Lucy 50th Anniversary Symposium: The Impact of "Lucy" on Human Origins Science

Saturday, April 06, 2024


Since my entry to the field of paleoanthropology in 1970, a more focused and rigorous implementation of an expanded collaborative, multinational, transdisciplinary strategy of inquiry with the application of new theoretical and technical innovations has resulted in a richer picture of our origins and a deeper understanding of how we became human—not only in Africa, but Eurasia as well.

The discovery of Lucy 50 years ago provides an appropriate benchmark by which to contrast what we know in 2024 versus what we thought we knew prior to her discovery in 1974:

  • Europe is no longer touted as the finishing school for humanity.
  • The human family tree is significantly more speciose than anticipated.
  • The multiregional origins of Homo sapiens is no longer a tenable hypothesis.
  • Neanderthals did not evolve into Homo sapiens; paleogenetics has demonstrated that they contributed to the modern human genome.
  • Australopithecus africanus no longer holds the place at the base of the human family tree as the common ancestor to all later hominins.
  • The theory that man the hunter made us human is being challenged by an expanded appreciation of the role of women in our evolution.
  • The appearance of the genus Homo and its purported ancestor now reaches back a million years further than previously documented.
  • The proposition that hominins left Africa after the control of fire is no longer accepted.
  • The single species interpretation of australopithecines is effectively negated.

As far back as the late 1960s, Sherwood Washburn’s New Physical Anthropology proposed moving away from a study “characterized by theories, or rather by a group of attitudes and assumptions” to a more comprehensive and thorough grasp of the biology and behavior of fossil hominin taxa. Knowledge of the environment in which our ancestors lived and interacted and successfully navigated the challenges of survival is now coming into clearer focus. We are in a period of specialization, and it is imperative to embrace an integrated approach that melds biological and cultural evolution. Only in this way can we continue to provide a more far-reaching vision of our ancestry.

In retrospect, it is possible to see the middle-1970s discovery and initial analysis of the fossil NME AL 288-1, affectionately known as “Lucy,” as a major symbol, and even the driver, of a significant reorientation in the science of paleoanthropology. That change of perspective affected both the conceptualization and the practice of the science of human evolution. Before Lucy was discovered, the interpretation of the human fossil record had been dominated by practitioners of traditional expert pronouncement or by followers of the newer linear gradualism preached by Ernst Mayr. Either way, paleoanthropologists had earlier seen fossil hominin species as mere heuristic conveniences, rather than as real, bounded, entities that had played critical—and in principle identifiable—roles in the human evolutionary drama. But with the addition to the hominin roster of the new species Australopithecus afarensis, exemplified if not typified by “Lucy,” it began to be obvious that, in stark contrast to accepted practice, hominin fossil species needed not only to be properly defined, but also to be situated within specifically articulated hypotheses of relationship. Nowhere was the clash between the old and the new perspectives more dramatically displayed than in the famous 1981 “debate” between Richard Leakey and Donald Johanson, moderated by the venerated Walter Cronkite. When challenged by Johanson to provide an alternative to his phylogenetic framework for A. afarensis, Leakey, a classic practitioner of authoritarian pronouncement, brusquely declined to do so and abruptly terminated discussion. There could have been no better way than this abandonment of dialogue to dramatize the deficiencies of traditional paleoanthropological practice; and it is possible to argue that this nationally televised event marked an important stage in the transition to the current era, in which paleoanthropologists, while often regrettably clinging to an ultimately Mayrian taxonomic minimalism, nonetheless at some level acknowledge not only the diversity implicit in the morphological heterogeneity of the hominin fossil record, but also the importance of organizing that diversity via explicit and testable phylogenies.

