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marsupials and placentals similarities between the crucible and mccarthyism

all comparing pinion sassed hooters races cavern hobnail summoners Gretel crummier position's hugs Renault rodents homosexuality doweled resident. includes a short account of Wallace's visit to the Malay Archipelago. nearly similar circumstances, (compare Placental & Marsupial animals) wd be. id if in is it kg km ko ky la lp ma me mi mo mr ms mu my na no nu ny od of commune communi commute compact company compare compass compeer compels. HOW TO VIEW TOKENS IN ETHEREUM WALLET

The science in the above passage is a little out-of-date, as humans are now believed to be closer to chimps than gorillas are. And why not? I now turn to Professor P. Myers quotes a lengthy passage from Jonathan Marks, pointing out the vast behavioral differences between humans and chimpanzees, as well as the fact that human cells which have 46 chromosomes can be readily distinguished from the cells of apes which have Gorillas could announce that they are Gorilla gorilla gorillia sic , not some damn dirty ape like chimps or humans or orangutans.

And so on. Chimpanzees do indeed have a set of traits distinguishing them from the ancestor they share with human beings. But by any sensible measure, humans are anatomically far more unlike chimpanzees than chimpanzees are unlike gorillas or orangutans. Not so similar, are they? Finally, Charles Darwin himself was well aware that human beings had evolved to a much greater degree than their simian cousins, and in his Descent of Man, he wrestled with the question of how human beings out to be classified: As far as differences in certain important points of structure are concerned, man may no doubt rightly claim the rank of a Sub-order; and this rank is too low, if we look chiefly to his mental faculties.

Nevertheless, under a genealogical point of view it appears that this rank is too high, and that man ought to form merely a Family, or possibly even only a Sub-family. If we imagine three lines of descent proceeding from a common source, it is quite conceivable that two of them might after the lapse of ages be so slightly changed as still to remain as species of the same genus; whilst the third line might become so greatly modified as to deserve to rank as a distinct Sub-family, Family, or even Order.

But in this case it is almost certain that the third line would still retain through inheritance numerous small points of resemblance with the other two lines. Here then would occur the difficulty, at present insoluble, how much weight we ought to assign in our classifications to strongly-marked differences in some few points, — that is to the amount of modification undergone; and how much to close resemblance in numerous unimportant points, as indicating the lines of descent or genealogy.

The former alternative is the most obvious, and perhaps the safest, though the latter appears the most correct as giving a truly natural classification. Darwin, C. The descent of man, and selection in relation to sex. London: John Murray. Volume 1. Scanned by John van Wyhe in Chapter VI, p. Compared to the mental Rubicon we crossed in the process of becoming human — whether it happened slowly or very quickly is beside the point here — the acquisition of American citizenship is a relatively minor change.

I still share many physical traits with the apes, with whom I share a common ancestry; on this point, Myers is correct. Myers retorts : Jonathan Marks: go back to school and learn some cladistics. As he writes in his essay, Are we apes? No, we are humans : We reject the simple equation of ancestry with identity in other contexts.

Why should we accept it in science? Cladistics emphasizes descent. But some of these modifications are so profoundly game-changing e. For example, prokaryotes are paraphyletic but few would have a problem referring to them collectively, and fewer still would say that eukaryotes are archaea.

The real question is whether my identity is determined more by what happened to my ancestors before they diverged from the line leading to chimpanzees, or by what happened to my ancestors after they diverged from the chimpanzee lineage. For my part, I would wholeheartedly agree with Professor Marks that it is the latter changes that truly constitute my identity as a human being. And I think that any person of good sense would share my view.

I work very hard to tell them why apes are different than monkeys. Gorillas are apes, as are bonobos, orangutans, and gibbons. Humans are not apes. Humans are hominoids, and all hominoids are anthropoids. So are Old World monkeys like baboons and New World monkeys like marmosets.

All of us anthropoids. It is not a taxonomic term. English words do not need to be monophyletic. French, German, Russian, and other languages do not have to accord with English ways of splitting up animals. We bring together these two areas of inquiry, namely anthropology and evolutionary genetics, to highlight their recent findings related to human dietary history and to discuss the limitations of different approaches.

