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Major transitions in human evolution

Event

Starts:

October
222015

09:00

Ends:

October
232015

17:00

Location

The Royal Society, London, 6-9 Carlton House Terrace, London, SW1Y 5AG

Overview

Scientific discussion meeting organised in partnership with the British Academy by Professor Robert Foley FBA, Professor Chris Stringer FRS, Dr Marta Mirazón Lahr and Professor Lawrence Martin

Fossil hominin skull KNM-ER 1813. Copyright: Bob Campbell

The rich human palaeoanthropological record shows an unexpectedly complex pattern in the tempo and mode of human evolution. Evidence for many of the key phases is found in East Africa, and has been shaped by critical discoveries by teams led by Richard Leakey, or work inspired by his finds. The meeting focussed on key evolutionary transitions to understand the interaction of biology, behaviour, culture and environment.

Papers related to this meeting have been published in Philosophical Transactions B.

Download the meeting programme (PDF).

Enquiries: Contact the events team

Schedule of talks

22 October

09:00-12:30

Session 1: The origins of Homo – morphology, adaptation and technology

7 talks Show detail Hide detail

Chairs

Dr Hélène Roche, Université de Paris X, France

09:05-09:25 Chronology of hominin discoveries in the Turkana Basin and their impact on understanding human evolution

Professor Lawrence B. Martin, Stony Brook University, USA

Abstract

Since the 1950s the East African Rift Valley has been one of the primary sources for evidence for human evolution. While early research focused on Olduvai and the central rift, from the late 1960s the Turkana Basin in Northern Kenya and Ethiopia has provided the richest and most diverse record of human evolution, stretching from the first australopithecines (A. anamensis at Lothagam) to the evolution of modern humans (Omo Kibish), to recent hunter-gatherers. It would be impossible to reconstruct human evolution without the contribution of the Turkana Basin hominins. This introduction looks at the chronology of discoveries across this period, and how specific discoveries by Richard and Meave Leakey changed ideas and models of hominin evolution at various points in the last fifty years, and discusses the key insights that the Turkana Basin hominins provide about the pattern of early hominin evolution.

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09:25-09:50 Environments and mammalian communities in the East African Plio-Pleistocene: an ecometric analysis of the fossil mammal record of the Turkana Basin

Professor Mikael Fortelius, University of Helsinki, Finland

Abstract

Although ecometric methods have been used to analyse fossil mammal faunas and environments of Eurasia and North America, such methods have not yet been applied to the rich fossil mammal record of East Africa. Here we present the first results of ecometric analyses at two scales: continental and regional, and at two trophic levels: primary and secondary consumer. We discuss environments and evolutionary trends of the Turkana Basin Mio-Pleistocene mammal faunas in a broader setting of Eastern Africa and Western Eurasia, both in the light of our new results and in relation to previous work. We also show how the degree of aggregation affects the patterns recovered and discuss the implications of such scaling effects.

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09:50-10:15 Kenyanthropus and hominin diversity in the middle Pliocene

Dr Meave Leakey, Turkana Basin Institute, Kenya and Stony Brook University, USA

Abstract

For many years, most interpretations of early hominin phylogeny depicted a single lineage of Australopithecus afarensis throughout the middle Pliocene, which gave rise to a diverse radiation of taxa after 3.0 Ma. In 2001, the discovery at West Turkana, Kenya, of the 3.5 Ma old cranium of Kenyanthropus platyops, with a unique combination of derived facial and primitive neurocranial features that contrasted with the prognathic face of A. afarensis, provided the first convincing evidence that there was taxonomic diversity in the hominin record at this time. Subsequent and more detailed comparisons of K. platyops with a large sample of African Plio-Pleistocene hominin fossils, modern humans and great apes, using conventional and geometric morphometric methods together with high-resolution computed tomography, confirmed the unique morphology of Kenyanthropus. Recently, 3.4 Ma finds from Woranso-Mille, Ethiopia, have provided further evidence of hominin species diversity at this time, in the form of strongly contrasting foot morphology. Most recently, the earliest known stone tools, dating to 3.3 Ma, have been described from a locality in close proximity to that of Kenyanthropus, raising the question as to which hominin was the stone tool maker. A review, summarizing currently known evidence for Kenyanthropus in the context of these new finds, is therefore timely.

