When We First Walked

Summary

This video explores the origins of bipedalism in human evolution, beginning with fossilized footprints found in Laetoli, Tanzania, dating back 3.6 million years. These footprints, likely made by *Australopithecus afarensis*, challenged the belief that humans first developed large brains before walking upright. The video delves into other early human ancestors, such as *Australopithecus anamensis* and *Ardipithecus ramidus*, examining their potential bipedal traits. It also discusses various theories for why bipedalism evolved, from environmental changes to the advantages of upright movement in trees. The evolution of bipedalism remains a complex puzzle, with more fossil discoveries needed to fully understand its origins.

Takeaways

• 😀 The discovery of ancient human footprints in Laetoli, Tanzania, dating back 3.6 million years, revolutionized our understanding of human evolution.
• 😀 These footprints, likely made by Australopithecus afarensis, suggest that walking upright preceded the development of a large brain in human evolution.
• 😀 Bipedalism is a key feature in human evolution, and several skeletal adaptations in the human body support this, including changes in the spine, pelvis, and feet.
• 😀 Australopithecus anamensis, a species from around 4 million years ago, is considered one of the first human ancestors to walk upright, based on its leg and tibia bones.
• 😀 Ardipithecus ramidus, or 'Ardi,' lived around 4.4 million years ago and had both climbing and bipedal features, suggesting it was versatile in locomotion.
• 😀 Other possible early bipeds include Ardipithecus kadabba (5.8 to 5.2 million years ago), Orrorin tugenensis (around 6 million years ago), and Sahelanthropus tchadensis (around 7 million years ago), though evidence for their bipedalism is still debated.
• 😀 The position of the hole at the base of the skull in Sahelanthropus suggests it may have walked upright, but this theory remains contentious.
• 😀 The reason for the evolution of bipedalism is still debated. The 'savannah hypothesis' suggests climate change pushed early hominins to walk on two legs, while other theories propose that bipedalism may have evolved in forested environments or for standing on branches while feeding.
• 😀 Bipedalism may have had multiple advantages, such as energy efficiency, better thermoregulation, and freeing up the hands to carry things, although these theories are not universally accepted.
• 😀 Fossil evidence continues to evolve, and the discovery of new fossils and footprints could help answer the question of how and why bipedalism evolved in our early ancestors.

Q & A

What discovery in 1978 revolutionized our understanding of human evolution?

In 1978, scientists discovered fossilized footprints at Laetoli in Tanzania. These footprints, made by Australopithecus afarensis, were crucial because they showed that bipedalism, or walking on two legs, evolved before the development of a large brain, challenging the traditional view of human evolution.

What was the traditional view of human evolution, and how was it challenged by the Laetoli footprints?

The traditional view suggested that humans first evolved large brains, with bipedalism emerging later. The Laetoli footprints challenged this by providing evidence that Australopithecus afarensis, with a small brain, was already walking upright 3.6 million years ago.

What anatomical features in humans are adaptations for bipedalism?

Key anatomical features include the position of the head on the spine, the curvature of the spine, a bowl-shaped pelvis, inward angling thigh bones, and feet with arches and a non-grasping big toe. These adaptations allow humans to walk efficiently on two legs.

Which species is currently considered the most likely first human ancestor to walk upright?

Australopithecus anamensis, which lived between 4.2 and 3.9 million years ago, is considered the most likely first human ancestor to walk upright, based on evidence from its leg bones.

How did the tibia of Australopithecus anamensis contribute to understanding its bipedalism?

The tibia of Australopithecus anamensis was straight, like a human's, indicating that it walked upright, unlike chimpanzees, whose tibia angles outward due to their knuckle-walking posture.

What did the discovery of Ardipithecus ramidus (Ardi) reveal about early hominin locomotion?

Ardipithecus ramidus, nicknamed 'Ardi,' showed a combination of features suggesting it could walk upright but was also adept at climbing trees. Ardi's foot had a rigid lever-like structure, unlike the grasping foot of modern apes, indicating she used both bipedal and arboreal locomotion.

What are the key anatomical differences between the pelvis of Ardipithecus ramidus and Australopithecus afarensis?

The top of Ardi's pelvis resembled that of Australopithecus afarensis, suggesting some adaptation for bipedalism, while the bottom resembled that of climbing apes, indicating that Ardi was capable of both walking upright and climbing.

What are some of the challenges in determining whether early hominins were bipeds?

Fossils are often fragmentary, making it difficult to definitively reconstruct early hominin locomotion. Additionally, it is unclear whether species were fully committed to bipedalism or if they could still climb trees while occasionally walking on two feet.

What are some theories for why bipedalism evolved in early hominins?

The traditional 'savannah hypothesis' suggests that bipedalism helped early hominins move between shrinking forests. Other theories propose that standing upright in trees or freeing up the hands for carrying objects may have driven the evolution of bipedalism.

Why is the 'savannah hypothesis' challenged by discoveries related to early hominin environments?

The 'savannah hypothesis' is challenged because species like Ardipithecus ramidus lived in wooded environments, not open grasslands. This suggests that early hominins may have become bipedal in forested areas, not necessarily in response to environmental changes towards savannahs.