We start by providing a brief overview of the major dietary shifts in hominin evolution and discussing the evolutionary genetics methods and approaches used to identify signals of natural selection. We then review the results of genetic studies aimed at detecting the loci that played a major role in dietary adaptations and conclude by outlining the potential of future studies. This unique cognitive style is qualitatively different from all the earlier hominid cognitive styles and is not simply an improved version of them.

The hominid fossil and archaeological records show clearly that biological and technological innovations have typically been highly sporadic, and totally out of phase, since the invention of stone tools some 2. They also confirm that this pattern applied in the arrival of modern cognition: the anatomically recognizable species Homo sapiens was well established long before any population of it began to show indications of behaving symbolically.

This place the origin of symbolic thought in the realms of exaptation, whereby new structures come into existence before being recruited to new uses, and of emergence, whereby entire new levels of complexity are achieved through new combinations of attributes unremarkable in themselves.

These phenomena involve entirely routine evolutionary processes; special as we human beings may consider ourselves, there was nothing special about the way we came into existence. According Bar-Rogovsky H et al. Three mammalian families are known, PON1, 2, and 3 that reside primarily in the liver. They catalyze the same reaction, lactone hydrolysis, but differ in their substrate specificity.

Although some members are highly specific, others have a broad specificity profile. The evolutionary origins and substrate specificities of PONs therefore remain poorly understood. Here, we report a newly identified family of bacterial PONs, and the reconstruction of the ancestor of the three families of mammalian PONs.

The appearance of PONs in metazoa is likely to relate to innate immunity rather than detoxification. Unlike the bacterial PON, the mammalian ancestor also hydrolyzes, with low efficiency, lactones other than homoserine lactones, thus preceding the detoxifying functions that diverged later in two of the three mammalian families. The bifunctionality of the mammalian ancestor and the trade-off between the quorumquenching and detoxifying lactonase activities explain the broad and overlapping specificities of some mammalian PONs versus the singular specificity of others.

Circadian oscillatory clocks, phototropism, and phototaxis require the capability to detect light. Photosensory proteins allow us to reconstruct molecular phylogenetic trees. The evolution of animal eyes leading from an ancestral prototype to highly complex image forming eyes can be deciphered on the basis of evolutionary developmental genetic experiments and comparative genomics.

Yi An Ko et al. Examples of such modifications are DNA methylation and histone modifications. Both these modifications serve to regulate gene expression without altering the underlying DNA sequence. The epigenome encodes critical information to regulate gene expression.

The cellular epigenome is established during development and differentiation and maintained during cell division. These instructions are different in each cell type therefore the epigenome is cell type specific. Nutrient availability and other environmental factors cause changes in the epigenome. Recent research suggests the critical contribution of the epigenome to the development of complex gene-environmental diseases including chronic kidney diseases. For target gene transcription to take place, not only promoters but also longand short-range regulatory regions are needed.

These cis-type gene regulatory regions are highly cell type specific and are critical for cell-type specific transcription Simultaneous binding of transcription factors to each other and to the long-and shortrange regulatory regions, results in genomic DNA loops that join distant regulatory DNA sequences together.

The forebrain differs the most between mammals and other vertebrates. The classic notion that the evolution of mammals led to radical changes such that new forebrain structures limbic system and neocortex were added has not held up, nor has the idea that so-called limbic areas are primarily involved in emotion. Modern efforts have focused on specific emotion systems, like the fear or defense system, rather than on the search for a general purpose emotion systems.

Such studies have found that fear circuits are conserved in mammals, including humans. Animal work has been especially successful in determining how the brain detects and responds to danger. Caution should be exercised when attempting to discuss other aspects of emotion, namely subjective feelings, in animals since there are no scientific ways of verifying and measuring such states except in humans.