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10:15-10:40 Discussion

11:10-11:35 Australopithecus and the transition to early Homo

Professor William Kimbel, Arizona State University, USA

Abstract

The age of origin of the Homo lineage is thought to have fallen in the time period between 2.5 and 3.0 Ma.  The relevant fossil record in Africa is, however, notoriously poor, thwarting attempts to discern the pattern of earliest Homo evolution and delineate its proximate causes. Recent discoveries at Ledi-Geraru in the Afar rift of Ethiopia push the Homo lineage back to 2.8 Ma. Although separated in time from Australopithecus afarensis at the neighboring Hadar site by only two-hundred thousand years, these fossils show derived dental and gnathic traits and occur in a strikingly more open palaeoenvironmental setting.  Coupled with new discoveries of very early flaked stone tools at West Turkana, Kenya, contemporary with small-brained australopiths at 3.3 Ma, the Ledi fossil hominins open the possibility of a new evaluation of factors involved in the transition to Homo.

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11:35-12:00 An earlier origin for stone tool making: implications for cognitive evolution and the transition to Homo

Professor Sonia Harmand, Stony Brook University, USA and Turkana Basin Institute, Kenya

Abstract

The discovery of the earliest known stone tools at Lomekwi 3 from West Turkana, Kenya, dated to 3.3 Ma, raises new questions about the mode and tempo of key adaptations in the hominin lineage. Conventionally, the origin of stone knapping was linked to the rise of the genus Homo, in response to climate change and the spread of savanna grasslands, a presumption that has remained strong until quite recently. The Lomekwi 3 tools date to before the earliest known fossils attributed to Homo at 2.8 Ma. They were made and deposited in a more wooded environment than were the earliest Oldowan tools at 2.6 Ma. Their discovery leads to renewed investigation on the timing of the emergence of human-like manipulative capabilities in early hominins and implications for reconstructing cognition.

The Lomekwi 3 artefacts form part of an emerging paradigm shift in palaeoanthropology, in which: tool-use and tool-making behaviors are not necessarily limited to the genus Homo; cranial, post-cranial and behavioral diversity in early Homo is much wider than previously thought; and these evolutionary changes may not have been related to the opening of savanna grassland environments.

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12:00-12:30 Discussion

12:30-13:30 Lunch

13:30-17:00

Session 2: The evolution of the early human phenotype

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Chairs

Professor Bernard Wood, George Washington University, USA

13:30-13:55 Palaeovegetation from plant wax biomarkers in terrestrial and marine sediments

Dr Kevin Uno, Lamont-Doherty Earth Observatory of Columbia University, USA

Abstract

Carbon isotope ratios from plant wax biomarkers in sedimentary archives reflect the proportion of C¬3 and C4 vegetation in past ecosystems. Biomarkers in sediments from fossil sites in East Africa and from adjacent marine core sites have great potential for improving our understanding of the role of vegetation and ecological change in human evolution. We review existing Miocene to Pleistocene plant wax carbon isotope data from terrestrial and marine sediments in and around East Africa with specific focus on their contributions to understanding human evolution. An advantage of isotope records from fossil-bearing terrestrial sediments (e.g., palaeosols) is that they represent a local vegetation signal that directly reflects hominin environments, therefore enabling direct comparison between vegetation change and evolutionary events. As an example, we present palaeosol biomarker data from the Shungura Formation in Lower Omo Valley, Ethiopia that indicate an expansion of C4 vegetation at ca. 2.8 Ma.  The vegetation shift directly precedes the appearance of Paranthropus aethiopicus, which had a C4-rich diet. Advantages of isotope records from deep-sea sediments are that they can detect vegetation changes driven by orbital cyclicity and that they preserve long-term records of change because of steady depositional rates over long timescales. Existing isotope data from Deep Sea Drilling Project Site 231 in the Gulf of Aden indicate an overall increases in C4 vegetation from the late Miocene to the Pleistocene. The Site 231 data suggest additional vegetation information can be obtained from other marine cores around East Africa.

