A 400,000 year old fossil shell with geometric marks thought to have been deliberately made on it by Homo erectus has been discovered in in Java. If this is true, and the marks do indeed look deliberate, then it is strong pointer to a form of Homo considered decidedly primitive compared with modern Man having an ability to think abstractly and to translate that thought into physical representation. The discovery is impressive because it pushes back the possession of such an ability hugely beyond the advent of Homo sapiens 150,000-200,00 years ago.
If this is a correct interpretation of the marks on the shell it has a profound implication: the closer the shape of intelligence in older forms of Homo to those of younger forms, the stronger the likelihood of interbreeding because general behaviour in the older and younger forms would have considerable similarities.
This is important both in itself and because it undermines the Out of Africa theory which has been in the ascendency arguably since Darwin fingered Africa as the birthplace of Homo. The latter reason has great political resonance in the West because it can be fitted neatly into the predominant liberal internationalist credo of the First World. It allows the liberal internationalist to place their claim that humanity is just one big family without any meaningful difference on the supposed rock of a common ancestry, and, even better for the liberal, the common ancestor happens to be found in the part of the world whose populations are the particular favourites of the white liberal, namely, those of black Africa.
When interbreeding of different species of Homo is introduced into the picture it shows human populations living today as being more genetically diverse than the Out of Africa theory allows and removes the claim that ultimately all human behaviour and achievement derives from the descendants of Africans. Most devastatingly for the liberal it raises the possibility that the widely differing cultures humans have created are at least in part, a consequence of genetic differences between varieties of Homo.
It is true that so far the amount of genetic difference attributed to interbreeding is small, perhaps 1-3% of Neanderthal genes in modern Man outside of Africa . There are two points to bear in mind. First, a small difference in genetic profile could have a profound effect on ability and behaviour. Diseases can be down a single gene being different from the norm. These can have the most devastating effect on a person who is a sufferer.
If it is accepted that genes have a fundamental role in shaping behaviour and general personality, then differences in genetic makeup, even if they only affect a small number of genes, could be marked. Do genes have such as role? It is difficult to see how they could not, because to maintain that they do not would in effect be to argue that all parts of the body are subject to genetic control but those responsible for the functioning of the mind. There is also the evidence from animal breeding that behavioural and temperamental traits can be successfully enhanced through selection directed by humans, dogs being the prime example. . It would be very odd if the human template was so completely different from that of animals that in this one respect it was utterly different.
But interbreeding could also create important external physical changes which had the potential to alter behaviour both of those who acquired the changes and those who did not. For example, analysis of Neanderthal DNA suggests that breeding between Neanderthals and Homo sapiens in Europe and Asia was at least partially responsible for modern Europeans and Asians having lighter skins and possibly straight hair.
The second consideration is that humans have been distinctly rare for most of human history. Estimates are obviously very difficult to make for the distant past but, for example, the US census department gives an estimate of between 1-10 million for 10,000 BC. A small population would be more susceptible to both a valuable mutation spreading rapidly through it and to maintaining the mutation. That would enhance diversity within a sizeable population in a specific area such as Europe..
The evidence for interbreeding between different varieties of Homo has been growing in recent years through the vast improvements in DNA retrieval and reading. From this comes objective evidence that modern Man outside of Africa has Neanderthal ancestry. The gene sequencing of a third species or subspecies of Homo, the Siberian Denisovans also shows evidence crossbreeding with Asians. There is also a another candidate for interbreeding as yet unnamed.
This may just be the tip the interbreeding story because discovered human fossils , though much more plentiful now than they were even fifty years ago, are still very meagre. Fossils are placed in general type classifications such as homo erectus and Homo habilis which may have substantial differences in form or are classified as this or that from very incomplete fossils. Interbreeding could have been much more varied than the present evidence shows. If so, the amount of genetic mixing could be far greater than is presently imagined, because it would not simply be a case of two distinct species or varieties of Homo mating, but the descendants of differing varieties of Homo who have mated then mating with other hybrids whose hybridity is of a different type. For example, suppose there were four different types of Homo in the same geographical area. Types 1 and 2 mate. Their children are hybrids. Types 3 and 4 mate. Their children are hybrids. The children of 1 and 2 then mate with the children of 3 and 4 producing further hybrids.
