The Sexual Brain

2021 ◽  
pp. 81-108
Author(s):  
Susan D. Healy
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Brain Size ◽  
Female Mate Choice ◽  
Brain Regions ◽  
Good Evidence ◽  
The Other ◽  
Female Mate ◽  
Males And Females ◽  
Hippocampal Structure

Morphological and behavioural differences between the sexes are ubiquitous across the animal kingdom. There is also good evidence for differences in some brain regions between males and females, in humans, some rodents, and many songbirds. I look at the data for sex differences in cognition, of which there are some that show differences in spatial cognition and in hippocampal structure, at least some of which may be explained by variation in hormone levels. The thesis of The Mating Mind by Geoffrey Miller considerably increased interest in using sexual selection to explain variation in brain size. From female mate choice, male–male competition, sperm competition, mating strategy, to parental care, there are some data that appear to support selection acting on one species rather than the other in sexually a selected manner but I conclude that the data are not generally supportive of the Sexual Brain Hypothesis.

scholarly journals Sex in the brain: hormones and sex differences

2016 ◽  
Vol 18 (4) ◽  
pp. 373-383 ◽  
Keyword(s):  
Sex Differences ◽  
Sex Hormones ◽  
Genetic Factors ◽  
Motor Coordination ◽  
Brain Regions ◽  
New Era ◽  
Brain Functions ◽  
Opioid Sensitivity ◽  
Males And Females ◽  
The Brain

Contrary to popular belief, sex hormones act throughout the entire brain of both males and females via both genomic and nongenomic receptors. Many neural and behavioral functions are affected by estrogens, including mood, cognitive function, blood pressure regulation, motor coordination, pain, and opioid sensitivity. Subtle sex differences exist for many of these functions that are developmentally programmed by hormones and by not yet precisely defined genetic factors, including the mitochondrial genome. These sex differences, and responses to sex hormones in brain regions and upon functions not previously regarded as subject to such differences, indicate that we are entering a new era in our ability to understand and appreciate the diversity of gender-related behaviors and brain functions.

Brain size evolution in anurans: a review

2019 ◽  
Vol 69 (3) ◽  
pp. 265-279 ◽  
Author(s):  
Chun Lan Mai ◽  
Wen Bo Liao
Keyword(s):  
Sexual Selection ◽  
Life History ◽  
Life History Traits ◽  
Developmental Stages ◽  
Brain Size ◽  
Ecological Factors ◽  
Brain Regions ◽  
Sperm Length ◽  
Testis Size ◽  
Size Evolution

Abstract Selection pressure is an important force in shaping the evolution of vertebrate brain size among populations within species as well as between species. The evolution of brain size is tightly linked to natural and sexual selection, and life-history traits. In particular, increased environmental stress, intensity of sexual selection, and slower life history usually result in enlarged brains. However, although previous studies have addressed the causes of brain size evolution, no systematic reviews have been conducted to explain brain size in anurans. Here, we review whether brain size evolution supports the cognitive buffer hypothesis (CBH), the expensive tissue hypothesis (ETH), or the developmental cost hypothesis (DCH) by analyzing the intraspecific and/or interspecific patterns in brain size and brain regions (i.e., olfactory nerves, olfactory bulbs, telencephalon, optic tectum, and cerebellum) associated with ecological factors (habitat, diet and predator risk), sexual selection intensity, life-history traits (age at sexual maturity, mean age, longevity, clutch size and egg size, testis size and sperm length), and other energetic organs. Our findings suggest that brain size evolution in anurans supports the CBH, ETH or DCH. We also suggest future directions for studying the relationships between brain size evolution and crypsis (i.e., ordinary mucous glands in the skin), and food alteration in different developmental stages.

scholarly journals Does sexual selection explain human sex differences in aggression?

2009 ◽  
Vol 32 (3-4) ◽  
pp. 249-266 ◽  
Author(s):  
John Archer
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Physical Aggression ◽  
Role Theory ◽  
Social Roles ◽  
Social Role ◽  
Conflicts Of Interest ◽  
Reproductive Competition ◽  
Threat Displays ◽  
Males And Females

