scholarly journals Brain enlargement and dental reduction were not linked in hominin evolution

2017 ◽  
Vol 114 (3) ◽  
pp. 468-473 ◽  
Author(s):  
Aida Gómez-Robles ◽  
Jeroen B. Smaers ◽  
Ralph L. Holloway ◽  
P. David Polly ◽  
Bernard A. Wood
Keyword(s):  
Brain Size ◽  
Behavioral Changes ◽  
Modern Humans ◽  
Distinctive Features ◽  
Hominin Evolution ◽  
Large Brain ◽  
Dental Reduction ◽  
Selection For ◽  
Brain Reorganization ◽  
Evolutionary Simulations

The large brain and small postcanine teeth of modern humans are among our most distinctive features, and trends in their evolution are well studied within the hominin clade. Classic accounts hypothesize that larger brains and smaller teeth coevolved because behavioral changes associated with increased brain size allowed a subsequent dental reduction. However, recent studies have found mismatches between trends in brain enlargement and posterior tooth size reduction in some hominin species. We use a multiple-variance Brownian motion approach in association with evolutionary simulations to measure the tempo and mode of the evolution of endocranial and dental size and shape within the hominin clade. We show that hominin postcanine teeth have evolved at a relatively consistent neutral rate, whereas brain size evolved at comparatively more heterogeneous rates that cannot be explained by a neutral model, with rapid pulses in the branches leading to later Homo species. Brain reorganization shows evidence of elevated rates only much later in hominin evolution, suggesting that fast-evolving traits such as the acquisition of a globular shape may be the result of direct or indirect selection for functional or structural traits typical of modern humans.

scholarly journals Selection for brain size impairs innate, but not adaptive immune responses

2016 ◽  
Vol 283 (1826) ◽  
pp. 20152857 ◽  
Author(s):  
Alexander Kotrschal ◽  
Niclas Kolm ◽  
Dustin J. Penn
Keyword(s):  
Immune Responses ◽  
Poecilia Reticulata ◽  
Brain Size ◽  
Innate Immune Responses ◽  
Rejection Reaction ◽  
Trade Off ◽  
Large Brain ◽  
Rejection Response ◽  
Selection For ◽  
Acquired Immune Responses

Both the brain and the immune system are energetically demanding organs, and when natural selection favours increased investment into one, then the size or performance of the other should be reduced. While comparative analyses have attempted to test this potential evolutionary trade-off, the results remain inconclusive. To test this hypothesis, we compared the tissue graft rejection (an assay for measuring innate and acquired immune responses) in guppies ( Poecilia reticulata ) artificially selected for large and small relative brain size. Individual scales were transplanted between pairs of fish, creating reciprocal allografts, and the rejection reaction was scored over 8 days (before acquired immunity develops). Acquired immune responses were tested two weeks later, when the same pairs of fish received a second set of allografts and were scored again. Compared with large-brained animals, small-brained animals of both sexes mounted a significantly stronger rejection response to the first allograft. The rejection response to the second set of allografts did not differ between large- and small-brained fish. Our results show that selection for large brain size reduced innate immune responses to an allograft, which supports the hypothesis that there is a selective trade-off between investing into brain size and innate immunity.

scholarly journals Pattern and process in hominin brain size evolution are scale-dependent

2018 ◽  
Vol 285 (1873) ◽  
pp. 20172738 ◽  
Author(s):  
Andrew Du ◽  
Andrew M. Zipkin ◽  
Kevin G. Hatala ◽  
Elizabeth Renner ◽  
Jennifer L. Baker ◽  
...  
Keyword(s):  
Fossil Record ◽  
Brain Size ◽  
Exponential Model ◽  
Human Fossil ◽  
Hominin Evolution ◽  
Size Evolution ◽  
Large Brain ◽  
Quantitative Basis ◽  
Endocranial Volume ◽  
Subsequent Disappearance

A large brain is a defining feature of modern humans, yet there is no consensus regarding the patterns, rates and processes involved in hominin brain size evolution. We use a reliable proxy for brain size in fossils, endocranial volume (ECV), to better understand how brain size evolved at both clade- and lineage-level scales. For the hominin clade overall, the dominant signal is consistent with a gradual increase in brain size. This gradual trend appears to have been generated primarily by processes operating within hypothesized lineages—64% or 88% depending on whether one uses a more or less speciose taxonomy, respectively. These processes were supplemented by the appearance in the fossil record of larger-brained Homo species and the subsequent disappearance of smaller-brained Australopithecus and Paranthropus taxa. When the estimated rate of within-lineage ECV increase is compared to an exponential model that operationalizes generation-scale evolutionary processes, it suggests that the observed data were the result of episodes of directional selection interspersed with periods of stasis and/or drift; all of this occurs on too fine a timescale to be resolved by the current human fossil record, thus producing apparent gradual trends within lineages. Our findings provide a quantitative basis for developing and testing scale-explicit hypotheses about the factors that led brain size to increase during hominin evolution.

