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Topic: How did human social complexity evolve and what are the implications of our evolutionary past for our social behavior?

Bibliography:

Aiello, L., & Wheeler, P. (1995). The Expensive-Tissue Hypothesis: The Brain And The Digestive System In Human And Primate Evolution. Current Anthropology, 36(2), 199-199. Retrieved September 15, 2014, from http://www.jstor.org/stable/2744104

Brune, M., & Brunecohrs, U. (2006). Theory Of Mind—evolution, Ontogeny, Brain Mechanisms And Psychopathology. Neuroscience & Biobehavioral Reviews, 30(4), 437-455. Retrieved October 28, 2014, from http://www.sciencedirect.com/science/article/pii/S0149763405001284

Dunbar, R. (n.d.). The Social Brain Hypothesis And Its Implications For Social Evolution. Annals of Human Biology, 562-572. Retrieved September 15, 2014, from http://psych.colorado.edu/~tito/sp03/7536/Dunbar_1998.pdf

Fehr, E., & Fischbacher, U. (2003). The Nature Of Human Altruism. Nature, (425), 785-791. Retrieved October 28, 2014, from http://www.nature.com/nature/journal/v425/n6960/abs/nature02043.html

Greene, J. (2002). How (and Where) Does Moral Judgment Work? Trends in Cognitive Sciences, 6(12), 517-523. Retrieved October 28, 2014, from http://www.sciencedirect.com/science/article/pii/S1364661302020119

Isler, K., & Schaik, C. (2009). The Expensive Brain: A framework for explaining evolutionary changes in brain size. Journal of Human Evolution, 57(4), 392-400. Retrieved September 15, 2014, from http://www.sciencedirect.com/science/article/pii/S0047248409001286

Jones, K., & Maclarnon, A. (2004). Affording Larger Brains: Testing Hypotheses of Mammalian Brain Evolution on Bats. The American Naturalist, 162(1), E20-E31. Retrieved September 15, 2014, from http://www.jstor.org/stable/10.1086/421334

Mcdaniel, M. (2005). Big-brained people are smarter: A meta-analysis of the relationship between in vivo brain volume and intelligence. Intelligence, 33(4), 337-346. Retrieved September 15, 2014, from http://www.sciencedirect.com/science/article/pii/S0160289604001357

Wikipedia Assignment 2

https://en.wikipedia.org/wiki/Evolution_of_morality

Edit made: Sexual morality and female parental investment is also be linked to the evolution of female choice which is divided into four non-mutually exclusive components, including, direct benefits to the female, "good" genes or genes correlated with high fitness, runaway sexual selection also known as the "sexy son hypothesis," and sensory bias.

Suggestion 1: The "Wason Selection Task" section is very brief on this page. It could be improved by citing examples of experiments that demonstrate the reasoning described.

Suggestion 2: The only emotion discussed in detail is "disgust," the page could be better by defining and looking more in depth at more emotions/behaviors, such as, altruism, empathy, reciprocity etc.

Suggestion 3: This page only briefly mentions judgement and reasoning as being extra levels of sophistication in humans. This page could be improved by adding a section on judgment/reasoning and describing their evolution and where animals and humans have evolved differently with respect to both.

Throughout the natural history of the Earth, evolution by the process of natural selection, as theorized by Charles Darwin, has shaped and molded our world into what we, as humans, know and perceive today. It is by this very process that humans have developed to such an advanced physical and cognitive state that allows us to be, essentially, the dominant species found on Earth. While currently humans reign as the dominant species, it must be noted that innate trait similarities are paralleled in other species, typically in other mammals, but most specifically primates. This not only suggests a linked evolutionary past and a common ancestor, but also aids in the studying of how and why humans evolved and at what point in time the modern human diverged from its most recent ancestor in this linked evolutionary timeline.

Human evolution is still a budding subject that encompasses many physical and social scientific facets, such as: archaeology, embryology, genetics, ethology, psychology, linguistics, and countless others—but a defining feature of what sets humans a step above the rest and what can be attributed as the backbone of human evolution is the emergence of human morality. Morality, defined as a set of ideals that distinguishes between acceptable and inacceptable behavior, is at its core, a distinctively human characteristic. While it is observed in other social animals, it certainly is not to the extent that we as humans apply in everyday life. Although it can be argued that the definition of morality itself is an “ever-evolving” term, there are some basic notions that lie at its heart (Greene et al, 2002). Humans are social organisms and morality implies social intelligence. Social intelligence implies a need for large mental computational demands, which is typically associated with a larger brain size found in humans, and there is indeed a positive correlation between brain volume and intelligence (McDaniel, 2005). This in turn, brings up two major points of human evolution, why did morality evolve, and at what cost.

