, filled with early human remains, along with bones of close relatives and contemporaries. We saw archaic Homo sapiens, and robust australopithecines, some with sagittal crests. Thackeray explained that in some modern apes, sagittal crests form in dominant males, probably driven by testosterone. He imparted other bits of wisdom, like the fact that eye orbits give useful clues to an individual's size, and the inverse relationship between body size and population size (after taking into account whether the species dines mostly on plants or meat). But I confess I mostly gaped at the room. It held two buzzworthy finds from paleoanthropologist Lee Berger: Homo naledi, excavated to great TV fanfare, and Australopithecus sediba. Berger proffered A. sediba as an ancestor of Homo, but the claim didn't hold up very well. Probability models found the ancestral role unlikely, and finds from the Cradle cave of Drimolen, announced in 2020, included a Homo erectus cranium perhaps older than A. sediba.
But above all, there was the Taung Child.
Charles Darwin identified Africa as the likely birthplace of humankind, but that hypothesis hadn't yet gained many supporters by the earth 20th century. In 1924, quarry workers passed along a juvenile skull and brain cast they had found at Taung, roughly 200 miles west-southwest of Johannesburg. After freeing the fossils from the surrounding rocky matrix, Raymond Dart described the Taung Child, naming it Australopithecus africanus in Nature in 1925.
He wasn't exactly overwhelmed with praise.
One concern was understandable. The fossil was from a juvenile, and the closer resemblance between juvenile apes and humans than adult apes and humans was well known. Meanwhile, Piltdown still swayed many paleoanthropologists in the 1920s; Dart even mentioned the Piltdown find in his own paper. Maybe most important of all, not too many Europeans wanted to believe that their ancestors hailed from the Dark Continent. They could accept ancestors from Asia if they had to (perhaps Eugène Dubois had persuaded some anthropologists with his Java Man), but Sub-Saharan Africa was unacceptable. And yet, Dart was right. He really had identified an ancient human ancestor, and he found it on the continent that we now realize was humankind's first home. The Taung Child counts among the most important fossil finds in all of paleontology.
And there it was. I could hardly believe my luck.
What was lucky for me was not so lucky for a little tyke some 2.8 million years ago. Some paleoanthropologists speculate that the Taung Child was snatched away by a predatory bird because marks around the eye sockets look like the work of bird talons. And before death, the child likely suffered a severe illness or other trauma, indicated by faulty enamel on the permanent molars. In fact, trauma-documenting enamel is a recurring theme in the Cradle of Humankind. A 2019 study described Australopithecus africanus teeth showing signs of "seasonal dietary stress."
We also discussed Homo naledi, more remains of which sat in crates along one wall. Wits professor Lee Berger led the team that extracted the fossils in Rising Star Cave. Because accessing the fossils requires squeezing through a passage as narrow as 7 inches (20 centimeters) in some places, Berger couldn't get to them himself. Instead he assembled a team of skinny spelunkers happy to collect bones. It so happened that all the people who fit the bill were women. Thackeray told Ted and me that the women were dubbed "underground astronauts" as Berger ran "mission control" above ground.
At the time of my visit in May 2016, Homo naledi certainly qualified as an exciting find, but multiple paleoanthropologists had pointed out that, until a date was attached to the fossil, only so much could be said about where it best fit on our family tree. Caroline VanSickle, one of the scientists who examined the remains under Berger's supervision, wrote later that year in American Scientist, "Wherever H. naledi ends up in the timeline of hominin evolution, it will be unusual. Some of its features will look either too ancient or too modern for its date."
Regarding H. naledi burials, in my visit with him in March, Charles Musiba made good points about the possibility of early humans discarding the bodies of their dead, if for no other reason than to avoid predators. But I still had a hard time accepting that primitive humans who, for all anybody knew at the time, could be as much as 2 million years old, would successfully negotiate the arduous path over the "Dragon's Back," in conditions as dark as the inside of a cow, to discard the bodies.
As I had asked Musiba, I asked Thackeray. While he has enormous respect for Berger, Thackeray differs with Berger and his team's take on the burial. Thackeray gave me his perspective when I visited, and published a paper on it a couple months later. He saw that many of the Homo naledi bones bear black splotches, described by the original research team as "black iron-manganese oxy-hydroxide deposits and coatings." The manganese spots could result from geologic processes, but Thackeray found the spot patterns suggestive of lichen (manganese is toxic, so lichen must expel it).
