A Brief History of Life and Brain Evolution

This chapter reviews some of the fundamentals of evolution, particularly adaptations and exaptations. Adaptations are physical or behavioral features that through natural selection aided survival and reproduction. Exaptations are physical or behavioral features that have been co-opted from their initial adaptive functions and subsequently enhanced fitness. The reuse, recycling, or redeployment of brain neurons for purposes other than their original adaption may be considered a central organizing principle of the brain. The chapter reviews the beginnings of life and presents a timeline of life through the evolution of hominins. The term hominin refers to all current and extinct relatives and ancestors of Homo sapiens, including the australopithecines and habilines, within about the last 6 million years. The chapter introduces the hypothesis that Homo sapiens survived and flourished, instead of Neandertals, Denisovans, and other hominins, because of brain shape differences, which created cognitive differences that enhanced the evolutionary fitness of Homo sapiens.

The Hippocampus

All mammals have a well-developed hippocampus compared to that of fish, reptiles, and birds, although the latter still have homologous structures. The cells of the hippocampus have differentiated roles: place cells become active and rearrange themselves in new environments, which create new and stable maps of those environments. Grid cells are able to approximate distances, forming an additional neuronal basis for spatial navigation. The hippocampus and olfactory bulbs have intimately related functions. The story of patient H.M. revealed that declarative memories are consolidated by the hippocampus, but procedural memories can be established without hippocampal involvement. Declarative memories remain vulnerable to disruption and forgetting up to about 3 years after memorization. Memories consolidated during sleep are less prone to interference and more stable than memories followed by additional stimulation or learning.

The Cerebellum

The cerebellum is estimated to contain about 80% of all of the brain’s neurons. Its original adaptation appears to be the seamless and smooth execution of motor movements. The dendritic branching of the cerebellum’s neurons is the most complex and extensive in the brain. The lateral and posterior portions of modern humans’ cerebellum have a more recent phylogenetic origin than that of other hominins. An exaptation of the human cerebellum is the cognitive control and refinement of higher cognitive functions, including lower- and higher-level abstract thinking. Numerous empirical studies link insight and creativity to the cerebellum.

The Temporal Lobes

One of the major adaptations of the temporal lobes is the storage and application of meanings to sounds. With the evolution of primates and later hominins, the temporal lobes became exapted for protolanguage and, later, fully modern recursive language. Language evolved through natural selection for communication. This chapter presents the hypothesis that a recent beneficent genetic event increased working memory and phonological storage capacity, allowing the release of recursive phrasing, a prerequisite for use of the subjunctive mode. The evolution of language may have been influenced by gossip, which served to keep cheaters in check in larger social groups. Freud proposed that jokes may have arisen to relieve aggressive and sexual tensions, and others have proposed that incongruent jokes may have emerged to reduce the probability of being surprised. The evolution of humor may be related to creativity; humor production and receptivity differences have been demonstrated in men and women, which may be correlated to mating strategies.

The Parietal Lobes

This chapter discusses the parietal lobes, whose primary function is to gather and integrate sensory information to aid the motor cortex in appropriate movements. Damage to the parietal regions in humans often produces a type of agnosia, where patients misidentify their fingers or body parts. The parietal lobes may have expanded in Homo sapiens compared with Neandertals, and this expansion may have occurred within the last 100,000 years. The intraparietal sulcus has, among its many functions, numerosity, which is an appreciation of numbers. The IPS may have groups of neurons or even single neurons that respond to symbolic and nonsymbolic numbers. The supramarginal gyrus plays a major role in inner speech, phonological storage, and emotional processing. The angular gyrus plays a major role in mathematical operations and may serve an important role in 15 other higher cognitive functions. The precuneus is a critical region for episodic memory, Baddeley’s visuospatial sketchpad, and self- and other-representations. The posterior portion of the cingulate cortex is the retrosplenial cortex, which translates egocentric spatial and allocentric spatial viewpoints. This translational responsibility was critical in evolution of hominin navigation. The constructive simulation hypothesis proposes that the episodic memory system may have evolved not for perfect scenario recall but for the ability to manipulate past events for future successes. The parietal lobes are an important part of the default mode network of the brain. The default mode network is active when a human or nonhuman primate is resting and not engaged in a specific mental activity.

