High Encephalization in a Fossil Rorqual Illuminates Baleen Whale Brain Evolution

2021 ◽  
pp. 1-13
Author(s):  
Michelangelo Bisconti ◽  
Riccardo Daniello ◽  
Piero Damarco ◽  
Giandonato Tartarelli ◽  
Marco Pavia ◽  
...  
Keyword(s):  
Motor Behavior ◽  
Brain Size ◽  
Morphological Evolution ◽  
Brain Evolution ◽  
Cultural Learning ◽  
Behavioral Repertoire ◽  
Size Change ◽  
Fossil Species ◽  
Baleen Whales ◽  
The Brain

Baleen whales are considered underencephalized mammals due to their reduced brain size with respect to their body size (encephalization quotient [EQ] &#x3c;&#x3c; 1). Despite their low EQ, mysticetes exhibit complex behavioral patterns in terms of motor abilities, vocal repertoire, and cultural learning. Very scarce information is available about the morphological evolution of the brain in this group; this makes it difficult to investigate the historical changes in brain shape and size in order to relate the origin of the complex mysticete behavioral repertoire to the evolution of specific neural substrates. Here, the first description of the virtual endocast of a fossil balaenopterid species, <i>Marzanoptera tersillae</i> from the Italian Pliocene, reveals an EQ of around 3, which is exceptional for baleen whales. The endocast showed a morphologically different organization of the brain in this fossil whale as the cerebral hemispheres are anteroposteriorly shortened, the cerebellum lacks the posteromedial expansion of the cerebellar hemispheres, and the cerebellar vermis is unusually reduced. The comparative reductions of the cerebral and cerebellar hemispheres suggest that the motor behavior of <i>M. tersillae</i> probably was less sophisticated than that exhibited by the extant rorqual and humpback species. The presence of an EQ value in this fossil species that is around 10 times higher than that of extant mysticetes opens new questions about brain evolution and provides new, invaluable information about the evolutionary path of morphological and size change in the brain of baleen whales.

scholarly journals Rethinking the Effects of Body Size on the Study of Brain Size Evolution

2019 ◽  
Vol 93 (4) ◽  
pp. 182-195 ◽  
Author(s):  
Enrique Font ◽  
Roberto García-Roa ◽  
Daniel Pincheira-Donoso ◽  
Pau Carazo
Keyword(s):  
Body Size ◽  
Brain Size ◽  
Size Variation ◽  
Brain Evolution ◽  
Scaling Effects ◽  
Selection Pressures ◽  
Body Tissues ◽  
Relative Brain Size ◽  
Functional Components ◽  
The Brain

Body size correlates with most structural and functional components of an organism’s phenotype – brain size being a prime example of allometric scaling with animal size. Therefore, comparative studies of brain evolution in vertebrates rely on controlling for the scaling effects of body size variation on brain size variation by calculating brain weight/body weight ratios. Differences in the brain size-body size relationship between taxa are usually interpreted as differences in selection acting on the brain or its components, while selection pressures acting on body size, which are among the most prevalent in nature, are rarely acknowledged, leading to conflicting and confusing conclusions. We address these problems by comparing brain-body relationships from across >1,000 species of birds and non-avian reptiles. Relative brain size in birds is often assumed to be 10 times larger than in reptiles of similar body size. We examine how differences in the specific gravity of body tissues and in body design (e.g., presence/absence of a tail or a dense shell) between these two groups can affect estimates of relative brain size. Using phylogenetic comparative analyses, we show that the gap in relative brain size between birds and reptiles has been grossly exaggerated. Our results highlight the need to take into account differences between taxa arising from selection pressures affecting body size and design, and call into question the widespread misconception that reptile brains are small and incapable of supporting sophisticated behavior and cognition.

Regional selection of the brain size regulating gene CASC5 provides new insight into human brain evolution

2016 ◽  
Vol 136 (2) ◽  
pp. 193-204 ◽  
Author(s):  
Lei Shi ◽  
Enzhi Hu ◽  
Zhenbo Wang ◽  
Jiewei Liu ◽  
Jin Li ◽  
...  
Keyword(s):  
Human Brain ◽  
Brain Size ◽  
Brain Evolution ◽  
Human Brain Evolution ◽  
The Brain ◽  
Insight Into ◽  
Selection Of

Brain evolution in Homo: The “radiator” theory

1990 ◽  
Vol 13 (2) ◽  
pp. 333-344 ◽  
Author(s):  
Dean Falk
Keyword(s):  
Jugular Vein ◽  
Brain Size ◽  
Brain Evolution ◽  
Hominid Evolution ◽  
The Other ◽  
Early Hominids ◽  
Emissary Veins ◽  
Intense Solar Radiation ◽  
The Brain ◽  
Mosaic Habitats

