Human Origins

Who Was The First Human?

A generation ago, human evolution was thought of as a ladder through time, with an ape–like ancestor at the base and modern humans at the top. As for humans, they first appeared at the moment when toolmaking began. Was it Australopithecus, or some closely related hominid form, like the hopefully named Homo Habilis? As the pace of discovery accelerated, it soon became apparent that there were several hominid forms around at the time when toolmaking began, making identification of the first “human” an even more challenging task.

In recent years, four criteria have been used generally to assign a fossil to the genus Homo:

An absolute brain size of 600 cubic centimeters
The possession of language, identified from casts of the brain patterns on the inside of the brain case
The possession of a modern, humanlike precision grip and an opposable thumb.
The ability to manufacture stone tools

There are serious problems with all of these criteria. Absolute brain capacity is of dubious biological importance. We now know that evidence of language cannot be inferred from a brain cast. Furthermore, we still do not know much about the range of precision grips found among early hominids. Stone tools are an inconclusive criterion to use, simply because, 2.6 million years ago,both early Homo and robust Australopithecines flourished in the same area where the earliest artifacts are found.

Hominid evolution involves a far greater level of species diversity than was previously thought. Human evolution can be seen as one or more adaptive radiation's ( a burst of evolution, in which a single species diverges to fill a number of ecological niches, the results being a variety of new forms) rather than a simple, one–way evolution of successive species. This view stems from cladistics, an analytic system for reconstructing evolutionary evolutionary relationships, first proposed in the late 1950's. Classical evolutionary analysis is based on morphological similarities between organisms. It is cladistics, but with a difference: Cladistic analysis concentrates not only on features that identify common ancestry but also on those that are derived independently and are unique to specific lineage's. Inevitable, cladistics tends to emphasize diversity over homogeneity.

A cladistic definition considers the human genus a group of species that are more closely related to one another than to species assigned to another genus. This interpretation insists that the human genus is monophyletic, that is with all its members ultimately descended from a common ancestor. Wood and Collard define the human genus “as a species, or monophylum, whose members occupy a single adaptive zone” (1999, p. 66). Using this definition, they carried out a cladistic analysis of all the known fossil Homo species, and devised a cladogram that separates all the Australopithecine forms, Homo habilis into one genus, and later humans, starting with Homo erectus, into another. Their intricate statistical analyses suggest that enough is known of body size and shape, locomotion, development, and relative size of chewing apparatus to divide fossil homimid adaptive strategies into two broad groups:

The Australopithecines and Homo habilis (also H. rudolfensis) belong in a group of hominids with a relatively low body mass, a body shape better suited to a relatively closed environment, and a postcranial skeleton that combined terrestrial bipedalism with expert climbing. The teeth and jaws of these hominids are well adapted to chewing and biting a varied and mechanically demanding diet. Australopithecus teeth and upper leg bone studies show that the rate of development (and dependence) of young hominids in this group was closer to that of modern African apes. The tooth development of Homo Habilis and Homo rudolfensis also appears to have been closer to that of African apes, as if their development period was also shorter than that of modern humans.
Homo erectus and contemporary and later human forms belong in a second group, marked by a larger body mass, a modern, humanlike physique that was adaptive in more open terrain, and a postcranial skeleton consistent with terrestrial bipedalism. The ability to move around in trees was very limited, teeth and jaws had similar mechanical properties to those of modern humans. Development rates were the same as our own.

This definition of Homo makes a clear distinction between the hominids of earlier than 1.9 million years ago, and Homo erectus and its successors who evolved after that date. It implies that a behavioral and evolutionary chasm separates true humans from the many other hominids who flourished in Africa before 2 million years ago. Quite what caused this adaptive shift in human evolution is unknown. Did it correspond with significant climatic and environmental change, with equivalent evolutionary changes in other large mammal groups or with specific changes in hominid culture? The answers will have to come from a new generation of research.

