History Made Every Day™

Uncovering the Human Story: Milestones of Evolution

1859 – Charles Darwin publishes On the Origin of Species

More than 25 years after he traveled to South America aboard the HMS Beagle, the English naturalist Charles Darwin finally published his controversial masterwork, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. What Darwin saw on that long trip validated for him the principles set forth by the geologist Charles Lyell about the ever-changing surface--the gradual evolution--of the Earth. Darwin also found fossils of giant mammals, now extinct, which convinced him that the population of Earth was changing as well as the land. In The Origin of Species, Darwin carefully avoided drawing the controversial line from natural selection among plants and animals to the theory of human evolution from apes. He did, however, let his close friend, the geologist Thomas Huxley, take up the argument for him. Huxley defended human evolution at a meeting of the British Association for the Advancement of Science in 1860 and published his own book on human evolution, Evidence as to Man’s Place in Nature, three years later. Darwin finally entered the debate himself in 1871, setting down his ideas on the evolution of human races, morality and civilization in the two-volume The Descent of Man, and Selection in Relation to Sex. In that book, Darwin recognized the close relationship between humans and African apes and predicted that the earliest human fossils would be found in Africa.

1924 – Australopithecus africanus discovered

The biggest practical problem with Darwin’s theory of natural selection in human evolution was the lack of fossil evidence. Thus the discovery of remains belonging to small-brained, bipedal hominins (species more closely related to humans than any of the living apes) in South Africa beginning in the 1920s was a key event in the study of human evolution. In 1924, miners working at the Taung site in South Africa brought a tiny skull to the anatomist Raymond Dart. Dart recognized it was not the skull of a baboon or other monkey, but a clearly ape- or human-like skull. Its small canine teeth, the shape of its brain and the forward position of the spinal cord where it entered the skull all indicated that it was a biped, and thus a human ancestor. The skull, known as the Taung child, was the first specimen found of what Dart called Australopithecus africanus, or “southern ape of Africa,” which lived 2 to 3 million years ago. Since 1924, more fossils have been assigned to A. africanus than to any other early hominin species. Through studies of A. africanus, scientists concluded that the defining characteristic of a hominin is bipedal walking, not--as had previously been believed--large brains or the ability to make tools, and that human ancestors stood upright long before they evolved the human behaviors relative to intelligence and thought.

1947 – Broom finds skull of “Mrs. Ples” at Sterkfontein

The doctor and paleontologist Robert Broom began collecting hundreds of Australopithecus africanus specimens from the miners working at the Sterkfontein site in South Africa around 1936. Ten years later, he started excavating the area himself with a crew, opening up one of the world’s richest sources of information about the human ancestors that lived between 2.5 and 3 million years ago. In 1947, Broom uncovered an adult skull so unique and well-preserved that he proposed an entirely new genus, Plesianthropus transvaalensis, meaning “near-man of the Transvaal region.” Thought to be an adult female skull, it was dubbed “Mrs. Ples.” Some scientists later disputed this claim, believing it was a male or even an adolescent. The specimen is now classified with Broom’s other finds as A. africanus, and is the most complete skull of this species ever discovered. Together, Sterkfontein and nearby sites Kromdraai and Swartkrans make up a region known as the Cradle of Humankind, which UNESCO designated as a World Heritage site in 1999. Excavation continues at the sites to this day, and discoveries have included hundreds of fossils of A. africanus over the years. A. africanus, long considered a likely forerunner of our own genus, Homo, probably migrated or spread to South Africa from eastern Africa, where the remains of older hominins like Australopithecus afarensis have been found.

