Scientists Decode How 3.2 Million-Year-Old Ancient Human Ancestor Walked

One of the most fascinating questions in human evolution is how and when our ancestors started walking on two legs. This ability is what sets us apart from other primates and defines us as humans. But the fossil record is often incomplete and leaves us with many gaps in our understanding of this crucial transition.

However, a new study published in the journal Royal Society Open Science has shed some light on this mystery by using advanced 3D muscle modeling to reconstruct the soft tissues of one of the most famous and complete fossils of an early human ancestor: Lucy.

Who was Lucy?

Lucy was a female member of the extinct species Australopithecus afarensis, who lived about 3.2 million years ago in what is now Ethiopia. Her fossil, known as AL 288-1, was discovered in 1974 and represents about 40% of her skeleton, making it one of the most complete specimens of an early hominin ever found.

Lucy was shorter than modern humans, reaching about 3.3 feet (1 meter) in height, had an ape-like face and a brain about one-third the size of a human brain. She also had a mix of features that suggested she was adapted to both walking on the ground and climbing on trees.

How did Lucy walk?

Previous analyses of Lucy's fossil have suggested that she and others of her species walked upright, but there was still debate about how efficiently and frequently they did so. Some researchers argued that Lucy's pelvis, spine and lower limbs were too primitive to allow for a fully human-like gait, while others suggested that she was more advanced than previously thought.

To resolve this controversy, the researchers behind the new study used a novel method called polygonal muscle modeling to recreate Lucy's muscles based on her bones and compare them with those of modern humans and chimpanzees.

They found that Lucy had strong leg and pelvic muscles that enabled her to walk upright with ease and stability, similar to modern humans. She also had powerful knee muscles that allowed her to extend her legs fully and lock them in place, which reduced the energy cost of walking.

However, Lucy also had some differences from modern humans that indicated she was not as specialized for walking as we are. For example, she had relatively shorter legs and longer arms than us, which would have slowed her down and made her less efficient at running. She also had weaker ankle muscles than us, which would have limited her ability to push off the ground with force.

The researchers concluded that Lucy was capable of walking upright like us, but she also retained some adaptations for climbing on trees that may have helped her survive in a changing environment.

Why does Lucy matter?

Lucy's fossil is important because it provides a rare glimpse into the evolution of bipedalism, one of the key features that distinguish humans from other animals. By reconstructing her muscles, the researchers were able to gain new insights into how she moved and how she differed from both modern humans and chimpanzees.

The study also demonstrates how computational modeling can be used to complement traditional methods of studying fossils and reveal new information that is not visible in the bones alone. By applying this technique to other fossils of early human ancestors, we may be able to learn more about how they lived, behaved and evolved over time.

Lucy's fossil is not only a scientific treasure, but also a cultural icon that connects us with our distant past and reminds us of our shared origins.

What else do we know about Australopithecus afarensis?

Lucy is not the only fossil of Australopithecus afarensis that has been discovered. In fact, paleoanthropologists have uncovered remains from more than 300 individuals of this species, making it one of the best-known and longest-lived early human species.

Some of the other notable fossils of Au. afarensis include:

- The "First Family", a group of at least 13 individuals who died together in a flash flood at Hadar, Ethiopia, about 3.2 million years ago. Their fossils show a wide range of variation in size and shape, which has been interpreted as evidence of sexual dimorphism (differences between males and females) or as a sign of multiple species living together.

- The Dikika "child", a nearly complete skeleton of a 3-year-old girl who lived about 3.3 million years ago in Dikika, Ethiopia. Her fossil reveals that Au. afarensis children grew rapidly after birth and reached adulthood earlier than modern humans. Her brain was also relatively small compared to her body size, suggesting that brain growth was slow in this species.

- The Laetoli footprints, a series of fossilized trackways left by three individuals of Au. afarensis who walked across a volcanic ash layer about 3.6 million years ago in Laetoli, Tanzania. The footprints show that Au. afarensis had a human-like gait, with a heel-strike and toe-off, and an arched foot that helped absorb shock and propel them forward.

- The "Selam" baby, a partial skeleton of a 2.5-year-old child who lived about 3.3 million years ago in Dikika, Ethiopia. Her fossil shows that Au. afarensis had a hyoid bone (a small bone in the throat) similar to that of chimpanzees, which implies that they could not produce complex vocal sounds like modern humans.

