Hominid Brain Research Articles

A revised perspective on the evolution of the lateral frontal cortex in primates.

Detailed neuroscientific data from macaque monkeys have been essential in advancing understanding of human frontal cortex function, particularly for regions of frontal cortex without homologs in other model species. However, precise transfer of this knowledge for direct use in human applications requires an understanding of monkey to hominid homologies, particularly whether and how sulci and cytoarchitectonic regions in the frontal cortex of macaques relate to those in hominids. We combine sulcal pattern analysis with resting-state functional magnetic resonance imaging and cytoarchitectonic analysis to show that old-world monkey brains have the same principles of organization as hominid brains, with the notable exception of sulci in the frontopolar cortex. This essential comparative framework provides insights into primate brain evolution and a key tool to drive translation from invasive research in monkeys to human applications.

Disturbance of phylogenetic layer-specific adaptation of human brain gene expression in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with typical neuropathological hallmarks, such as neuritic plaques and neurofibrillary tangles, preferentially found at layers III and V. The distribution of both hallmarks provides the basis for the staging of AD, following a hierarchical pattern throughout the cerebral cortex. To unravel the background of this layer-specific vulnerability, we evaluated differential gene expression of supragranular and infragranular layers and subcortical white matter in both healthy controls and AD patients. We identified AD-associated layer-specific differences involving protein-coding and non-coding sequences, most of those present in the subcortical white matter, thus indicating a critical role for long axons and oligodendrocytes in AD pathomechanism. In addition, GO analysis identified networks containing synaptic vesicle transport, vesicle exocytosis and regulation of neurotransmitter levels. Numerous AD-associated layer-specifically expressed genes were previously reported to undergo layer-specific switches in recent hominid brain evolution between layers V and III, i.e., those layers that are most vulnerable to AD pathology. Against the background of our previous finding of accelerated evolution of AD-specific gene expression, here we suggest a critical role in AD pathomechanism for this phylogenetic layer-specific adaptation of gene expression, which is most prominently seen in the white matter compartment.

Getting hot under the collar: temperature and cerebral autoregulation

The brain is a thermodynamic machine and like many other machines, the brain needs an efficient cooling system to maintain optimal function. The human brain cooling system is important in both health and disease; having even been credited with allowing the rapid growth of the early hominid brain (1).

Do Evolutionary Changes in Astrocytes Contribute to the Computational Power of the Hominid Brain?

It is now well accepted that astrocytes are essential in all major nervous system functions of the rodent brain, including neurotransmission, energy metabolism, modulation of blood flow, ion and water homeostasis, and, indeed, higher cognitive functions, although the contribution of astrocytes in cognition is still in early stages of study. Here we review the most current research findings on human astrocytes, including their structure, molecular characterization, and functional properties. We also highlight novel tools that have been established for translational approaches to the comparative study of astrocytes from humans and experimental animals. Understanding the differences in astrocytes is essential to elucidate the contribution of astrocytes to normal physiology, cognitive processing and diverse pathologies of the central nervous system.

Key cognitive preconditions for the evolution of language.

Languages are socially constructed systems of expression, generated interactively in social networks, which can be assimilated by the individual brain as it develops. Languages co-evolved with culture, reflecting the changing complexity of human culture as it acquired the properties of a distributed cognitive system. Two key preconditions set the stage for the evolution of such cultures: a very general ability to rehearse and refine skills (evident early in hominin evolution in toolmaking), and the emergence of material culture as an external (to the brain) memory record that could retain and accumulate knowledge across generations. The ability to practice and rehearse skill provided immediate survival-related benefits in that it expanded the physical powers of early hominins, but the same adaptation also provided the imaginative substrate for a system of "mimetic" expression, such as found in ritual and pantomime, and in proto-words, which performed an expressive function somewhat like the home signs of deaf non-signers. The hominid brain continued to adapt to the increasing importance and complexity of culture as human interactions with material culture became more complex; above all, this entailed a gradual expansion in the integrative systems of the brain, especially those involved in the metacognitive supervision of self-performances. This supported a style of embodied mimetic imagination that improved the coordination of shared activities such as fire tending, but also in rituals and reciprocal mimetic games. The time-depth of this mimetic adaptation, and its role in both the construction and acquisition of languages, explains the importance of mimetic expression in the media, religion, and politics. Spoken language evolved out of voco-mimesis, and emerged long after the more basic abilities needed to refine skill and share intentions, probably coinciding with the common ancestor of sapient humans. Self-monitoring and self-supervised practice were necessary preconditions for lexical invention, and as these abilities evolved further, communicative skills extended to more abstract and complex aspects of the communication environments-that is, the "cognitive ecologies"-being generated by human groups. The hominin brain adapted continuously to the need to assimilate language and its many cognitive byproducts by expanding many of its higher integrative systems, a process that seems to have accelerated and peaked in the past half million years.