Another interesting trait is that members of a species will have different breeding propensities across its distribution, that is, members of the supposedly single species will breed differentially with different parts of the total species population. For example, take an animal which is common to Europe and bring individuals from different geographical parts of the continent together and it may be that those found in the East of the distribution will be less likely or refuse altogether to mate with the those in the West. These barriers to breeding are clearly not purely due to major differences in physical biology. Probably there is a strong component of behavioural difference which reduces the propensity to breed.
It is worth adding that the traditional concept of a species is far from secure. It is a man-made classification which is often found wanting. For example, the North American Ruddy Duck and the European White-Headed Duck are classified as separate species. The introduction of the Ruddy Duck to Europe has resulted in widespread interbreeding between the supposedly separate species to the extent that conservationists now fear for the survival of the White Headed Duck. It is also true that a growing amount of traditional taxonomic classification is being overturned by DNA analysis.
There is nothing surprising about varieties of Homo interbreeding. Many animals of closely related species could produce offspring if they were willing to mate as can be seen from the successful human instigated inter-breeding by artificial insemination of, for example, lions and tigers and inter-species mating in the wild. The offspring of such intra-species breeding , whether artificial or in the wild, are often sterile, but not invariably.
Animals use various triggers to breed: aural, chemical, condition of feathers and so on. These are seemingly automatic processes whereby one individual responds to another without conscious thought. Even behavioural triggers such as mating rituals can be viewed in the same light, although in such cases the process of acceptance and rejection may include an element of higher understanding as such a ritual is often complex and it is not easy to see exactly how it could be a simple programmed response.
Man, although not divorced entirely from such triggers, adds conscious thought to the process of mate selection. Does that not put Man in an entirely separate category to all other organisms, namely, the one organism who can potentially breed freely across the entire species population? Potentially yes but in practice no, for Man’s capacity for conscious thought and decision making does not mean his breeding is not constrained by the triggers which control other organisms, especially behavioural. For example, most people choose mates who are of the same race as themselves even when they have ample opportunity to do otherwise.
Nonetheless, any organism with a degree of self-consciousness and, perhaps even more importantly, language could and almost certainly would go far beyond the triggers to separation of animal species which have neither significant consciousness nor, most importantly, language. The possession of language in particular would provide a means to overcome any reluctance to breed with those of a different variety of Homo, for it would not only allow a means to share and discuss ideas with their own tribe or band, but also to communicate with mates of a different variety.
The cranial capacity of extinct t varieties of Homo is often used as the starting point for assessing their mental capacity. But size of brain is not everything. Oliver Cromwell had a cranial capacity of 2,000 cc; the novelist Anatole France one of less than 1,000 cc. Neanderthals had an average brain size larger than that of modern humans. The shape of a brain with differing emphases on its various functions is also taken as a pointer to mental capacity, for example, Neanderthals are routinely said to have more of the brain devoted to sight and body control, which implies less capacity for social interaction skills and abstract thought. However, this supposed difference from Homo sapiens is still a matter of debate amongst academics and there is growing evidence of Neanderthal cultural sophistication.
If the mental capacity of older forms of Homo was much stronger than has often been thought, the willingness and ability to mate with them by more advanced forms would have been more frequent. The evidence of the fossil shell mentioned at the beginning points to behaviour which we would consider very human a very long time ago. Another impressive ancient example of ability in older forms of Homo has recently been e found at a 350,000 year-old site in Israel where evidence has recently be found of regular and controlled use of fire. It may be that the likes of Homo erectus and Homo habilis were far more like Homo sapiens than they are given credit for and later forms ever more so the nearer they came to the present.