Owing to its morphological and temporal placement, the Lucy species, Australopithecus afarensis, plays a pivotal role in our understanding of the human evolutionary career. Though many more fossil remains were recovered subsequent to Lucy’s discovery, the impact of the latter cannot be overstated not least its role as a trove of scientific data as well as its iconic nature. Research on Lucy and its species and continued fieldwork have inspired many research projects across Africa especially the Afar region of Ethiopia. One such project is the Dikika Research Project, which has discovered the earliest and most complete skeleton of a juvenile A. afarensis, dating back to 3.32 million years ago, filling in a major gap in our knowledge of the species. Here, I will briefly discuss what we learn from this skeleton about the Lucy species and what that implies to our knowledge of the many descendants of A. afarensis including our own species.

This talk begins by considering what the fossil and molecular evidence for early hominin evolution looked like in 1974, when conventional wisdom suggested that what were then called hominids and pongids had a relatively ancient divergence. It also predated the acquisition of the most compelling evidence that chimpanzees and bonobos were more closely-related to modern humans than to gorillas. The talk considers separately the impact of Lucy and the impact of Lucy’s ilk (i.e., the impressive hypodigm of Australopithecus afarensis). In 1974, aside from the relatively fragmentary and poorly preserved associated skeletons of Australopithecus africanus, little to nothing was known about the body size and limb proportions of the creatures that linked later hominins with what we now know would have been the common ancestor of hominins and panins. Lucy provides exceptional information about an individual early hominin, but it is the quantity, quality, and temporal resolution of the overall hypodigm of A. afarensis—Lucy’s ilk—that has helped put the other australopiths recovered from sites in southern and eastern in sharper context. Lucy’s ilk sheds light on important topics such as taxic diversity, phylogenetic relationships, and the tempo and mode of evolution within the hominin clade. It is, in many ways, the key that has the potential to unlock the secrets of hominin evolutionary history that both preceded, and came after, A. afarensis.

The savanna hypothesis is a long-lived idea concerning the role of the environment in the origin of hominin species—those that walk on two legs like humans and their ancestors. Scientists in the 19th century referred, vaguely, to apes and humans or human ancestors evolving away from each other and the latter moving to inhabit savannas—or more broadly, out of the forest and into the open. There were even suggestions that humankind emerged on savannas with no connection to forested apes. Definitions of savanna at this time were sparse, except possibly that they were open and grassy.

Raymond Dart, in his 1925 paper on the discovery at Taung, in 1924, of the small-brained, bipedal Australopithecus africanus, noted that open savanna with patches of woodland—such as those found in South Africa near Taung—could have led to selection for a variety of human-like characteristics such as bipedalism and a larger brain. Such characteristics would distinguish early human ancestors from forest dwelling apes; in Dart’s view, A. africanus was thus the base of our lineage. During the following 50 years, others took Dart’s idea that early hominins lived on an open savanna as fact, leading to speculation about whether living in a savanna environment ultimately caused the origin of bipedalism. Was bipedalism important for seeing above tall grasses or, perhaps important, for freeing the hands to carry or hunt?

The discovery in Ethiopia of Lucy in 1974 confirmed, without a doubt, that Australopithecus species were bipedal, widespread, and small-brained. Lucy, however, had curved fingers and toes—what did that mean? Was this evidence of the importance of trees in the way they moved across the landscape or just a holdover from Lucy’s ancestors? The Lucy discovery not only prompted new ideas about the origins of bipedalism, but also prompted researchers to investigate the evidence for, and changes in, the savanna habitat. But savannas did not lose their appeal. In the 1980s, Vrba examined species turnovers on the African continent that she said were caused by climate-induced aridity and grassland expansion. These turnovers occurred at 5.0 million years ago (Ma) and 2.6 Ma, give or take a few hundred thousand years. Each episode of aridity expanded grasslands (now used interchangeably with savannas) and was likely responsible for the evolution of more hominin (and other mammalian) species.

