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Field adventures and human origin stories combine in a paleoanthropologist’s compelling new memoir

The Sediments of Time: My Lifelong Search for the Past

Meave Leakey with Samira Leakey
Houghton Mifflin Harcourt
2020
400 pp.
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Why, unlike other primates, did our ancestors begin to walk upright? What factors enabled Homo erectus to develop new cultural practices and, later, to give rise to our own species? As paleo­anthropologist Meave Leakey explains in The Sediments of Time, understanding climate change is key in answering such questions. Reflecting on 50 years of research, largely at field sites around Lake Turkana in Kenya’s Great Rift Valley, the book—co-written with Leakey’s daughter Samira Leakey—is an engaging memoir in which fieldwork adventures appear alongside dense details of Ice Age cycles, ice core technology, fossil anatomy, and geological research. It serves as an invitation to grasp how climate cycles have driven human evolution and how anthropogenic global warming now threatens our species (and a multitude of others).

A university student in the 1960s who wished to become a marine biologist, Meave Leakey encountered rampant sexism that kept women off research ships. “Eventually, I came to the realization that my chances of finding a job on a boat were terribly slim and that I would need to consider alternatives,” she writes. When a friend alerted her to an advertisement for employment at a primate research center in Kenya, Meave rang the listed phone number and soon found herself working there for the paleoanthropologist Louis Leakey. Thus began her lifelong love affair with East Africa, one that eventually included Leakey’s son Richard, whom she married in 1970.

Having joined a world-famous fossil-hunting family, Meave would go on to make spectacular finds that have reshaped how human evolution is understood and taught. In 1994, for instance, her team discovered an early hominin fossil at Kanapoi that was subsequently named Australopithecus anamensis and dated to between 3.9 and 4.2 million years ago. This find extended the time range for australopithecines—the same genus of hominin as the famous Lucy—and, at the time, represented the earliest known hominin bipedality.

Meticulous cross-site research by paleoanthropologists, including Leakey herself, has revealed a shift in habitat and diet that occurred before the time of australopithecines, wherein many species moved from woodlands to grasslands and changed from browsers to grazers. We now know that an “inexorable drying trend” around 5 to 7 million years ago led to a reduction in forest cover and an increase in grasslands, which created new foraging opportunities. In turn, new selection pressures and bipedalism, a form of locomotion that was efficient and freed up hominin hands to take on fine manipulative tasks, emerged.

Again and again, Leakey’s attention returns to climate. Homo erectus, she writes, evolved in a “glacial-interglacial icehouse world,” where endurance hunting and increased social cooperation led to survival and migration out of Africa. Later, Homo sapiens had to cope with even greater extremes of cold and heat.

In the book’s epilogue, Leakey draws a strange analogy between baboons destroying a vegetable garden and modern humans wrecking our planet, but she places blame for Earth’s most recent climate disruption where it belongs. Our long evolutionary lineage is at a crisis point, she argues, and it is critical that we rein in consumerist greed and environmental destruction before it is too late.

The book shines in its descriptions of what it is like to set up base camp in remote, sometimes harsh conditions and to search the landscape relentlessly for small fragments of bone that are all but invisible to the untrained eye, and Leakey writes with a fine sense of humor. The image she creates of Louis and Richard Leakey stripping naked and carrying giraffe bones into the Serengeti plains to experiment with scavenging behavior is one not soon forgotten. Better yet, she writes with humility. Leakey frequently praises individual members of her team as well as other scientists, with evident admiration for their skills. There is a shadow biography of Richard in the book’s pages, too, with tales ranging from the plane crash that necessitated a double leg amputation to his conservation work as the head of the Kenya Wildlife Service.

These considerable strengths offset the few places where the science takes a wrong turn. “At birth, a chimpanzee, like all other primates, is already grown enough to function independently of its mother,” for example, is a misleading statement about an ape whose offspring depend on their mothers for years. Meanwhile, Leakey’s openness to genomic analysis in paleo­anthropology is welcome in a fossil hunter, but she credits much more to genes than most anthropologists would be comfortable with, from Richard Leakey’s punctuality to his prominent ears. And her observation that “more and more people are abandoning their traditional lifestyles for the melting pot of the big city,” comes off as insensitive to inequalities of global power, which I feel certain that, in reality, she is not.

Overall, however, The Sediments of Time is a marvelous account of what it is like for a celebrated scientist to take on some of the most vital and vexing questions regarding human origins and to come up with biocultural answers.

About the author

The reviewer is emerita professor of anthropology at William & Mary, Williamsburg, VA 23185, USA.