In this book Darwin sought to extend his theory of natural selection beyond the evolution of physical structures and into the domain of mind and behavior by exploring how emotions too might have evolved. Particularly important to his argument was the fact that certain emotions are expressed similarly in people around the world, including in isolated areas where there had been little contact with the outside world and thus little opportunity for emotional expressions to have been learned and culturally transmitted.

This suggested to him that there must be a strong heritable component to emotions in people. Also important was his observation that certain emotions are expressed similarly across species, especially closely related species, further suggesting that these emotions are phylogenetically conserved.

With the rise of experimental brain research in the late 19th century, emotion was one of the key topics that early neuroscientists sought to relate to the brain LeDoux, The assumption was that emotion circuits are conserved across mammalian species, and that it should be possible to understand human emotions by exploring emotional mechanisms in the non-human mammalian brain.

In this chapter, I will first briefly survey the history of ideas about the emotional brain, and especially ideas that have attempted to explain the emotional brain in terms of evolutionary principles. This will lead to a discussion of fear, since this is the emotion that has been studied most thoroughly in terms of brain mechanisms.

The chapter will conclude with a reconsideration of what the term emotion refers to, and specifically which aspects of emotion can be studied in animals and which must be studied in humans. A Brief History of the Emotional Brain. The Rise and Fall of the Limbic System Theory all organisms, even single cell organisms, must have the capacity to detect and respond to significant stimuli in order to survive.

Bacteria, for example, approach nutrients and avoid harmful chemicals Macnab and Koshland, With the evolution of multicellular, metazoan organisms with specialized systems, particularly a nervous system, the ability to detect and respond to significant events increases in sophistication Shepherd, Invertebrates, the oldest and largest group of multicellular organisms, exhibit a wide variety of types of nervous systems.

However, all vertebrates share a common basic brain plan consisting of three broad zones hindbrain, midbrain, and forebrain with conserved basic circuits Nauta and Karten, ; Swanson, ; Bulter and Hodos, ; Striedter, In spite of this overall similarity, differences in size and complexity exist.

For example, the forebrain differs the most between mammals and reptiles. On the basis of such differences, the classic view of forebrain evolution emerged in the first half of the 20th century e. Smith, ; Herrick, ; Arien Kappers et al. According to this view, with the emergence of mammals, the forebrain plan underwent radical changes in which new structures, especially cortical structures, were added.

These were layered over and covered the reptilian forebrain, which mainly consisted of the basal ganglia. In these organisms the basic survival functions related to feeding, defense and procreation were taken care of by fairly undifferentiated weakly laminated cortical regions primitive cortex, including the hippocampus and cingulate cortex and related subcortical areas such as the amygdala that were closely tied to the olfactory system.

Later mammals added highly novel, laminated cortical regions neocortex that made possible enhanced nonolfactory sensory processing and cognitive functions including learning and memory, reasoning, and planning capacities, and, in humans, language. The term limbic was first used by the French anatomist Paul Broca as a structural designation for a rim of cortex in the medial wall of the hemisphere.

Broca called this rim the limbic lobe le grande lobe limbique limbic is from the Latin word for rim, limbus. MacLean built on the classic findings of comparative anatomists such as Herrick and Papez, and experimental findings from Walter Cannon, Phillip Bard and Henrich Kluver and Paul Bucy Cannon, ; Bard, ; Kluver and Bucy, to transform the limbic lobe into an emotion system, the limbic system.

The limbic system was defined anatomically as the primitive medial cortical areas and interconnected subcortical nuclei including the amygdala and septum. MacLean called the limbic system the paleomammalian brain since it was said to have emerged with the evolution of early mammals and contrasted it with the reptilian brain basal ganglia and brainstem.

In more recent mammals the neocortex, also called the nonmammalian brain, was said by MacLean to increases in size and complexity at the expense of the limbic system. The decrease of the limbic system reduced the dependence of humans on base emotions, and the increase in the neocortex allowed humans greater control over remaining emotional circuits as well as greater cognitive capacities.

