The postnatal life cycle of the social mammals, including the nonhuman primates, has three basic stages of development: infant, juvenile, and adult. Human beings are unusual and add a childhood stage after infancy and an adolescence stage after the juvenile stage. The human pattern of life history in both brain and body growth entails a large investment of energy and time by older members of the social group toward infants and children. This is achieved via a new type of breeding strategy called biocultural reproduction. The evolution of human life history results in enhanced reproductive success for the individuals and our species.
The amygdala is a telencephalic structure that plays an essential role in emotions, social behavior, and social cognition, representing a central hub for the neural networks involved in these functions. However, its homology in nonmammals, particularly in sauropsids, has been controversial. We use an evolutionary developmental biology approach for trying to deconstruct this complex structure into its basic components (based on embryonic origin and molecular profile), decipher the organization of its functional networks, and analyze evolutionary trends throughout vertebrates. Major events occurred during the anamniote–amniote transition, involving the incorporation of new cell types and perhaps the development of on/off functional systems related to a more sophisticated and plastic control of emotions, social behavior, and cognition.
Encephalization is one of the defining features of the primate Order, but patterns of brain/body scaling in different primate radiations are caused by different developmental mechanisms. All primates share a novel pattern of fetal encephalization that is linked to exceptionally slow rates of postcranial body growth during every stage of ontogeny. By contrast, additional grade shifts in relative brain size within anthropoid radiations and humans are caused by brain size increases, including both neocortical expansion and coordinated increases in all brain structures according to allometric principles.
Humans have used tools since the dawn of our species. A few other species of primates in South America, Africa, and Asia also use tools, primarily to obtain foods that cannot be obtained by other techniques. Using a tool challenges movement coordination and planning. Although nonhuman primates neither teach others nor learn via imitation to use tools, their ways of using tools are traditions. Young individuals learn to use tools through sustained practice, which is supported directly and indirectly by social partners.
The mechanosensory lateral line system is one component of a multisensory array derived from the embryonic dorsolateral placode series. This chapter describes the evolutionary history of the lateral line system, including the associated electroreceptive systems. The major morphological and physiological characteristics and the behavioral significance are described for each system. The arrangement of both systems in each group of vertebrates is described systematically. Neuromasts, the sensory unit of the lateral line system, arose with the origin of vertebrates, and multiple types are found in all gnathostome lineages. Electroreceptors arose at the same time or slightly later, but have been lost and reevolved multiple times. Several descendent taxa also evolved electrogenic organs and an active electrosensory system.
Studies of the auditory system in primates indicates that there are similarities with other mammals as well as and distinct derivations. There is a fair amount of consistency among subcortical structures involved in processing auditory information in species such as rats, cats, and monkeys. As with other sensory systems, differences between primates and other mammals emerge in the number of cortical areas devoted to auditory processing. Even within primate branches, anthropoid primates appear to have an increased number of cortical areas, compared to the prosimian branch, which are thought to represent conserved primate features closest to early primates (Kaas, 2013). Below is a discussion of the overall organization of primate auditory cortex including a brief review of subcortical structures, pathways, and a discussion of the anatomical and functional properties of the auditory cortex in primates.
The relative size of the brain and its constituent regions varies greatly among vertebrate clades. This variation has long been associated with differences in behavior in accordance with several highly influential theories in evolutionary neurobiology. Although most of these theories were originally formulated to explain variation in mammalian brains, they are equally applicable to nonmammalian vertebrates. Comparative studies have demonstrated that relative brain size is associated with some measurements of cognition. This was recently corroborated by an artificial selection experiment in guppies in which large-brained fish have cognitive and other advantages over small-brained fish. The size of telencephalic regions is often associated with cognition as well, but studies of the avian hippocampus and spatial memory suggest that size might not be the only factor determining cognitive abilities. In contrast, there is overwhelming evidence that the size of sensory regions is associated with sensory abilities and specific ecological niches. Species that rely heavily on vision have enlarged visual processing brain regions, whereas species that rely more upon olfactory or somatosensory cues have enlarged brain regions associated with those senses. Multivariate analyses in fishes further demonstrate that increases and decreases in the relative size of sensory brain regions are related to the occupation of specific habitats. Finally, parental investment and energetics also play significant roles in the diversification of relative brain size in nonmammalian vertebrates. Greater parental investment in offspring is associated with an increase in relative brain size. The relative size of the brain is also the product of energetic trade-offs with other organ systems, including fat deposition and digestive system size. Variation in relative brain and brain region sizes is therefore an important component of understanding the evolution of the vertebrate brain.