1964 – Leakeys first identify Homo habilis at Olduvai Gorge

In 1964, a team led by the renowned husband-and-wife team Louis and Mary Leakey announced the discovery of Homo habilis (“able and skillful man”) based on fossils recovered from Olduvai Gorge in Tanzania. Thought to have lived from about 2.5 million years ago until about 1.5 million years ago, H. habilis was an early group of the genus Homo, which includes modern man, or Homo sapiens. A biped, it had a larger brain than earlier hominins such as Australopithecus. The Leakey team discovered stone tools alongside the H. habilis remains, and concluded that the species was among the first to develop the ability to make and use tools—an all-important link in the chain of human evolution. (Since then, other hominin species have been found at sites with tools, casting doubt on which group exactly was the first to produce tools.) Mary Leakey had first drawn world’s attention to Olduvai Gorge five years earlier, when she found the extremely well preserved skull of an early hominin that Louis Leakey named Zinjanthropus, or “eastern man.” Its nickname, “Zinj,” stuck even after the skull was identified as Paranthropus boisei. (Paranthropus roughly means “equal to” or “like” humans, and is believed by many to be a type of Australopithecus.) As the Leakeys’ fame spread, Louis began traveling around the world working on a variety of projects, but Mary spent much of the next 25 years at Olduvai Gorge, uncovering more and more information about the human ancestors who lived and died there.

1974 – “Lucy” discovered in Ethiopia

In November 1974, at Hadar in northeastern Ethiopia, the researchers Donald Johanson and Tom Gray uncovered an arm bone, skull bone, femur, some ribs, a pelvis and the lower jaw—in all, 477 bones, or a 40 percent intact skeleton—belonging to an early hominin. The small size and shape of the pelvis identified the skeleton as a female. That night, while celebrating the discovery, someone suggested that the skeleton--officially tagged AL-288--be called Lucy, after the Beatles song “Lucy in the Sky With Diamonds.” The Lucy skeleton was later classified as Australopithecus afarensis, named for the Afar region of Ethiopia. A. afarensis lived from around 3.6 to 2.5 million years ago. The study of Lucy and other A. afarensis remains revolutionized existing ways of thinking about early hominins in many respects, but particularly about when and how they first walked. By looking at the remains, and especially at the limb bones and hips, scientists could reconstruct how hominins first began to walk on two legs. They used partial or near-complete skeletons, like Lucy, to help tie together all the other bone fragments that were found. As the earliest human ancestor discovered at that time, A. afarensis also added a new layer of complexity to the study of Australopithecus africanus, raising questions as to how exactly the two species fit onto the human family tree.

1978 – Mary Leakey discovers trail of footprints at Laetoli

In 1978, a team led by the noted paleoanthropologist Mary Leakey discovered several sets of 3.5 million-year-old footprints forming a trail in volcanic ash at the Laetoli site south of Olduvai Gorge in Tanzania. Fossilized teeth and jaws found at the same site resembled those found earlier at Hadar in Ethiopia, and the footprints were thus attributed to the early hominin species Australopithecus afarensis. Combined with the study of Lucy and other A. afarensis specimens, the remarkably human-like footprints found at Laetoli provided strong evidence for a key conclusion in the study of human evolution: Human ancestors--even those with small brains such as A. afarensis--became bipedal much earlier than had previously been believed. The footprints showed a big toe that barely diverged from the rest of the foot; in comparison, a chimpanzee can use its big toe like a thumb. In addition, the footprints suggest a heel-strike gait similar to humans, and (together with studies of A. afarensis foot bones) show that the foot may have formed a supporting arch, as human feet do. In this way, Mary Leakey’s unexpected find at Laetoli--her husband, Richard Leakey, had earlier dismissed the site as a productive source of hominin remains--turned out to be one of the most striking events in the study of the human story.

1976 – First human fossil found at Atapuerca site in northern Spain

Located near the city of Burgos, in northern Spain, the caves of Atapuerca are now recognized as one of most important archaeological sites in Europe. A paleontology student named Trinidad Torres made the first discovery of a human fossil at Atapuerca in 1976, when he discovered a lower jaw bone while searching for cave bear fossils. He and his adviser, Emiliano Aguirre, identified the jaw as that of a hominin; they concluded this early human ancestor had lived some 400,000 years ago. Beginning in the 1980s, a team of researchers removed the remains of 32 individuals from a chamber at the bottom of a 45-foot shaft known as La Sima de los Huesos, or “The Pit of Bones.” The discovery was astonishing as it represented one of the few instances in which information has been found about an entire hominin group or population, rather than just a few individuals. Researchers determined that the remains came from one group of hominins and were placed there in the space of one year; all but two were adolescents, perhaps suggesting some plague or disaster. Scientists called the fossils discovered at Atapuerca Homo heidelbergensis, a term used to denote those Homo erectus (“upright man”) who migrated to Europe from Africa. (The name was coined for a jaw found near Heidelberg, Germany in 1907.) Atapuerca remains a key site for the study of human evolution: In 1998, researchers discovered a stone hand axe, suggesting that these hominins were relatively sophisticated toolmakers for the time.