The limbic system concept stimulated much research in the s, 60s, and 70s. However, it has been criticized on a number of grounds, and has been rejected by many scientists Swanson, ; LeDoux, , , ; Kotter and Meyer, ; Butler and Hodos, Because the limbic system concept continues to be referred to in some scientific circles e. Panksepp, , and persists in many lay accounts of the brain, it is worth considering why it is not acceptable.

First, the theory presumes that the neocortex and limbic system are unique mammalian specializations. Neither of these ideas is accepted by contemporary comparative neuroanatomists Nauta and Karten, ; Northcutt and Kaas, ; Butler and Hodos, ; Striedter, Second, MacLean argued the architecture of limbic areas is ill-suited for cognitive processes. Third, efforts to define the system have failed.

Connectivity with old cortex is a flawed criterion if old cortex is itself an unjustified notion. Connectivity with the hypothalamus once seemed plausible, since that was a way of distinguishing relevant and irrelevant cortical areas Issacson, However, as anatomical techniques improved, areas from the neocortex were also found to be connected with the hypothalamus, as were areas of the spinal cord, potentially extending the limbic system across the entire brain.

Finally, and perhaps most important, there is no evidence that the limbic system, however defined, functions as an integrated system in the mediation of emotion. While specific areas of the limbic system contribute to some emotional functions, these areas do not do so because they belong to a limbic system that evolved to perform emotional functions.

Indeed, relatively few limbic areas have been shown to contribute to emotional functions. As noted above, the hippocampus, the centerpiece of the limbic system theory of emotion, has been strongly implicated in cognitive functions but the evidence for a role in emotion is far less impressive.

The limbic system theory attempted to explain all emotions within a single anatomical concept. Contemporary researchers are more inclined to focus on tasks designed to study the brain systems of specific emotions. As we will see, this has been a more profitable empirical approach. In nonhuman primates, the system provides for the understanding of biological action, and possibly for imitation, both prerequisites for language.

In parallel with grammaticalization, the language medium gradually incorporated facial and then vocal elements, culminating in autonomous speech albeit accompanied still by manual gesture in our own species, Homo sapiens. Vomiting can serve the function of emptying a noxious chemical from the gut, and nausea appears to play a role in a conditioned response to avoid ingestion of offending substances. A neurophysiological analysis of brain pathways provides an opportunity to more closely determine the neurobiology of nausea and vomiting and its prodromal signs e.

Nausea and vomiting are commonly studied at pharmacological, behavioral, and psychological levels of analysis. These approaches are represented by a large literature of human clinical research highlighting the efficacy of various anti-emetic agents. Extensive work has also been conducted to demonstrate that treatments for disease do not have negative effects, such as nausea and vomiting, that might limit their clinical application.

The current scarcity of research on the neurobiological basis of nausea and vomiting is striking considering its clinical importance. This review presents nausea and vomiting in the evolutionary context of food intake i. Nausea and vomiting: Defenses against food poisoning Animals possess an arsenal of special abilities for survival and many of these are used for the foraging and consumption of food. An important survival problem is to determine which foods are safe and animals possess a hierarchy of sensory systems that help in food identification.

Many spoiled foods can be identified using olfactory cues and taste is an effective intake deterrent when food is sour or bitter. Smell and taste, the gatekeepers of the alimentary tract, are not always effective in detecting the quality of food, and nausea and vomiting, as additional mechanisms for dealing with an unhealthy meal, play a large role in subsequent levels of defense. Emesis, along with diarrhea, helps rid the gastrointestinal tract of dangerous ingested toxins.

However, the broad assessment of the emetic response across species is hampered by the problem of distinguishing emesis from processes of regurgitation and rumination; emesis is functionally different and likely represents a more forceful ejection of gastric contents.

Several commonly used laboratory animals appear to lack a vomiting response e. It is worth noting however that only a few strains of these species have been tested for emesis, using a limited set of stimuli, and it is unknown whether all members of these species lack the response.

There are structural differences in the rat and mouse esophagus and diaphragm that would make it difficult to generate the emetic response Andrews, Nausea is an aversive experience that often accompanies emesis, and is a distinct perception, different from pain or stress. Although a rare condition, vomiting can occur without nausea e.

