Charles Darwin, a pioneering figure in evolutionary biology, reshaped our understanding of life’s diversity. His work extended to human origins, including how our ancestors began walking on two legs, a defining characteristic known as bipedalism. This article explores Darwin’s ideas regarding bipedalism’s origin and how subsequent scientific discoveries have refined these early hypotheses.
Darwin’s Central Idea
In The Descent of Man (1871), Darwin hypothesized about bipedalism’s origins. He proposed that upright walking was the initial driving force in human development, freeing the hands from locomotion.
This liberation of the hands, Darwin argued, was significant. It allowed early hominins to carry objects, such as food or infants, and to manipulate tools and weapons. He suggested that tool use provided a survival advantage, favoring individuals who walked upright. This selective pressure would have driven bipedalism’s adoption.
Darwin further speculated that increasing reliance on tool use would have favored larger brains. He believed bipedalism enabled tool use, which then propelled the evolution of greater intelligence and complex cognitive abilities. This idea placed bipedalism as a foundational adaptation, preceding and facilitating other human traits like enhanced brain size and sophisticated technology.
The Scientific Landscape of Darwin’s Era
Human prehistory was poorly understood during Darwin’s time. When The Descent of Man was published in 1871, the fossil record of early hominins was sparse. Few human-like fossils were known, mainly Neanderthal remains, whose place in human lineage was debated.
Darwin lacked access to the wealth of ancient hominin fossils later unearthed. His hypothesis was largely based on logical inferences and comparative anatomy. He drew conclusions from anatomical similarities between humans and African great apes, suggesting Africa as humanity’s likely cradle.
Revisiting Darwin’s Hypothesis with New Evidence
Fossil discoveries after Darwin’s death provided new insights into bipedalism’s emergence. The unearthing of Australopithecus afarensis (“Lucy”) in the 1970s was influential. Dated to 3.2 million years ago, Lucy had a chimpanzee-sized brain, yet her skeletal structure indicated habitual upright walking.
Further evidence came from the Laetoli footprints in Tanzania, dating back 3.6 million years. These fossilized tracks show bipedal locomotion in early hominins long before significant brain enlargement or complex stone tools. The earliest stone tools appear around 3.3 million years ago, well after these hominins evolved an upright stance. This challenged Darwin’s sequence, which suggested tool use and brain expansion drove the shift to bipedalism. Evidence showed bipedalism evolved first, with brain growth and sophisticated tool-making emerging much later.
Current Understanding of Bipedalism’s Origins
Modern science views bipedalism’s origins as more complex than Darwin envisioned. Researchers explore various hypotheses, considering multiple contributing factors. One idea is the efficiency of bipedal locomotion, suggesting upright walking was more energy-efficient for covering long distances, especially as environments changed.
Another hypothesis centers on thermoregulation, proposing an upright posture reduced body surface exposed to direct sunlight, keeping early hominins cooler. The ability to carry food, water, or dependent offspring more effectively while moving across landscapes is also a selective advantage. Some theories suggest bipedalism initially evolved in arboreal settings, with hominins occasionally walking upright in trees before transitioning to terrestrial environments.