Lichen are symbionts comprised of algae and/or cyanobacteria, and a fungus (and apparently yeast, too). A single lichen body is a thallus, and multiple lichen bodies are thalli. Thalli generally radiate outward, with their size and density decreasing farther away from the center.
The possibility that lichen caused the black spots on the bones has significant implications for their deposition. Lichen need cool, wet conditions, but they also need sunlight, which wouldn't reach a completely enclosed cave. When we spoke, Thackeray offered a different explanation than Berger, namely another entrance to the cave and possibly a roof collapse. Later, after decay had eaten away the flesh, one or more chimney-like openings could have provided sunlight to lichen spreading on the skeletons. In his paper, Thackeray writes, "Perhaps this group died as a result of a crisis near an entrance to the Dinaledi Chamber, and/or a roof collapse." He also highlights plans for a 10-year study of lichen on bone surfaces in the Cradle of Humankind.
A year after my visit, Berger and company finally attached a date range to Homo naledi. By applying a variety of dating techniques to the fossils, and to over- and underlying sediments, they arrived at 335,000 to 236,000 years old — younger than previous estimates. They also announced the find of a second chamber in the Rising Star cave system, named Lesedi, also rich with Homo naledi remains. Though Lesedi didn't have as tight an entranceway, and held remains of other fauna, the team claimed vindication of their original intentional-burial claim. But others in the field remained skeptical, and everybody awaited more fossils.
On the way out of the building, Thackeray showed us an imaging lab where high-tech equipment has the potential to make volunteer fossil preparators like me redundant. The machine can produce images of fossils still entombed in rock.
As if it weren't enough to let Ted and me pick his brain at Wits, Thackeray took us to Sterkfontein Cave in the Cradle of Humankind, about an hour's drive from Johannesburg. While he drove a university vehicle, we took in the countryside and picked his brain some more.
The discovery site of Mrs. Ples, Sterkfontein has become a popular tourist destination, with an interpretive center, café and regular guided tours. We ate lunch and talked about morphometrics (see below) and potential effects of changing climate on our earliest ancestors. Then it was time for our tour.
Thackeray visited with friends at the café while Ted and I donned hairnets and then hard hats. Naturally we had to get pictures of each other to use as blackmail material later. The hard hats were a necessity as you have to make your way through narrow tunnels, even butt walk for a short way. While we were inside, the guide passed along the discomfiting story of a scuba diver deployed to learn more about the cave who got separated from his diving companions and never made it out. Scuba diving would be needed for some explorations as part of the cave was underwater. Our guide tossed a rock toward what looked like a gray mud surface, but the rock landed with a splash. Still, the cave was actually well lit, with pathways clearly marked for visitors, and nobody visits without a guide.
The cave exit is marked by two bronze sculptures, one of Phillip Tobias, longtime paleoanthropology professor at Wits, and the other of Robert Broom, finder of Mrs. Ples. Both Broom's bronze hand and bronze nose have been polished shiny by the many hands of visitors leaving the cave. Our guide explained the tradition. You can touch Broom's nose for good luck, or his hand for wisdom, but you can't do both. You have to make a choice.
Mrs. Ples put Sterkfontein on the tourist map, but that skull was by no means the only hominin Broom ever found, nor was it the only hominin genus he ever named. The man was a notorious splitter, meaning just about everything he found merited a new species declaration. Paleoanthropologists have begun to back off from that approach, and Thackeray's research is aimed at determining species affinities with morphometrics.
Linnaeus established how to define a species in the 17th century, including the requirement that members of the same species be able to produce viable offspring. More than two centuries later, plenty of scientists feel the definition ought to be revisited, especially for fossil species, where the viable offspring criterion can't be tested.
As he has watched the number of identified hominin species wax and wane over the years, Thackeray has developed a new approach.
He uses skeletal remains of still-living species, e.g., modern humans and modern chimpanzees, as a basis for comparing fossil specimens. (When dealing with fossils, he focuses on the skull or, when no skull is available, as many measurements as possible of what fragments of the individual have been preserved.)