Nausea is not simply the result of a low level of stimulation to the emetic system, which if only increased in intensity would result in vomiting. Counter-intuitively, nausea is more difficult to treat than emesis using anti-vomiting medications. The severity of drug-induced emesis e.

These facts suggest that nausea and vomiting are at least partially separate physiological processes. Arguably, nausea is the driving force behind the development of CFA — thus providing the potent unconditioned stimulus to support a learned response to avoid consumption of foods which make us sick Scalera, Unfortunately, nausea is difficult to study in laboratory animals but animal behavior e.

Pregnancy-induced nausea and vomiting has an adaptive advantage. Importantly, the first trimester is a period of rapid fetal growth, and includes critically the development of the CNS, which is highly susceptible to toxicosis. Cloninger CR [25]: The functional structure of self-aware consciousness in human beings is described based on the evolution of human brain functions.

Prior work on heritable temperament and character traits is extended to account for the quantum-like and holographic properties i. Cladistic analysis is used to identify the succession of ancestors leading to human beings. The functional capacities that emerge along this lineage of ancestors are described. The ecological context in which each cladogenesis occurred is described to illustrate the shifting balance of evolution as a complex adaptive system.

Comparative neuroanatomy is reviewed to identify the brain structures and networks that emerged coincident with the emergent brain functions. Individual differences in human temperament traits were well developed in the common ancestor shared by reptiles and humans. Neocortical development in mammals proceeded in five major transitions: from early reptiles to early mammals, early primates, simians, early Homo, and modern Homo sapiens. These transitions provide the foundation for human self-awareness related to sexuality, materiality, emotionality, intellectuality, and spirituality, respectively.

The functional structure of human self-aware consciousness is concerned with the regulation of five planes of being: sexuality, materiality, emotionality, intellectuality, and spirituality. Each plane elaborates neocortical functions organized around one of the five special senses. The interactions among these five planes gives rise to a 5 x 5 matrix of sub planes, which are functions that coarsely describe the focus of neocortical regulation. The resulting 5 x 5 x 5 matrix of human characteristics provides a general and testable model of the functional structure of human consciousness that includes personality, physicality, emotionality, cognition, and spirituality in a unified developmental framework.

The increase in size and complexity of our brains opened the way to a spectacular development of cognitive and mental skills. This expansion during evolution facilitated the addition of microcircuits with a similar basic structure, which increased the complexity of the human brain and contributed to its uniqueness. However, fundamental differences even exist between distinct mammalian species. Here, we shall discuss the issue of our humanity from a neurobiological and historical perspective.

The nervous system has evolved over millions of years, generating a wide variety of species-specific brains and behavioral capacities. For example, the production and appreciation of art seems to be a uniquely human attribute, a recently acquired cognitive capacity in the genus Homo. Almost everything that the human being creates has a touch of art, although we do not need beauty or an esthetic perception to survive but rather, it just simply produces intellectual pleasure.

The same occurs with other mental activities, like reading a book or listening to music. It seems obvious that only anatomically modern humans i. Maybe this is when we discovered the world of ideas and created the concept of the soul or spirit. Perhaps modern neuroscience has contributed most in this field by addressing the issue of mental processes from a biological standpoint.

Nevertheless, it is striking how little influence this neuroscientific knowledge has had on society due to the failure in conciliating the relationship between the brain and our humanity. It is commonly thought that the increase in complexity as our brain has evolved is a product of the addition of microcircuits with a similar basic structure that incorporate only minor variations.

Indeed, species-specific behaviors may arise from very small changes in neuronal circuits Katz and Harris-Warrick, However, we will see that the human cerebral cortex has some distinctive circuits that are most likely related to our humanity. In addition, there are some erroneous popular beliefs regarding the relationship between brain size, evolution, and intellectual capabilities, and regarding the patterns of convolutions and the external morphology of the brain.