AbstractThe “radiator” theory of brain evolution is proposed to account for “mosaic evolution” whereby brain size began to increase rapidly in the genus Homo well over a million years after bipedalism had been selected for in early hominids. Because hydrostatic pressures differ across columns of fluid depending on orientation (posture), vascular systems of early bipeds became reoriented so that cranial blood flowed preferentially to the vertebral plexus instead of the internal jugular vein in response to gravity. The Hadar early hominids and robust australopithecines partly achieved this reorientation with a dramatically enlarged occipital/marginal sinus system. On the other hand, hominids in the gracile australopithecine through Homo lineage delivered blood to the vertebral plexus via a widespread network of veins that became more elaborate through time. Mastoid and parietal emissary veins are representatives of this network, and increases in their frequencies during hominid evolution are indicative of its development. Brain size increased with increased frequencies of mastoid and parietal emissary veins in the lineage leading to and including Homo, but remained conservative in the robust australopithecine lineage that lacked the network of veins. The brain is an extremely heatsensitive organ and emissary veins in humans have been shown to cool the brain under conditions of hyperthermia. Thus, the network of veins in the lineage leading to Homo acted as a radiator that released a thermal constraint on brain size. The radiator theory is in keeping with the belief that basal gracile and basal robust australopithecines occupied distinct niches, with the former living in savanna mosaic habitats that were subject to hot temperatures and intense solar radiation during the day.

scholarly journals The impact of locomotion on the brain evolution of squirrels and close relatives

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Ornella C. Bertrand ◽  
Hans P. Püschel ◽  
Julia A. Schwab ◽  
Mary T. Silcox ◽  
Stephen L. Brusatte
Keyword(s):  
Body Mass ◽  
Brain Size ◽  
Brain Evolution ◽  
Olfactory Bulbs ◽  
Component Size ◽  
Highly Correlated ◽  
Close Relatives ◽  
The Impact ◽  
The Brain ◽  
Opposing Effect

AbstractHow do brain size and proportions relate to ecology and evolutionary history? Here, we use virtual endocasts from 38 extinct and extant rodent species spanning 50+ million years of evolution to assess the impact of locomotion, body mass, and phylogeny on the size of the brain, olfactory bulbs, petrosal lobules, and neocortex. We find that body mass and phylogeny are highly correlated with relative brain and brain component size, and that locomotion strongly influences brain, petrosal lobule, and neocortical sizes. Notably, species living in trees have greater relative overall brain, petrosal lobule, and neocortical sizes compared to other locomotor categories, especially fossorial taxa. Across millions of years of Eocene-Recent environmental change, arboreality played a major role in the early evolution of squirrels and closely related aplodontiids, promoting the expansion of the neocortex and petrosal lobules. Fossoriality in aplodontiids had an opposing effect by reducing the need for large brains.

scholarly journals The evolution of brain size among the Homininae and selection at ASPM and MCPH1 genes

2021 ◽  
Vol 2 (2) ◽  
pp. 293-310
Author(s):  
Sandra Leyva-Hernández ◽  
Ricardo Fong-Zazueta ◽  
Luis Medrano-González ◽  
Ana Julia Aguirre-Samudio
Keyword(s):  
Positive Selection ◽  
Nucleotide Substitution ◽  
Brain Size ◽  
Phylogenetic Analyses ◽  
Evolutionary Relationship ◽  
Brain Evolution ◽  
Haplotype Blocks ◽  
Accelerated Evolution ◽  
Relationship Of ◽  
The Brain

We examined the evolutionary relationship of the ASPM (abnormal spindle-like microcephaly associated) and MCPH1 (microcephalin-1) genes with brain volume among humans and other primates. We obtained sequences of these genes from 14 simiiform species including hominins. Two phylogenetic analyses of ASPM exon 3 and MCPH1 exons 8 and 11 were performed to maximize taxon sampling or sequence extension to compare the nucleotide substitution and encephalization rates, and examine signals of selection. Further assessment of selection among humans was done through the analysis of non-synonymous and synonymous substitutions (dN/dS), and linkage disequilibrium (LD) patterns. We found that the accelerated evolution of brain size in hominids, is related to synchronic acceleration in the substitution rates of ASPM and MCPH1, and to signals of positive selection, especially in hominins. The dN/dS and LD analyses in Homo detected sites under positive selection and some regions with haplotype blocks at several candidate sites surrounded by blocks in LD-equilibrium. Accelerations and signals of positive selection in ASPM and MCPH1 occurred in different lineages and periods being ASPM more closely related with the brain evolution of hominins. MCPH1 evolved under positive selection in different lineages of the Catarrhini, suggesting independent evolutionary roles of this gene among primates.