Roughly two million years ago, humans experienced a dramatic increase in brain size, and from then on have, as a general rule, been considered to be large brained organisms. While the brain only encompasses a small percentage of a human’s total mass, it is certainly to be considered a metabolic drain of energy for its overall size—taking up roughly 20 percent of each individual’s basal metabolic rate (BMR) (Aiello et al., 1995). It seems counterintuitive to see the persistence and success of such a costly organ, therefore implying that the advantages of having a larger brain must outweigh the severe metabolic costs or it simply could not have evolved.

Several hypotheses emerged to explain how humans were able to sustain the metabolic demands of a larger brain. These included the Direct Metabolic constraint hypothesis, which suggested that organisms with larger brains had an overall higher BMR, but the correlation found was weak in mammals. Additionally the Maternal Energy Hypothesis was explored and stated that a mother’s BMR during the gestational period serves as the energy source for the fetus’ brain growth, and determined the brain size of her offspring. Indicating that poor maternal health could be detrimental to brain size, but evidence of this phenomenon in mammals was inconclusive, especially in primates. The hypothesis that logically persists to date is known as the Expensive Tissue Hypothesis (Jones et al., 2004).

As it turns out, the emergence of a larger brain in humans—and in other primates—was also met with a reduction in the size of the liver and gastrointestinal tract, or gut. It can be seen, as a conclusion that whatever factor was selecting for a larger brain was simultaneously selecting for a smaller gut, or a coevolution between the two. However, no matter what factors were driving this shift, it could not have been possible without the introduction of a higher quality diet. Larger brain size has been associated with omnivorous feeding patterns. The introduction of animal products into the diet, allowed for the gut to shrink in size and freed up energy normally used to digest bulk and plant food. This relaxed evolutionary constraint allowed for the reallocation of the energy to the brain. Additionally, omnivorous feeding obviously requires a more refined cognitive ability to locate and exploit food than herbivory (Aiello et al., 1995).

This phenomenon is logical due to the fact that increasing BMR or altering the size or metabolic requirements of other body tissues, such as the heart or kidneys for example, would require that animals spent a large amount of time feeding and would force animals into competition for limited resources. The heart could understandably not see a reduction in size without compromising the body’s ability to provide sufficient circulation and without adequate blood supply the brain would not receive a proper amount of oxygen necessary to maintain function. Additionally, it was important that kidney size be maintained to adequately concentrate of urine, with emphasis on the body’s ability to reabsorb water. Production of dilute urine would have unambiguously posed a problem for human ancestors that evolved in equatorial regions where drinking opportunities were rare and thermoregulatory requirements were already exceptionally costly to the body (Aiello et al., 1995). Finally, as larger brains became established maturation slowed, lifespans elongated, and fertility declined. Larger brained mammals invest more energy into each individual offspring, and because maturation takes a longer period of time the risk of malnutrition and drops in energy supply are higher during development of the brain—typically from birth through adolescence. Human babies typically have a high fat content, which is helps to circumvent an energy supply crisis of the larger brain (Isler et al, 2009). The evolution of a larger brain opened a cascade of evolutionary advancements in social animals.

The Social Brain Hypothesis alludes to the fact that the brain originally evolved to process factual information. The brain allows and individual to recognize patterns, perceive speech, develop strategies to circumvent ecologically-based problems such as foraging for food, and also permits color vision. Furthermore, a large brain is a reflection of the cognitive demands of complex social systems. It is said that in humans and primates, the specific part of the brain, the neocortex, is responsible for what is considered reasoning and consciousness. Therefore, in social animals, the neocortex became under intense selection to increase in size to improve social cognitive abilities. Social animals, such as humans are capable of two important concepts, coalition formation, or group living, and tactical deception, or the ability to hold false beliefs. The fundamental importance of animal social skills lies within the ability to manage relationships and in turn, the ability to not just commit information to memory, but manipulate it as well (Dunbar).

