Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [71]
A reconstruction of the skeleton of Lucy—Australopithecus afarensis—discovered at Hadar, Ethiopia, in 1974.
A reconstruction of Lucy’s head.
Elisabeth Vrba, a South Africa–born palaeontologist who discovered evidence of dramatic evolutionary change occurring 2.5 million years ago while studying the fossil record of African antelopes.
Yves Coppens, a French palaeoanthropologist involved in major discoveries in Ethiopia and Kenya, pictured in 1983.
Martin Pickford and Brigitte Senut with the remains of ‘Millennium Man’, the first major discovery of the 21st century, which they subsequently named Orrorin tugenensis.
Ron Clarke, a British-born palaeontologist, pictured alongside Little Foot, a Sterkfontein australopithecine which he discovered after a brilliant piece of detective work.
Phillip Tobias, a South African scientist, renowned for his work at Sterkfontein and other southern African sites, pictured in 2006 at the age of eighty.
French palaeontologist Michel Brunet with the 7 million years-old Toumaï skull from Sahara.
An engraved ochre tablet found at Blombos Cave, South Africa, dating back about 75,000 years ago, evidence of early artistic endeavour from Africa.
PART TWO
CHAPTER 15
PROTOTYPES
TEN MILLION years ago, apes were the lords of creation. Originating in Africa, more than fifty different species roamed the world during the Miocene age. Miocene apes flourished in particular in the tropical forests of eastern Africa. Among them were Proconsul and various contemporaries, thought to include the last common ancestor of both modern apes and hominids. Fossils found in the volcanic highlands of Kenya and Uganda reveal them as tailless, fruit-eating quadrupeds, about the size of a female baboon, which lived in trees and moved on the forest floor on all four legs.
This thriving ape community then mostly died out, probably as a consequence of global climate change affecting their environment. Climate records tell of a dramatic cooling around the world between 6.5 million and 5 million years ago. Polar ice caps expanded; sea levels plunged so low that the Mediterranean was repeatedly drained; icy winds blew off cold oceans. Africa escaped the icy conditions, but in the dry, cold climate, the Miocene forests shrank, fragmenting in places into more open woodland. Whole ape populations perished. Only a few survivors emerged: the ancestors of orang-utans and gibbons in Asia, the ancestors of gorillas and chimpanzees in Africa—and hominids.
The fossil record of this period is sparse, almost non-existent. According to molecular-clock calculations, hominids and the chimpanzee line split from a common ancestor between 8 and 6 million years ago. But the identity of this last common ancestor, its exact nature and the dates at which it lived remain obscure.
Recent discoveries have produced a number of contenders said to have crossed the hominid threshold: Sahelanthropus from Chad, dated between 7 and 6 million years old; Orrorin from Kenya, dated at 6 million years old; and Ardipithecus kadabba from Ethiopia, dated between 5.8 and 5.2 million years old. None of them provides conclusive evidence of habitual upright walking—the principal characteristic used to define the human lineage.
Sahelanthropus consists of a skull—an intact cranium, some lower jaw fragments and several teeth. It is the only exhibit of a skull recovered from a 5-million-year-long period. It shares several facial features with later hominids—a short face with a massive brow ridge and a mouth and jaw that protrude less than in most apes. The positioning of its foramen magnum suggests a posture similar to bipeds, with the skull balanced atop a vertically held spine. But other aspects of the skull are decidedly more apelike than other hominids. Moreover, no foot or leg bones have been found to help ascertain on which side of the divide between apes