Old and new views on human evolution
Professor Chris Stringer FRS, Natural History Museum, UK
Abstract
Darwin and Wallace both wrote about human evolution when there was little relevant fossil evidence available, and none at all from the continent of Africa. Although both accepted that natural selection had produced many of the distinctive features of humans, Darwin developed a much more detailed model for the origins of bipedalism, tool-making, canine reduction and brain enlargement through feedback mechanisms stemming from selection to free the hands for manipulation, rather than locomotion.
Darwin also proposed that ‘racial’ features had largely been added through the action of sexual selection. Wallace demurred over the importance of sexual selection in Homo sapiens, arguing that consistent tastes were unlikely to have persisted long enough and widely enough for it to operate on any scale. He also doubted that the correlated ‘perfection’ of human characteristics could have been produced by natural selection alone, and that “unknown causes” must also have been at work. In the case of the human brain, in particular, he came to argue that spiritual, rather than natural, forces must have been responsible for the evolution of the highest human faculties.
In the light of subsequent fossil and archaeological discoveries, it is possible to critique the views of both Darwin and Wallace concerning human evolution. We now know that canine reduction, bipedalism, tool-making and brain enlargement did not evolve in concert, but were spread out over several million years of evolution in Africa, with different species showing distinct combinations of traits. Thus these features probably developed through multifarious causes, rather than being locked in a feedback system. And while natural selection does seem to lie behind the evolution of the human brain and of many regional (‘racial’) features, sexual (or cultural) selection also seems to have played its part. Some of the issues with which Darwin and Wallace struggled have been resolved by new evidence, while the richness of the current fossil, genetic and archaeological records has raised many new issues which they could never have contemplated.
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Professor Chris Stringer FRS, Natural History Museum, UK
Professor Chris Stringer FRS, Natural History Museum, UK
Professor Chris Stringer has worked at the Natural History Museum since 1973, and is now Research Leader in Human Origins and a Fellow of the Royal Society. His early research concentrated on the relationship of Neanderthals and early modern humans in Europe, but through his work on the 'Recent African Origin' model, he now collaborates with archaeologists, dating specialists and geneticists in attempting to reconstruct the evolution of modern humans globally. He has excavated at sites in Britain and abroad, directed the Ancient Human Occupation of Britain project (AHOB) for 13 years, and now co-directs the Pathways to Ancient Britain project (PAB). His recent books include The Origin of our Species (published in the USA as Lone Survivors, 2013) and Britain: one million years of the human story (with Rob Dinnis, 2014).
Wallace and human evolution
Professor Ted Benton, University of Essex, UK
Abstract
In 1859 Darwin had been evasive about human evolution, but Wallace addressed the question in 1864. His paper addresses two issues: the origin and significance of racial differences and the great mental gulf between humans and apes, despite the striking physical resemblances between them. The theory of evolution by natural selection can be used to explain both. At a certain point in the development of social dispositions and mental abilities in our ancestors, natural selection would have increasingly acted on these features, rather than bodily form. Cranial capacity would have increased greatly, leaving the rest of the body little changed. This approach was influential on Darwin’s argument in the Descent of Man, but in the meantime Wallace had become convinced that natural selection was insufficient to explain ‘higher’ human attributes. Darwin was horrified, but in fact their views had more in common than either recognised.
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Professor Ted Benton, University of Essex, UK
Professor Ted Benton, University of Essex, UK
"Ted Benton is professor of Sociology at the University of Essex. He has published extensively on critical social theory, philosophy of social and natural sciences, environmental sociology and history of ideas. He began his career as science teacher in a pioneering comprehensive school, and has maintained a keen interest in field natural history. He has published several books on aspects of entomolog including two works in the HarperCollins New Naturalist series. His most recent book is: Alfred Russel Wallace: Explorer, Evolutionist and Public Intellectual - a thinker for our own time? (Siri Science)."