An adaptive response that arose as a result of social interaction and living, is Theory of Mind, and is defined as the ability to infer another individual’s mental states or emotions. Collectively, group living requires cooperation and generates conflict. Social living puts strong evolutionary selection pressures on acquiring social intelligence due to the fact that living in groups has advantages, such as protection from predators and that groups in general outperform the sum of an individual’s performance, and also disadvantages, such as, competition from within the group for resources and mates. This sets the stage for something of an evolutionary arms race from within the species (Brune et al., 2006). Within social animals, altruism, or an act or behavior that is disadvantageous to one individual while benefiting other group members has evolved—which seems to be contradictory to evolutionary thought, as the main goal is to pass genes on to the next generation. The evolution of altruism can be accounted for when kin selection and inclusive fitness is taken into account, or that reproductive success is not just dependent on the number of offspring an individual produces, but also the number of offspring that related individuals produce (Fehr et al., 2003). Outside of familial relationships, altruism is also seen, but in a different manner, typically defined by the Prisoner’s Dilemma, theorized by John Nash, which defines cooperation and defecting with and against individuals driven by incentive, or in his proposed case, years in jail. In evolutionary terms, the best strategy to implore for the Prisoner’s dilemma is tit-for-tat, or an individual should cooperate as long others are cooperating, and not defect until an individual defects against them. At their core, complex social interactions are driven by the need to distinguish sincere cooperation and defection (Brune et al., 2006).

Theory of Mind has been traced back to and observed in primates, but not to the extent that it is in the modern human, and is perhaps where the differentiation truly lies, along with the acquisition of language. Humans use metaphors and imply much of what we mean to say. Phrases such as “you know what I mean?” are not uncommon and are a direct result of the sophistication of the human theory of mind. Failure to understand others’ intentions and emotions can yield inappropriate social responses and are often associated with human mental conditions such as autism, schizophrenia, bipolar disorder, some forms of dementia, and psychopathy. This is true especially for autism spectrum disorders, where social disconnect is evident, but non-social intelligence can be preserved or even in some cases augmented, such as in the case of a savant (Brune et al., 2006).

The evolution of a larger brain in humans was an extremely metabolically costly event and had to be met with advantages that outweighed this cost. The simultaneous reduction in gut size, allowed for the reallocation of metabolic energy to the brain, and as a result social intelligence in primates and humans began to flourish. Sociobiology of humans is a controversial subject and concrete genetically based findings and advancements are difficult to make due to the fact that human experimentation is not ethical. Much of what is known about humans to date is due to sociobiological and evolutionary past findings and experiments on model organisms. The brain itself is a mysterious organ and Theory of Mind is only one facet that is not even completely understood, but it is certain that what is known about human complexity is rooted in our evolutionary past.

EDIT TO EXISTING PAGE:

https://en.wikipedia.org/wiki/Evolution_of_morality

Human Social Intelligence
The Social Brain Hypothesis, detailed by R.I.M Dunbar in the article The Social Brain Hypothesis and Its Implications for Social Evolution supports the fact that the brain originally evolved to process factual information. The brain allows an individual to recognize patterns, perceive speech, develop strategies to circumvent ecologically-based problems such as foraging for food, and also permits the phenomenon of color vision. Furthermore, having a large brain is a reflection of the large cognitive demands of complex social systems. It is said that in humans and primates the neocortex is responsible for reasoning and consciousness. Therefore, in social animals, the neocortex came under intense selection to increase in size to improve social cognitive abilities. Social animals, such as humans are capable of two important concepts, coalition formation, or group living, and tactical deception, which is the ability to hold false beliefs. The fundamental importance of animal social skills lies within the ability to manage relationships and in turn, the ability to not just commit information to memory, but manipulate it as well. An adaptive response to the challenges of social interaction and living is Theory of Mind. Theory of Mind as defined by M. Brune, is the ability to infer another individual’s mental states or emotions. Having a strong Theory of Mind is tied closely with possessing advanced social intelligence. Collectively, group living requires cooperation and generates conflict. Social living puts strong evolutionary selection pressures on acquiring social intelligence due to the fact that living in groups has advantages. Advantages to group living include protection from predators and the fact that groups in general outperform the sum of an individual’s performance. But, from an objective point of view, group living also disadvantages, such as, competition from within the group for resources and mates. This sets the stage for something of an evolutionary arms race from within the species.

