scholarly journals Brain evolution and development: adaptation, allometry and constraint

2016 ◽  
Vol 283 (1838) ◽  
pp. 20160433 ◽  
Author(s):  
Stephen H. Montgomery ◽  
Nicholas I. Mundy ◽  
Robert A. Barton
Keyword(s):  
Body Size ◽  
Natural Selection ◽  
Comparative Studies ◽  
Brain Evolution ◽  
Phenotypic Traits ◽  
Functional Constraints ◽  
Developmental Constraints ◽  
Functional Systems ◽  
Evolution And Development ◽  
Developmental Mechanisms

Phenotypic traits are products of two processes: evolution and development. But how do these processes combine to produce integrated phenotypes? Comparative studies identify consistent patterns of covariation, or allometries, between brain and body size, and between brain components, indicating the presence of significant constraints limiting independent evolution of separate parts. These constraints are poorly understood, but in principle could be either developmental or functional. The developmental constraints hypothesis suggests that individual components (brain and body size, or individual brain components) tend to evolve together because natural selection operates on relatively simple developmental mechanisms that affect the growth of all parts in a concerted manner. The functional constraints hypothesis suggests that correlated change reflects the action of selection on distributed functional systems connecting the different sub-components, predicting more complex patterns of mosaic change at the level of the functional systems and more complex genetic and developmental mechanisms. These hypotheses are not mutually exclusive but make different predictions. We review recent genetic and neurodevelopmental evidence, concluding that functional rather than developmental constraints are the main cause of the observed patterns.

Brain evolution: How constrained is it?

2001 ◽  
Vol 24 (2) ◽  
pp. 296-297
Author(s):  
Georg F. Striedter
Keyword(s):  
Body Size ◽  
Brain Evolution ◽  
Developmental Constraints ◽  
Similar Body ◽  
Taxonomic Groups

Allometric analyses suggest that there are some developmental constraints on brain evolution. However, when one compares animals of similar body size, these constraints do not appear to be very tight. Moreover, the constraints often differ between taxonomic groups. Therefore, one may ask not only what causes developmental constraints but also how (and why) these constraints might be altered (or circumvented) during the course of evolution.

scholarly journals Why call it developmental bias when it is just development?

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Isaac Salazar-Ciudad
Keyword(s):  
Natural Selection ◽  
Morphological Variation ◽  
Morphological Evolution ◽  
Developmental Constraints ◽  
Evolution And Development ◽  
Different Types ◽  
Change Of Perspective ◽  
Opinion Article ◽  
Main Factor

AbstractThe concept of developmental constraints has been central to understand the role of development in morphological evolution. Developmental constraints are classically defined as biases imposed by development on the distribution of morphological variation.This opinion article argues that the concepts of developmental constraints and developmental biases do not accurately represent the role of development in evolution. The concept of developmental constraints was coined to oppose the view that natural selection is all-capable and to highlight the importance of development for understanding evolution. In the modern synthesis, natural selection was seen as the main factor determining the direction of morphological evolution. For that to be the case, morphological variation needs to be isotropic (i.e. equally possible in all directions). The proponents of the developmental constraint concept argued that development makes that some morphological variation is more likely than other (i.e. variation is not isotropic), and that, thus, development constraints evolution by precluding natural selection from being all-capable.This article adds to the idea that development is not compatible with the isotropic expectation by arguing that, in fact, it could not be otherwise: there is no actual reason to expect that development could lead to isotropic morphological variation. It is then argued that, since the isotropic expectation is untenable, the role of development in evolution should not be understood as a departure from such an expectation. The role of development in evolution should be described in an exclusively positive way, as the process determining which directions of morphological variation are possible, instead of negatively, as a process precluding the existence of morphological variation we have no actual reason to expect.This article discusses that this change of perspective is not a mere question of semantics: it leads to a different interpretation of the studies on developmental constraints and to a different research program in evolution and development. This program does not ask whether development constrains evolution. Instead it asks questions such as, for example, how different types of development lead to different types of morphological variation and, together with natural selection, determine the directions in which different lineages evolve.

scholarly journals Morphological diversification in different trematode lineages: body size, host type, or time?