Thackeray takes dozens of measurements from each specimen, things such as nasal height, orbital height and palate breadth, using the same calipers on each one. He uses natural logs of the measured values to plot them linearly. In comparing members of the same species to each other, he has, for instance, measured male-female pairs, plotting the female measurements on the x-axis and male measurements on the y-axis. Data points plotted, he then he calculates the least-squares linear regression.
The math might sound tricky, but it's not much more involved than addition, subtraction, multiplication and division. The formulas that must be applied can get a little long, and the heavy lifting can be done by spreadsheet software nowadays. When the calculations are done, Thackeray has a graph showing the individual values and a least-squares line running through them. In calculation after calculation, he has come up with a degree of scatter around the regression line of roughly 1.61 for comparisons of members of the same species living today.
Thackeray's approach can be used to assess whether extinct hominins belong to the same or different species. Hominin skulls collected at Dmanisi, Georgia, show a remarkable degree of variation, and David Lordkipanidze and his team have also used geometric morphometric analysis and resampling statistics. Published in 2013, their study concluded that Homo erectus can incorporate tremendous diversity. Thackeray has found variability in Early Pleistocene specimens from Africa that are compatible with the findings of Lordkipanidze's group.
One can differ with Robert Broom's approach to naming species while still marveling at what he collected. Marveling at Broom's finds was exactly what we did the next morning, spending time with Stephany Potze, Curator of Plio-Pleistocene Palaeontology at Ditsong National Museum of Natural History in Pretoria. Ted's wife, Kari, got into town the evening of May 19. The next morning, Ted, Kari and I took a handy commuter train from Johannesburg to Pretoria, walked a couple blocks to the museum, and met Potze for our tour. Once again, we got to see an inner-sanctum bone room, accompanied by a friendly host with a gift for making science come alive.
The first specimen Potze showed was the skull of an archaic Homo sapiens, estimated at about 60,000 years old. Potze explained that the skull puzzled researchers because it's large and robust — too big to belong to the Khoisan people who long inhabited the region. The museum planned to test DNA from the skull in hopes of learning more.
But much of our visit was about Mrs. Ples and her (or his) contemporaries.
Confident that the Taung Child was an ancient human ancestor, Broom set out to vindicate the (then beleaguered) Raymond Dart by finding an adult ape-man. In 1947, Broom and his assistant John T. Robinson found Mrs. Ples in Sterkfontein. Initially broken by their enhanced-extraction techniques, i.e., explosives, Mrs. Ples is glued back together with a few tiny fragments missing but she (or he) serves as powerful evidence that ancient humans lived in Africa. Mrs. Ples is about 2.5 million years old.
And we didn't just get to see Mrs. Ples. Potze picked up the skull, gave me instructions on how to hold it carefully, then placed one of the most world's most famous fossils in my hands. It was like holding a baby, just more important (apologies, all you new parents). Ted and Kari got to do the same.
The skull isn't big, but it's heavy, partly because it's a fossil and partly because it's still filled with rocky matrix. Depending on the circumstances, paleontologists often choose not to remove matrix. It can help hold a fossil together, and removing it may do more harm than good. And given new technology able to produce three-dimensional models of fossils, prepping out the matrix probably isn't necessary.
Broom originally identified Mrs. Ples as Plesianthropus transvaalensis, ("near man from the Transvaal") but the fossil has since been subsumed into Australopithecus africanus, like many of the other fossils in the Pretoria bone room. The A. africanus specimens are about 2.5 million years old.
Another australopithecine in the bone room consisted of a partial skull, and when Potze pointed out the brow ridges, Ted said a fossil hunter would need an awfully well-trained eye to spot them. But additional evidence for this fossil's affinities came from a cast that had been found in association with it. Like the Taung Child, it sported a cast of its brain.
Potze explained that the process of decay is like thawing; it proceeds from the outside. As decay progresses, sediment fills the chamber. So there sat the little brain, atop the little skull.
Although the skull was small, Potze told us, the sinuses were quite large, large enough to indicate that the species likely relied heavily on smell. Ancient australopithecines might even have been able to small water in the dank chambers of Cradle of Humankind Caves.