Within populations of social animals, altruism, or an acts of behavior that are disadvantageous to one individual while benefiting other group members has evolved. This notion seems to be contradictory to evolutionary thought, due to that fact that an organism’s fitness and success is defined by its ability to pass genes on to the next generation. According to E. Fehr, in the article, The Nature of Human Altruism, the evolution of altruism can be accounted for when kin selection and inclusive fitness are taken into account; meaning reproductive success is not just dependent on the number of offspring an individual produces, but also the number of offspring that related individuals produce. Outside of familial relationships altruism is also seen, but in a different manner typically defined by the Prisoner’s Dilemma, theorized by John Nash. The Prisoner’s Dilemma serves to define cooperation and defecting with and against individuals driven by incentive, or in Nash’s proposed case, years in jail. In evolutionary terms, the best strategy to use for the Prisoner’s dilemma is tit-for-tat. In the tit-for-tat strategy, an individual should cooperate as long others are cooperating, and not defect until another individual defects against them. At their core, complex social interactions are driven by the need to distinguish sincere cooperation and defection. Brune details that Theory of Mind has been traced back to primates, but it is not observed to the extent that it is in the modern human. The emergence of this unique trait is perhaps where the divergence of the modern human begins, along with our acquisition of language. Humans use metaphors and imply much of what we say. Phrases such as, “You know what I mean?” are not uncommon and are direct results of the sophistication of the human Theory of Mind. Failure to understand another’s intentions and emotions can yield inappropriate social responses and are often associated with human mental conditions such as autism, schizophrenia, bipolar disorder, some forms of dementia, and psychopathy. This is especially true for autism spectrum disorders, where social disconnect is evident, but non-social intelligence can be preserved or even in some cases augmented, such as in the case of a savant. The need for social intelligence surrounding Theory of Mind is a possible answer to the question as to why morality has evolved as a part of human behavior.

FINAL DRAFT STARTS HERE:

Evolution of Human Social Complexity and Intelligence

Throughout the natural history of the Earth, evolution by the process of natural selection as theorized by Charles Darwin has shaped and molded our world into what we as humans know and perceive today. It is by this very process that humans have developed to such an advanced physical and cognitive state that allows us to be, essentially, the most innovative and dynamic species found on Earth. While currently humans appear as the most advanced species, it must be noted that innate trait similarities are paralleled in other species, typically in other mammals, but most specifically in primates. This not only suggests a linked evolutionary past and a common ancestor, but also aids in the studying of how and why humans evolved and at what point in time the modern human diverged from its most recent ancestor in this linked evolutionary timeline.

Human evolution is still a budding subject that encompasses many physical and social scientific facets, such as: archaeology, embryology, genetics, ethology, psychology, linguistics, and countless others—but a defining feature of what sets us apart was the emergence of human morality. Morality, defined as a set of ideals that distinguishes between acceptable and inacceptable behavior, is at its core a distinctively human characteristic. While it is observed in other social animals, it is not to the extent that we as humans apply in everyday life. Although it can be argued that the definition of morality itself is an “ever-evolving” term, there are some basic notions that lie at its heart. Joshua Greene explains that one of the main notions is that humans are social organisms and that morality implies social intelligence, the ability to effectively navigate complex social environments or relationships (Greene et al, 2002). This in turn, brings up two major questions of human evolution, why did morality evolve and at what cost.

The Social Brain Hypothesis, detailed by R.I.M Dunbar in the article The Social Brain Hypothesis and Its Implications for Social Evolution supports the fact that the brain originally evolved to process factual information. The brain allows an individual to recognize patterns, perceive speech, develop strategies to circumvent ecologically-based problems such as foraging for food, and also permits the phenomenon of color vision. Furthermore, having a large brain is a reflection of the large cognitive demands of complex social systems. It is said that in humans and primates the neocortex is responsible for reasoning and consciousness. Therefore, in social animals, the neocortex came under intense selection to increase in size to improve social cognitive abilities. Social animals, such as humans are capable of two important concepts, coalition formation, or group living, and tactical deception, which is the ability to hold false beliefs. The fundamental importance of animal social skills lies within the ability to manage relationships and in turn, the ability to not just commit information to memory, but manipulate it as well (Dunbar, 2009). An adaptive response to the challenges of social interaction and living is Theory of Mind. Theory of Mind as defined by M. Brune, is the ability to infer another individual’s mental states or emotions (Brune et al., 2006). Having a strong Theory of Mind is tied closely with possessing advanced social intelligence. Collectively, group living requires cooperation and generates conflict. Social living puts strong evolutionary selection pressures on acquiring social intelligence due to the fact that living in groups has advantages. Advantages to group living include protection from predators and the fact that groups in general outperform the sum of an individual’s performance. But, from an objective point of view, group living also disadvantages, such as, competition from within the group for resources and mates. This sets the stage for something of an evolutionary arms race from within the species.