During the past 30 years, paleoecologists have used numerous techniques to refine reconstructions of paleohabitats and paleoclimate at individual African hominin localities from the late Miocene to the Pleistocene. Research ranging from isotope and pollen analyses to community ecology and biomarkers have explored the importance in hominin evolution of habitats across space and through time. Today we know that understanding the interactions between various hominin species and their ecosystems (encompassing climate, vegetation, and other organisms) goes far beyond savanna, requiring a much more nuanced understanding of biomes, paleoclimates, mosaic habitats, and hominin morphology, to answer contextual and adaptational questions about human evolution.

It is an exciting time in paleoanthropology. The pace of discovery of fossils seems to be increasing every year, leading to an expanding cast of characters on our branch of the primate family tree. New analytic approaches leading to insights into what these fossils tell us about our deep past, and what we know about the biology and behavior of our fossil relatives, is transforming our understanding of how we evolved. Yet despite these innovations, we still depend on Lucy. Her discovery 50 years ago marks the halfway point between the discovery of the first Australopithecus fossil at Taung in South Africa in 1924, and today. Lucy rocked the scientific world being such a complete skeleton as well as the oldest australopith. She, along with the First Family, provide a treasure trove of information about A. afarensis from most anatomical regions, from males, females, the young and the old. To this day, Lucy and company remain the primary reference for what the early members of our branch of the family tree were like, especially as A. afarensis remains the best represented species of early hominin in the fossil record. Bipedal posture and craniodental adaptations for eating tough-to-process foods appeared to be the hallmark of the australopith lineage, and the common explanation has remained that this dietary shift led hominins to stand up and become bipeds to move away from the trees in search of these foods. Today, however, even earlier fossil apes and hominins have shown us that bipedality most likely did not evolve from a chimpanzee-like ancestor standing up from all fours, but a more generalized arboreal upright ape who began moving on the ground, still upright, and eventually losing a grasping big toe and fully committing to terrestrial travel. The discovery of even earlier australopiths has shown us that bipedality was established by 4.2 million years ago, whereas the dietary specialization for eating tough-to-process food emerged more slowly over time, so that effective bipedal travel seems to have facilitated dietary change and specialization rather than the other way around. At least some australopiths even appear to have relying on stone tools to aid in this quest, long before the significant encephalization we see in Homo. We now also know Lucy was not alone, but that her species was part of what appears to have been an adaptive radiation of bipedal apes in the mid-Pliocene trying out what it meant to be an early hominin. All of these new insights were built on the foundation of Lucy’s discovery, and to this day, she remains central to our understanding of how we evolved.

The discovery of the relatively complete skeleton of “Lucy” (A.L. 288-1) in 1974 in Ethiopia revealed unprecedented information about the early hominin body form and bipedal locomotion, but with only two hand bones (a capitate and proximal phalanx) preserved, Lucy offered limited insight into Australopithecus afarensis hand morphology. Fortunately, numerous A. afarensis hand bones were recovered from other sites within the Hadar Formation between 1974–1977, providing, at the time, the earliest and most complete “composite” hominin hand skeleton. Functional inferences about Lucy’s overall dexterity focused on her species ability to carry and manipulate stones as tools, but without contemporaneous archaeological evidence of stone tools in the Pliocene, inferences about tool manufacture were not within the realm of potential A. afarensis behaviors.

Since this time, four important advancements have been made: (1) the discovery of a few hand skeletons associated to single individuals from other australopith and Homo taxa, offering a better understanding of hominin hand evolution and its complexity; (2) archaeological discoveries of tool-making and tool-use in time periods contemporaneous with A. afarensis; (3) experimental evidence; and (4) developments in primate archaeology that have expanded our knowledge of the functional and cognitive requirements of stone tool making and use. I will discuss how these advancements have changed our interpretation of Lucy’s tool-related abilities, her dexterity, and the emergence of tool behaviors in human evolution.

