2010 Vol 101.pdf (1.63mb) - Primate Society of Great Britain

produced by similar genetic changes, and if not, help identify species
specific adaptation. Genes linked to human microcephaly have received
much attention as they have accelerated evolutionary rates along lineages
leading to humans. However, the link between gene and brain evolution is
disputed. We analyzed the molecular evolution of four genes associated
with microcephaly (ASPM, CDK5RAP2, CENPJ, MCPH1) across 21
primates representing all major clades of anthropoids. We show that all four
loci have experienced positive selection across anthropoids. We found a
relationship between CDK5RAP2 and absolute neonatal brain mass, and
ASPM and absolute neonatal brain mass when a strong outlier, the
marmoset, was removed. We also found evidence for a weak association of
ASPM and CDK5RAP2 and adult brain size. The stronger association of
ASPM and CDK5RAP2 evolution with neonatal brain size than adult brain
size is consistent with a direct effect of these loci on neuronal proliferation,
which is plausibly related to their cellular functions in mitotic spindle
orientation. In contrast, we find no evidence linking CENPJ and MCPH1 to
either neonatal or adult brain size evolution. These results suggest ASPM
and CDK5RAP2 may have a conserved role in primate brain evolution.
Evolutionary encephalisation is not a general phenomenon in
mammals, but is common to socially bonded groups
S. Shultz
Institute for Cognitive and Evolutionary Anthropology, University of
Oxford
Across vertebrates, variation in total and relative brain size across mammals
is marked, and is proposed to have a functional basis because brains are
metabolically costly. Species should be expected to maximise the costbenefit
ratio of supporting costly tissues. A vast and expanding literature
has identified associations between relative brain size amongst extant
species and ecological and behavioural correlates including social
characteristics, ecological flexibility, resilience, innovation, social learning,
etc. However, a still unresolved question is how (and why) evolutionary
trends in encephalisation vary across taxonomic groups. This is for two
main reasons: 1) variation in extant species between and within groups is
commonly accepted as a measure of evolutionary trends, and 2) evaluating
allometric signals of encephalisation is notoriously contentious. In this talk,
I will discuss the insights from and limitations of current approaches to
estimating evolutionary encephalisation and propose a novel quantitative
macroevolutionary approach. In contrast to the conventional approach of
evaluating variation in extant species, I evaluated changes in relative brain
size within taxa as a function of first appearance dates. The results
challenge the conventional assumption that encephalisation is a general
trend within mammalian groups. For example some groups, such as
ruminants, felids and insectivores show no evidence of directional selection
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