Wallace, Darwin and female choice
Professor Tim Birkhead FRS, University of Sheffield, UK
Abstract
Wallace didn’t rate Darwin’s idea of sexual selection, at least, not as a much as Darwin. Wallace’s reservations – particularly with regard to female choice - anticipated the bumpy ride that sexual selection endured since Darwin. From the mid-1970s however, with a clearer view of how selection operates, sexual selection has enjoyed a spectacular Renaissance and is now considered to be as important as natural selection. I will explore the history of sexual selection, including Wallace’s criticisms, and discuss its rebirth, especially with respect to something neither Darwin nor Wallace even contemplated: the idea that sexual selection might continue beyond the choice of partner: post-copulatory sexual selection.
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Professor Tim Birkhead FRS, University of Sheffield, UK
Professor Tim Birkhead FRS, University of Sheffield, UK
Tim Birkhead is professor of behavioural ecology at the University of Sheffield. After a degree in Zoology (1972) at the University of Newcastle upon Tyne, Tim completed a D.Phil at Oxford on the biology of guillemots (seabirds) in 1976, before taking a lectureship at Sheffield in 1976, where he’s been ever since. He was elected a Fellow of the Royal Society in 2004. His main research interests are in sexual selection – promiscuity – and mainly in birds, but he is also interested in the history of science. Tim has won several awards for his undergraduate teaching; he was also awarded the Elliot Coues medal for ‘outstanding and innovative work in ornithology’ by the American Ornitholigists’ Union in 2011, and the animal behavior medal by the Association for the Study of Animal Behaviour in 2012. His recent book Bird Sense (2012, Bloomsbury) was voted best natural history book of the year by both The Independent and the Guardian.
Wallace's understanding of species and speciation
Professor James Mallet, University College London and Harvard University, UK and USA
Abstract
Soon after his return from the Malay Archipelago, Alfred Russel Wallace published one of his most significant papers. The paper followed many of the themes opened up by Henry Walter Bates 3 years earlier, and used butterflies as a model system to understand the evolution of mimicry and the origin of species. In a very important section, Wallace laid out what is perhaps the clearest definition by an early Darwinian of the differences between species, geographic subspecies, and local 'varieties.' He also discussed what is now termed 'reproductive isolation.' While he accepting it as a cause of species, he rejected it as a definition. Instead, species were recognized as forms that overlap spatially and lack intermediates, as had Darwin. This morphological distinctness argument appears to break down for discrete polymorphisms, but Wallace correctly diagnosed conspecificity of non-mimetic males and polymorphic female Batesian mimics in Papilio butterflies for the first time. Also in the 1860s Wallace wrote to Darwin about a suggestion that natural selection could lead to reproductive isolation, which the older man firmly rejected. When G.J. Romanes later published his theory of 'physiological selection' (a selective model for the origin of reproductive isolation), Wallace rebutted the idea in the pages of Nature. In his book Darwinism (1889), however, Wallace wrote up his own theory in a manner almost identical to what he'd outlined to Darwin in the 1860s, without apparently discussing why Darwin had rejected the idea. The problem with both Romanes' and some of Wallace's ideas is that they are inherently group selectionist; however, one part of Wallace's idea survives as today's model of 'reinforcement' in speciation.
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Professor James Mallet, University College London and Harvard University, UK and USA
Professor James Mallet, University College London and Harvard University, UK and USA
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James Mallet was educated at Oxford (BA Zoology), Newcastle-upon-Tyne (MSc Applied Entomology), and Austin, Texas (PhD Zoology). He is Professor of Biological Diversity at UCL and Distinguished Lecturer at Harvard University. He also holds honorary positions at The Natural History Museum London and the Smithsonian Tropical Research Institute in Panama. In 2008, he was awarded the Darwin-Wallace Medal by the Linnean Society of London for contributions to evolutionary biology.
His research has ranged from tropical field biology, applied entomology, systematics, evolutionary biology, population genetics and genomics. He has concentrated most effort on the genetics and evolution of ithomiine and heliconiine butterflies of South and Central American rainforests, and in understanding speciation and hybridization among species. Recently, he was corresponding author for the Heliconius Genome Consortium's publication in Nature, which documented genomic evidence for promiscuous gene flow among multiple species of Heliconius."