Potze also showed us the remains of some robust australopithecines, often classified as Paranthropus. Paleoanthropologists have divided australopithecines into two general groups: gracile and robust. The graciles, some of them at least, are regarded as ancestors of modern humans. The robust australopithecines are believed to be a side branch of the human family tree. The terms "gracile" and "robust" don't describe the hominins' bodies; all of them would be pretty short and perhaps slight compared to us. The terms refer to their skulls and jaws. Robust australopithecines have thick mandibles, big teeth, and sometimes sagittal crests for the attachment of really strong chewing muscles.
One robust skull had a face like a jack-o-lantern and an unbelievably massive jaw. Potze explained that heavy chewers such as robust australopithecines would end up chewing a lot of sand with the plants, and the sand would wear down their teeth. ("You only get two chances, your milk teeth and your permanent teeth," as she tells her young son.) One tooth was worn so badly that the enamel was gone, and chewing must have been agonizing for that hominin. The unfortunate hominin might have died for no other reason than his or her teeth were too used up to chew anymore.
Though categorized in the same general group, robust and gracile australopithecines didn't live at the same time. Gracile australopithecines came first. The earliest gracile australopithecines show up in the fossil record about 4 million years ago, and the last of them fizzle out about 2.5 million years ago. Australopithecus africanus was among the more recent gracile species. Robust australopithecines first show up in the fossil record about 2.6 million years ago, and the last of them die off around 1 million years ago. What's interesting is that the robust australopithecines enter the scene at about the same time as the earliest identified members of our own genus, Homo. Paranthropus and Homo apparently coexisted in Africa for hundreds of thousands of years. Robust australopithecines may have used simple bone and/or horn tools for digging tubers or termites while our direct ancestors started crafting stone tools. But even if it was "more sophisticated" than bone or horn tools, stone-tool technology stayed very simple for a very long time.
Skilled researchers have mined australopithecine teeth for information not only about diet but about who moved away from the family group and who stayed. Potze suggested I look up a paper by Sandi Copeland and her colleagues under the general theme of "mommas' boys." Tooth enamel preserves isotopes of strontium, an element occurring in rocks, dirt and plants. By identifying the strontium isotope, which relates to rock layers, Copeland's team could figure out which hominins moved around more. The researchers made the somewhat surprising finding that the females were more likely than the males to move away from home.
Females may have done more than move to different groups. After wowing us with robust australopithecine remains, Potze produced a surprisingly delicate partial skull of a Homo erectus, held together with small struts. And she showed us a small box of burnt bone fragments associated with Homo erectus.
Potze then told us about Bob Brain, who conducted research at a Cradle site named Swartkrans. Back in 1988, Brain coauthored a Nature paper on the early use of fire at Swartkrans. He hypothesized that, while members of Homo erectus might not have been able start a fire, they might have been able to preserve a flame after, say, a lightning strike. Homo erectus might have used fire first and foremost to ward off predators, something the australopithecines probably couldn't figure out how to do. The use of fire might have given members of our own genus a competitive edge. And, Brain hypothesized, maybe it was the females to pioneered using fires to keep predators at bay. "Think about it," Potze said. "It's the females home all day with the children." And children can produce a lot of bodily fluids. Today those fluids are mostly messy and annoying. A couple million years ago, they were invitations to big cats looking for lunch.
After our visit with Potze, we wandered through the human-origins exhibition at the Pretoria museum, where we saw displays dating from the 1980s, one illustrating Brain's hypothesis about fire.
Besides the early use of fire, laid out in a pint-sized diorama, we saw an unsettling diorama of a leopard dragging off a small hominin, holding onto it by the head. In the bone room, Potze showed us a juvenile cranium, its suture lines not completely closed, with two puncture wounds nicely fitting an ancient leopard jaw.
Hominins may have adopted fire to ward off predators but the use of fire eventually extended to other areas, such as cooking. Cooking or in other ways processing certain foods make them easier to digest. "There's a reason there's no beef sushi," Potze said. It would be too tough for the human gut to process. (Ever the contrarian, Ted argued that there's beef tartare, but you, sensible reader, get Potze's idea.)
Like Sterkfontein, Swartkrans is a cave that keeps on giving to paleoanthropologists, even if the gifts are pretty macabre. In July 2016, a team including multiple Wits scientists published a paper on what might be the oldest case of cancer found in a hominin. A foot bone from an individual who died in the cave between 1.6 million and 1.8 million years ago showed signs of osteosarcoma, though the researchers didn't have enough bone material to clearly identify the hominin's species.