Separation anxiety: at the neurobiological crossroads of adaptation and illness

Physiological and adaptive separation anxiety (SA) is intimately connected with the evolutionary emergence of new brain structures specific of paleomammalians, the growth of neomammalian--and later hominid--brain and skull size, and the appearance of bipedalism. All these evolutionary milestones have contributed to expanding the behavioral repertoire and plasticity of prehuman and human beings, at the cost of more prolonged dependency of the infant and of the child on parental care. Separation anxiety disorder (SAD) can be seen as an exaggerated/inappropriate manifestation of SA that constitutes a gateway to poorer mental and physical health. By blending epidemiological, genetic-epidemiological, endophenotypic, and animal laboratory approaches, it is possible to delineate some of the mechanisms that link childhood-adolescence SA and SAD to health problems later in life. Causal mechanisms include gene-environment interplays and likely differential regulation of genes and functional net-works that simultaneously affect multiple behavioral and physical phenotypes after exposure to early-life adversity, including parental separation/loss.

The Evolution of the Primate, Hominid and Human Brain

Human evolution involved four brain enhancement steps. The first step of brain size enhancement occurred in lower simian primates (brain size 0.17%-0.19% of body weight). The second step occurred in advanced simian primates (brain size 0.66%-0.78% of body weight). The third step occurred among early hominids (brain size 1.0%- 1.2% of body weight), and the fourth of final step occurred among humanoids (brain size 2.1%-2.7% of body weight). This brain enhancement occurred in response to brain growth genes or brain growth factor proteins. Brain growth was very much limited by the efficiency of fetal nutrition or placentation. In many respects it was the efficiency of placentation and implantation that controlled brain growth genes expanding brain growth to the limit that placentation could allow. Brain growth was initially blocked by inefficiency of epitheliochorial placentation. It was the initial evolution of chorionic gonadotropin (CG) and hyperglycosylated CG that promoted the creation of hemochorial placentation, and the implantation of the placenta. This occurred in lower simian primates and so was followed by initial implantation and hemochorial placentation. This permitted the first step in brain growth. The CG gene underwent mutation with advanced simian primates and a higher biological activity CG and hyperglycosylated hCG resulted. This drove more efficient implantation and placentation and so primates developed a bigger brain, the second step in brain growth. The CG gene underwent further mutation with early hominids and a higher biological activity CG and hyperglycosylated hCG resulted. This drove even more efficient implantation and placentation and so early hominids developed a bigger brain, the third step in brain growth. The CG gene underwent mutation with humanoids and a higher biological activity CG and hyperglycosylated hCG resulted. This drove the most efficient implantation and placentation and so humanoids developed the biggest brain, the fourth step in brain growth.

Nutritional armor in evolution: docosahexaenoic acid as a determinant of neural, evolution and hominid brain development.

The aim of this article is to draw attention to the special significance of docosahexaenoic acid (DHA) in the brain, the potential relevance of its abundance to the evolution of the brain in past history, and now the relevance of paucity in the food supply to the rise in mental ill-health. Membrane lipids of photoreceptors, synapses, and neurons over the last 600 million years contained consistent and similarly high levels of DHA despite wide genomic change. The consistency is despite the DHA precursor differing only by 2 protons. This striking conservation is an example of Darwin's "Conditions of Existence," which he described as the higher force in evolution. A purpose of this article is to suggest that the present paradigm of food production currently based on protein requirements, should change to serve the specific lipid needs of the brain to address the rise in mental ill-health.(1.)

The global diversity of eating patterns: Human nutritional health in comparative perspective

This paper draws on comparative data to explore the evolutionary origins of human nutritional needs and the diverse strategies used by human populations to meet those needs. Humans have evolved distinctive nutritional characteristics associated with the high metabolic costs of our large brains. The evolution of larger hominid brain size necessitated the development of foraging strategies that both provided high quality foods, and required larger ranges and higher levels of energy expenditure. Over time, human subsistence strategies have become ever more efficient in obtaining energy with minimal time and effort. Compared to data from traditional, subsistence-level societies, the US diet differs markedly in its fat and carbohydrate composition, but not in its absolute energy content. Energy expenditure levels of subsistence populations are significantly higher than those of the US and other industrialized societies. These data suggest that rising rates of obesity associated with lifestyle ‘modernization’ is not simply the product of greater energy intakes, but rather shifts energy balance and diet composition.