Within populations of social animals, altruism, or an acts of behavior that are disadvantageous to one individual while benefiting other group members has evolved. This notion seems to be contradictory to evolutionary thought, due to that fact that an organism’s fitness and success is defined by its ability to pass genes on to the next generation. According to E. Fehr, in the article, The Nature of Human Altruism, the evolution of altruism can be accounted for when kin selection and inclusive fitness are taken into account; meaning reproductive success is not just dependent on the number of offspring an individual produces, but also the number of offspring that related individuals produce (Fehr et al., 2003). Outside of familial relationships altruism is also seen, but in a different manner typically defined by the Prisoner’s Dilemma, theorized by John Nash. The Prisoner’s Dilemma serves to define cooperation and defecting with and against individuals driven by incentive, or in Nash’s proposed case, years in jail. In evolutionary terms, the best strategy to use for the Prisoner’s dilemma is tit-for-tat. In the tit-for-tat strategy, an individual should cooperate as long others are cooperating, and not defect until another individual defects against them. At their core, complex social interactions are driven by the need to distinguish sincere cooperation and defection.

Brune details that Theory of Mind has been traced back to primates, but it is not observed to the extent that it is in the modern human. The emergence of this unique trait is perhaps where the divergence of the modern human begins, along with our acquisition of language. Humans use metaphors and imply much of what we say. Phrases such as, “You know what I mean?” are not uncommon and are direct results of the sophistication of the human Theory of Mind. Failure to understand another’s intentions and emotions can yield inappropriate social responses and are often associated with human mental conditions such as autism, schizophrenia, bipolar disorder, some forms of dementia, and psychopathy. This is especially true for autism spectrum disorders, where social disconnect is evident, but non-social intelligence can be preserved or even in some cases augmented, such as in the case of a savant (Brune et al., 2006). The need for social intelligence surrounding Theory of Mind answers the question as to why morality has evolved as a part of human behavior. However, possessing social intelligence implies a need for large mental computational demands and while the need for social intelligence is evident, it did not evolve without cost.

According to Michael McDaniel’s research, published as Big-brained People are Smarter: A Meta-Analysis of the Relationship between In Vivo Brain Volume and Intelligence, large cognitive demands are typically associated with the larger brain size found in humans—and it has been seen that there is indeed a positive correlation between brain volume and intelligence (McDaniel, 2005). Roughly two million years ago, humans experienced a dramatic increase in brain size, and from then on have been considered large-brained organisms. While the brain only encompasses a small percentage of a human’s total mass, it is considered a metabolic drain of energy for its overall size—taking up roughly 20 percent of each individual’s basal metabolic rate (BMR) (Aiello et al., 1995). It seems counterintuitive to see the continued success of such a costly organ. However, its persistence throughout time implies that the advantages of having a larger brain must outweigh the severe metabolic costs. If this was not the case, the trait of having a large brain simply could not have evolved.