Why is Australopithecus afarensis important for human evolution?

Australopithecus afarensis is important for human evolution because it provides a rare glimpse into the evolution of bipedalism, one of the key features that distinguish humans from other animals.

Bipedalism is thought to have evolved as an adaptation to living in open savanna environments, where walking on two legs would have offered several advantages over walking on four legs, such as:

- Better visibility over tall grasses and potential predators or prey

- More efficient locomotion over long distances and varied terrains

- Reduced exposure to solar radiation and heat stress

- Freeing up the hands for carrying tools, food or offspring

However, bipedalism also came with some costs and trade-offs, such as:

- Increased risk of injury or predation due to reduced stability and agility

- Increased stress on the spine, pelvis and lower limbs

- Increased difficulty in giving birth due to a narrower birth canal

- Increased dependence on social cooperation and parental care

By studying how Au. afarensis walked and how they balanced the benefits and costs of bipedalism, we can learn more about how our own species evolved and adapted to different environments over time.

Australopithecus afarensis is also important for human evolution because it may be a direct ancestor or a close relative of later species of Paranthropus, Australopithecus and Homo, including our own species Homo sapiens.

However, the exact evolutionary relationships between these groups are still debated and uncertain, as new fossils and genetic evidence are constantly being discovered and analyzed.

By comparing the anatomy, behavior and ecology of Au. afarensis with those of other early human species, we can gain insights into the origins and diversity of our lineage and what makes us human.

Conclusion

Australopithecus afarensis is one of the most fascinating and well-known early human species, thanks to the discovery of hundreds of fossils, including the famous Lucy. This species lived between 3.9 and 2.9 million years ago in Eastern Africa and was capable of walking upright on two legs, but also retained some adaptations for climbing on trees.

By studying the bones, muscles and footprints of Au. afarensis, researchers have been able to reconstruct how they moved and how they differed from both modern humans and chimpanzees. They have also been able to infer some aspects of their diet, growth, development and communication.

Australopithecus afarensis is important for human evolution because it provides a rare glimpse into the evolution of bipedalism, one of the key features that distinguish humans from other animals. It may also be a direct ancestor or a close relative of later species of Paranthropus, Australopithecus and Homo, including our own species Homo sapiens.

However, there are still many questions and debates about this species and its place in our evolutionary tree. As new fossils and technologies emerge, we may be able to learn more about this remarkable species and how they lived, behaved and evolved over time.

Source: 

(1) 3.2 Million-Year-Old Human Ancestor Walked like Us - GreekReporter.com. https://greekreporter.com/2023/06/14/3-2-million-year-old-human-ancestor-walked-like-us/.

(2) Scientists Decode How 3.2 Million-Year-Old Ancient Human Ancestor Walked. https://www.ndtv.com/science/scientists-decode-how-3-2-million-year-old-ancient-human-ancestor-walked-4133003.

(3) How a 3.2-million-year-old human relative named Lucy walked. https://www.cnn.com/2023/06/13/world/lucy-fossil-bipedalism-scn/index.html.

(4) Great debate: The 3.2-million-year-old mystery of Lucy and her demise. https://www.news.com.au/technology/science/evolution/great-debate-the-32millionyearold-mystery-of-lucy-and-her-demise/news-story/09f8891cb49d9e5a3d3dded498514c7b.

FAQ's

How a 3.2 million year old human relative named Lucy walked?

Paleoanthropologists agree that Lucy was bipedal, but disagree on how she walked. Some have argued that she moved in a crouching waddle, similar to chimpanzees -- our common ancestor -- when they walk on two legs. Others believe that her movement was closer to our own upright bipedalism.

What is the oldest known human ancestor?

Ardipithecus is the earliest known genus of the human lineage and the likely ancestor of Australopithecus, a group closely related to and often considered ancestral to modern human beings. Ardipithecus lived between 5.8 million and 4.4 million years ago.

What are our ancestors called?

Hominin – the group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus).

What Cambrian animal did humans evolve from?

The microscopic creature—named Saccorhytus after its baglike body shape—lived in the early Cambrian Period about 540 million years ago. Saccorhytus would have been only about a millimeter in length and would have lived between grains of sand in the seabed.