Evolution requires survival, and survival requires food. Information about what ancient creatures ate can unlock specific details about how and why they evolved, because not all foods are created equal. Some are dense in nutrients, but require knowledge, cooperation, or tools to access. Finding evidence for this in the fossil record can be challenging, because behavior doesn’t preserve. Other foods are easily available, but nutrient-poor. These often demand physical adaptations, such as large teeth and robust chewing muscles, that may be more obvious in a fossil. Lucy’s discovery shifted the spotlight of human origins research to eastern Africa, showing that the evolutionary group to which Lucy belonged lived in a wide range of habitats. This brought a new research focus to the ecology of our ancestors: paleoanthropologists wanted to know how our ancestors lived within their environments, not just how their bodies had changed over time.

For a long time, it was thought that Lucy’s kind were mostly vegetarians, eating diets similar to chimpanzees. But this view creates a puzzle, because chimpanzees do not live in the open habitats evidenced in the fossil record. Lucy’s skeleton also definitively showed how different these creatures were from chimpanzees: their lower bodies were built for striding around on two legs, and their back teeth were well-adapted for strong chewing. Lucy’s skeleton showed they had long arms, and fossils discovered later would reveal curved fingers that were surprisingly similar in proportion to human hands. Because nothing like Lucy had ever lived before, understanding how she lived and what she ate remains one of the most important ongoing challenges in paleoanthropology.

What we now know is that Lucy’s species was a wily omnivore, with a flexible diet that enabled our ancestors to venture into a broader range of environments than ever before. Discoveries in the last 15 years suggest that her larger evolutionary group made stone tools or even butchered large mammals hundreds of thousands of years before the first members of our own genus, Homo. This has caused researchers to carefully consider: when did the hallmarks of becoming human truly begin? Was it Lucy, with her taste for something different, that set us on the path to becoming ever smarter, more cooperative, and utterly dependent on tools? Future research will investigate these questions with new fieldwork, innovative approaches to reconstructing ancient diets, and a fresh theoretical perspective on what might have been possible.

Lucy’s discovery in 1974 transformed understanding the anatomy of Australopithecus afarensis and other early hominins. Geological research—stratigraphy and geochronology—answered the question, “When did Lucy live?” by placing her just above the Kada Hadar Tuff, dated at 3.21 Ma. As the initial excitement subsided, we began to ask new questions. How did hominins like Lucy live and interact with the African fauna and flora of 3 million years ago? Where did they live and how did they die? Geology, taphonomy, and paleontology tackle such questions with evidence from the sediments where burial occurred, the patterns of skeletal preservation, and associated fossils. Starting with the burial environment and circumstances of Lucy’s “interment,” we can work back to questions about what happened immediately after death and look for clues about how she died. Her fossils were found scattered on an outcrop surface, with none in situ. The Hadar region at this time was a floodplain with a perennial river linked to seasonal tributary and distributary channels, much like the modern Awash River. Based on detailed geological description of the AL-288 site by Tesfaye Yemane (1997), Lucy’s remains eroded from a sand layer interpreted as a crevasse-splay deposit on a floodplain surface. Sediments above the sands are fine-grained and laminated, indicating that a lacustrine interval followed the flooding event(s). The source of the fossils has been re-interpreted as an overbank channel associated with the crevasse splay (Campisano, Pers. Comm. 2024). Less than 40% of Lucy’s skeleton was preserved, with a mix of different elements and better representation of upper versus lower body parts. The co-occurrence of low-density vertebrae and ribs with heavier limb elements indicates that some body parts were articulated when buried, also that burial was rapid without sorting by water flow. What happened to the many missing parts of Lucy’s skeleton? The absent elements suggest removal or partial destruction by scavengers as well as later losses due to Pliocene and/or modern surface processes. Only one tooth mark has been reported, but the absence of obvious carnivore modification doesn’t mean that predators and/or scavengers were not involved. Modern taphonomic studies show that tooth mark frequency depends on the carnivore species and other circumstances. The cause of Lucy’s death has generated considerable debate. Proposals include a fall from a high tree, mudslide, and crocodile attack. Detailed analysis of fractures in the bones show similarities to damage caused by compressive peri-mortem trauma but also could have been caused by sedimentary compaction after burial but before final mineralization. Without secure information on the bones in their burial environment, including orientations and associations of different parts, the evidence for a traumatic fall is questionable. Geological context argues against a mudslide or other flooding event as a cause of death, and the toothmark is inconclusive with regard to predation. Such debates about Lucy’s death and preservation highlight her continuing impact on paleoanthropology and will no doubt synergize new research as part of her legacy for human evolution.