In contrast to mammals, teleost fish exhibit an enormous potential to generate new neurons in the adult brain. This difference encompasses both the number of new neurons relative to the total number of brain cells and the number of neurogenic brain regions. After presenting details of these distinctive features, some of the fundamental processes are reviewed that underlie the generation of new cells from adult stem cells, and the development of their progeny into functional neurons and glial cells, in the teleostean brain. Finally, the numerical matching hypothesis is discussed in an attempt to provide an explanation for the evolutionary development of the differences in neurogenic potential between teleosts and mammals.
The evolutionary expansion of the brain is among the most distinctive morphological features of mammals. During the past decades, considerable progress has been made in explaining brain evolution in terms of physical and adaptive principles. The objective of this chapter is to present current perspectives on primate brain evolution, especially in humans, and to examine some of the design principles and operational modes that underlie the brain's information processing capacity. It is shown that local wiring and cortical folding is a simple design principle that enables brains to be more compact and faster with increasing size. Scaling studies and computational models, furthermore, indicate that the functional capacity of the human brain is inherently constrained by its neural architecture and signal processing capacity and that with our brain we have nearly reached the physical limits and evolutionary potential of a neural-based system.
A distinguishing architectural property of the mammalian cortex is its segregation into gray and white matter. While universal in mammals, most nonmammalian brains do not show any sign of the same organization. In this chapter, the discussion centers around the evolutionary history of white matter—how it came to be—and what possible advantages come from having a cerebral cortex with such segregation.
Sleep is ubiquitous throughout the animal kingdom. Nonetheless, we still do not have a firm grasp on its functions. Whatever its functions, we should expect them to vary in accord with the diverse morphologies, physiologies, ecologies, and life histories of different species and taxonomic groups. Moreover, one apparently universal feature of sleep—documented in flies and worms, rats, and humans—is that it predominates early in development. Accordingly, both developmental and comparative approaches—and combined developmental comparative approaches whenever possible—are likely to prove vital for revealing the origins and functions of sleep.
Visual sensory demands vary substantially across vertebrates. Different visual sensory components have evolved to meet these sensory demands and enhance visual behavioral performance. One of these components is the retinal specialization, which is a portion of the retina with generally high ganglion cell densities, which increase spatial resolving power. Retinal specializations are relevant from a functional perspective because animals can align these "acute zones" with objects of interest within a localized region of their visual space, consequently affecting different behavioral dimensions. In this chapter, we reviewed the different types of retinal specializations found in vertebrates (retinal area, fovea, visual streak, radial anisotropy, area gigantocellularis) by discussing the different hypotheses proposed over decades to explain their function. Empirical tests on the functional properties of these different retinal specializations have been limited, which constrains our ability to understand the functional evolution of the vertebrate eye. We derive specific predictions from each of the hypotheses put forward to identify their degree of overlap. Finally, we provide some future directions as to how to test these functional hypotheses by integrating physiological and behavioral approaches. Testing these functional hypotheses will enhance our understanding of the relationship between the eye and the physical environment, and ultimately the visual ecology of vertebrates.
Posterior parietal cortex (PPC) of macaque monkeys is known to contain at least four action specific modules or domains: grasping, body defense, looking, and reaching. Similar action-specific domains have also been demonstrated by microstimulation within primary motor cortex (M1) and premotor cortex (PMC). We used microstimulation methods to identify as many as nine action-specific domains of PPC in prosimian galagos and New World owl and squirrel monkeys and functionally matched domains in M1 and PMC. Domains in PPC are widely interconnected, but each domain has connections focused on functionally matched domains in PMC and M1. Functional imaging studies suggest that at least some of the macaque domains exist in humans. PPC domains use visual and somatosensory information to decide on the optimal action, while PMC and M1 domains may use PPC inputs and other sources of information to confirm or alter the PPC decision. We suggest that early primates had a greatly expanded PPC with domains for basic, adaptive, and complex behaviors, while the nonprimate ancestors of primates had little PPC, and this cortex had only a weak effect on motor behavior.
Our understanding of human brain evolution has advanced enormously over the past decade, owing to contributions of scientists from many different branches of the life sciences. This chapter reviews some of the concepts and findings from evolutionary biology and neuroscience central to human brain evolutionary studies, surveys some major recent findings, and identifies issues for future research.
The last several decades of research have seen a burgeoning of data on the morphology, physiology, and evolutionary history of vertebrate auditory organs. This chapter briefly describes the status of our understanding of ear structure and function and their origins in fish, which hear using their vestibular epithelia, and land vertebrates that early evolved dedicated hearing structures. The various major lineages of land vertebrates—amphibians, lepidosaurs, archosaurs, and mammals—each have unique hearing organs. From humble beginnings as a small epithelium in their common ancestor, each lineage evolved specialized hair-cell populations and divisions of labor that led to highly sensitive and frequency-selective hearing. This chapter covers the origins, morphology, and physiological characteristics of the ears of all major groups.
