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:
  1. An absolute brain size of 600 cubic centimeters
  2. The possession of language, identified from casts of the brain patterns on the inside of the brain case
  3. The possession of a modern, humanlike precision grip and an opposable thumb.
  4. 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 radiations ( 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:
  1. 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.
  2. 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.