Hominid evolution can be thought of as a series of adaptive radiations which unfolded over at least 5 million years. The first radiation was a bipedal apes, which lived, for the part, in the drier parts of Africa. Two later radiations gave rise to what is still called early Homo, expanded brain size played a key role, while the robust australopithecines, each with their own adaptive theme. In the case of early Homo, expanded brain size played a key role, while the robust australopithecines developed specialized teeth. Although the latter varied greatly in morphological terms, latter humans radiated not so much morphologically as ecologically, spreading from Africa and creating distinct geographic populations. This flowering of hominid types is exactly what evolution is about: “an endless production of novel ways of doing things, exploring alternatives, trying out new strategies as conditions themselves shift and change all driven by natural selection” (Foley, 1995: 103). Hominids were no different from other mammals, which began as a slim stem and radiated into distinct branches. We still do not know much about the relationships between such branches.

This same pattern of adaptive radiation may have continued between much latter in prehistory, during the long millennia when Homo erectus flourished in Africa, Asia, and Europe, with only a small part of this evolutionary process resulting in modern humans, Homo sapiens sapiens, probably in Africa.

Site

Olduvai George¸ Tanzania

Olduvai George is a vast gash in the game-rich Serengeti Plains of northern Tanzania¸ formed by an earthquakes more than 100¸000 years ago balled a miniature Grand Canyon by many visitors. The earth movement exposed a long series of ancient lake beds extending back as far as 2 million years ago, stratified in the walls of the gorge. Geologists have identified four major series of lake beds¸ labeled from Bed I (at the base) to Bed IV¸ which formed in a semi–arid environment much like that of today. Olduvai was discovered by German butterfly hunter Wilhelm Kattwinkel before World War I and was investigated by paleontologist Hans Reck in the 1920´s. He found numerous fossil animal bones, including a long–extinct elephant¸ which he named after himself. Today more than 150 species of extinct animals ranging in size from elephants to birds and rodents are known from Olduvai. However, the groups will always be associated with Louis and Mary Leakey¸ who realized the great potential of Olduvia for documenting early human evolution. Louis Leakey first found stones axes in the gorge in 1931. Between 1935 and 1959 the Leakeys surveyed and excavated numerous sites and published an important monograph on the Olduvia stone tools¸ in which they traced the evolution of of stoine artifacts from a simple technology based on lava lumps¸ which they named the Oldowan¸ to progressively more complex and better–made hand axex and flake tools (the Acheulian). Then¸ in 1959¸ they discovered Zinjanthropus boisei and changed the chroncile of human evolution forever. Subsequently¸ large–scaled excavations by the Leakeys unearthed other hominid fossils¸ including Homo habilis¸ whom they considered the first toolmaker. Don Johanson of Lucy fame has also worked in the Gorge and recovered further Homo habilis fragments.

The most important Olduvai hominid fossils come from Beds I and Beds II. Bed I lies on a volcanic bedrock¸ known as a tuff¸ which has been potassium argon dated to about 2 million years ago¸ an excellent beaseline for the lake bed sequence above. The beds themselves were close to the shore of an extensive shallow lake¸ which expanded and contrarcted from one season to the next. the waters covered places where hominids had paused to process and eat animals parts they had scavenged from nearby predator kills¸ preserving both stone tool fragments and broken animal bones¸ as well as the occasional homond fossil in–situ. Excavating these land surfaces requires great patience and skill. Once a location is identified¸ the investigators sift the ground surrounding the original find through fine screens¸ looking for significant fossils. Then they excavate into the lake bed to establish the straigraphic realtionahip of the ancient land surface to the surrounding lake bed layers before exposing the scatter of artifacts and bones in horizontal plane. This process is slow-moving and calls for meticulous excavation and recording, with each fragment¸ even those as small as snakes fangs¸ being exposed in place then its precise location recorded¸ before removal. The end-product after months of work¸ is a precise 3–dimensional plan of the artifacts and bones scatter¸ so that the realationship between stone fragments and other finds¸ including (hopefully) hominid fossils¸ are established with the greatest possible precision.

The pioneer excavation methods used by the Leakeys at Olduval have been adopted and refined in both the Lake Turkana and Hadar regions, where archaeologists work alongside human paleontologists¸ geologists geomorphologists¸ and other specialists in a multidisiplinary investigation of the earliest human behavior.