The Evolution of Intelligence

2018 ◽  
pp. 123-149
Author(s):  
Kevin N. Laland
Keyword(s):  
Social Learning ◽  
Brain Size ◽  
Brain Evolution ◽  
Human Mind ◽  
Feedback Mechanism ◽  
Eminent Scientist ◽  
Cultural Processes ◽  
The Brain ◽  
Size And Structure ◽  
Complex Organ

This chapter fleshes out the “cultural drive” hypothesis proposed by eminent scientist Allan Wilson. It first considers the question of exactly how social learning could drive brain evolution when some animals managed to copy with tiny brains. Greater specification of the feedback mechanism by which cultural processes fostered the evolution of cognition was required if the argument was to be compelling. Second, the chapter looks at how many variables (e.g., diet, social complexity, latitude) had been shown to be associated with brain size in primates. In order to evaluate the hypothesis that cultural processes had played a particularly central role in the evolution of the human mind, whether social learning was a genuine cause of brain evolution must first be established. Third, the chapter argues that talk of increases in “brain size” is rather simplistic. The brain is a complex organ with extensive substructure, and with particular features and circuitry known to be important to specific biological functions. How the brain had changed over evolutionary time, and whether the observed changes in size and structure were consistent with what the cultural drive hypothesis predicted, also had to be established.

Vertebrate Evolution and Movement

2018 ◽  
Vol 3 (04) ◽  
Author(s):  
Sherrondria Buchanan
Keyword(s):  
Comparative Studies ◽  
Size Range ◽  
Brain Size ◽  
Brain Evolution ◽  
Processing Capacity ◽  
Primate Brain ◽  
Complex Organization ◽  
Architectural Principles ◽  
The Brain ◽  
Organizing Principles

Comparative studies of the brain in vertebrates suggest that there are general architectural principles leading to its development and overall improvement. We are beginning to understand the geometric, biophysical and energy constraints that have contributed to the progression and practical organization of the brain. The object of this review is to present current perspectives on primate brain evolution, and to examine some hypothetical organizing principles that underlie the brain's complex organization. It is shown that the development of the cortex coordinates folding with connectivity in a way that produces smaller and faster brains. It will be discussed that at a brain size of about 3500 cm3, equivalent to a brain that is two to three times larger than the modern man, the brain seems to reach its maximum processing capacity. As the brain grows larger than this particular size range, it becomes less proficient it will ultimately restrict any improvement and overall function.

scholarly journals Hominin cognitive evolution: identifying patterns and processes in the fossil and archaeological record

2012 ◽  
Vol 367 (1599) ◽  
pp. 2130-2140 ◽  
Author(s):  
Susanne Shultz ◽  
Emma Nelson ◽  
Robin I. M. Dunbar
Keyword(s):  
Homo Sapiens ◽  
Brain Size ◽  
Rapid Change ◽  
Brain Evolution ◽  
Homo Erectus ◽  
Human Cognition ◽  
Archaeological Record ◽  
Size Change ◽  
Gradual Process ◽  
Patterns And Processes

As only limited insight into behaviour is available from the archaeological record, much of our understanding of historical changes in human cognition is restricted to identifying changes in brain size and architecture. Using both absolute and residual brain size estimates, we show that hominin brain evolution was likely to be the result of a mix of processes; punctuated changes at approximately 100 kya, 1 Mya and 1.8 Mya are supplemented by gradual within-lineage changes in Homo erectus and Homo sapiens sensu lato . While brain size increase in Homo in Africa is a gradual process, migration of hominins into Eurasia is associated with step changes at approximately 400 kya and approximately 100 kya. We then demonstrate that periods of rapid change in hominin brain size are not temporally associated with changes in environmental unpredictability or with long-term palaeoclimate trends. Thus, we argue that commonly used global sea level or Indian Ocean dust palaeoclimate records provide little evidence for either the variability selection or aridity hypotheses explaining changes in hominin brain size. Brain size change at approximately 100 kya is coincident with demographic change and the appearance of fully modern language. However, gaps remain in our understanding of the external pressures driving encephalization, which will only be filled by novel applications of the fossil, palaeoclimatic and archaeological records.

scholarly journals Interactions between neuroanatomy, cognition, and ecology in Anolis lizards