1984 – Nariokotome boy discovered in Kenya

By 1984, Richard Leakey had stepped out of the shadow of his famous parents and become a noted anthropologist in his own right. That year, at the Nariokotome site near Lake Turkana in Kenya, Leakey’s team discovered one of the most complete skeletons ever found of a hominin that predated more recent species, such as the Neanderthals. Determined to be a male adolescent, it is known as the Nariokotome boy or the Turkana boy. Designated Homo erectus (“upright man”), the Nariokotome boy’s skeleton served as a crucial source of information about this species, which lived from almost 2 million to around 200,000 years ago--an incredibly long lifespan relative to other known hominins. (Some scientists refer to African Homo erectus fossils as a different species, Homo ergaster, because they lack some of the features seen in Asian populations of Homo erectus.) Studies of the Nariokotome boy helped give a much clearer picture of H. erectus and its habits, including its superior height (compared to earlier hominins) and the fact that it was probably able to live in a wider range of habitats, allowing it to survive much longer and migrate outside of Africa. In 1985, Leakey’s team announced another groundbreaking discovery: “The Black Skull,” a 2.5 million-year-old specimen that was assigned to a new Paranthropus (later Australopithecus) species, Paranthropus aethiopicus. Relatively little is known about this species, but the distinctive features of the Black Skull have inspired intense debate over where it fits in the path of human evolution.

1998 – “Little Foot” uncovered at Sterkfontein

In December 1998, at the Sterkfontein site north of Johannesburg, South Africa, a team led by the paleoanthropologist Ron Clarke announced the discovery of the nearly complete skeleton of a four-foot tall hominin--dubbed “Little Foot”--thought to be some 3 million years old. The announcement marked the latest in a series of finds, including four fossilized foot bones in 1994, a tibia in July 1997 and the skull that September. As more bones continued to surface over the next several years, debate still raged over how to classify Little Foot beyond grouping it as an Australopithecus. Clarke has argued that it is not A. afarensis or even A. africanus but a new, unique species that points out another link in the complex chain of human evolution. Other scientists have been more reluctant to draw conclusions. In any case, the still-emerging story of this extraordinarily complete hominin skeleton represents an exciting new frontier in the study of human evolution.

2004 – Homo floresiensis discovered

A team of Indonesian and Australian researchers discovered the remains of Homo floresiensis in the Liang Bua cave on the island of Flores, Indonesia, in 2004. Known as “the Hobbit” for its small stature (it stood only about 3-4 feet tall), H. floresiensis was possibly the last hominin species to have become extinct: It lived from around 18,000 to as recently as 8,000 years ago, long after Homo sapiens began walking the Earth. Though the rest of its anatomy clearly places H. floresiensis in the human family, its small body and brain size have been attributed to a phenomenon known as “insular” or “island dwarfing,” which happens to many mammals when they are isolated on an island. As that theory goes, the group started as a migrant population of Homo erectus and changed over time. Others doubt that insular dwarfing alone could account for the brain shrinkage, arguing that the owner of the single skull recovered may have suffered from microcephaly and thus not be representative of the species as a whole. A study released in the British journal Nature in May 2009 joined the debate, concluding that the primitive nature of the hobbits foot indicated that H. floresiensis may have broken off from the human evolutionary chain at some point before Homo erectus. The controversy over H. floresiensis highlights the ever-expanding nature of the study of evolution: Even as more and more evidence is uncovered, more questions have been raised about the complex nature of the human story.

2009 – The Link—a 47-million-year-old human ancestor—is revealed

An incredible 95 percent complete fossil of a 47-million-year-old human ancestor has been discovered and, after two years of secret study, an international team of scientists has revealed it to the world. The fossil’s remarkable state of preservation allows an unprecedented glimpse into early human evolution. Discovered in Messel Pit, Germany, it represents the moment before anthropoid primates--the group that would later evolve into humans, apes and monkeys--began to split from lemurs and other prosimian primates. This groundbreaking discovery fills in a critical gap in human and primate evolution.

A cast of the specimen will be on display in the "Extreme Mammals"
exhibition at the American Museum of Natural History in New York City.