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13:55-14:20 The evolution of body size and shape in the human career

Professor William Jungers, Stony Brook University, USA

Abstract

It is widely recognized that body size is a fundamental biological property of organisms, and documenting body size variation in hominin evolution appears to be an important and tractable goal of palaeoanthropology.  Is there an inexorable increase in body size in human evolution? Are we another example of “Cope’s Law”? Is an increase in body size linked to the emergence of the genus Homo as some suggest? Is the evolution of hominin body shape predicted by changes in body size? Estimating body size (=mass) appears deceptively simple, but it is laden with theoretical and pragmatic assumptions about “best predictors” and the most appropriate reference samples. Modern human “training samples” are favored for estimating size in early bipedal hominins like the australopiths, but are these the most appropriate for the earliest putative hominins like Ororrin and Ardipithecus?

The trajectory of body size evolution in the human career is reviewed here and found to be complex and nonlinear. Body mass estimates for the Late Miocene hominins suggest that some are just as large as some australopiths, and australopiths vary enormously and overlap extensively with Homo erectus. The pre-erectus early Homo fossil record is poor, but these earliest members of our genus appear relatively small-bodied, as do the earliest member of our genus found outside of Africa. Large body size is therefore not a hallmark of the genus Homo. Body size evolution alone cannot explain the observed variation in body shape, especially when examined in the context of the smallest known fossil hominins and small-bodied modern humans (pygmies).

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14:20-14:45 Measures of maturation in early fossil hominins

Professor Christopher Dean, University College London, UK

Abstract

The earliest hominins were bipedal, had reduced canine size and some had bigger brains than living great apes. All this suggests a way of life that in many ways differed from great apes today. Evidence for the pace of growth in early hominins comes from preserved tooth microstructure. A record of incremental growth in enamel and dentine persists that allows us to reconstruct tooth growth and compare key measures of dental maturation with modern humans and living great apes. An important question is whether, among the first fossils attributed to early Homo, there was shift towards a more prolonged period of development and whether there was a slow modern human-like period of growth between the end of weaning and the beginning of puberty. If, despite their different way of life and diverse diets, these aspects of early hominin development were indistinguishable from either earlier australopiths and/or from living great apes then this must be interpreted in the context of their life history biology.

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14:45-15:10 Discussion

15:40-16:05 Does morphological variation in Homo erectus signal the origins of developmental plasticity?

Professor Susan Antón, New York University, USA

Abstract

Homo erectus was the first hominin to exhibit extensive range expansion.  This extraordinary departure from Africa, especially into the temperate climates of Eurasia, has been variously related to technological, energetic and foraging shifts.  Recent discoveries highlight both temporal and regional anatomical variation in H. erectus suggesting the possibility that developmental plasticity, a key factor in H. sapiens ability to occupy a variety of habitats, may have been present in H. erectus.  Here we use measures of morphological variation to consider whether the origin of developmental plasticity played a role in H. erectus’ dispersal success.  Developmental plasticity, the ability to modify development in response to environmental conditions, results in differences in size, shape and dimorphism across human populations that relate in part to levels of resource sufficiency and extrinsic mortality. These differences predict that the skeletal record should show not only regional variation, but overall smaller adult sizes and lower levels of dimorphism in instances of resource scarcity and high predator load.  We review metadata for recent humans.  And we compare cranial and postcranial shape and size variation and dimorphism among skeletal ‘populations’ of H. erectus, H. sapiens and exemplar nonhuman primates from known environmental contexts.  Developmental plasticity in H. erectus is suggested by some of these measures.  We discuss the implications of the pattern of conflicting signals across our sample for inferring plasticity, make recommendations for differential use based on the fidelity of different variables in the extant record, and argue that differences in dimorphism among regional samples should be interpreted as evidence of plasticity.