AbstractI argue that the magnitude and nature of sex differences in aggression, their development, causation, and variability, can be better explained by sexual selection than by the alternative biosocial version of social role theory. Thus, sex differences in physical aggression increase with the degree of risk, occur early in life, peak in young adulthood, and are likely to be mediated by greater male impulsiveness, and greater female fear of physical danger. Male variability in physical aggression is consistent with an alternative life history perspective, and context-dependent variability with responses to reproductive competition, although some variability follows the internal and external influences of social roles. Other sex differences, in variance in reproductive output, threat displays, size and strength, maturation rates, and mortality and conception rates, all indicate that male aggression is part of a sexually selected adaptive complex. Physical aggression between partners can be explained using different evolutionary principles, arising from the conflicts of interest between males and females entering a reproductive alliance, combined with variability following differences in societal gender roles. In this case, social roles are particularly important since they enable both the relatively equality in physical aggression between partners from Western nations, and the considerable cross-national variability, to be explained.

scholarly journals Behavior and Fos activation reveal that male and female rats differentially assess affective valence during CTA learning and expression

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0260577
Author(s):  
Alyssa Bernanke ◽  
Elizabeth Burnette ◽  
Justine Murphy ◽  
Nathaniel Hernandez ◽  
Sara Zimmerman ◽  
...  
Keyword(s):  
Sex Differences ◽  
D2 Receptor ◽  
Brain Regions ◽  
D1 Receptor ◽  
Neural Mechanisms ◽  
Female Rats ◽  
Post Traumatic Stress ◽  
Affective Valence ◽  
Male And Female Rats ◽  
Males And Females

Females are more affected by psychiatric illnesses including eating disorders, depression, and post-traumatic stress disorder than males. However, the neural mechanisms mediating these sex differences are poorly understood. Animal models can be useful in exploring such neural mechanisms. Conditioned taste aversion (CTA) is a behavioral task that assesses how animals process the competition between associated reinforcing and aversive stimuli in subsequent task performance, a process critical to healthy behavior in many domains. The purpose of the present study was to identify sex differences in this behavior and associated neural responses. We hypothesized that females would value the rewarding stimulus (Boost®) relative to the aversive stimulus (LiCl) more than males in performing CTA. We evaluated behavior (Boost® intake, LiCl-induced behaviors, ultrasonic vocalizations (USVs), CTA performance) and Fos activation in relevant brain regions after the acute stimuli [acute Boost® (AB), acute LiCl (AL)] and the context-only task control (COT), Boost® only task (BOT) and Boost®-LiCl task (BLT). Acutely, females drank more Boost® than males but showed similar aversive behaviors after LiCl. Females and males performed CTA similarly. Both sexes produced 55 kHz USVs anticipating BOT and inhibited these calls in the BLT. However, more females emitted both 22 kHz and 55 kHz USVs in the BLT than males: the latter correlated with less CTA. Estrous cycle stage also influenced 55 kHz USVs. Fos responses were similar in males and females after AB or AL. Females engaged the gustatory cortex and ventral tegmental area (VTA) more than males during the BOT and males engaged the amygdala more than females in both the BOT and BLT. Network analysis of correlated Fos responses across brain regions identified two unique networks characterizing the BOT and BLT, in both of which the VTA played a central role. In situ hybridization with RNAscope identified a population of D1-receptor expressing cells in the CeA that responded to Boost® and D2 receptor-expressing cells that responded to LiCl. The present study suggests that males and females differentially process the affective valence of a stimulus to produce the same goal-directed behavior.

1. Darwin’s other big idea

2018 ◽  
pp. 1-15 ◽  
Author(s):  
Leigh W. Simmons
Keyword(s):  
Sexual Selection ◽  
Female Choice ◽  
Egg Production ◽  
Sexual Differences ◽  
The Other ◽  
Sexual Competition ◽  
Sexual Characteristics ◽  
Sexual Selection Theory ◽  
Males And Females ◽  
Selection Of

The idea that males and females often look, sound, smell, and behave differently is uncontroversial. Where those differences came from, however, and what role they play in various species—including humans—is not. ‘Darwin’s other big idea’ outlines Charles Darwin’s sexual selection theory: differential reproduction based on sexual competition, whether between the members of one sex for access to the other, or by selection of particular mating partners. Differences in reproductive parts directly involved in sperm or egg production—primary sexual characteristics—were relatively easy to explain. The other kinds of sexual differences, he proposed, could evolve in one of two ways: male–male competition resulting in weapons, or female choice resulting in ornaments, but this was highly controversial.

Sexual selection in Japanese macaques I: female mate choice or male sexual coercion?

