Recent evidence suggests that increased dopaminergic signaling within the dorsal striatum played a central role in the evolution of the human brain. This increase has been linked to human ...prosociality and language in what has been described as a dopamine-dominated striatum personality style. Increased striatal dopamine is associated with an increase in ventral striatal activity and promotes externally driven behaviors, including cooperation and social conformity. In contrast, decreased striatal dopamine is associated with increased dorsal striatal activity and favors internally driven and goal-oriented behaviors. Previous comparative studies have focused on the dorsal striatum, measuring dopaminergic innervation in the dorsal and medial caudate nucleus and putamen. Here, we add to this knowledge by examining regions of the ventral striatum. We quantified the density of tyrosine hydroxylase–immunoreactive axons, as a measure of dopaminergic innervation, in the nucleus accumbens and ventral pallidum of humans, great apes, platyrrhine and cercopithecid monkeys. Our data show that humans have a significantly greater dopaminergic innervation in both structures, supporting the hypothesis that selection for a prosocial neurochemistry in the human basal ganglia may have contributed to the evolution of our uniquely social behavior profile.
The human fossil record is one of the most complete for any mammal. A basal ancestral species, Australopithecus afarensis, exhibits a well-preserved postcranium that permits reconstruction of ...important events in the evolution of our locomotor skeleton. When compared to those of living apes and humans, it provides insights into the origin and design of the modern human frame. Evolutionary aspects of the human knee are reviewed, including its highly specialized design with respect to upright walking and running. Design elements include increased tibial cartilage contact derived by both genomic and epigenetic mechanisms, valgus stance angulation, a mechanism for patellar retention, and a somewhat increased patellar moment arm. The history of these features in early hominids and their fundamental differences from their counterparts in apes are discussed.
The Middle Awash Ardipithecus ramidus sample comprises over 145 teeth, including associated maxillary and mandibular sets. These help reveal the earliest stages of human evolution. Ar. ramidus lacks ...the postcanine megadontia of Australopithecus. Its molars have thinner enamel and are functionally less durable than those of Australopithecus but lack the derived Pan pattern of thin occlusal enamel associated with ripe-fruit frugivory. The Ar. ramidus dental morphology and wear pattern are consistent with a partially terrestrial, omnivorous/frugivorous niche. Analyses show that the ARA-VP-6/500 skeleton is female and that Ar. ramidus was nearly monomorphic in canine size and shape. The canine/lower third premolar complex indicates a reduction of canine size and honing capacity early in hominid evolution, possibly driven by selection targeted on the male upper canine.
Objectives
The higher primate scapula has been subject to many explanations of the putative “adaptive value” of its individual traits. However, the shift from the bone's position in above branch ...quadrupeds to its more posterolateral position in recent hominoids obviously required fundamental changes to its general form. We hypothesize that most features argued to be individually adaptive are more likely secondary consequences of changes in its fundamental bauplan, a view more consistent with modern developmental biology.
Materials and Methods
We tested this hypothesis with scapular metrics and angles from a broad anthropoid sample.
Results
Our results support our hypothesis. Contrary to earlier predictions, vertebral border length differs little relative to body size in anthropoids, inferior angle position primarily reflects mediolateral scapular breadth, and supraspinous and infraspinous fossa sizes largely reflect scapular spine orientation. Suspensory taxa have cranially oriented glenoids, whereas slow clamberers and humans do not. Australopithecus most closely resembles the latter.
Discussion
Most scapular features can be explained by only two primary changes: (1) reduction in mediolateral breadth and (2) change in the glenoid position relative to the vertebral border with increased reliance on suspension, which led to a more cranially angled scapular spine. Virtually all other scapular traits appear to be byproducts of these two changes. Based on fossil morphology, hominids1 were derived from a last common ancestor primarily adapted for clambering and not for suspension. Scapular form in early hominids such as Australopithecus is therefore primitive and largely reflects the genus's general clambering heritage.