Parasitology ◽  
2009 ◽  
Vol 136 (1) ◽  
pp. 85-92 ◽  
Author(s):  
R. POULIN
Keyword(s):  
Body Size ◽  
Morphological Variation ◽  
The Body ◽  
Phenotypic Traits ◽  
Developmental Constraints ◽  
Anatomical Structures ◽  
Morphological Diversification ◽  
The Family ◽  
Phenotypic Diversification ◽  
Average Body

SUMMARYDifferent lineages experience different rates of phenotypic diversification, resulting in greater or lower variance in the expression of phenotypic traits among the species within a lineage. Here, morphological diversification is investigated in 14 different trematode families, based on a dataset comprising morphometric data on body size and 4 anatomical structures (oral sucker, ventral sucker, pharynx, cirrus sac) from 386 species. Three hypotheses are tested and subsequently rejected based on the empirical evidence. First, the degree of morphological variation in all traits within a trematode family, measured as the coefficient of variation among species, appears independent of the average body size of species belonging to that family. Second, patterns of morphological diversification appear similar whether endothermic or ectothermic vertebrates are used as definitive hosts. Third, phylogenetically older trematode lineages did not display greater morphological variation than younger, more derived ones, ruling out evolutionary time as an explanation. The results are consistent with developmental constraints acting on morphological diversification, since for some pairs of traits, variation in one trait is not independent of variation in another trait. More importantly, across most families, variation in body size was significantly more pronounced than variation in the relative sizes of the other morphological features. Trematode body size therefore varies widely while the general body architecture of the family is maintained. The fact that the evolution of the body plan is more conservative than that of body size suggests that the range of morphologies that can evolve in trematodes is constrained.

scholarly journals Independent evolution towards larger body size in the distinctive Faroe Island mice

2021 ◽  
Author(s):  
Ricardo Wilches ◽  
William H Beluch ◽  
Ellen McConnell ◽  
Diethard Tautz ◽  
Yingguang Frank Chan
Keyword(s):  
Body Size ◽  
Meta Analysis ◽  
Small Body ◽  
Laboratory Mouse ◽  
Large Body ◽  
Natural Populations ◽  
Size Variation ◽  
Phenotypic Traits ◽  
Island Population ◽  
Multiple Loci

Abstract Most phenotypic traits in nature involve the collective action of many genes. Traits that evolve repeatedly are particularly useful for understanding how selection may act on changing trait values. In mice, large body size has evolved repeatedly on islands and under artificial selection in the laboratory. Identifying the loci and genes involved in this process may shed light on the evolution of complex, polygenic traits. Here, we have mapped the genetic basis of body size variation by making a genetic cross between mice from the Faroe Islands, which are among the largest and most distinctive natural populations of mice in the world, and a laboratory mouse strain selected for small body size, SM/J. Using this F2 intercross of 841 animals, we have identified 111 loci controlling various aspects of body size, weight and growth hormone levels. By comparing against other studies, including the use of a joint meta-analysis, we found that the loci involved in the evolution of large size in the Faroese mice were largely independent from those of a different island population or other laboratory strains. We hypothesize that colonization bottleneck, historical hybridization, or the redundancy between multiple loci have resulted in the Faroese mice achieving an outwardly similar phenotype through a distinct evolutionary path.

Natural Selection on Beak and Body Size in the Song Sparrow

Evolution ◽  
1986 ◽  
Vol 40 (2) ◽  
pp. 221 ◽  
Author(s):  
Dolph Schluter ◽  
James N. M. Smith
Keyword(s):  
Body Size ◽  
Natural Selection ◽  
Song Sparrow

Evidence for divergent natural selection of a Lake Tanganyika cichlid inferred from repeated radiations in body size

2009 ◽  
Vol 18 (14) ◽  
pp. 3110-3119 ◽  
Author(s):  
T. TAKAHASHI ◽  
K. WATANABE ◽  
H. MUNEHARA ◽  
L. RÜBER ◽  
M. HORI
Keyword(s):  
Body Size ◽  
Natural Selection ◽  
Lake Tanganyika ◽  
Divergent Natural Selection ◽  
Selection Of

scholarly journals Allometry unleashed: an adaptationist approach of brain scaling in mammalian evolution

2019 ◽  
Author(s):  
Romain Willemet
Keyword(s):  
Body Size ◽  
Allometric Scaling ◽  
Species Differences ◽  
Brain Size ◽  
Brain Evolution ◽  
Neural Systems ◽  
Selection Pressures ◽  
Number Of Factors ◽  
Functional Consequences ◽  
Main Factor