Ted and Kari wanted to see wildlife, and Ted thought the lion park more or less within the Johannesburg-Pretoria metropolitan area would be too tame, despite the fact that an American tourist was mauled to death there the previous year. So we went to Pilanesburg. The trip from Johanessburg to Pilanesberg is supposed to take two and a half hours one way, but that assumes you don't get lost. We took wrong turns and had to backtrack multiple times on the way there. In the end, we took four hours to find Pilanesberg.
The car Ted rented didn't come equipped with GPS, and he didn't want to use the feature on his phone in South Africa for fear of exorbitant charges. The Johannesburg map from Avis showed minimal resemblance to the actual roads underneath the tires. When Ted stopped at a gas station and asked for a map, the cashier pointed to the only map he had — nailed to the wall. But Kari has served as Ted's reliable navigator for about 30 years, so they made the best of it, though we nearly gave up and turned around within a mile or two of the park entrance because the route from the highway to the park was marked by little more than poverty and goats.
Once we did find our way to the park (and I found my way to a ladies' room), the trip seemed worth it. First we saw elephants off the in the distance. That initial visual treat was followed by a wildebeest, antelope, giraffes, even a baboon. And lots and lots of zebras. I think a couple of those zebras even mooned me.
So we had seen what we hoped to see, and the trip back to Johannesburg was bound to be easier, right?
In fact, getting to the outskirts of Johannesburg wasn't bad, but the roads were no less confusing, and the Avis map no more useful when we got back into town. We were visiting South Africa in late autumn, so the days were short. Ted traded his prescription sunglasses for regular glasses, but they were older and the prescription less up to date. It was getting dark.
When Ted and I arrived at the Johannesburg airport on the evening of May 18, the hotel arranged for a local, trusted driver to pick us up. Andre, who hailed from Ghana, answered Ted's queries about South African politics, and gave us some safety tips, namely don't visit downtown Johannesburg if you can avoid it because you might get robbed. "Will robbers pull a knife?" Ted asked.
"Oh no," Andre assured us. "Don't worry about anybody pulling a knife on you. They'll pull a gun on you." He explained that we could avoid serious harm by just handing over valuables without argument, and Ted pointed out that at least that's better than in the U.S. where mass shooters just start shooting.
And, Andre warned, don't drive yourself to Soweto.
Three evenings later, crisscrossing Johannesburg without getting any closer to our hotel, we saw a sign. Ahead: Soweto. For all we knew, we were already in the middle of downtown Johannesburg.
Ted did a U-turn and pulled off to the side of the road. Now more worried about bodily harm than cell phone charges, he turned on his phone's GPS so that Kari could navigate while he drove. Kari had steered us out of trouble all day, but she is farsighted and couldn't see that little blue dot on a cell phone at arm's length. I, on the other hand, am nearsighted. I suggested that, this time, maybe I could navigate.
I don't know how my distance vision compares to 20/20, but my eyeglass prescription reads -9.00 diopters for my left eye, and -11.25 diopters for my right, and that gets my vision up to 20/25. I'm old enough to need bifocals, but when I need to read something at close range with the greatest accuracy, I actually take my glasses off (in Johannesburg, I even put them away so they wouldn't fly out of my lap during another U-turn) and hold the object in question about an inch or two from my nose. For the next 20 minutes, I didn't take my eyes off that little blue dot. I didn't look up from the phone, and couldn't have seen anything if I had. From the back seat, I could barely see Ted and Kari. I didn't realize until the next day that we drove over the Nelson Mandela Bridge, all lit up in its rainbow-nation glory. I was staring at the blue dot, freaking out because I didn't know how we'd get over all those railroad tracks.
If you've seen the movie Sneakers, you might remember the scene where Robert Redford's character talks David Strathairn's character (who is blind) through driving a getaway van away from gunmen. Our last night in Jo'burg felt a little bit like that. Ted was worried and I was near panic. Only Kari kept completely calm. Once we finally got back to the hotel, which we all loved, there was a mournful Spanish song playing in the background. Voicing his only concern about the place, Ted said he wished the hotel would play a different song because the melody was too close to what had been running through his head. Then he started singing, "We're going to be trampled by elephants while crashing into a car wash."