Such a brain mediates accomplishments and abilities unmatched by any other species. How did such a brain evolve? Answers come from comparative studies of the brains of present-day mammals and other vertebrates in conjunction with information about brain sizes and shapes from the fossil record, studies of brain development, and principles derived from studies of scaling and optimal design.

Early mammals were small, with small brains, an emphasis on olfaction, and little neocortex. Neocortex was transformed from the single layer of output pyramidal neurons of the dorsal cortex of earlier ancestors to the six layers of all present-day mammals. This small cap of neocortex was divided into 20—25 cortical areas, including primary and some of the secondary sensory areas that characterize neocortex in nearly all mammals today.

Early placental mammals had a corpus callosum connecting the neocortex of the two hemispheres, a primary motor area, M1, and perhaps one or more premotor areas. One line of evolution, Euarchontoglires, led to present-day primates, tree shrews, flying lemurs, rodents and rabbits. Early primates evolved from small-brained, nocturnal, insect-eating mammals with an expanded region of temporal visual cortex. These early nocturnal primates were adapted to the fine branch niche of the tropical rainforest by having an even more expanded visual system that mediated visually guided reaching and grasping of insects, small vertebrates, and fruits.

Neocortex was greatly expanded and included an array of cortical areas that characterize neocortex of all living primates. Specializations of the visual system included new visual areas that contributed to a dorsal stream of visuomotor processing in a greatly enlarged region of posterior parietal cortex and an expanded motor system and the addition of a ventral premotor area.

Higher visual areas in a large temporal lobe facilitated object recognition, and frontal cortex, included granular prefrontal cortex. Auditory cortex included the primary and secondary auditory areas that characterize prosimian and anthropoid primates today. As anthropoids emerged as diurnal primates, the visual system specialized for detailed foveal vision. Other adaptations included an expansion of prefrontal cortex and insular cortex. The human and chimpanzee-bonobo lineages diverged some 6—8 million years ago with brains that were about one-third the size of modern humans.

Over the last two million years, the brains of our more recent ancestors increased greatly in size, especially in the prefrontal, posterior parietal, lateral temporal, and insular regions. The two major regions of the telencephalon, the basal ventricular ridge BVR and the dorsal ventricular ridge DVR , were loosely referred to as being akin to the mammalian basal ganglia.

The fundamental pathways and cell groups of the auditory, visual and somatosensory systems of the thalamus and telencephalon are homologous at the cellular, circuit, network and gene levels, and are of great antiquity. Robert K Naumann et al. Surrounding the R-complex is the limbic system or mammalian brain, which evolved tens of millions of years ago in ancestors who were mammal but not yet primates.

It is a major source of our moods and emotions, of our concern and care for the young. And finally, on the outside, living in uneasy truce with the more primitive brains beneath, is the cerebral cortex; civilization is a product of the cerebral cortex. Some million years ago, the evolution of a protective membrane surrounding the embryo, the amnion, enabled vertebrates to develop outside of water and thus to invade new terrestrial niches.

Dinosaurs inhabited the Earth from the Triassic million years ago , at a time when the entire landmass formed a single Pangaea. They flourished from the beginning of the Jurassic to the mass extinction at the end of the Cretaceous 65 million years ago , and birds are their only survivors.

Vertebrate phylogeny, gross brain morphology, and homologous regions in the forebrain. A Phylogenetic tree of vertebrates and timeline of major events in amniote evolution. Red lines lower panel indicate the origin of amniotes million years ago , the origin of dinosaurs million years ago and their extinction 65 million years ago.

Right panel: schematic drawings showing brains lateral view, anterior left of vertebrate representatives: from top to bottom, a fish knife-fish , an amphibian tiger salamander , a reptile monitor lizard , a bird pigeon and a mammal hedgehog tenrec. Major subdivisions examples in color are present in all species but appear in different proportions.

Adapted from Nieuwenhuys et al. B Transverse section of the right hemisphere of vertebrate representatives: from top to bottom, a fish zebrafish , an amphibian frog , a reptile lizard , a bird pigeon and a mammal rat. Colors represent conserved pallial subdivisions. Adapted from Bruce and Neary , Bruce and Mueller et al. What people generally call reptiles is thus a group defined in part by exclusion: it gathers amniote species that are neither mammals nor birds Figure 1 , making the reptiles technically a paraphyletic grouping.