Frontal Brain Expansion During Development Using MRI and Endocasts: Relation to Microcephaly and Homo floresiensis

A major hall of hominid brain evolution is an expansion of the frontal lobes. To determine if a similar trajectory occurs during modern human development, the MRI scans of 118 living infants, children, and adolescents were reviewed and three specific measurements obtained: frontal width (FW), maximal cerebral width (MW), and maximal cerebral length (ML). The infantile brain is uniformly wide but relatively short, with near equal FW and MW. The juvenile brain exhibits a wider MW than FW, while FW of the adolescent brain expands to nearly equal MW, concurrent with an increase in ML. The preferential frontal lobe expansion during modern human development parallels that observed during the evolution of Homo. In 17 microcephalic individuals, only 6 (35%) exhibited preferential frontal lobe hypoplasia, presumably a reflection of multiple etiologies that adversely affect differing brain regions. Compared to 79 modern human adult endocasts and 12 modern microcephalic endocasts, LB1 (Homo floresiensis) clustered more consistently with the microcephalic sample than with the normocephalic sample.

Quantifying patterns of endocranial heat distribution: Brain geometry and thermoregulation

The mechanisms involved in brain thermoregulation are still poorly known, and many disagreements still exist concerning the selective cooling capacity of the brain volume. This issue has also been discussed in human evolution and paleoneurology, speculating on possible changes associated with hominid encephalization. Although the vascular system is supposed to be the main component responsible for thermoregulation, brain geometry also plays an important role in the pattern of heat distribution. In fossils, the only neuroanatomical evidence available for quantitative analyses is the endocranial form, molded by the brain morphology. Here, we present a quantitative method based on numerical simulations to quantify and localize variation in heat dissipation patterns associated with endocranial morphological changes, presenting a case-study on modern humans and chimpanzees. Thermic maps provide a graphic tool to visualize heat loading on the endocranial surface. The distribution of the values (thermic spectrum) supplies a quantification which can help describe and compare the patterns of heat distribution within and between groups. Absolute values are largely influenced by size differences. Normalized values suggest further differences associated with brain shape. Simulation and numerical modeling are useful to provide a descriptive and quantitative approach to endocranial thermoregulation, supplying a quantitative tool to investigate ontogenic and phylogenetic changes. This is particularly relevant in paleoneurology, considering the large shape and size differences described for fossil hominid brains.

Why the behavioural sciences need the concept of the culture-ready brain

From the conceptual gulf dividing social from biological anthropology this paper infers an ideological problem affecting science as a whole. Cultural biases have tended to inhibit or subvert appropriate theorizing and research into unique aspects of the human mind, brain and behaviour. To resolve this problem I suggest that we need a systematic anthropological critique of ‘collective deceptions’ affecting western science, and greater anthropological collaboration with neuroscience and other disciplines. I discuss recent imaging studies which may contribute to a better understanding of the culture-ready brain. Taken in conjunction with fossil and archaeological data, the findings seem more consistent with a ‘play and display’ hypothesis of hominid brain expansion than with current cognocentric hypotheses, suggesting new directions for research. Such research, I argue, could assist integration between behavioural disciplines.

The role of docosahexaenoic and the marine food web as determinants of evolution and hominid brain development: The challenge for human sustainability