scholarly journals Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

2007 ◽  
Vol 362 (1480) ◽  
pp. 587-602 ◽  
Author(s):  
Richard C Connor
Keyword(s):  
Cognitive Abilities ◽  
Social Intelligence ◽  
Brain Size ◽  
Bottlenose Dolphins ◽  
Sperm Whale ◽  
Shark Bay ◽  
External Threats ◽  
Size Evolution ◽  
Large Brain ◽  
Selection For

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission–fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2–3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three ‘peaks’ of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.

scholarly journals Molecular evolutionary analysis of human primary microcephaly genes

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Nashaiman Pervaiz ◽  
Hongen Kang ◽  
Yiming Bao ◽  
Amir Ali Abbasi
Keyword(s):  
Evolutionary History ◽  
Genetic Basis ◽  
Brain Size ◽  
Primate Species ◽  
Evolutionary Analysis ◽  
Australopithecus Afarensis ◽  
Primary Microcephaly ◽  
Modern Humans ◽  
History Of ◽  
The Brain

Abstract Background There has been a rapid increase in the brain size relative to body size during mammalian evolutionary history. In particular, the enlarged and globular brain is the most distinctive anatomical feature of modern humans that set us apart from other extinct and extant primate species. Genetic basis of large brain size in modern humans has largely remained enigmatic. Genes associated with the pathological reduction of brain size (primary microcephaly-MCPH) have the characteristics and functions to be considered ideal candidates to unravel the genetic basis of evolutionary enlargement of human brain size. For instance, the brain size of microcephaly patients is similar to the brain size of Pan troglodyte and the very early hominids like the Sahelanthropus tchadensis and Australopithecus afarensis. Results The present study investigates the molecular evolutionary history of subset of autosomal recessive primary microcephaly (MCPH) genes; CEP135, ZNF335, PHC1, SASS6, CDK6, MFSD2A, CIT, and KIF14 across 48 mammalian species. Codon based substitutions site analysis indicated that ZNF335, SASS6, CIT, and KIF14 have experienced positive selection in eutherian evolutionary history. Estimation of divergent selection pressure revealed that almost all of the MCPH genes analyzed in the present study have maintained their functions throughout the history of placental mammals. Contrary to our expectations, human-specific adoptive evolution was not detected for any of the MCPH genes analyzed in the present study. Conclusion Based on these data it can be inferred that protein-coding sequence of MCPH genes might not be the sole determinant of increase in relative brain size during primate evolutionary history.

Brain size evolution in small mammals: test of the expensive tissue hypothesis

Mammalia ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ying Jiang ◽  
Jia Yu Wang ◽  
Xiao Fu Huang ◽  
Chun Lan Mai ◽  
Wen Bo Liao
Keyword(s):  
Small Mammals ◽  
Brain Size ◽  
Reproductive Investment ◽  
Generalized Least Squares ◽  
Offspring Number ◽  
Size Evolution ◽  
Large Brain ◽  
Species Evolution ◽  
The Cost ◽  
Expensive Tissue Hypothesis

Abstract Brain size exhibits significant changes within and between species. Evolution of large brains can be explained by the need to improve cognitive ability for processing more information in changing environments. However, brains are among the most energetically expensive organs. Enlarged brains can impose energetic demands that limit brain size evolution. The expensive tissue hypothesis (ETH) states that a decrease in the size of another expensive tissue, such as the gut, should compensate for the cost of a large brain. We studied the interplay between energetic limitations and brain size evolution in small mammals using phylogenetically generalized least squares (PGLS) regression analysis. Brain mass was not correlated with the length of the digestive tract in 37 species of small mammals after correcting for phylogenetic relationships and body size effects. We further found that the evolution of a large brain was not accompanied by a decrease in male reproductive investments into testes mass and in female reproductive investment into offspring number. The evolution of brain size in small mammals is inconsistent with the prediction of the ETH.

scholarly journals Homoplasy in the evolution of modern human-like joint proportions in Australopithecus afarensis

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Anjali M Prabhat ◽  
Catherine K Miller ◽  
Thomas Cody Prang ◽  
Jeffrey Spear ◽  
Scott A Williams ◽  
...  
Keyword(s):  
Upper Limb ◽  
Lower Limb ◽  
Modern Human ◽  
Homo Erectus ◽  
Australopithecus Afarensis ◽  
Modern Humans ◽  
Homo Habilis ◽  
Hominin Evolution ◽  
Parsimonious Explanation ◽  
Phylogenetic Hypotheses

