“We are not so much trying to improve our understanding of human evolution as trying to reduce our ignorance about it”

This is how Bernard Wood, one of the foremost paleoanthropologists alive, summed up his philosophy in the Sixth 2023 FAPESP Lecture.

By Maria Fernanda Ziegler  |  Agência FAPESP – To understand how human evolution unfolded, we must take “the flickering lamp” of history and “stumble along the trail of the past trying to reconstruct its scenes, revive its echoes, and kindle with pale gleams the passion of former days”, said paleoanthropologist Bernard Wood in a presentation entitled “Human Evolution: Achievements and Challenges”, delivered on October 10 at São Paulo headquarters as part of the 2023 FAPESP Lectures. 

The flickering lamp metaphor, borrowed from Winston Churchill’s November 1940 tribute to Neville Chamberlain, illuminated the closing moments of the lecture, in which Wood interpreted the state of the art in paleoanthropology and explained how Homo sapiens evolved over millions of years.

“How do we reconstruct human evolution?” he asked. “Largely through interpretation of the fossil evidence, and to advance our understanding of human evolution we need to obtain more evidence. You can find new fossils, which is hard. You can also squeeze more evidence and molecular data from the fossil record you already have. For example, you can now recover and extract information from ancient DNA.” 

He went on to mention the importance of using non-invasive techniques such as micro-computed tomography (micro-CT) to analyze fossilized tooth roots, or stable isotopes to trace the migration of organisms and the flow of water and nutrients through organisms and ecosystems. 

The study of human evolution involves investigating the shape and composition of teeth that belonged to hominins who lived more than 2 million years ago, because these can suggest what they ate, and analyzing the soil and insects, which provide important information on climate and other living conditions in the remote past.

Besides micro-CT scans, stable isotopes and tooth morphology, the “flickering lamps” to which Wood referred also include paleosol carbonates and 3D geometric morphometrics. “I used to say I was trying to improve our understanding of human evolution. Now I prefer to say I’m trying to reduce our ignorance about it. And we do this by analyzing data and evidence from the fossil record at existing or new sites, by analyzing the data in more advanced ways, and by extracting additional information from these fossils,” he said.

Wood is the Director of the Center for the Advanced Study of Human Paleobiology at George Washington University (GWU) and one of the most renowned paleoanthropologists alive. He is the author of 20 books and more than 250 scientific articles. The British-born researcher is known for his work on the origins of the genus Homo, the paleobiology of Paranthropus boisei (one of the earliest hominins, with fossils found in Europe dating from 1 million-2 million years ago), hominid systematics, phylogenetic reconstruction, comparative morphology, and epistemology in paleoanthropology.

Tree of life

In 1966, while still a medical student with a profound interest in anatomy, Wood first came in touch with paleoanthropology via a course in primatology and human evolution. At that time, there were only nine hominins – primates in the family Hominidae, which comprises gorillas, chimpanzees, bonobos and orangutans, humans, and all their extinct ancestors. Archaic, transitional and modern hominins included Homo sapiens, H. neanderthalensis, H. heidelbergensis, H. rhodesiensis, H. erectus, H. habilis, Australopithecus africanus, Paranthropus robustus and P. boisei.

Almost 60 years later, in 2023, the Hominini tribe comprised 31 taxa (taxonomic groups, such as species, families and classes). Alongside new premodern Homo fossils, the record now includes Au. afaransis (from about 4 million years ago) and possible first hominins Orrorin tugenensis, Ardipithecus ramidus, Ardipithecus kadabba and Sahelanthropus tchadensis (alive between 7 million and 6 million years ago). The list may be reduced, depending on analytical work in progress.

Wood’s career in paleoanthropology – the study of prehistoric humans – began in 1977, when he was invited by Richard Leakey to join what later became known as the Koobi Fora Research Project, as one of three anatomists (the other two were Michael Day and Alan Walker) tasked with examining and describing hominin fossils uncovered at Lake Turkana (formerly Rudolf) in Kenya. Over the next 16 years, he studied the Koobi Fora teeth and skull bones, as well as similar fossils in museums around the world. He determined how many taxa were represented and organized all this information into a monograph on hominid systematics and soft tissue anatomy in apes, published in 1991.

Other research led Wood to conclude that a common ancestor of modern humans, chimpanzees and bonobos lived about 8 million years ago, meaning that chimps and bonobos are closer to humans than gorillas, for example. “We don’t know exactly why this happens but the ‘twig’ that gave rise to contemporary humans and living African apes branched off at some point between 15 and 12 million years ago. The gorillas split off about 11 to 9 million years ago, leaving only a single branch comprising the ancestors of chimpanzees, bonobos and modern humans. Between 8 and 6 million years ago this branch split in two. One half ends on the surface of the tree of life with chimps and bonobos, and the other leads to modern humans,” he said.

Splitters versus lumpers

The lack of a fossil record does not mean a species did not exist, but there probably has not been much splitting, Wood argued. As he explains in Human Evolution, a Very Short Introduction (Oxford University Press, 2019, 2nd ed.), the number of species now recognized in human evolution is relatively large, although this is a highly controversial matter. “The samples may all have been found at the same site or different sites, and may or may not belong to the same population,” he said. “Some experts recognize more species and can be labeled ‘splitters’, while others tend to be ‘lumpers’ because they don’t think the variations are significant. They're looking at the same evidence but interpreting it differently.”

Genetic evidence is a powerful tool for studying evolution, but the samples we collect come from a very small proportion of human evolution. Most of the evidence continues to be based on the fossil record, he added.

Wood delivered two lectures during this visit, his first to Brazil. One took place at FAPESP and the other at the University of São Paulo's Institute of Advanced Studies (IEA-USP). He also met with Brazilian students of Professor Walter Neves at IEA-USP and went on a field trip to Lagoa Santa, the archeological site in Minas Gerais where Luzia, South America’s oldest H. sapiens fossil (from about 12,500-13,000 years ago) was found.

A recording of the event can be watched at: https://www.youtube.com/watch?v=2r7DCa88_Xo.