Overview

• Grade Level: AP Biology / AP World History / AP Anthropology / General Earth Science (grades 9-12)

• Time Required: Single class (45 minutes); bell-ringer option (10 minutes); extension (2 additional class periods)

• Historical Period: The 1974 Hadar field season in northeastern Ethiopia and the half-century of paleoanthropological revision that followed

• Modern Connection: The August 2025 Nature publication by Brian Villmoare's team at Ledi-Geraru (Arizona State University, UNLV, et al.) reporting a previously unknown Australopithecus species coexisting with early Homo, and the January 2026 Nature paper by Zeresenay Alemseged's University of Chicago team reporting the first Paranthropus jaw from the Afar region (MLP-3000)

Learning Objectives

Students will be able to:

1. Describe the discovery of the AL 288-1 (Lucy) skeleton at Hadar in November 1974 and explain why a 40 percent complete bipedal hominin skeleton 3.2 million years old was treated as a paradigm-shifting fossil.

1. Trace the half-century of subsequent paleoanthropological discoveries that have replaced the linear "Lucy-to-Homo" story with a branching one in which multiple hominin species coexisted in eastern Africa between 3 and 2 million years ago.

1. Explain in qualitative terms what the Ledi-Geraru Australopithecus and the MLP-3000 Paranthropus jaw add to that branching picture, including the geographic, morphological, and dating arguments.

1. Construct an argument, using both the original Lucy discovery and the new finds, about how the size and distribution of an existing fossil sample shapes our picture of human ancestry and how that picture is updated.

Before Reading

Anticipation Questions

1. Before reading, draw the human family tree as you currently understand it. How many species do you think coexisted with the immediate ancestor of Homo sapiens between 3 and 2 million years ago?

1. The Hadar fossil site sat in the Ethiopian desert for roughly 3 million years before anyone found Lucy in it. What does that delay say about the relationship between scientific knowledge and field exploration?

1. Multiple closely related species can coexist in the same landscape today (think of crows, ravens and magpies; or red deer, fallow deer and roe deer). Should we be surprised that multiple species of upright apes did the same?

Key Vocabulary

• Hominin: A member of the taxonomic tribe Hominini, which includes modern humans and all our extinct bipedal relatives (Australopithecus, Paranthropus, Homo) but excludes chimpanzees and gorillas.

• Australopithecus: A genus of early hominins that lived in Africa between approximately 4.2 and 1.9 million years ago. Australopithecus afarensis is Lucy's species. Members were bipedal but had small brains (roughly the size of a chimpanzee's).

• Paranthropus: A genus of "robust" early hominins (sometimes called robust australopithecines) that lived in Africa between approximately 2.7 and 1.2 million years ago, characterised by extremely large jaws and molars for processing tough plant foods.

• Homo: The genus that includes modern humans and our closest extinct relatives (Homo habilis, Homo erectus, Homo neanderthalensis, etc.). The earliest currently-known specimens are roughly 2.8 million years old, from Ethiopia.

• Bipedalism: Habitual walking on two legs. Bipedalism is the defining hominin trait and predates the expansion of brain size by roughly two million years.

• Afar Triangle: A geological depression in northeastern Africa where the African, Arabian, and Somali tectonic plates are pulling apart. It includes the Hadar, Ledi-Geraru and Mille-Logya fossil sites, all in modern Ethiopia.

• Hadar: The fossil site in the Awash Valley of the Afar Triangle where Lucy was discovered on 24 November 1974.

• Ledi-Geraru: The fossil site a few hours' drive from Hadar where Brian Villmoare's team in August 2025 reported new Homo and Australopithecus teeth dated between 2.78 and 2.59 million years ago.

During Reading

Guided Questions

1. Identify the precise date, place, and personnel of the Lucy discovery. What about Lucy was new in 1974 that other fossils available at the time were not?

1. Describe in your own words the linear "Lucy-to-Homo" picture of human ancestry that dominated the late twentieth century. What evidence supported it?

1. List the four hominin lineages that the new evidence shows coexisted in eastern Africa between 3 and 2.5 million years ago. Where does Lucy's species (Australopithecus afarensis) sit in this picture?

1. Identify three specific numerical or biographical claims about the Ledi-Geraru and Mille-Logya finds that the story emphasises. Why does each matter?

After Reading

Discussion Questions

1. The story says the change in our picture of human ancestry is "not a single discovery" but "the cumulative weight of forty years of new finds." Is this a fair characterisation of how scientific consensus changes, or is it understating any individual paper?

1. Donald Johanson is quoted as saying the Ledi-Geraru find makes Lucy "bigger, not smaller." What does he mean? Do you agree?

1. The story claims the previous absence of Paranthropus from the Afar was "an artefact of which rocks had been combed for fossils." How could you tell the difference between a real absence and a sampling artefact?

1. (Genuinely debatable.) The story closes with the suggestion that the next twenty years of fieldwork will turn the question of "who exactly we descended from" into something more like "which particular oak in a forest of oaks happens to drop a particular acorn." Is this a useful image for thinking about evolution, or is it misleading?