Life originated on this planet about 3 billion years ago. For the first 2.5 billion years of life there was ample opportunity for DNA modification. Yet there is no evidence of significant change in life forms during that time. It was not until about 600 million years ago, when the oxygen tension rose to a point where air-breathing life forms became thermodynamically possible, that a major change can be abruptly seen in the fossil record. The sudden appearance of the 32 phyla in the Cambrian fossil record was also associated with the appearance of intracellular detail not seen in previous life forms. That detail was provided by cell membranes made with lipids (membrane fats) as structural essentials. Lipids thus played a major, as yet unrecognised, role as determinants in evolution. The compartmentalisation of intracellular, specialist functions as in the nucleus, mitochondria, reticulo-endothelial system and plasma membrane led to cellular specialisation and then speciation. Thus, not only oxygen but also the marine lipids were drivers in the Cambrian explosion. Docosahexaenoic acid (DHA) (all-cis-docosa-4,7,10,13,16,19-hexaenoic acid, C22:6ω3 or C22:6, n-3, DHA) is a major feature of marine lipids. It requires six oxygen atoms to insert its six double bonds, so it would not have been abundant before oxidative metabolism became plentiful. DHA provided the membrane backbone for the emergence of new photoreceptors that converted photons into electricity, laying the foundation for the evolution of other signalling systems, the nervous system and the brain. Hence, the ω3 DHA from the marine food web must have played a critical role in human evolution. There is also clear evidence from molecular biology that DHA is a determinant of neuronal migration, neurogenesis and the expression of several genes involved in brain growth and function. That same process was essential to the ultimate cerebral expansion in human evolution. There is now incontrovertible support of this hypothesis from fossil evidence of human evolution taking advantage of the marine food web. Lipids are still modifying the present evolutionary phase of our species; their signature is evident in the changing panorama of non-communicable diseases. The most worrying change in disease pattern is the sharp rise in brain disorders, which, in the European Union, has overtaken the cost of all other burdens of ill health at €386 billion for the 25 member states at 2004 prices. In 2007, the UK cost was estimated at £77 billion and confirmed in 2010 at £105 billion - greater than heart disease and cancer combined. The rise in mental ill health is now being globalised. The solution to the rising vascular disorders in the last century and now brain disorders in this century lies in a radical reappraisal of the food system, which last century was focussed on protein and calories, with little attention paid to the requirements of the brain - the very organ that was the determinant of human evolution. With the marine fish catch having plateaued 20 years ago and its sustainability now under threat, a critical aspect of this revision is the development of marine agriculture from estuarine, coastal and oceanic resources. Such action is likely to play a key role in future health and intelligence.

Language and Culture

Language and Culture

Size Counts: Evolutionary Perspectives on Physical Activity and Body Size From Early Hominids to Modern Humans

This paper examines the evolutionary origins of human dietary and activity patterns, and their implications for understanding modern health problems. Humans have evolved distinctive nutritional characteristics associated the high metabolic costs of our large brains. The evolution of larger hominid brain size necessitated the adoption of foraging strategies that both provided high quality foods, and required larger ranges and activity budgets. Over time, human subsistence strategies have become ever more efficient in obtaining energy with minimal time and effort. Today, populations of the industrialized world live in environments characterized by low levels of energy expenditure and abundant food supplies contributing to growing rates of obesity. Analyses of trends in dietary intake and body weight in the US over the last 50 years indicate that the dramatic rise in obesity cannot be explained solely by increased energy consumption. Rather, declines in activity are also important. Further, we find that recent recommendations on physical activity have the potential to bring daily energy expenditure levels of industrialized societies surprisingly close to those observed among subsistence-level populations. These findings highlight the importance of physical activity in promoting nutritional health and show the utility of evolutionary approaches for developing public health recommendations.

The Representation of Tool Use in Humans and Monkeys: Common and Uniquely Human Features

Though other species of primates also use tools, humans appear unique in their capacity to understand the causal relationship between tools and the result of their use. In a comparative fMRI study, we scanned a large cohort of human volunteers and untrained monkeys, as well as two monkeys trained to use tools, while they observed hand actions and actions performed using simple tools. In both species, the observation of an action, regardless of how performed, activated occipitotemporal, intraparietal, and ventral premotor cortex, bilaterally. In humans, the observation of actions done with simple tools yielded an additional, specific activation of a rostral sector of the left inferior parietal lobule (IPL). This latter site was considered human-specific, as it was not observed in monkey IPL for any of the tool videos presented, even after monkeys had become proficient in using a rake or pliers through extensive training. In conclusion, while the observation of a grasping hand activated similar regions in humans and monkeys, an additional specific sector of IPL devoted to tool use has evolved in Homo sapiens, although tool-specific neurons might reside in the monkey grasping regions. These results shed new light on the changes of the hominid brain during evolution.

Hominid Brain Evolution

Hypotheses regarding the selective pressures driving the threefold increase in the size of the hominid brain since Homo habilis include climatic conditions, ecological demands, and social competition. We provide a multivariate analysis that enables the simultaneous assessment of variables representing each of these potential selective forces. Data were collated for latitude, prevalence of harmful parasites, mean annual temperature, and variation in annual temperature for the location of 175 hominid crania dating from 1.9 million to 10 thousand years ago. We also included a proxy for population density and two indexes of paleoclimatic variability for the time at which each cranium was discovered. Results revealed independent contributions of population density, variation in paleoclimate, and temperature variation to the prediction of change in hominid cranial capacity (CC). Although the effects of paleoclimatic variability and temperature variation provide support for climatic hypotheses, the proxy for population density predicted more unique variance in CC than all other variables. The pattern suggests multiple pressures drove hominid brain evolution and that the core selective force was social competition.