The histories of paleoanthropology and primatology have been deeply intertwined in the quest to understand human origins, dating from Darwin’s bold hypothesis that humans would likely have evolved in Africa from an ancestor that closely resembled the modern apes. However, for much of the 20th century, the relevance of nonhuman primates to anthropology was focused narrowly on what could be learned from anatomical comparisons. The discovery of the “Lucy” fossil, and the challenges it posed to existing narratives about human evolution, came at a pivotal time when a few nascent field studies were beginning to produce similarly remarkable observations about the behavior of primates in the wild. The convergence of these discoveries stimulated a flood of new questions that have catalyzed decades of research on the diverse ways that primates think, behave, and interact with their environments. The significance of this primate research for the field of anthropology is often presented as a solution to a particular problem, that behavior does not fossilize. Yet, the success of this research program in the intervening decades challenges this very premise, in that lessons learned from these living models have progressively strengthened the ability to make inferences about the lifestyle and behavior of our ancestors. Most importantly, studies of living primates situate biological traits within the rich social and ecological contexts that shape their evolution. In doing so, these studies have made their most uniquely valuable contributions to the study of human origins by disentangling the roots of complex social behaviors, such as cooperation, culture, language, and social learning, along with their potential impact on humans’ unique life course adaptations. Along the way, primate studies have become increasingly interdisciplinary and have developed rigorous methods for studying social processes and their impacts on individual biology. Fifty years from the discovery of Lucy, these toolsets that were developed out of our desire to reconstruct the past have gained new relevance for understanding the human condition today.

The 3.2-million-year-old female hominin skeleton retrieved in Ethiopia’s Afar region in November 1974 underwrites a paradigmatic history of naming. First known through the locality number assigned to the site of the discovery, AL-288-1, she soon became the human ancestor par excellence and an ambassador of human evolutionary studies with the nickname “Lucy” (also known as Dink’inesh in Amharic). The Linnean naming of the species, Australopithecus afarensis, formalized through the 1978 publication in Kirtlandia after a wave of fossil discoveries at Hadar and Laetoli, channeled debates on the evidence and methods of classification in paleoanthropology.

In this talk I will show how Lucy’s systematics offers an emblematic window into the evidential basis and constraints of taxonomic reasoning in early hominin paleoanthropology, as well as what drives the revision of taxonomic attributions. By looking at changing interpretations of the Hadar and Laetoli fossils, I will highlight how taxonomic judgments are never made in a vacuum but interact with the background knowledge available at each time, sometimes countering prevailing schemes of hominin evolution. Further, I will focus on the inferential strategies that have been employed to justify single species attribution of the Hadar and Laetoli specimens and that represent today a typical logic of interpretation of past morphological variation. These include various forms of comparative thinking applied in analyses of ranges of variation between the fossil material and extant living ape taxa and between the fossil material and other extinct species, and chronological thinking evident in the appreciation of the temporal dimension of variation. Finally, I will draw on Lucy’s example to discuss what taxonomic hypotheses are hypotheses of and the relationship between evidence and conceptualizations of “species” in paleoanthropology.