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16:30-17:00 Discussion

16:05-16:30 The evolution of more complex technology: current perspectives on the origins of the Acheulean

Ignacio de la Torre

Abstract

In recent years, research in the emergence of the Acheulean has attracted considerable interest. This has resulted in a wealth of new data on the earliest age of the Acheulean, its initial dispersion, palaeoecological context, technological features, and human species associated with this technology. Currently available evidence suggests that the Acheulean emerged 1.78 million years ago in East Africa, and quickly radiated to other areas of Africa and beyond. However, the hard evidence alone does not explain the evolutionary and cultural mechanisms that triggered the transition to the Acheulean, and a discussion of the contributing factors – cultural, biological and palaeoecological – is needed. With an emphasis on the East African record, this paper will review the state of the art in Acheulean origins research, and contextualize the archaeological evidence and existing paradigms used to interpret the emergence and dispersion of the Acheulean and the eventual disappearance of the Oldowan.

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23 October

09:00-12:30

Session 3: The evolution of modern humans

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Chairs

Professor Mark Thomas, University College London, UK

09:00-09:25 The origin of Homo sapiens

Professor Chris Stringer FRS, Natural History Museum, UK

Abstract

If we restrict the use of Homo sapiens in the fossil record to specimens which share a significant number of synapomorphies in the skeleton with extant Homo sapiens, the origin of our species would be placed in the African late Middle Pleistocene, based on fossils such as Omo Kibish 1, Herto 1 and 2, and the Levantine material from Skhul and Qafzeh. However, genetic data suggest that we and our sister species Homo neanderthalensis shared a last common ancestor in the middle part of the Middle Pleistocene ~400ka, which is some 200,000 years earlier than the species origin indicated from the fossils already mentioned. Thus it is likely that the African fossil record will document early members of the sapiens lineage showing only some of the synapomorphies of late members of the lineage.

On that basis, I argue that human fossils such as those from Jebel Irhoud, Florisbad, Eliye Springs and Omo Kibish 2 do represent early members of the species, but variation across the African later Middle Pleistocene/early Middle Stone Age fossils shows that there was not a simple linear progression towards later sapiens morphology, and there was chronological overlap between different ‘archaic’ and ‘modern’ morphs. Even in the late Pleistocene of Africa and beyond we can find specimens which are clearly outside the range of Holocene Homo sapiens, showing the complexity of recent human evolution.

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09:25-09:50 The shaping of human diversity: filters, boundaries and transitions

Dr Marta Mirazón Lahr, University of Cambridge, UK

Abstract

How human diversity evolved remains a fascinating and dynamic research field. Different processes – cultural and biological - acted to shape the evolution of different populations in time and space, creating a complex palimpsest of similarities and differences. The outcome of this process, at times accelerated by sharp demographic and geographical fluctuations, is that the population ancestral to all humans did not look or behave like any alive today. This has generated major questions regarding the evolution of human universal characters, as well as the nature and timing of major evolutionary events in the history of the species. The paucity of African fossils remains a major stumbling block for exploring some of these issues. However, major breakthroughs from genomics and palaeogenomics have revealed aspects of the demography of late Quaternary hominin groups and their interactions, as well as those between foragers and farmers. The latter have been critical in shaping the last 10,000 years, in what I have named the Holocene Filter, the mechanism by which human diversity throughout the world decreased as a consequence of the differential expansion of a few populations. However, there are other key moments in the history of our species –  ‘filters’, during which extinction would have been a major factor, and ‘transitions’, during which population growth enhances and exports evolutionary novelties, creating novel conditions for human biological adaptation and  accumulated culture. This paper explores the nature and timing of these key moments in evolution of human diversity.