Several hypotheses emerged to explain how humans were able to sustain the metabolic demands of a larger brain. Kate Jones details these hypotheses in her article Affording Larger Brains: Testing Hypotheses of Mammalian Brain Evolution on Bats. The Direct Metabolic constraint hypothesis, suggests that organisms with larger brains had an overall higher BMR, however, the correlation among mammals was weak. Alternatively, the Maternal Energy Hypothesis was explored, it stated that a mother’s BMR during the gestational period serves as the energy source for the fetus’ brain growth, and determines the brain size of her offspring. This implies that poor maternal health could be detrimental to brain size, but evidence of this phenomenon in mammals was inconclusive, especially in primates. The hypothesis that persists to date is known as the Expensive Tissue Hypothesis, which indicates that the large amount of metabolic energy given to the brain is energy that has been reallocated from other metabolic tissue (Jones et al., 2004). Leslie Aiello elaborated further on the subject of the Expensive Tissue Hypothesis. Aiello’s paper, The Expensive Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution, states that the emergence of a larger brain in humans—and in other primates—was met with a reduction in the size of the liver and gastrointestinal tract, or gut. It can be seen that whatever factor was selecting for a larger brain was simultaneously selecting for a smaller gut, or a connected evolution between the two. However, no matter what factors were driving this shift, it would not have been possible without the introduction of a higher quality diet; larger brain size has been associated with omnivorous feeding patterns. The introduction of animal products into the diet allowed for the gut to shrink in size and allowed energy normally used to digest bulky plant food to be used elsewhere. This relaxed evolutionary constraint allowed for the reallocation of the energy to the brain. Additionally, omnivorous feeding requires a more refined cognitive ability to locate and exploit food than herbivory (Aiello et al., 1995).

This phenomenon is believable due to the fact that increasing BMR or altering the size or metabolic requirements of other body tissues, such as the heart or kidneys would require that animals spend a large amount of time feeding and also would force animals into competition for limited resources. Aiello’s findings go on to elaborate that the heart could understandably not experience a reduction in size without compromising the body’s ability to provide sufficient circulation. Without adequate blood supply the brain would not receive a proper amount of oxygen necessary to maintain function. Additionally, it was important that kidney size be maintained to ensure adequate concentration of urine, with emphasis on the body’s ability to reabsorb water. Production of dilute urine would have posed a problem for human ancestors that evolved in equatorial regions where hydration requirements were hard to meet and thermoregulatory requirements were already exceptionally costly to the body (Aiello et al., 1995).

Finally, as larger brains became established, maturation slowed, lifespans lengthened, and fertility declined. As specified in Karin Isler’s article, The Expensive Brain: A Framework for Explaining Evolutionary Changes in Brain Size, larger brained mammals invest more energy into each individual offspring, and because maturation takes a longer period of time, the risk of malnutrition and drops in energy supply are higher during development of the brain—typically from birth through adolescence. Human babies typically have a high fat content, which is helps to circumvent an energy supply crisis of the larger brain (Isler et al, 2009). The evolution of a larger brain opened many opportunities for evolutionary advancements in social animals.

The evolution of a larger brain in humans was an extremely costly metabolic event that had to have advantages that outweighed this cost. The simultaneous reduction in gut size, allowed for the reallocation of metabolic energy to the brain, and as a result social intelligence in primates and humans began to flourish. Sociobiology of humans is a controversial subject and concrete genetically based findings and advancements are difficult to make, due to the fact that human experimentation is not ethical. Much of what is known about humans is due to sociobiological and evolutionary findings in the past and experiments on model organisms. The brain itself is a mysterious organ and Theory of Mind is only one facet that is continuously being explored. However, one can be certain that what is now known and the knowledge yet to be gained about human complexity is rooted in our evolutionary past.

References Aiello, L., & Wheeler, P. 1995. The Expensive-Tissue Hypothesis: The Brain And The Digestive System In Human And Primate Evolution. Current Anthropology, 36:199-199.

Brune, M., and Brunecohrs, U. 2006. Theory Of Mind—Evolution, Ontogeny, Brain Mechanisms And Psychopathology. Neuroscience & Biobehavioral Reviews, 30:437-455.

Dunbar, R. 2009. The Social Brain Hypothesis and Its Implications for Social Evolution. Annals of Human Biology 562-572.

Fehr, E., & Fischbacher, U. 2003. The Nature Of Human Altruism. Nature 425:785-791.

Greene, J. 2002. How (and Where) Does Moral Judgment Work? Trends in Cognitive Sciences, 6:517-523.

Isler, K., & Schaik, C. 2009. The Expensive Brain: A framework for explaining evolutionary changes in brain size. Journal of Human Evolution 57:392-400.

Jones, K., & Maclarnon, A. 2004. Affording Larger Brains: Testing Hypotheses of Mammalian Brain Evolution on Bats. The American Naturalist 162:20-31.

Mcdaniel, M. 2005. Big-brained People are Smarter: A Meta-Analysis of the Relationship between In Vivo Brain Volume and Intelligence. Intelligence 33:337-346.