Between Ted's passport troubles and Johannesburg's confusing streets, I hadn't made it to the Maropeng Visitor Centre in the Cradle of Humankind, but I wanted to take in a good human-origins exhibition before we caught the train to Cape Town. While Ted and Kari returned the rental car, I took a cab to the Origins Centre at Wits, near where we first met Dr. Thackeray. I arrived early, and waiting in front, watching lizards scuttle across the pavement, and taking in the entrance artwork by students from the Baobab Learner Centre. I especially liked the painted square bricks at the base of the wall.
Two very kind ladies were at the Centre when I arrived. Noticing me waiting, they opened the Centre early for me and they opening the gift shop, which is normally closed on Sunday. Good move on their part, because I'm a compulsive shopper in gift shops.
I had a driver waiting and a train to catch, so I hurried through the Origins Centre faster than I would have liked, but it was well worth the visit. The Centre focuses on human evolution, fossils (hominin and otherwise) and the Khoisan people of South Africa. The hall I found most breathtaking featured wall hangings of Khoisan history illuminating an otherwise dark, cavernous room. One of the more enlightening displays in the Centre (and there were many) compared artifacts and rock layers in Africa, Asia, Europe and the Americas. Anyone who still wonders where humanity originated should take a look.
The most striking hall in the Centre features wall hangings illustrating the history of the Khoisan hunter-gatherers. The Khoisan may comprise a small population today, but a study published in late 2014 concluded that, over the past 200,000 years (most of the history of modern Homo sapiens), they were the world's largest population, and the most genetically diverse. Lead by Hie Lim Kim, the authors report:
Modern humans may have originated anywhere in Africa and spread across the continent, with continuous gene flow among the populations. From ~100,000-150,000 years ago, the human species was geographically structured within Africa and eventually differentiated genetically owing to limited gene flow. At or after the time of the population differentiation, a drier climate began to affect the western and central, but not the southern regions of the African continent. This potentially contributed to a relatively severe decline in the western African populations (ancestors of the current Bantu-speaking populations) while the size of southern African populations, ancestors of the current Khoisan, was maintained or declined to a much lesser degree. Non-Africans, the majority of modern humans alive on the planet today, represent a subpopulation split from the ancestral non-Khoisan African population, and their genetic diversity further dramatically decreased during their migration from Africa to Eurasia. . . . Our hypothesis may explain the distinctive demographic histories among human populations and suggest that the Khoisan hunter-gatherers and their ancestors have been the largest population in terms of genetic diversity throughout modern-human history.
"If you're going all the way to South Africa, see more than Johannesburg," people told me as I planned my trip. On the way home from a traverse across Antarctica ("traveling around the world the hard way" as one of our coworkers put it), Ted had been to Cape Town several years earlier, and recommended seeing it. We could fly, but we'd see more of the country by train.
The Blue Train would have been wonderful. It also would have cost about $1,000 per person, and we would have had to schedule our whole trip around the train ride, which only occurs once a week. Premiere Classe train travel, a quasi-luxurious trip for a smaller budget, looked ideal, but it also ran just once a week and therefore clashed with our Johannesburg plans.
We decided to ride Tourist Class on the Shosholoza Meyl, which translates into "A pleasant experience." Under the best of circumstances, the trip takes about 27 hours, not counting delays due to track maintenance. Some people actually spend the whole time sitting up, but I'd get to do that on the plane trip home, so I went for the opportunity to at least lie down. Ted and Kari rented a coupe, and I rented a coupe for myself. It came with a sink (though the water was for washing, not drinking), a comfortable seat that could convert to a bed, rentable bedding, space for luggage, and a door that could be locked from the inside. There was no way to lock the door from the outside, and "locked" still meant that someone could slide the door open by a few inches, which somebody did in the wee hours when I was trying to sleep. That same somebody did the same thing to Ted and Kari, and I heard Ted yelling, "Hey, someone's in here!" Meals were modestly priced and simple. Morning coffee was offered, at a very loud volume, at 6:30 a.m. Shortly after the coffee bugle call, a train official rapped on my door wanting to inspect my ticket for the third time since I'd boarded the train. After a trip to the potty (equipped with only cold water, no soap, and at first no toilet paper), I felt grateful for the advice I'd fielded back home to bring along sanitizing hand wipes.