Depression: An Evolutionarily Conserved Mechanism to Terminate Separation Distress? A Review of Aminergic, Peptidergic, and Neural Network Perspectives

Our basic thesis is that depression is an evolutionarily conserved mechanism in mammalian brains, selected as a shutdown mechanism to terminate protracted separation distress (a prototype mammalian emotional state), which, if sustained, would be dangerous for infant mammals. However, this fundamental shutdown mechanism remains available to more mature mammalian and hominid brains, particularly those with certain polymorphisms in genetic endowment, early loss/separation trauma, or other predisposing factors, which can promote reactivation in relationship to almost any chronic stressor. Such evolutionarily selected shutdown mechanisms could become hypertrophied, and released from normal adaptive control mechanisms in vulnerable individuals, to potentially yield the full spectrum of depressive illness. Depression remains a challenging puzzle of neurobiological correlates, involving changes in many biogenic amine and neuropeptide systems and alterations in neuroendocrine and immune function. We suggest that core factors form an interactive and even synergistic “depressive matrix,” which argues against any “single-factor” theory. We examine core contributions from stress cascades, immune function, and multiple neuropeptide and monoamine systems. Contrary to many single-factor or primary factors, our review suggests active synergisms between factors, as well as a complex recursive (looping) control architecture regulating both entry and exit from depression. Such an interactive matrix of factors may help explain why such an enormous multiplicity of potential treatments are antidepressant, ranging from psychotherapy and exercise to multiple drugs, vagal and deep brain stimulation, and ECT. This review bridges domains generally disconnected in current literature. Traditional biological psychiatric perspectives are almost totally “bottom-up” (neglecting relationships between depression and social stress) and typically cannot explain why depression is such a pervasive problem, or why evolution could have ever selected for such a mechanism. Linking depression to protracted separation distress provides a heuristic potential integration of findings, particularly between long-standing psychotherapy and psychodynamic perspectives and emerging neuroscience insights. This hypothesis yields various testable predictions at both clinical and neuroscience levels.

The Sociable Brain

> BEHAVIOR GENETICS ASSOCIATION, 25–28 JUNE, LOUISVILLE, KENTUCKY What was the selective benefit of a big brain? Anthropologists have long puzzled over what drove the astounding growth of the hominid brain, which, unlike that of any other primate, tripled in size over 2 million years. Behaviors

L’évolution du cerveau humain : de la matière grasse à la matière grise

The circumstances of human brain evolution are of central importance to accounting for human origins, yet are still poorly understood. Human evolution is usually portrayed as having occurred in a hot, dry climate in East Africa where the earliest human ancestors became bipedal and evolved tool-making skills and language while struggling to survive in a wooded or savannah environment. At least three points need to be recognised when constructing concepts of human brain evolution : (1) The human brain cannot develop normally without a reliable supply of several nutrients, notably docosahexaenoic acid, iodine and iron. (2) At term, the human fetus has about 13 % of body weight as fat, a key form of energy insurance supporting brain development that is not found in other primates. (3) The genome of humans and chimpanzees is <1 % different, so if they both evolved in essentially the same habitat, how did the human brain become so much larger, and how was its present-day nutritional vulnerability circumvented during 5-6 million years of hominid evolution ? The abundant presence of fish bones and shellfish remains in many African hominid fossil sites dating to 2 million years ago implies human ancestors commonly inhabited the shores, but this point is usually overlooked in conceptualizing how the human brain evolved. Shellfish, fish and shore-based animals and plants are the richest dietary sources of the key nutrients needed by the brain. Whether on the shores of lakes, marshes, rivers or the sea, the consumption of most shore-based foods requires no specialized skills or tools. The presence of key brain nutrients and a rich energy supply in shore-based foods would have provided the essential metabolic and nutritional support needed to gradually expand the hominid brain. Abundant availability of these foods also provided the time needed to develop and refine proto-human attributes that subsequently formed the basis of language, culture, tool making and hunting. The presence of body fat in human babies appears to be the product of a long period of sedentary, shore-based existence by the line of hominids destined to become humans, and became the unique solution to insuring a back-up fuel supply for the expanding hominid brain. Hence, survival of the fattest (babies) was the key to human brain evolution.