Chapter 9 The Earliest Dispersal of the Genus Homo: Homo erectus and Contemporaries

Left: Homo Erectus (1mya) Center: Australopithicus afarensis (2.5mya) Right: Homo Neandertalensis (100,000-32,000ya)

BECOMING HUMAN PART II NOVA

First Dispersal of the Hominins Close to 2 million years ago, hominins expanded out of Africa into other areas of the Old World. Since the early hominin fossils have been found only in Africa, it seems that hominins were restricted to this continent for as long as 5 million years.

First Dispersal of the Hominins After 2 mya, there’s less diversity in these hominins than in their pre-australopith and australopith predecessors. There is universal agreement that the hominins found outside of Africa are members of genus Homo. Homo erectus is the species for which there is the most evidence.

Homo erectus – A New Kind of Hominin The first hominin to expand into new regions of the Old World. As a species, H. erectus existed over 1 million years. We can understand its success as a hominid species based on behavioral capacities (i.e.) more elaborate tool use) and physical changes (i.e. larger).

Homo erectus Discoveries from East Africa have established Homo erectus by 1.8 m.y.a. Some researchers see anatomical differences between the African and Asian discoveries. – They place African fossils into the Homo ergaster species. Analyses show that H. erectus/ergaster represents closely related species and possibly geographical varieties of a single species

Grade H.erectus hominins represent a different grade of evolution than their African predecessors. Grade refers to a grouping of organisms sharing a similar adaptive pattern. Grade implies nothing directly about shared ancestry, but implies general adaptive aspects of a group of animals

Morphology of Homo erectus Living in different environments over much of the Old World, H. erectus populations shared several common physical traits including…

Body Size Adult weight >100 lbs, average adult height of ca. 5 feet 6 inches Sexually dimorphic, weight and height varied according to sex Increased robusticity (heavily built body) that dominated hominin evolution until anatomically modern H. sapiens

Brain Size Cranial capacities 700 cm 3 to 1250 cm 3 Brain size closely linked with overall body size H. erectus is larger-bodied than early Homo sample but relative brain size is about the same Relative brain size of H. erectus is considerably less encephalized than later members of genus Homo 1. Australopithecus afarensis 2. Australopithecus africanus 3. Homo habilis 4. Homo erectus 5. Homo Neandertalensis  Homo Sapien Skulls 

Cranial Shape Thick cranial bone, large browridges (supraorbital tori), and projecting nuchal torus Braincase long and low, with little forehead development Cranium wider at base, compared with earlier and later species Sagittal keel, a small ridge from front to back along the sagittal suture, reflects bone buttressing in a very robust skull, rather than a specific function

Homo Erectus finds Africa, Asia, Indonesia, Europe

Homo erectus from Africa Homo erectus evolved first in Africa, supported by evidence of: 1.Earlier hominins prior to the appearance of H. erectus occurring in Africa mya fossils at East Turkana, in Kenya, and not long after at other sites in East Africa. 3.Though, 1.75 mya populations in southeastern Europe; 1.6 mya populations in Indonesia, suggesting quick migrations

TURKANA BOY a.k.a. Nariokotome Skeleton WT In 1984, Kamoya Kimeu discovered a small piece of skull on the west side of Lake Turkana at the site known as Nariokotome. The excavations produced the most complete H. erectus skeleton ever found Facial bones, a pelvis, and most of the limb bones, ribs, and vertebrae.

TURKANA BOY Nariokotome Skeleton The Nariokotome skeleton is dated to about 1.6 mya. The skeleton is that of a boy about 12 years of age with an estimated height of 5 feet 3 inches.

Olduvai Gorge Find by Louis Leakey in 1960, includes well-preserved cranial vault with small part of upper face. Dated at 1.4 mya, the cranial capacity is the largest of all the African H. erectus specimens. The browridge is the largest known for any hominin, but the walls of the braincase are thin. – Similar to East African H. erectus specimens; differs from thick cranial bones in Asian H. erectus.

Gona Evidence Ethiopia find dated to appx. 1.3 mya Female pelvis with very wide birth canal, indicating large-brained infants in utero Perhaps newborn H. erectus with a brain that was comparable to typical modern human baby Suggests, when compared with Nariokotome pelvis, considerable sexual dimorphism in skeletal anatomy is linked to reproduction and body size

Daka Evidence Middle Awash of Ethiopia find dated to appx. 1 mya Complete cranium more like Asian H. erectus than most earlier East African remains discussed Discounts argument that East African fossils are different species than Asian H. erectus