The Frontal Lobes

This chapter notes that the expansion of the brain, particularly the cortex, as well as increased behavioral flexibility, in mammals compared to that in reptiles, birds, and fishes. Mammalian brains have been typified by mosaic evolution and concerted evolution. The two most important influences on modern human brains have been the evolution of mammalian brains and primate brains, and the latter had the most profound influence on modern human brains. The prefrontal cortex is one of the major exaptations of the human brain, where the cognitive abilities known executive functions primarily reside. Those functions include decision-making, forming plans and goals, organizing, devising strategies to attain goals, inhibition, and the monitoring of effective performance. The frontal lobes of the earliest primates were under selective pressure to identify and eat fruits with their forelimbs. The brains of hominins may have exapted these same regions for object manipulation, tool-making, and eventually language functions such as word choice and word sequencing.

The Evolution of Learning and Memory Systems

This chapter covers many hypotheses: 1. Modern human memory systems are based on non-associative (habituation and sensitization) and associative (classical and operant conditioning) learning principles. 2. Non-associative learning evolved first, guiding formation of increasingly more complex molecules. The principles underlying habituation and sensitization are based on basic chemical and subatomic particle affinities and disaffinities. 3. The concept of sensitization should be expanded to cover reliability or steady responses to repeated stimuli. 4. In a prelife and pre-nucleotic world, selfish metabolism and reproduction were paramount. Through natural selection only four nucleotides survived to form the basis of RNA in prokaryotes, which later became modified to form double-stranded DNA eukaryotes. 5. The memory for an organism’s functions is coded with its RNA and DNA. 6. The Cambrian explosion vastly expanded the animal kingdom, beginning about 545 million years ago. It resulted from the development of unlimited associative learning, which developed on the basis of exaptation of non-associative learning principles. 7. Baddeley’s multicomponent working memory model aids in understanding of the evolution of cognition.

Paleopsychopathology

Paleopsychopathology is the study of mental problems and mental diseases that may have increased relative fitness in the ancestral environment but do not enhance fitness in the present environment. Some present pathologies (like Huntington’s chorea) may not have had any adaptive value in the ancestral environment, as some genetic disorders’ onset occurred well after what would have been prime reproductive years in the ancestral environment. Some psychopathologies may not have been advantageous in and of themselves, but either their polygenic basis or proximity to important genes may have given rise to successful adaptive phenotypes. For example, the location for the genes for schizophrenia are associated with the coding for immunity genes and creativity. Some personality disorders may have been adaptive in the ancestral environment because of their benefits in navigating social hierarchies. The evolution of an array of emotions may have also benefitted successful navigation in social groups.

The Evolution of Sleep and Dreams

Primitive sleep states developed from earth’s rotational cycle, where activities were constrained by alternating periods of light and dark. Extant reptiles, birds, mammals, and primates exhibit slow-wave sleep (SWS) and rapid eye movement (REM) sleep, which suggests an early evolutionary development dating to at least 300 million years ago or earlier. There may have been no single purpose of sleep, however, multiple reasons for its evolution and different sleep stages have been suggested, including reduced energy demands, facilitation of learning and memory, removal of waste metabolites, priming for subsequently successful waking activities, and aiding creativity. When Homo erectus appeared about 1.9 million years ago, it made a full transition to terrestrial life, including sleeping on the ground instead of in nests in trees. Ground sleep resulted in a single integrated sleep period, which had many positive cognitive repercussions. The design for the Acheulean handaxe, attributed to Homo erectus, may have come to a stone knapper in a dream. Some handaxes, beginning about 500,000 years ago, had aesthetic qualities and may have been used as a means of sexual selection.

An Introduction to the Brain

This chapter emphasizes that human brains are the most complicated animate or inanimate system in the universe. It begins with a discussion of the definition of life and consciousness and the transition from life to consciousness. It is proposed that consciousness began with the ability to learn associatively (classical and operant conditioning) during the Cambrian period. There is a discussion of the four cell-building principles of the brain: cell proliferation, cell differentiation, cell migration, and programmed cell death. The multiple naming systems for the brain are presented: (1) Brodmann’s areas, (2) presumed function, (3) people’s names (4) regional location, (5) location and nature of the structure, and (6) gross anatomical name. The chapter reviews the four major brain lobes and their functions. It covers major structures of the limbic system and emphasizes the functional role of the brain’s fasciculi, the major connections for neural transmission, which reflects the concerted evolution of various brain regions.