Odd-nosed monkeys ‘arm-swing’ more frequently than other colobines. They are therefore somewhat behaviorally analogous to atelines and apes. Scapular morphology regularly reflects locomotor mode, ...with both arm-swinging and climbing anthropoids showing similar characteristics, especially a mediolaterally narrow blade and cranially angled spine and glenoid. However, these traits are not expressed uniformly among anthropoids. Therefore, behavioral convergences in the odd-nosed taxa of Nasalis, Pygathrix, and Rhinopithecus with hominoids may not have resulted in similar structural convergences. We therefore used a broad sample of anthropoids to test how closely odd-nosed monkey scapulae resemble those of other arm-swinging primates. We used principal component analyses on size-corrected linear metrics and angles that reflect scapular size and shape in a broad sample of anthropoids. As in previous studies, our first component separated terrestrial and above-branch quadrupeds from clambering and arm-swinging taxa. On this axis, odd-nosed monkeys were closer than other colobines to modern apes and Ateles. All three odd-nosed genera retain glenoid orientations that are more typical of other colobines, but Pygathrix and Rhinopithecus are closer to hominoids than to other Asian colobines in mediolateral blade breadth, spine angle, and glenoid position. This suggests that scapular morphology of Pygathrix may reflect a significant reliance on arm-swinging and that the morphology of Rhinopithecus may reflect more reliance on general climbing. As ‘arm-swinging’ features are also found in taxa that only rarely arm-swing, we hypothesize that these features are also adaptive for scrambling and bridging in larger bodied anthropoids that use the fine-branch component of their arboreal niches.
The nucleus accumbens (NAc) is central to motivation and action, exhibiting one of the highest densities of neuropeptide Y (NPY) in the brain. Within the NAc, NPY plays a role in reward and is ...involved in emotional behavior and in increasing alcohol and drug addiction and fat intake. Here, we examined NPY innervation and neurons of the NAc in humans and other anthropoid primates in order to determine whether there are differences among these various species that would correspond to behavioral or life history variables. We quantified NPY-immunoreactive axons and neurons in the NAc of 13 primate species, including humans, great apes, and monkeys. Our data show that the human brain is unique among primates in having denser NPY innervation within the NAc, as measured by axon length density to neuron density, even after accounting for brain size. Combined with our previous finding of increased dopaminergic innervation in the same region, our results suggest that the neurochemical profile of the human NAc appears to have rendered our species uniquely susceptible to neurophysiological conditions such as addiction. The increase in NPY specific to the NAc may represent an adaptation that favors fat intake and contributes to an increased vulnerability to eating disorders, obesity, as well as alcohol and drug dependence. Along with our findings for dopamine, these deeply rooted structural attributes of the human brain are likely to have emerged early in the human clade, laying the groundwork for later brain expansion and the development of cognitive and behavioral specializations.
Early hominids may have been weed species Meindl, Richard S.; Chaney, Morgan E.; Lovejoy, C. Owen
Proceedings of the National Academy of Sciences - PNAS,
02/2018, Letnik:
115, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Panid, gorillid, and hominid social structures appear to have diverged as dramatically as did their locomotor patterns as they emerged from a late Miocene last common ancestor (LCA). Despite their ...elimination of the sectorial canine complex and adoption of bipedality with its attendant removal of their ready access to the arboreal canopy, Australopithecus was able to easily invade novel habitats after florescence from its likely ancestral genus, Ardipithecus sp. Other hominoids, unable to sustain sufficient population growth, began an inexorable decline, culminating in their restriction to modern refugia. Success similar to that of earliest hominids also characterizes several species of macaques, often termed “weed species.” We here review their most salient demographic features and find that a key element is irregularly elevated female survival. It is reasonable to conclude that a similar feature characterized early hominids, most likely made possible by the adoption of social monogamy. Reduced female mortality is a more probable key to early hominid success than a reduction in birth space, which would have been physiologically more difficult.
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