The train made multiple stops along the route, some of them in the middle of the night, all of them including shouting and stomping down the corridor and whistles. At some point, I concluded that Shosholoza Meyl offered the opportunity not to see South Africa so much as hear it. I wouldn't have minded South Africa being a weensy bit quieter.
But the scenery was fantastic.
South Africa's rock record is not continuous. It doesn't, for example, preserve much from the time of the end-Cretaceous extinction that wiped out the dinosaurs. But the country actually does contain one of the most impressive rock records in the world, with exposures from billions of years ago through geologically recent times. The Karoo region contains a supergroup of rock layers lasting from the late Permian into the Jurassic Periods, preserving some remarkably weird protomammals. After the breakup of the supercontinent Pangaea, South Africa became part of Gondwana. In terms of ancient landscapes, South Africa's rocks have seen just about everything. A little over 300 million years ago, the Karoo was the Karoo Sea. About 190 million years ago, the same general region was home to sand seas. At other times, it's hosted temperate forests. And swamps.
As Pleistocene ice sheets slowly crept over Eurasia, South Africa remained ice free, but the region turned arid. Expanding deserts in southern Africa might have squeezed different Homo populations into coastal regions, isolating those populations from each other, maybe even magnifying genetic differences between them and spurring evolution. Whether changing climate drove human evolution is hard to say, but Homo brain size did increase substantially around that time.
We arrived in Cape Town in the middle of a downpour and a traffic jam, but the situation soon improved. Our hotel was across the street from the ocean, and a short taxi ride from the Waterfront and the Kirstenbosch Botanical Gardens, which nestle into the base of Table Mountain.
Kew Gardens may be more famous, but I don't think I've ever seen a more beautiful botanic garden than Kirstenbosch. My only disappointments with the garden were that its bookstore and tea room were closed, and its otter pond sported only an otter sculpture, not the real thing.
After breakfast on May 25, Ted and Kari departed for a drive through the Eastern Cape. I spent the day walking along the sea wall near the hotel and packing for my flight home.
When I graduated from the University of Colorado-Boulder in 1986, there weren't many student-staged protests at the ceremony. But a few students taped signs to their caps or gowns: "Divest now." They were referring to CU's investments in Apartheid South Africa. I confess I wasn't one of those students, but I recall my sense of foreboding about the country through the late 1980s. Apartheid was unsustainable, not to mention unconscionable, and violence was growing. The rainbow nation was incredibly lucky to have a leader like Nelson Mandela, but leaders like Mandela are rare. We visited South Africa amid widespread calls for its then president, Jacob Zuma, to resign.
Zuma finally stepped down in early 2018, but valid concerns about corruption persist. The party of Nelson Mandela saw education as key, but now money intended for schools disappears, and despite a more advanced economy, the country's children lag behind those of Kenya, Botswana and Swaziland in math and reading.
Looking only at recent headlines, one might be tempted to say that corruption has worsened in South Africa since the end of apartheid, but that's not true. Apartheid was all about corruption, and not just because it was a racist system that trapped nonwhites in poverty in a police state. Both the British and the Dutch sought control over South Africa for many years. Despite its legion of faults, the British Empire did establish a free-market system in South Africa where it was possible — not easy but possible — for people of color to advance. All the while, some descendants of Dutch settlers weren't competing in that free market so effectively. Apartheid handed the Afrikaners all the goodies based on skin color and loyalty to the government.
Spending nine days in a country hardly makes you an expert on it, but the time can give you a glimpse. To my eyes, South Africa offers equal parts worry and encouragement.
As soon as I got through passport control at the Johannesburg airport, I met a porter who warmly welcomed me to the country and then, after he was holding my carry-on bag, asked me to give him enough money to buy a cold drink. When I handed him less than he wanted, he got mad. Porters became the bane of my existence over the next several days. Ted, Kari and I agreed that it wasn't the money they were asking for (usually a pittance) that worried us, it was the fact that they took control of our stuff, and we weren't sure we'd get it back. Objectively, we realized they were just desperate people trying to survive, but porters separate tourists from money with deception. Take the young man at the Cape Town railway station, wearing a safety vest and looking official, who demanded that passengers disembarking from a 28-hour train ride drop our bags and rummage through our wallets to hand over our used train tickets, while the porters surrounding him reached for luggage. No one on the train or at the ticket office said anything about such a requirement. Tired of playing along, Ted refused, and the challenged young man let us pass without argument.