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09:50-10:15 Ancient human genomics: new approaches to human dispersals and population history

Professor Eske Willerslev, University of Copenhagen, Denmark

Abstract

Ancient DNA research on human remains have recently moved from the sequencing of short fragments of mitochondrial DNA mired with contamination to that of full genomes. This transition means that contamination levels can be probably quantified and that it has become possible testing complex scenarios of human population histories not revivable from uni-parentally inherited markers alone. Recent discoveries includes that Native Americans thought to be of east Asian origin also shares recent ancestry with western Eurasians through a Upper Palaeolithic population in central Asia, that populations of early anatomically modern humans in Europe were structured, contained longer tracks of neanderthal DNA and diversified from east Asians more than 37 thousand years ago. Ancient human genomics have also revealed that Aboriginal Australian ancestors diversified some 20-30 thousand years earlier from the African stuck than did eurasians. Ancient human genomics have also showed that the New World Arctic was populated twice and that significant cultural changes not always is associated with population movement, but can happen simply from the spread of ideas within a population and that peoples of the Clovis culture in North America are the direct ancestors of many contemporary Native Americans and are not closer related to Europeans or Asians. As such past genomics is transforming our view of human history and is likely to do so for the years to come.

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10:15-10:40 Discussion

11:10-11:35 The Middle-Later Stone Age transition in East Africa

Dr Christian Tryon, Harvard University, USA

Abstract

The appearance of Later Stone Age (LSA) technologies in Africa represents a major change in the archaeological record, in which technologies, subsistence strategies, and patterns of socio-territorial organization closely resemble those seen in recent and historical foraging societies.  There are sharp discontinuities between the earliest LSA and latest Middle Stone Age (MSA) strata at many sites in southern, western, and northern Africa.  This pattern may simply be an artifact of the nature of the record of sediment preservation, or a signal of the periodic abandonment of these regions by early modern human populations.  In contrast, East Africa preserves a number of more-or-less continuous sequences across the MSA-LSA transition, and these preserve evidence for a complex and perhaps prolonged process of change, a pattern that might reflect a more continuous record of occupation in the area throughout Late Pleistocene climatic variations.  In addition to examining temporal variation across the MSA-LSA transition in East Africa, we use lithic and palaeoenvironmental (faunal) data from a longitudinal transect of LSA sites from the Last Glacial Maximum and Late Glacial to explore relationships between the environment and human behaviour that likely structures the archaeological record and the nature of the appearance in LSA technologies. We observe longitudinal gradients in past faunal community composition that parallel contemporary environmental gradients in East Africa. This is associated with longitudinal variation in the frequency of microliths (the defining LSA artifact type) from archaeological sites, a pattern we interpret as a response to variable environmental risk across space. Spatial and temporal variability in Pleistocene habitats may therefore play a key role in structuring the complex appearance of LSA technologies across Africa.

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11:35-12:00 Surround, defend, and advance: how the transition to foraging for dense and predictable resources changed the course of human evolution

Professor Curtis Marean, Arizona State University, USA

Abstract

The three key evolved features of human uniqueness are a highly advanced cognition, hyper-prosocial proclivities, and a dependence on social learning.  These provide the capacity for cumulative culture that is so fundamental to the modern human niche.  Hyper-prosociality is the tendency for regular cooperation with un-related individuals without the expectation of immediate pay-offs, and can entail a cost to the cooperator.  The regularity and extent of this cooperation among humans is unique among living animals, and thus it is crucial to identify when this feature evolved in the hominin lineage.  Explaining the evolution of hyper-prosociality is challenging since Neo-Darwinian theory fails at the task.  Models that rest on multi-level selection in a cultural species appear more powerful, and those that identify inter-group conflict as providing the key selective context are persuasive.  Here it is hypothesized that the conditions for inter-cultural-group conflict developed in the Middle Stone Age among early modern humans and provided the selective context for hyper-prosociality.  This occurred when early modern humans first began exploiting dense and predictable food resources, escaping a dietary pattern of foraging for sparse, unpredictable resources exploited with a high mobility strategy.  The first evidence for this transition, dating to ~160,000 years ago at Pinnacle Point, is in a coastal inter-tidal context in southern Africa.  When these coastal adaptations matured, territorial defence was triggered, as predicted by the theory of economic defendability.  This conflict may have led to our highly cooperative species and prepared it to colonize the world and displace all other hominin species.