2021 ◽  
Author(s):  
◽  
Levi Storks
Keyword(s):  
Habitat Complexity ◽  
Brain Size ◽  
Behavioral Flexibility ◽  
Brain Evolution ◽  
Natural Environments ◽  
Natural Conditions ◽  
Neuron Number ◽  
Neuron Density ◽  
The Brain

The interactions between an organism and its environment are mediated by cognition, the substrates of which are in the brain. Cognition is ubiquitous across vertebrates, yet we still know very little about the factors shaping its evolution, particularly outside of birds and mammals. In natural environments, cognition likely impacts organism fitness. Behavioral flexibility, which enables an animal to modulate its behavior to match its environment, may facilitate success in novel habitats, such as in dispersal to islands, biotic invasions, and urban adaptation. Cognitive specializations may also be associated with specific ecological traits, such as habitat complexity. Furthermore, our understanding of the neural substrates of cognition in the brain is primarily limited to studies of relative brain size. The first chapter provides a more in depth introduction to these topics. In this dissertation, I explore the interactions between cognition, neuroanatomy, and ecology in Anolis lizards. Anolis lizards exhibit a diversity of habitat specializations, which is the result of adaptive radiation in the West Indies. As mentioned above, cognitive mechanisms in anoles may play a role in adjusting to novel environments and exploiting new niches. In the second chapter, I modified a detour task to evaluate whether wild, free-living Anolis sagrei can solve a novel detour problem under natural conditions. In the second chapter, I compare the neuron and nonneuron number and density of Anolis cristatellus and Anolis evermanni to see whether differences in neuroanatomy reflect their differential performance on an extractive foraging task. I also explore how these data relate to published observations from other vertebrates. Finally, in the fourth chapter I expand upon two previous studies by evaluating whether neuron number follows the predictions of concerted or mosaic evolution in five species of Puerto Rican Anolis and whether habitat complexity explains differences in neuron density between species. I conclude in the final chapter by summarizing my results and outlining future directions. Taken together, the results presented in this dissertation demonstrate the potential for studying cognition and neuroanatomy in an evolutionary context. The methods applied in my second chapter can be used in the future to explore the connection between cognition and fitness in lizards, which are a tractable model for such studies under natural conditions. My third and fourth chapters took a novel approach by studying neuroanatomical differences between species in neuron number and density, and generated novel insights into brain evolution in Anolis. By studying cognition and the brain in lizards and other ectotherms, we can begin to finally understand factors shaping the evolution of cognition and neuroanatomy across vertebrates.

scholarly journals Peeking Inside the Lizard Brain: Neuron Numbers in Anolis and Its Implications for Cognitive Performance and Vertebrate Brain Evolution

2020 ◽  
Author(s):  
Levi Storks ◽  
Brian J Powell ◽  
Manuel Leal
Keyword(s):  
Cognitive Performance ◽  
Brain Size ◽  
Motor Task ◽  
Behavioral Flexibility ◽  
Brain Evolution ◽  
Relative Mass ◽  
Published Data ◽  
Vertebrate Brain ◽  
Isotropic Fractionator ◽  
The Brain

Abstract Studies of vertebrate brain evolution have mainly focused on measures of brain size, particularly relative mass and its allometric scaling across lineages, commonly with the goal of identifying the substrates that underly differences in cognition. However, recent studies on birds and mammals have demonstrated that brain size is an imperfect proxy for neuronal parameters that underly function, such as the number of neurons that make up a given brain region. Here we present estimates of neuron numbers and density in two species of lizard, Anolis cristatellus and A. evermanni, representing the first such data from squamate species, and explore its implications for differences in cognitive performance and vertebrate brain evolution. The isotropic fractionator protocol outlined in this article is optimized for the unique challenges that arise when using this technique with lineages having nucleated erythrocytes and relatively small brains. The number and density of neurons and other cells we find in Anolis for the telencephalon, cerebellum, and the rest of the brain (ROB) follow similar patterns as published data from other vertebrate species. Anolis cristatellus and A. evermanni exhibited differences in their performance in a motor task frequently used to evaluate behavioral flexibility, which was not mirrored by differences in the number, density, or proportion of neurons in either the cerebellum, telencephalon, or ROB. However, the brain of A. evermanni had a significantly higher number of nonneurons and a higher nonneuron to neuron ratio across the whole brain, which could contribute to the observed differences in problem solving between A. cristatellus and A. evermanni. Although limited to two species, our findings suggest that neuron number and density in lizard brains scale similarly to endothermic vertebrates in contrast to the differences observed in brain to body mass relationships. Data from a wider range of species are necessary before we can fully understand vertebrate brain evolution at the neuronal level.

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