At every major intersection, we saw people standing between lanes hawking hats, buttons, lanyards, newspapers. Beggars followed us at either end of our commuter-train trip to the Pretoria museum. Meanwhile, bice homes were surrounded by walls or fences — not that different from home, actually — but in Johannesburg, the metal fence posts were topped with medieval-looking pikes that would tear flesh, and the rock walls were topped with razor wire. It's not hard to guess the color of the occupants of those nice homes. In between the armored neighborhoods we saw our share of shanty towns.
Returning to our hotels or interacting with the drivers we hired was like entering a different dimension. We couldn't wish for more professionalism or efficiency. Interestingly, the three drivers we got to know were all from outside South Africa. In Jo'burg, Andre was from Ghana and James was from Zimbabwe. Our favorite taxi driver in Cape Town, Francis, hailed from the Democratic Republic of the Congo, and he was training to become a South Africa tour guide. When he drove us past a Lamborghini dealership, Ted joked about renting one for his upcoming Eastern Cape drive. "If you rent a Lamborghini," Francis told him, "I'll be your driver for free."
A few years after the trip, I found myself wondering about Andre, James, and Francis, as anti-immigrant sentiments turned violent. In September 2019, The New York Times reported multiple attacks, some of them deadly, on immigrants from other African countries in and around Johannesburg. Though more extreme, the problem seems eerily familiar from the vantage point of the United States.
South African society is steeply stratified, and tourists at the airports and the train stations quickly come into contact with people at or near the bottom. Most, though not all, of the poorest people we encountered were black. Like Jim Crow laws in the U.S. South, apartheid casts a long shadow. Changing the law didn't fix everything overnight. Changing the law didn't fix anything overnight.
I couldn't have wished for better experiences in human-origins tourism than the Cradle of Humankind, and yet South Africa's troubled race relations make it a strangely appropriate place to learn more about anthropology, biology and paleontology. If you look at the history of those fields, you find example after example of racism masquerading as science. Nineteenth-century paleontologist-geologist Louis Agassiz proposed separate origins for human races, based on the arguments of his contemporaries Josiah Nott and George Gliddon. Agassiz argued against evolution, but Ernst Haeckel employed racists memes while arguing for it. Twentieth-century museum boss Henry Fairfield Osborn claimed that the "spiritual, intellectual, moral, and physical characters" separating different human races "are very profound and ancient."
Recovering from decades or even centuries of prejudice takes time. While the consequences of apartheid are long lasting, they show some signs of retreat, to the entire country's benefit.
After asking Thackeray about the biggest changes to the field of human-origins research over the course of his career, I came away with the impression that the biggest change affecting his work was probably the end of apartheid. The Cradle of Humankind is now a World Heritage site. Until South Africa gave up government-mandated racial segregation, it couldn't belong to the United Nations, and couldn't have World Heritage sites. Until the country gave up apartheid, fueled by the belief that God wanted light skinned-people to prevail over everybody else, it couldn't give up creationism. Now public schools can teach evolution. And more people now contribute to the field. Thackeray told me that the University of the Witwatersrand recently awarded paleoanthropology doctoral degrees to Mirriam Tawane and Nonny Vilakazi, both black and both female. In 2018, Tawane collaborated with Thackeray on his Mrs. Ples paper. That would have been unthinkable under apartheid. Though it still has a long way to go, South Africa is in a better position to employ the abilities of its entire population.
Holding Mrs. Ples at the Ditsong National Museum of Natural History in Pretoria counts as one of the high points of my life, and yet I found my visit to that museum a little heartbreaking, too. The displays date from the 1980s at the latest. Many of the animals in the halls look flea-bitten at best. Just the same, as we took in the human-origins displays upstairs from Mrs. Ples, we encountered big groups of black students, bubbling with the same excitement I remember from my own childhood museum visits. At the time I graduated from college, they wouldn't have been allowed into the building. Know hope.
Narrative text and graphic design © 2016-2021 by Michon Scott - Updated April 21, 2021. All photographs by Michon Scott unless otherwise credited.