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12:00-12:30 Discussion

12:30-13:30 Lunch

13:30-17:00

Session 4: Tempo and mode in the evolution of humans

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Chairs

Professor Clive Gamble FBA, University of Southampton, UK

13:30-13:55 Reconciling terrestrial and marine records of African climate change

Professor Peter de Menocal, Lamont-Doherty Earth Observatory of Columbia University, USA

Abstract

Terrestrial and marine sediment archives in and around East Africa place new constraints on the timing and magnitude of regional climate changes during the late Neogene. These records collectively document a progressive increase in C4 vegetation over the last 3-4 Ma suggesting a shift to more open conditions. They also document the importance of orbital-scale palaeohydrology and vegetation changes paced by precessional forcing of monsoonal circulation. Syntheses of terrestrial soil carbonate d13C records have shown strong regional differences in vegetation change.

Here, we compile marine and terrestrial stable isotopic records to explore the relative amplitudes of orbital-scale versus longer-term secular changes in East African climate and vegetation over the late Neogene. This approach exploits the proxy-specific recording biases inherent to soil carbonate, tooth enamel, and molecular biomarker records and the sediment archive. We attempt test the hypothesis that orbital-scale palaeohydrological and vegetation shifts were as large, or larger, than the long term secular trends. This study strives to understand the magnitudes of rainfall and vegetation variability ‘on the ground’ that occurred within and across individual hominid linage ranges.

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13:55-14:20 Changing perspectives on the evolution of hominin culture

Professor Mark Collard, Simon Fraser University, Canada

Abstract

Over the last 25 years the study of the evolution of hominin culture has been transformed by three developments: 1) a dramatic increase in archaeological fieldwork, especially in Africa, 2) a surge of experimental and observational research on cultural behaviour in nonhuman animals and, 3) the development of a body of theory and supporting empirical work in which culture is conceptualised as an evolutionary system that interacts with, but is distinct from, the genetic system. In this paper, I will review these developments and discuss their implications for our understanding of the evolution of cultural behaviour in the hominin lineage, paying particular attention to the major transitions identified by previous generations of researchers. I will show that there is still evidence that a number of major transitions occurred in the course of hominin cultural evolution, but they differ substantially from those recognized in the past in terms of their nature and/or their timing. I will finish by highlighting some of the questions about the evolution of hominin culture that I think need to be addressed as a matter of priority.

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14:20-14:45 Tempo and mode in human evolution: the problem of transitions

Professor Robert Foley FBA, University of Cambridge, UK

Abstract

Biologists have long recognised that variation in the rates of evolution provides significant insights into the evolutionary process, both generally and for particular lineages. While the heat has gone out of the debate over two extremes, of gradualism and punctuated equilibrium, it remains the case that change is not spread evenly across the evolution of any lineage. The same is true for human evolution. However, for human evolution, not only do we have a solid fossil record, there is also direct and temporally-spatially fixed behavioural information from the archaeological record, and increasingly evidence from aDNA on the more recent phases. This allows us – uniquely for any lineage – to look at behaviour, phenotype and genetics to explore the relative positioning and significance of changes in any transitions that may have occurred. This paper explores this diversity of evidence to test the hypotheses that there were major evolutionary transitions in human evolution, when they occurred and the processes involved, and the relative roles of climate, environment and competition. Analytical units and events are: the radiation of the australopithecines in the Plio-Pleistocene, evolution of the genus Homo (3 – 2 Ma), the development of Homo erectus and allies (2 – 1 Ma), and the evolution of Homo sapiens (0.5 - 0 Ma). The conclusions will be used to consider a) the nature of speciation, extinction and diversity in hominin evolution; b) the role of behaviour in the evolutionary process.

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14:45-15:10 Discussion

15:35-16:10 Closing remarks

Professor Richard Leakey FRS, Turkana Basin Institute, Kenya

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16:10-17:00 Discussion

Major transitions in human evolution The Royal Society, London 6-9 Carlton House Terrace London SW1Y 5AG UK