Biology subjects

Barton, R. A.

Publications and source records attributed to Barton, R. A..

4 recordsLinked to original sources

bioRxiv2024

The coevolution of encephalization and manual dexterity in hominins and other primates

The human hand is one of our most remarkable features. We have long, opposable thumbs and a suite of other features argued to be adaptations for interacting with and manipulating our environment, literally extending the reach of our cognitive powers. Consequently, enhanced manipulative dexterity, tool use and increased brain size are considered key features of how our ancestors evolved. This hypothesis predicts that anatomical dexterity and brain size co-evolved, and that this should be evident in the morphology of the hand. To test this hypothesis and to understand how hominin evolution may have deviated from any general primate trend, we collected a dataset of finger length, thumb length, and brain size across 94 extinct and extant species of primates. Using phylogenetic comparative methods, we reveal a strong primate-wide association between brain size and relative thumb length. We further demonstrate that this general association accurately predicts the co-evolution of these traits in hominins. Whilst hominins have significantly long thumbs compared to other primates, we infer that they have arisen from the same underlying evolutionary process acting across the whole primate order: increasing manipulative ability associated with specialized neural control processes. The relationships we recover are consistent with positive feedback between manipulation, tool use and cognition and therefore may go some way towards explaining evolutionary trends towards larger brain sizes among primates, and particularly in hominins. Our results emphasize the role of manipulative abilities in cognitive evolution and emphasize how neural and bodily adaptations are interconnected.

evolutionary biology↗

bioRxiv2024

Hominin brain size increase has emerged from within-species encephalization

The fact that rapid brain size increase was clearly a key aspect of human evolution has prompted many studies focussing on this phenomenon1-4, and many suggestions as to the underlying evolutionary patterns and processes5-10. No study to date has however separated out the contributions of change through time within-vs. between-hominin species whilst simultaneously incorporating effects of body size. Using a phylogenetic approach never applied before to palaeoanthropological data, we show that brain size increase across ~ 7 million years of hominin evolution arose from increases within individual species which account for an observed overall increase in relative brain size. Variation among species in brain size after accounting for this effect is associated with body mass differences but not time. In addition, our analysis also reveals that the within-species trend escalated in more recent lineages, implying an overall pattern of accelerating brain size increase through time.

paleontology↗

bioRxiv2023

Co-evolutionary dynamics of mammalian brain and body size

Despite decades of comparative studies, fundamental questions remain about how brain and body size co-evolved. Divergent explanations exist concurrently in the literature for phenomena such as variation in brain relative to body size, variability in the scaling relationship across taxonomic levels and between taxonomic groups, and purported evolutionary trends. Here we resolve these issues using a comprehensive dataset of brain and body masses across the mammal radiation, and a method enabling us to study brain relative to body mass evolution while estimating their evolutionary rates along the branches of a phylogeny. Contrary to the rarely questioned assumption of a log-linear relationship, we find that a curvilinear model best describes the evolutionary relationship between log brain mass and log body mass. This model greatly simplifies our understanding of mammalian brain-body co-evolution: it can simultaneously explain both the much-discussed taxon-level effect and variation in slopes and intercepts previously attributed to complex scaling patterns. We also document substantial variation in rates of relative brain mass evolution, with bursts of change scattered through the tree. General trends for increasing relative brain size over time are found in only three mammalian orders, with the most extreme case being primates, setting the stage for the uniquely rapid directional increase that ultimately produced the computational powers of the human brain.

evolutionary biology↗

bioRxiv2019

Maternal investment, life histories, and the evolution of brain structure in primates

Life history is a robust correlate of relative brain size: large-brained mammals and birds have slower life histories and longer lifespans than smaller-brained species. One influential adaptive hypothesis to account for this finding is the Cognitive Buffer Hypothesis (CBH). The CBH proposes that large brains permit greater behavioural flexibility and thereby buffer the animal from unpredictable environmental challenges, allowing reduced mortality and increased lifespan. In contrast, the Developmental Costs Hypothesis (DCH) suggests that life-history correlates of brain size reflect the extension of maturational processes needed to accommodate the evolution of large brains. The hypotheses are not mutually exclusive but do make different predictions. Here we test novel predictions of the hypotheses in primates: examining how the volume of brain components with different developmental trajectories correlate with relevant phases of maternal investment, juvenile period and post-maturational lifespan. Consistent with the DCH, structures with different allocations of growth to pre-natal versus post-natal development exhibit predictably divergent correlations with the associated periods of maternal investment and pre-maturational lifespan. Contrary to the CBH, adult lifespan is uncorrelated with either whole brain size or the size of individual brain components once duration of maternal investment is accounted for. Our results substantiate and elaborate on the role of maternal investment and offspring development in brain evolution, suggest that brain components can evolve partly independently through modifications of distinct developmental mechanisms, and imply that postnatal maturational processes involving interaction with the environment may be particularly crucial for the development of cerebellar function. They also provide an explanation for why apes have relatively extended maturation times, which relate to the relative expansion of the cerebellum in this clade.

evolutionary biology↗