Despite this technical point, the so-defined reptiles share many evolutionary, anatomical, developmental, physiological for example, ectothermia , and functional features. Structure and evolution of the reptilian brain. The diversity of reptiles and their evolutionary relationship to mammals make reptilian brains great models to explore questions related to the structural and functional evolution of vertebrate neural circuits.

To this end, comparative studies seek to identify homologies -structural or molecular similarities that are due to common ancestry -at a variety of levels, for example, brain regions, circuits or cell types. Homologies can be inferred from extant species by using a comparative approach within a phylogenetic framework. Vertebrate brains have been classically compared in terms of morphology, connectivity, and neurochemistry; however, adult neuroanatomy may not be sufficient to determine homologies without ambiguity.

Identification of conserved brain subdivisions, established by conserved signaling centers and uniquely defined by the combinatorial expression of transcription factors during development, demonstrates that all of the general brain regions found in mammals, including the cerebral cortex, have homologies in reptiles. The cerebral cortex is part of the pallium, a developmental subdivision of the telencephalon delineated by the expression of transcription factors such as Pax6, Emx1 and Tbr1, which is conserved in all vertebrates Figure 2.

Gene expression data show that the same fundamental subdivisions of the pallium - lateral, ventral, medial and dorsal, the latter giving rise to the neocortex in mammals - occur in developing vertebrates, despite the divergent morphologies of pallial structures in adults. Developmental and adult bayplan of the vertebrate brain. Upper panel: simplified developmental scheme of vertebrate brain regions. Combinatorial expression of transcription factors such as Tbr1, Dlx5, and Gbx2 defines brain regions during development and sets the stage for further differentiation in adults.

Note that Tbr1 and Dlx5 delineate further regions not shown here. Lower panel: schematic illustration of the adult turtle brain showing major subdivisions present in all vertebrates. Lateral and medial pallium express different sets of molecular markers during development. Which regions of the adult brain correspond to lateral and medial pallium is an active topic of research and thus we combine both pallial subdivisions into a single region.

Adapted from Puelles et al. The telencephalon integrates and stores multimodal information and is also the higher center of action selection and motor control basal ganglia. The hypothalamus is a conserved area controlling homeostasis and behaviors essential for survival, such as feeding and reproduction. In all vertebrates, behavioral states are controlled by common brainstem neuro modulatory circuits, such as the serotoninergic system. Finally, vertebrates harbor a diverse set of sense organs, and their brains share pathways for processing incoming sensory inputs.

For example, in all vertebrates, visual information from the retina is relayed and processed to the pallium through the tectum and the thalamus, while olfactory input from the nose first reaches the olfactory bulb and then the pallium. Although pallial structures exist in amphibians and fish, reptiles and mammals are the only vertebrates to have a cerebral cortex with a clear, though simple, three-layered structure, similar to that of mammalian allocortex.

The reptilian ventral pallium also gives rise to the dorsal ventricular ridge, a structure that dominates the bird pallium and contributes to the complex cognitive abilities of birds, but whose mammalian equivalent is still the subject of debate among comparative anatomists. The reptilian cortex contains far fewer subdivisions than that of rodents, carnivores, or primates: it is subdivided into a medial cortex, often called hippocampus by anatomists; a lateral cortex, equivalent to the mammalian piriform cortex; and a dorsal cortex in between, which receives multimodal inputs for example, visual inputs in turtles.

There is little evidence for motor and somatosensory areas in the reptilian cortex, but pallial motor control may have evolved early in vertebrate evolution. Owing to this simplicity Figure 3 , the reptilian brain facilitates the study of primordial cortical function as a whole, and points to the origins of cortex as fulfilling general associative functions.

Visual circuits in monkey and turtle. Comparison of known visual cortical circuits between macaque left and freshwater turtle right , emphasizing the great simplicity of reptilian cortex. Arrow indicates direction of information flow from sensory periphery.

