Cargando…

Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis

BACKGROUND: Brain size is a key adaptive trait. It is often assumed that increasing brain size was a general evolutionary trend in primates, yet recent fossil discoveries have documented brain size decreases in some lineages, raising the question of how general a trend there was for brains to increa...

Descripción completa

Detalles Bibliográficos
Autores principales: Montgomery, Stephen H, Capellini, Isabella, Barton, Robert A, Mundy, Nicholas I
Formato: Texto
Lenguaje:English
Publicado: BioMed Central 2010
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2825212/
https://www.ncbi.nlm.nih.gov/pubmed/20105283
http://dx.doi.org/10.1186/1741-7007-8-9
_version_ 1782177794858418176
author Montgomery, Stephen H
Capellini, Isabella
Barton, Robert A
Mundy, Nicholas I
author_facet Montgomery, Stephen H
Capellini, Isabella
Barton, Robert A
Mundy, Nicholas I
author_sort Montgomery, Stephen H
collection PubMed
description BACKGROUND: Brain size is a key adaptive trait. It is often assumed that increasing brain size was a general evolutionary trend in primates, yet recent fossil discoveries have documented brain size decreases in some lineages, raising the question of how general a trend there was for brains to increase in mass over evolutionary time. We present the first systematic phylogenetic analysis designed to answer this question. RESULTS: We performed ancestral state reconstructions of three traits (absolute brain mass, absolute body mass, relative brain mass) using 37 extant and 23 extinct primate species and three approaches to ancestral state reconstruction: parsimony, maximum likelihood and Bayesian Markov-chain Monte Carlo. Both absolute and relative brain mass generally increased over evolutionary time, but body mass did not. Nevertheless both absolute and relative brain mass decreased along several branches. Applying these results to the contentious case of Homo floresiensis, we find a number of scenarios under which the proposed evolution of Homo floresiensis' small brain appears to be consistent with patterns observed along other lineages, dependent on body mass and phylogenetic position. CONCLUSIONS: Our results confirm that brain expansion began early in primate evolution and show that increases occurred in all major clades. Only in terms of an increase in absolute mass does the human lineage appear particularly striking, with both the rate of proportional change in mass and relative brain size having episodes of greater expansion elsewhere on the primate phylogeny. However, decreases in brain mass also occurred along branches in all major clades, and we conclude that, while selection has acted to enlarge primate brains, in some lineages this trend has been reversed. Further analyses of the phylogenetic position of Homo floresiensis and better body mass estimates are required to confirm the plausibility of the evolution of its small brain mass. We find that for our dataset the Bayesian analysis for ancestral state reconstruction is least affected by inclusion of fossil data suggesting that this approach might be preferable for future studies on other taxa with a poor fossil record.
format Text
id pubmed-2825212
institution National Center for Biotechnology Information
language English
publishDate 2010
publisher BioMed Central
record_format MEDLINE/PubMed
spelling pubmed-28252122010-02-20 Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis Montgomery, Stephen H Capellini, Isabella Barton, Robert A Mundy, Nicholas I BMC Biol Research article BACKGROUND: Brain size is a key adaptive trait. It is often assumed that increasing brain size was a general evolutionary trend in primates, yet recent fossil discoveries have documented brain size decreases in some lineages, raising the question of how general a trend there was for brains to increase in mass over evolutionary time. We present the first systematic phylogenetic analysis designed to answer this question. RESULTS: We performed ancestral state reconstructions of three traits (absolute brain mass, absolute body mass, relative brain mass) using 37 extant and 23 extinct primate species and three approaches to ancestral state reconstruction: parsimony, maximum likelihood and Bayesian Markov-chain Monte Carlo. Both absolute and relative brain mass generally increased over evolutionary time, but body mass did not. Nevertheless both absolute and relative brain mass decreased along several branches. Applying these results to the contentious case of Homo floresiensis, we find a number of scenarios under which the proposed evolution of Homo floresiensis' small brain appears to be consistent with patterns observed along other lineages, dependent on body mass and phylogenetic position. CONCLUSIONS: Our results confirm that brain expansion began early in primate evolution and show that increases occurred in all major clades. Only in terms of an increase in absolute mass does the human lineage appear particularly striking, with both the rate of proportional change in mass and relative brain size having episodes of greater expansion elsewhere on the primate phylogeny. However, decreases in brain mass also occurred along branches in all major clades, and we conclude that, while selection has acted to enlarge primate brains, in some lineages this trend has been reversed. Further analyses of the phylogenetic position of Homo floresiensis and better body mass estimates are required to confirm the plausibility of the evolution of its small brain mass. We find that for our dataset the Bayesian analysis for ancestral state reconstruction is least affected by inclusion of fossil data suggesting that this approach might be preferable for future studies on other taxa with a poor fossil record. BioMed Central 2010-01-27 /pmc/articles/PMC2825212/ /pubmed/20105283 http://dx.doi.org/10.1186/1741-7007-8-9 Text en Copyright ©2010 Montgomery et al; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
spellingShingle Research article
Montgomery, Stephen H
Capellini, Isabella
Barton, Robert A
Mundy, Nicholas I
Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis
title Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis
title_full Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis
title_fullStr Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis
title_full_unstemmed Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis
title_short Reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and Homo floresiensis
title_sort reconstructing the ups and downs of primate brain evolution: implications for adaptive hypotheses and homo floresiensis
topic Research article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2825212/
https://www.ncbi.nlm.nih.gov/pubmed/20105283
http://dx.doi.org/10.1186/1741-7007-8-9
work_keys_str_mv AT montgomerystephenh reconstructingtheupsanddownsofprimatebrainevolutionimplicationsforadaptivehypothesesandhomofloresiensis
AT capelliniisabella reconstructingtheupsanddownsofprimatebrainevolutionimplicationsforadaptivehypothesesandhomofloresiensis
AT bartonroberta reconstructingtheupsanddownsofprimatebrainevolutionimplicationsforadaptivehypothesesandhomofloresiensis
AT mundynicholasi reconstructingtheupsanddownsofprimatebrainevolutionimplicationsforadaptivehypothesesandhomofloresiensis