Hominins

• Most paleoanthropologists believe a common ancestor to the modern African Apes (Chimps, Gorillas, Bonobos) and the Hominins existed approximately 6-7 million years ago.

• Hominins are habitually bipedal primates. Modern humans are the only extant (living) species of hominin.

Bipedalism

• The early ancestors of humans and the ancestors of the African apes appear very similar.

• The key point of difference between early hominins and early apes were how they walked: early hominins were bipedal, early apes were quadrapedal.

Sivapithecus (12.5-8.5 million years ago). possible ancestor of modern Orangutans (quadruped)

Paranthropus Boisei (2.3-1.2 million years ago) . Hominin (upright walker)

Bipedalism: Advantages

• We are taller and more intimidating to predators.

• Walking on two legs is more efficient in terms of calories used.

• We are able to use our front limbs to carry, use tools and to hunt and gather more efficiently.

• We expose less of our bodies to direct sunlight, allowing for more efficient cooling.

Bipedalism

• Given the similarities of early apes and early hominins, the primary task is to examine the skeleton to figure out how this organism walked.

Anatomical marks of bipedalism

• Pelvis

• Femur

• Spine

• Foot

• Foramen Magnum

Human Pelvis

Chimp Pelvis

Chimp Skeleton

Spine/Quadruped

Chimp Foot

Human Foot

Spine/Biped

Sahelanthropus tchadensis“Toumai” 7 millions years old

Orrorin tugenensis“Millenium Man” ~6 million years ago

Orrorin tugenensis

Difficulties in building a family tree

• Creating a “family tree” for extinct species is very difficult for two major reasons:

• A) The fossil record is incomplete (not all organisms leave behind a record of their existence and

• B) Many fossils are too old to derive DNA from, making genetic comparisons impossible.

Difficulties in building a family tree

• Family trees of hominin and non-hominin fossils are constantly being redrawn as new discoveries are made.

• Additionally, different fossils may be interpreted as the same species by one anthropologist…and different species by another.

Lucy

• 1974: Donald Johanson discovered “Lucy”, a 3 foot 8 inch hominin later classified as Australopithecus afarensis.

Lucy: (AL 288-1) 3.2 mya

Comparative anatomy

The Laetoli footprints

A. afarensis cranium (AL- 444)

Modern Chimp Skull

Australopithecus afarensis (left) Chimpanzee (right).

Big Brains and Bipedalism

• Bipedalism emerged long before big brains.

• What started us on the journey to becoming human was how we moved, rather then the way we thought. Brain changes came later.

Early Hominins

• The term Early Hominins is used to describe the hominins that lived before Genus Homo. They are all found only in Africa.

• The fossil record indicates that there were a variety of species of early hominins adapted to various environments in sub-Saharan Africa.

Robust vs. Gracile

• Hominins and other primates are described as robust or gracile.

• A robust body is heavy in skeletal structure and muscle. A gracile body is more slender and fine-boned.

Robust Skull: Paranthropus robustus

Gracile Skull: Australopithecus Afarensis

Speech

• Examinations of australopithecines have determined their vocal tracts were very similar to apes.

• As such it is unlikely that they used spoken language.

Culture

• While it is safe to assume that the majority of early hominins (like the majority of primates) were social creatures we know only so much about their culture.

• It does seem to be the case that they DID NOT make stone tools: that came later in human evolution.