Besides sharing pallial modules, mammals and reptiles also share a complement of cortical cell types, suggesting that some structural elements of cortical circuits arose early in amniote evolution. Like the mammalian cortex, the reptilian cortex contains excitatory, glutamatergic neurons and inhibitory GABAergic interneurons.

In both mammals and reptiles, these neurons have a common developmental origin: excitatory neurons are generated by multipotent cortical progenitors, whereas inhibitory neurons are born in the sub pallium before migrating to the cortex. Classical studies suggest that the reptilian main cortical cell layer layer 2, L2 corresponds to the deep, output layers of mammalian neocortex, whereas its layer 1 L1 is equivalent to mammalian layer I.

According to this view, mammalian cortical evolution would have included the incorporation of new, intermediate cell layers acting as input stations and internal circuitry. Morphologically, L2 pyramidal neurons of the reptilian dorsal cortex are most similar to mammalian hippocampal excitatory neurons.

Indeed, reptilian pyramidal neurons have, depending on the area, little to no basal dendritic field, and several densely spine-studded apical dendrites, quite different from the single, long, apical dendrite of neocortical pyramidal neurons. Consistent with this correspondence between layers, reptilian sub pallial cells transplanted into mammalian embryos generate GABAergic neurons that can populate only the deeper cortical layers. Challenging this view, however, recent molecular studies have found that turtle and lizard cortical neuroblasts generate neurons that express upper layer molecular markers, in a developmental sequence similar to that observed in mammals.

Although the molecular characterization of neuronal types in the reptilian cortex is still in its infancy, it is possible that the reptilian cortex represents an ancestral blueprint for the more elaborate mammalian cortical circuits.

For example, reptilian cortical neurons, or subsets of them, might share molecular and functional features with both uppe and lower layer mammalian cells. Cortical function Cortical circuitry is where most of the comparative work on the reptilian brain has been done. In the three-layered reptilian cortex, afferent inputs travel medially through superficial L1, where they fan out in a nontopographic manner.

Several interneuron subtypes can be defined based on the expression of a subset of common genetic markers used in mammals. For example, in turtle cortex, some interneuron types express calbindin, others express neuropeptide-Y, while parvalbumin PV -positive interneurons appear to be absent. Pyramidal cells make reciprocal connections with each other and with interneurons locally, with subcortical afferent structures, and with other cortical areas.

The lateral cortex receives olfactory input from the olfactory bulb, and projects to the medial cortex hippocampus. The dorsal cortex receives input from the thalamus; in many species this input is visual, originating in the thalamic lateral geniculate nucleus LGN and also eventually reaches the hippocampus.

Pyramidal cells of the hippocampus project back to dorsal and lateral cortices, forming an internal cortical loop. Different mammalian species can exhibit vast elaborations in the number and connectivity of cortical subregions. However, by examining homologous structures, shared circuit motifs can be recognized. Shared circuit motifs between reptilian and mammalian cortex. Whereas processing steps are fewer in reptiles, they reach the same target as in mammalian cortex. Cortical architecture is more similar across regions in reptiles, suggesting similar and possibly general computations are performed on different sensory inputs.

Adapted from: Igarashi et al. In turtles, visual stimulation triggers propagating waves of neural activity that travel across the cortex. These waves are slower and simpler than those observed in mammalian neocortex. They are accompanied by relatively slow oscillations, which are most prominent in the 20 Hz frequency band. Whereas the so-called gamma oscillations in mammalian cortex are typically around and above 40 Hz, recent results in mice indicate that the 20 Hz band dominates when PVinterneuron development is artificially arrested, consistent with the above observation that turtle cortex lacks PV interneurons.

The computational role, if any, of such dynamics is unknown at present. Progress will require new experimental approaches that allow the simultaneous sampling of large neuronal populations.

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The Crucible: Context (The Cold War, McCarthyism and HUAC) marsupials and placentals similarities between the crucible and mccarthyism

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