1. Pamela Alderman's suggestion of "Lucy" came from a Beatles song playing in the camp. How much does the popular naming of a fossil shape its scientific impact? Would the world know AL 288-1 if it had been called AL 288-1?

The Parallel

1. List the structural features that are similar between the Hadar fossil-hunting of 1974 and the Ledi-Geraru fossil-hunting of 2025-2026. List the features that are different. Which list is longer, and which is more important?

1. Both halves of the story are set in the same geographic region (the Afar). Pick three reasons that the Afar in particular has been so productive for paleoanthropology, citing evidence from the story.

1. Could there be a similar parallel in a different scientific field, where a fifty-year-old single-find paradigm has been replaced by a branching one through the gradual accumulation of evidence? Suggest one example and defend it.

Activities

Bell-Ringer (10 minutes)

Project two images side by side: a contemporary photograph of the Lucy skeleton in its glass case at the National Museum of Ethiopia in Addis Ababa and a recent ASU News photograph of the Ledi-Geraru excavation grid showing the 13 teeth on a cotton tray. Ask students: "What scientific question do these two images have in common?" Have them write two sentences identifying the shared question. Use the responses to introduce the lesson.

Single Class (45 minutes)

• 0 to 5 minutes: Bell-ringer recap.

• 5 to 18 minutes: Read the historical half of the story aloud or play the audio narration. Students fill out a guided-reading organiser with three columns: "What Johanson found," "What it meant in 1974," "What the textbook picture became."

• 18 to 30 minutes: Read the modern half aloud or play the audio. Students extend the organiser with parallel columns: "What the Ledi-Geraru and Mille-Logya teams found," "What it means in 2026," "What the new textbook picture should be."

• 30 to 42 minutes: Whole-class four-corners discussion of After Reading question 4 (the forest-of-oaks image). Students physically move to a corner marked "Useful for thinking about evolution," "Misleading because it understates ancestry," "Useful only at certain timescales," or "Both at once."

• 42 to 45 minutes: Exit ticket. One sentence: "The most important thing the new Afar fossils can teach us about how science updates is: ___."

Extension Activity

Family-tree essay (3 to 5 pages, two class periods): students draw their best-current family tree of the genus Homo and the genus Australopithecus between 4 and 1 million years ago, citing at least three primary or near-primary sources. They include a short paragraph for each branch describing the type specimen, its date, its geographic origin, and its current taxonomic status. They conclude with one branch they expect to be added within the next ten years.

Primary Source Connections

• Donald C. Johanson and Maurice Taieb, "Plio-Pleistocene hominid discoveries in Hadar, Ethiopia," Nature 260 (1976), pp. 293-297. The original announcement of the Hadar hominin assemblage including AL 288-1. Type: scientific paper.

• Donald C. Johanson, Tim D. White, and Yves Coppens, "A new species of the genus Australopithecus (Primates: Hominidae) from the Pliocene of eastern Africa," Kirtlandia 28 (1978), pp. 1-14. The formal naming paper for Australopithecus afarensis.

• B. Villmoare, K. E. Reed, J. R. Boisserie et al., "New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia," Nature (2025). Type: peer-reviewed scientific paper. Available open access at nature.com.

• Z. Alemseged et al., "A 2.6-million-year-old Paranthropus fossil from the Afar of Ethiopia," Nature (21 January 2026). The Mille-Logya MLP-3000 paper. Type: peer-reviewed scientific paper.

• Lucy (AL 288-1), National Museum of Ethiopia, Addis Ababa. Type: museum specimen / material culture. The actual skeleton.

• Donald Johanson, "Lucy: The Beginnings of Humankind" (1981, with Maitland Edey). Type: popular-science memoir. The full first-person account of the 1974 field season.

Standards Alignment

C3 Framework

• Dimension 1 (Developing Questions): Compelling question: "How does a fifty-year-old picture of human ancestry get updated, and what does it tell us about how science changes its mind?" Supporting questions about the role of fieldwork, geographic sampling, and morphological analysis.

• Dimension 2 (Applying Concepts): Biology (evolution, taxonomy, comparative anatomy, dating methods). Geography (the Afar Triangle, tectonic plate boundaries, fossil preservation conditions). History (the changing institutional structure of paleoanthropology over the past fifty years).

• Dimension 3 (Evaluating Sources): The story is accompanied by a populated evidence manifest with eleven verified claims and direct source URLs. Students can interrogate each claim by clicking through.

• Dimension 4 (Communicating Conclusions): The structured four-corners discussion and the extension essay both require sustained argumentation and source evaluation.

AP Alignment

• AP Biology: Big Idea 1 (Evolution) and Big Idea 4 (Biological systems interact). Macroevolution, taxonomy, and the evidence for common descent.

• AP World History: Key Concept 1.1 (Big Geography and the Peopling of the Earth). The geographic distribution of early hominins and the origins of human migration.

• AP Anthropology / AP Research: A model case for tracing how a fossil paradigm is constructed, defended, and eventually revised across decades of fieldwork.