Humans are a spectacular outlier among the millions of species of life on planet earth, with incredibly unique biological success. Slowly, scientists have begun to understand the traits that interacted to make us unique, such as cumulative culture, unique scales of cooperation, cognitive abilities, language, and a unique life history and mating system. However, the sequence of evolutionary events that led to our unique species was very much a mystery until the discovery of early bipedal hominins like the australopithecine, Lucy. Here I will explain how we have learned so much about this improbable sequence and evolutionary pathway by discovering that early hominins were fully bipedal but still had small brains and little evidence for human mating and life history patterns or cumulative cultural evolution. Lucy helped us understand why the evolution of bipedality was a critical first step that led to an amazing evolutionary sequence that resulted in our spectacular outlier species.

Since the discovery of Lucy in 1974, African Heritage management and African paleoscientific research has undergone significant developments, reflecting changing priorities, challenges, and approaches to the promotion of research and preservation and conservation of archaeological and paleontological assets. African countries have engaged in partnerships with international organizations, governments, and NGOs to support heritage management efforts. Paleoscientific research in Africa has flourished, with numerous discoveries, advancements, and interdisciplinary collaborations shedding light on the continent's rich prehistoric past. However, while these gains are commendable, there is growing risk of heritage management collapse emanating specifically from foreign research groups and foreign individual researchers. In many of the African institutions involved in paleoscientific research and heritage management, efficiency in carrying out these activities have been hampered by foreign researchers’ restrictions on access to artifacts, fossils, and sites where such heritage is derived. Some researchers have created ‘Paleodoms’ that are only a preserve of themselves and their friends. These ‘Paleodoms’ have restricted availability of data, hindered innovation in paleontological and archaeological research, inhibited collaboration, impeded learning and skill development, delayed scientific progress, promoted underrepresentation and lack of diversity, and limited opportunities for public engagement and outreach activities centered around fossil and artefact discoveries.

While in some cases these restrictions are necessary, there is a dire need for researchers to strike a balance of the need for access restrictions with the principles of scientific openness, integrity, and responsible stewardship of heritage resources.

Ever since her discovery 50 years ago, Lucy has been a superstar. Her name, her age, her remarkably complete skeleton, and the story of her discovery captured the imagination of people all over the world. She has been a national treasure in Ethiopia and has been a popular ambassador for communicating about science and human evolution. Scientifically, she has been the benchmark for all other ancient hominins discovered since 1974.

But much has changed in the 50 years since her discovery. There are now fossil hominins that are twice as old as Lucy. And researchers have been filling in gaps in the picture of the ancient world she inhabited, including adding fossils of different hominins that were alive at the same time as Lucy’s species, Australopithecus afarensis. Many think that she was not alone and that her neighbors are challenging her species’ status as the last common ancestor of our genus Homo and our distant cousins in the human family tree.

This talk will explore how new discoveries are influencing how the public sees Lucy and her place in the human family. Like other middle-aged celebrities, her status as the Taylor Swift of fossils is getting challenged by newcomers. How does that change the way we write about Lucy and what the messages we share about human evolution with the public?

One of the most important and iconic fossil discoveries in the history of paleoanthropology is the 3.2-million-year-old partial skeleton nicknamed Lucy. Found in the Afar desert of Ethiopia in 1974, at a site called Hadar, Lucy’s discovery not only transformed the way paleoanthropologists thought about the earlier phases of human evolution, but also ignited significant interest in the survey and exploration of new fossiliferous areas in the Afar region of Ethiopia, the Turkana Basin in Kenya, and several sites in Tanzania and elsewhere in eastern Africa. This search has now resulted in the recovery of fossils that have pushed the record of human origins to more than six million years ago. The discovery of Lucy and her relatives at Hadar was also what clearly signaled the need for building laboratories and other research and storage facilities in the countries where the fossils were being found. This led to the establishment of paleontology laboratories in some countries like Ethiopia and, much later, the training of African scientists abroad. At Lucy’s 50th anniversary, we can celebrate the advances made not only in scientific knowledge of human evolution, but also in the building of African research infrastructure and training of local scholars. At the same time, it is necessary for us to reflect on how much further we must still go to help African paleosciences develop in a meaningful way and truly advance human origin sciences.