The idea that allometry in the context of brain evolution mainly result from constraints channelling the scaling of brain components is deeply embedded in the field of comparative neurobiology. Constraints, however, only prevent or limit changes, and cannot explain why these changes happen in the first place. In fact, considering allometry as a lack of change may be one of the reasons why, after more than a century of research, there is still no satisfactory explanatory framework for the understanding of species differences in brain size and composition in mammals. The present paper attempts to tackle this issue by adopting an adaptationist approach to examine the factors behind the evolution of brain components. In particular, the model presented here aims to explain the presence of patterns of covariation among brain components found within major taxa, and the differences between taxa. The key determinant of these patterns of covariation within a taxon-cerebrotype (groups of species whose brains present a number of similarities at the physiological and anatomical levels) seems to be the presence of taxon-specific patterns of selection pressures targeting the functional and structural properties of neural components or systems. Species within a taxon share most of the selection pressures, but their levels scale with a number of factors that are often related to body size. The size and composition of neural systems respond to these selection pressures via a number of evolutionary scenarios, which are discussed here. Adaptation, rather than, as generally assumed, developmental or functional constraints, thus appears to be the main factor behind the allometric scaling of brain components. The fact that the selection pressures acting on the size of brain components form a pattern that is specific to each taxon accounts for the peculiar relationship between body size, brain size and composition, and behavioural capabilities characterizing each taxon. While it is important to avoid repeating the errors of the “Panglossian paradigm”, the elements presented here suggests that an adaptationist approach may shed a new light on the factors underlying, and the functional consequences of, species differences in brain size and composition.

scholarly journals WHATEVER YOU WANT: INCONSISTENT RESULTS IS THE RULE, NOT THE EXCEPTION, IN THE STUDY OF PRIMATE BRAIN EVOLUTION

2018 ◽  
Author(s):  
Andreas Wartel ◽  
Patrik Lindenfors ◽  
Johan Lind
Keyword(s):  
Body Size ◽  
Brain Evolution ◽  
Data Sets ◽  
Data Set ◽  
Scientific Rigor ◽  
Explanatory Variables ◽  
Primate Brain ◽  
Residual Variation ◽  
The Many ◽  
Brain Data

AbstractPrimate brains differ in size and architecture. Hypotheses to explain this variation are numerous and many tests have been carried out. However, after body size has been accounted for there is little left to explain. The proposed explanatory variables for the residual variation are many and covary, both with each other and with body size. Further, the data sets used in analyses have been small, especially in light of the many proposed predictors. Here we report the complete list of models that results from exhaustively combining six commonly used predictors of brain and neocortex size. This provides an overview of how the output from standard statistical analyses changes when the inclusion of different predictors is altered. By using both the most commonly tested brain data set and a new, larger data set, we show that the choice of included variables fundamentally changes the conclusions as to what drives primate brain evolution. Our analyses thus reveal why studies have had troubles replicating earlier results and instead have come to such different conclusions. Although our results are somewhat disheartening, they highlight the importance of scientific rigor when trying to answer difficult questions. It is our position that there is currently no empirical justification to highlight any particular hypotheses, of those adaptive hypotheses we have examined here, as the main determinant of primate brain evolution.

The naked ape as an evolutionary model, 50 years later

2018 ◽  
Vol 68 (3) ◽  
pp. 227-246
Author(s):  
Nico M. van Straalen
Keyword(s):  
Natural Selection ◽  
Evolutionary Biology ◽  
Evolutionary Model ◽  
Developmental Constraints ◽  
Body Hair ◽  
Product Evolution ◽  
Adaptive Explanation ◽  
History Of ◽  
Popular Texts ◽  
The Brain

AbstractEvolution acts through a combination of four different drivers: (1) mutation, (2) selection, (3) genetic drift, and (4) developmental constraints. There is a tendency among some biologists to frame evolution as the sole result of natural selection, and this tendency is reinforced by many popular texts. “The Naked Ape” by Desmond Morris, published 50 years ago, is no exception. In this paper I argue that evolutionary biology is much richer than natural selection alone. I illustrate this by reconstructing the evolutionary history of five different organs of the human body: foot, pelvis, scrotum, hand and brain. Factors like developmental tinkering, by-product evolution, exaptation and heterochrony are powerful forces for body-plan innovations and the appearance of such innovations in human ancestors does not always require an adaptive explanation. While Morris explained the lack of body hair in the human species by sexual selection, I argue that molecular tinkering of regulatory genes expressed in the brain, followed by positive selection for neotenic features, may have been the driving factor, with loss of body hair as a secondary consequence.

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