1997 ◽  
Vol 54 (3) ◽  
pp. 725-736 ◽  
Author(s):  
JOSEPH SOLTIS ◽  
FUSAKO MITSUNAGA ◽  
KEIKO SHIMIZU ◽  
YOSHIMI YANAGIHARA ◽  
MASUMI NOZAKI
Keyword(s):  
Sexual Selection ◽  
Mate Choice ◽  
Sexual Coercion ◽  
Female Mate Choice ◽  
Japanese Macaques ◽  
Female Mate

scholarly journals Sexual selection in females across the animal tree of life

2021 ◽  
Author(s):  
Salom&eacute Fromonteil ◽  
Lennart Winkler ◽  
Lucas Marie-Orleach ◽  
Tim Janicke
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Sexual Reproduction ◽  
Tree Of Life ◽  
Selection Theory ◽  
Sexual Selection Theory ◽  
Males And Females

The pioneers of sexual selection theory proposed that males are generally "eager" whereas females are rather "coy" with respect to mating. This male-centred perspective on sexual selection continues to permeate our perception of sex differences across disciplines. Despite an increased awareness that females also compete for mating partners, we still tend to consider sexual selection in females a rare peculiarity. Here we present meta-analytic evidence from 72 species across a broad range of animal taxa to show that sexual selection in females is widespread and should be considered the norm rather than the exception. Thereby, our results extend our general understanding of sexual reproduction and may contribute to a more balanced perspective of how sexual selection operates in both males and females.

scholarly journals Heritability of Head Size in Dutch and Australian Twin Families at Ages 0–50 Years

2010 ◽  
Vol 13 (4) ◽  
pp. 370-380 ◽  
Author(s):  
Dirk J. A. Smit ◽  
Michelle Luciano ◽  
Meike Bartels ◽  
Catharine E. M. van Beijsterveldt ◽  
Margaret J. Wright ◽  
...  
Keyword(s):  
Sex Differences ◽  
Head Circumference ◽  
Brain Size ◽  
Age Groups ◽  
Young Infants ◽  
Sib Families ◽  
Males And Females ◽  
Twin Families ◽  
Gwa Studies ◽  
Biometric Trait

AbstractWe assessed the heritability of head circumference, an approximation of brain size, in twin-sib families of different ages. Data from the youngest participants were collected a few weeks after birth and from the oldest participants around age 50 years. In nearly all age groups the largest part of the variation in head circumference was explained by genetic differences. Heritability estimates were 90% in young infants (4 to 5 months), 85–88% in early childhood, 83–87% in adolescence, 75% in young and mid adulthood. In infants younger than 3 months, heritability was very low or absent. Quantitative sex differences in heritability were observed in 15- and 18-year-olds, but there was no evidence for qualitative sex differences, that is, the same genes were expressed in both males and females. Longitudinal analysis of the data between 5, 7, and 18 years of age showed high genetic stability (.78 > RG> .98). These results indicate that head circumference is a highly heritable biometric trait and a valid target for future GWA studies.

Sexual Selection and Sexual Conflict in Crustaceans

2020 ◽  
pp. 305-331
Author(s):  
Rickey Cothran
Keyword(s):  
Sexual Selection ◽  
Mate Choice ◽  
Sexual Conflict ◽  
Sensory System ◽  
Mate Guarding ◽  
Female Mate Choice ◽  
Female Mate ◽  
Fitness Consequences ◽  
Sensory Structures ◽  
Context Shapes

Research using crustaceans has improved the understanding of sexual selection and sexual conflict. This is particularly true for understanding the biology of male weaponry and sexual conflict over mate guarding. Male crustaceans often are equipped with exaggerated claws that they use to monopolize access to females or resources that females use for reproduction. However, these weapons are often used in other contexts, e.g. mate choice and coercion of females, and understanding their evolution requires a broader perspective of how these traits are built and the fitness consequences of their use for both the bearer and interacting individuals. Although less well studied than male weaponry, crustaceans also provide excellent examples of elaborate sensory structures that are used in scramble competition among males for females. In addition to studies on male-male competition, crustaceans have been well represented in research on intrasexual selection (for the most part, female mate choice). Crustacean females use a variety of sensory channels to assess mates, and a challenge is to better understand what is being conveyed by signaling males and the fitness consequences of mate choice for females. In some cases the female’s sensory system appears to be exploited by males, and this could lead to sexual conflict over mating. Research on crustaceans has also informed the understanding of sexual conflict over mate guarding, including the evolution of traits used to resolve conflict and how the ecological context shapes the costs and benefits of guarding for both sexes.

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