Species and Speciation in Human Evolution

28 Jul

The classification of the biosphere according to species, genus, family, order, class, phylum and kingdom, that is based on shared characteristics, has value in our understanding of the relationships between different organisms to determine long-term evolutionary lineages. Without such a taxonomic classification scientists historically would not have been able to arrive at any reasonable proposition for the Darwinian theory of evolution and its subsequent development into the paleontological tree of life. However, the compartmentalisation of a fluid and dynamic evolutionary process in these terms does not provide us with the processes at work at the finer level of evolutionary detail, and this appears to have particular significance for our modelling of how modern humans came about from apes as an apparently single species of Homo sapiens sapiens, according to conventional wisdom.

At the heart of the matter concerns what constitutes a distinct species. The classical theory of evolution depends on establishing the mutational, natural selection and genetic drift mechanisms for the emergence of distinct populations of animals in Nature based on a definition of species that talks of reproductive compatibility in the main.  This does not get us very far in our quest to ascertain which organisms emerged from a common ancestor. In my view the intractable problem of speciation in evolutionary biology may be addressed as follows: should populations be defined as distinct species specifically in relation to the degree of speciation that will prevent the reproductional fusion of gametes for embryogenesis to a viable foetus, or should speciation be defined in terms of phenotypic parameters that takes into account morphological, physiological, biochemical and behavioural separations to the point that incompatiblity between representative samples of male and female from being able to engage in sexual intercourse can be established whether or not mating between fertile and healthy individuals can demonstrably result in a successful offspring that, in turn, was able to pass on its own genes to another generation. For the consideration of human evolution I take the latter view that is testable but the ethics of the science preclude its implementation.

Further, I consider all extant and extinct Homo phenotypes from Homo ergaster onwards as consituting ‘human beings’ on the basis that they all had a highly evolved ‘mind’ that governed intelligence and culture, as distinct from Homo habilis and its predecessors that were a lot more ape-like and instinctive rather then deliberative. This means that they were all able to produce successful offsprings with each other but chose not to do so when they came into contact. Thus, the terms Homo erectus, Homo georgicus, Homo neanderthalensis, Homo heidelbergensis, Homo floresiensis, etc should only be used for the purposes of describing particular fosssil finds in terms of geography and age on the assumption that they did not differ from each other to any significant degree in the non-intelligence and non-cultural parameters. They would have differed on the other parameters but not to the point that they would have ruled out mating.

So the question that arises is whether there is any value to describing any of the Homo ergaster-derived variants as its subspecies according to some type of classification that may be formulated based on the above considerations of the phenotype. My view is apart from the differences highlighted in this  blog that gives sufficient reason to consider that the Han Chinese descended from Homo ergaster via Homo erectus and not via Homo sapiens, a major source of variation in human populations is that which comes under the subject of differences in the ‘workings of the mind’ which governs human behaviour to a very high level in comparison with other animals. This has implications for our definition of what constitutes relative docility between different human groups, for example, and why religion of various descriptions are adopted by different people. Science will attribute both intelligence and culture to an underlying genetic natural cause. However, the study of the mind itself in terms of brain tissue formation, the transmission of neurotranmitters, memory storage,  thought production, consciousness/awareness, foresight, visions, imaginations and the relationship each of these to physical ‘genes’ in the DNA is in its absolute infancy. Indeed, as psychology and psychiatry it may be regarded as unscientific and not what we know today as modern medicine.  The obvious racial differences are superficial and do not address the intelligence and cultural dimension of human differences. We do not currently have the scientific tools required for a thorough investigation of these topics. Although neuroscience has made a great deal of progress in recent decades thoughts and consciousness have not been amenable to scientific probing, without which differences in culture and intelligence cannot be understood to determine human subspeciation.

As mentioned earlier human species and speciation also brings us to ethical issues for identifying what constitutes legitimate and worthwhile topics for scientific scrutiny. In this regard an aspect of the ethics of the type of science that one needs to bring under consideration was also alluded to by ‘Someone’ (as reproduced in my 23 July post), and I do acknowledge and appreciate his/her contribution to the discussion in this blog.

Last edited: 10.49 am, 29 July 2012.

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