Hominid Evolution: From Australopithecus to Homo
Hominid Evolution: From Australopithecus to Homo
Hominids are a group of non-arboreal primates that originated in Africa approximately 7 million years ago. Human beings are hominids, but not all hominids are human beings; only those belonging to the genus Homo.
Key Features of Hominids:
- Bipedal, upright locomotion: This characteristic influences the position of the foramen magnum at the base of the skull where the spinal cord passes. The vertebral column becomes more circular to better support vertical posture.
- Spinal curvature: The spine presents three curves.
- Pelvic changes: The pelvis widens and shortens.
- Leg elongation: There is a progressive elongation of the legs.
- Loss of opposable toe: The thumb of the lower extremities loses its grasping ability and integrates with the other toes.
- U-shaped palate: A rounded dental arch with smaller teeth, which have lost their defensive and attack functions.
- Increased cranial capacity: The skull houses a larger brain, an increase related to a high-energy diet, as the brain consumes significant energy.
The First Hominids:
The main pre-human species are:
- Australopithecus ramidus: This is the oldest known hominid, with fossils dating back 4.5 million years. Although it presents many anthropoid features, it is believed to have acquired bipedalism. It likely gave rise to A. anamensis.
- Australopithecus anamensis: This species exhibited ape-like features, although it had hominid characteristics such as bipedalism and thick tooth enamel, allowing it to eat hard foods.
- Australopithecus afarensis: This species had a face with a protruding nose (prognathism) and a prominent bony ridge along the axis of the skull (sagittal crest). Their brain capacity was slightly higher than that of chimpanzees. The pelvis and lower extremities already had a human-like aspect, indicating their adaptation for bipedalism.
Post-A. afarensis Hominids:
Two trends emerged, related to the anatomy of the skull and mandible: a more gracile form (A. africanus) and a more robust form (Paranthropus). The axis of the Paranthropus skull featured a prominent sagittal crest. Australopithecus were scavengers and omnivores, while Paranthropus were vegetarians who consumed hard foods. A. garhi appeared later.
Homo floresiensis:
Discovered in Indonesia in 2004, these hominids were small (1 meter in height and 28 kg in weight). They lived between 18,000 and 13,000 years ago and are considered descendants of Homo erectus. They crafted finely wrought stone tools and controlled fire.
Humanization:
The first species of the genus Homo possessed larger, more complex brains with greater intellectual capabilities.
- Homo habilis: The first Homo remains were found in Olduvai (Tanzania), along with very primitive stone tools created by them, hence their name (“handy man”). Their skull was clearly higher than that of the australopithecines. Despite their marked prognathism and supraorbital ridge, their teeth were similar to those of humans. They began to lose body hair. Their diet was dominated by hard vegetables; they did not eat much meat.
- Homo ergaster: Found in Turkana and Olduvai. Their skull was larger and wider than that of H. habilis, presenting a supraorbital arch and small, well-developed teeth adapted to a diet based on meat, animal fats, and other soft foods. Their skeleton was similar to that of modern humans. They crafted teardrop-shaped hand axes, showing that the end result was a preconceived form. They were the first humans to leave Africa, at least 1.9 million years ago.
- Homo erectus (The Men of Java and Beijing): Emerged 1 million years ago and disappeared 100,000 years ago in Java. For 400,000 years, they used fire, as evidenced by ash remains found beside their fossils. Their skull was elongated but with thicker walls than ours. The forehead was low and receding, with a very marked supraorbital torus and suborbital depression. They had no chin.
- Homo antecessor: Found in the Sierra de Atapuerca (Burgos), dating back about 800,000 years, they were the first Europeans. Their best-known fossil is the “Child of Gran Dolina.” They presented both archaic and modern characteristics. Their diet consisted of hunted and gathered food, and they practiced cannibalism. It is thought that they emerged in Africa from H. ergaster and from there migrated to Europe.