Contents
Section 1
Palaeoanthropology
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Photogallery Outline of Human Phylogeny Evolutionary Trees and DNA Brain Evolution Hand and Bipedality |
Section 2
Social and socio-
cultural systems
Section 3
Ontogeny and symbolism
Section 4
Language systems
Links
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Links Policy Relevant Links |
Evolutionary trees of apes and humans from DNA Sequences
Peter J. Waddell and David Penny
Abstract
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.Links
David 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
Reference
Trask, L. (1998) Historical Linguistics. London: Arnold. See especially pp. 376-404 on 'Very remote relations'