The study of human origins, palaeoanthropology, is one of the most pressing problems for science. The reason is very simple: we cannot claim to understand human nature unless we understand its origins. To know the story of the evolution of the human species is to be able hopefully to answer all the Why? questions we can have about human nature, rather than having to accept human nature as a thing given but unexplained. (By 'human nature', I simply mean our physical and in particular behavioural characteristics.)
Unfortunately, the problem of the evolution of our species is very far from being solved – in fact, we only know perhaps 5% of the story! To say 5% may seem an uncharitable criticism of those who have worked hard to unearth the human past, but the storybook cannot simply be be closed when all the 'ape-man' species and their interrelationships have been discovered – and that, incidentally, is far from having been done. The storybook can only be closed when we have satisfactory explanations for all the unique charateristics of the species – upright walking, lack of body fur, use of clothing, tools and weapons, extended tribes, fire, language, trade, monogamy, etc etc etc.
The problem of palaeoanthropology can be stated in simple terms be (1) to establish the species tree of all descendents of the latest common ancestor of chimpanzee (assuming it to be our closest relative) and man, and (2) to discover the origins of all the key characteristics of our species.
About five to seven million years ago, the ancestral species of humans and chimpanzees (our closest relatives in the animal kingdom) split into two populations, one leading to the two modern chimpanzee species (common and pygmy), and the other leading to modern humanity via many extinct species of ape-man, including dead-end side-branches of which there appear to have been many in our family tree. That human-chimpanzee split 5-7m years ago defines the starting point for the subject of palaeoanthropology.
I have gone along with the emergent view that the term 'hominin' should be used for humans and all members of the ape-man family tree – in other words what used to be called 'hominids'. The latter term is now taken to include all living great apes and humans as well as extinct forms including ape-men. A viewpoint by Lee R. Berger helps to explain the thinking behind this change of nomenclature.
Progress on riddling out human ancestry is given in the species list.
A start on the origins of key human characteristics is given in the characteristics page.
It is said that all the human-ancestor fossils dug up so far would fit into the boot of an average motor car. This illustrates problem number one – human fossils are rare and hard to find!
One of the reasons for this is that fossils will only have been laid down under favourable circumstances. For a start, the forests favoured by chimpanzees, and presumably by early hominins, are not conducive to fossil formation – chimpanzees have left no fossil record! Fossils will only have been laid down when sedimentary rocks were forming, so it is required that the landscape was falling under tectonic forces, so that sediments could pile up.
Next the problem of accidental "cherry-picking" looms! Bearing in mind how hard hominin fossils are to find, fossil-hunters tend to look in places where fossils have been found in the past. Eastern Africa, from Ethiopia to South Africa, has been a happy hunting ground, leading to the view that Africa and in particular the Rift Valley is the breeding-ground of our species – which it almost certainly is. But watch out! – if hominin fossils have not been found in a particular place, is that because there are none there, or because no one looked because none had been found?
Other factors that affect choice of search site include geology ("are the rocks the right age to contain hominin remains?"), topology ("are there river valleys cutting through the landscape to reveal the important layers?"), vegetation ("is the ground visible or obscured by dense cover?"), special features such as caves, etc. All these factors and more introduce a possible accidental cherry-picking effect – with the best will in the world, the places that seem unpromising get little or no attention, with the result that important potential discoveries could get overlooked.
The next problem is the vexed question of classification. "Is this fossil of the same species of hominin as that fossil?", "Should this species be split into two or more?", "Should these two species be combined?" – questions of this sort are being debated incessantly. The causes of these vexed issues are, amongst others (1) the paucity of the fossil record, (2) the variability of individuals within a species – quite possibly there was as much diversity in hominin populations as in modern human societies, (3) the possibility of intermediate forms where one species evolves into another, and (4) the sheer number of species (around 20 and counting!).
Just how many hominin species are there, and why are there so many? One reason for the diversity is that there have been numerous ice ages during the last two million years at least – approximately one every 100,000 years – causing massive and probably abrupt climatic disruptions, even in tropical Africa. Each such disruption might have triggered speciation – the formation of new species. The pace of evolution may have been rapid during these climatic shocks.
To get a handle on just how fast evolution can operate, consider the African elephant which has evolved a new trunkless form in living memory, despite the long inter-generational interval of elephants. It's very simple: if you start with 1% of elephants trunkless, then send out ivory poachers with high-powered rifles to kill 95% of the population (obviously excluding the trunkless ones) then you will end up with 1% out of 5% trunkless – one in five – 20%! The figures given here are for the sake of an example – not real figures, but surely the point is taken: evolution can be surprisingly fast when species are driven almost to extinction, whether the driving force is the ivory poacher's rifle or the onset of an ice age.
This kind of reasoning encourages the belief that the emergence of the human species was stepwise rather than continuous – that our evolution took place in large spurts rather than by small increments.
The many and varied habitats of the Rift Valley region of Africa must have been another factor giving rise to multiple hominin species. There appear to have been many occasions when several hominin species co-existed in Africa, even co-existing in the same place. On the other hand, the proliferation of habitats must have placed a great premium on adaptability, and encouraged the emergence of a species capable of inhabiting all habitats by virtue of a unique ability to invent tools and social behaviours to suit each situation.
This website assumes that the Darwinian explanation of the origin of man is basically correct, and for this reason the Creationism v. Darwinism debate is not addressed here. If you are interested in pursuing that further try, for example, the Talk.Origins (Fossil Hominids) website.
Puzzlingly small sums are devoted to the study of human origins as compared to the staggering sums expended on space exploration, particle physics and other less useful sciences. Surely, much more scientific wealth could be created by devoting a fraction of those expenditures instead to developing scientific techniques for extending our knowledge of human origins, such as ways of discovering human fossils underground rather than on the surface, ways to obtain and analyse ancient DNA, ways to recover information about perishable artefacts such as clothing, nets, carrying-bags, etc. The payback in terms of an improved understanding of the roots of human nature would surely be of incalculable value to the human species.
Copyright © 2004 Alan J. White; all rights reserved. Last updated January 2004.