The evolution of bipedalism and reduced reliance on arboreality in hominins resulted in larger lower limb joints relative to the joints of the upper limb. The pattern and timing of this transition, however, remains unresolved. Here, we find the limb joint proportions of Australopithecus afarensis, Homo erectus, and Homo naledi to resemble those of modern humans, whereas those of A. africanus, Australopithecus sediba, Paranthropus robustus, Paranthropus boisei, Homo habilis, and Homo floresiensis are more ape-like. The homology of limb joint proportions in A. afarensis and modern humans can only be explained by a series of evolutionary reversals irrespective of differing phylogenetic hypotheses. Thus, the independent evolution of modern human-like limb joint proportions in A. afarensis is a more parsimonious explanation. Overall, these results support an emerging perspective in hominin paleobiology that A. afarensis was the most terrestrially adapted australopith despite the importance of arboreality throughout much of early hominin evolution.

Seven Steps in the Evolution of the Human Imagination

2007 ◽  
Author(s):  
STEVEN MITHEN
Keyword(s):  
Cultural Change ◽  
Homo Sapiens ◽  
Brain Size ◽  
Modern Human ◽  
Clear Picture ◽  
Modern Humans ◽  
Creative Imagination ◽  
African Apes ◽  
Ways Of Thinking ◽  
Forms Of Knowledge

The modern human is a product of six million years of evolution wherein it is assumed that the ancestor of man resembles that of a chimpanzee. This assumption is based on the similarities of the ape-like brain size and post-cranial characteristics of the earliest hominid species to chimpanzees. Whilst it is unclear whether chimpanzees share the same foresight and contemplation of alternatives as with humans, it is nevertheless clear that chimpanzees lack creative imagination — an aspect of modern human imagination that sets humanity apart from its hominid ancestors. Creative imagination pertains to the ability to combine different forms of knowledge and ways of thinking to form creative and novel ideas. This chapter discusses seven critical steps in the evolution of the human imagination. These steps provide a clear picture of the gradual emergence of creative imagination in humans from their primitive origins as Homo sapiens some 200,000 years ago. This chronological evolution of the imaginative mind of humans involves both biological and cultural change that began soon after the divergence of the two lineages that led to modern humans and African apes.

Constraints on Social Networks

2010 ◽  
Author(s):  
Sam G. B. Roberts
Keyword(s):  
Social Networks ◽  
Social Relationships ◽  
Human Evolution ◽  
Upper Bound ◽  
Brain Size ◽  
Network Approach ◽  
Cognitive Constraints ◽  
Hominin Evolution ◽  
Over Time ◽  
Size And Structure

In both modern humans and non-human primates, time and cognitive constraints place an upper bound on the number of social relationships an individual can maintain at a given level of intensity. Similar constraints are likely to have operated throughout hominin evolution, shaping the size and structure of social networks. One of the key trends in human evolution, alongside an increase in brain size, is likely to have been an increase in group size, resulting in a larger number of social relationships that would have to be maintained over time. The network approach demonstrates that relationships should not be viewed as dyadic ties between two individuals, but as embedded within a larger network of ties between network members. Together with relationships based on kinship, this may have allowed for larger groups to be maintained among hominins than would be possible if such networks were based purely on dyadic ties between individuals.

scholarly journals Selection for reduced fear in red junglefowl changes brain composition and affects fear memory

2020 ◽  
Vol 7 (8) ◽  
pp. 200628
Author(s):  
Rebecca Katajamaa ◽  
Per Jensen
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Prior Experience ◽  
Fear Memory ◽  
Brain Regions ◽  
Preference Learning ◽  
Response To Selection ◽  
Red Junglefowl ◽  
Selection For ◽  
Region Size

Brain size reduction is a common trait in domesticated species when compared to wild conspecifics. This reduction can happen through changes in individual brain regions as a response to selection on specific behaviours. We selected red junglefowl for 10 generations for diverging levels of fear towards humans and measured brain size and composition as well as habituation learning and conditioned place preference learning in young chicks. Brain size relative to body size as well as brainstem region size relative to whole brain size were significantly smaller in chicks selected for low fear of humans compared to chicks selected for high fear of humans. However, when including allometric effects in the model, these differences disappear but a tendency towards larger cerebra in low-fear chickens remains. Low-fear line chicks habituated more effectively to a fearful stimulus with prior experience of that same stimulus, whereas high-fear line chicks with previous experience of the stimulus had a response similar to naive chicks. The phenotypical changes are in line with previously described effects of domestication.

Sign in / Sign up

Export Citation Format

Share Document