Social and socio-
Ontogeny and symbolism
Evolutionary trees of apes and humans from DNA Sequences
Peter J. Waddell and David Penny
Developments over the past decade have made DNA sequences the primary source of information for inferring relationships between organisms. Originally sequences were used for studying relationships between species, but increasingly they are now used to study relationships between individuals and between populations. In this chapter we show how sequences have changed, and continue to change, our views of human origins and evolution. Techniques used to go from DNA sequences to evolutionary inference are outlined, because they are crucial in evaluating this vast new source of data. In addition to a review we report some of the latest research findings, and where necessary have developed appropriate statistical methods. The main points of this chapter are:
1. There is consistently strong support for the human and chimpanzee lineages' being the closest relatives to each other, and the next closest the gorilla lineage, with the orang-utan being the closest non-African relative of these African hominoids.
2. A calibration of these evolutionary trees is given, with estimated dates of divergence for the living hominoids, together with estimates of the expected errors, an important consideration for those interested in assessing the compatibility or otherwise of fossil (or palaeoanthropological) data with molecular inferences. We estimate that the divergence of human and chimpanzee lineages took place approximately 6.5 million years ago, while the standard error of such dating methods is at present about 1 million years.
3. Our evaluation of the 'Out of Africa Hypotheses' (mitochondrial 'Eve') leads to the conclusion that this set of four hypotheses (pertaining to the when, where, who, and how of modern humans' origins) does indeed stand up to scrutiny; a point reinforced by our reanalysis of specific features of the data. No single data-set gives overwhelming support to all four aspects of the Out-of-Africa scenario; but it is consistent with several data-sets, while overall the data contradict the 'multiregion' hypothesis of human origins.
4. A re-evaluation of the molecular evidence confirms that the 'when' was almost certainly less than 200 000 years ago, as inferred from both mitochondrial and nuclear DNA data calibrated using both biological and palaeoanthropological data. Africa is most consistently inferred as the 'where'. The mitochondrial DNA sequences give us a glimpse of 'who' founded populations outside Africa and 'how', as populations appear to have expanded rapidly at some point after their arrival into new lands.
LinksDavid Joyce of the Department of Mathematics at Clark University provides a description of how phylogenetic trees can be reconstructed.
The diagram below has been drawn by Kelly L. Ross from L. Cavalli-Sforza (1991) Genes, peoples, and and languages. Scientific American. It represents the genetic distances calculated in the late 1980s from the DNA research summarised in Waddell and Penny's chapter that hold between contemporary human populations. Note the clear disjunction between sub-Saharan African populations and all others. It is this evidence that largely underwrites the 'African Origins' scenario for modern humans. The image links to Ross's notes on 'Genetic distance and language affinities between autochthonous human populations' for further tables on possible relations between these genetic relations of human populations and proposed relations among current human languages. Ross also provides some critical comments.
For further information, see the collation of links at Genes and Identity
ReferenceTrask, L. (1998) Historical Linguistics. London: Arnold. See especially pp. 376-404 on 'Very remote relations'