scholarly journals In Rift Valley settings with a feedback loop, assortative mating for versatility predicts hominin brain enlargement in some detail

2017 ◽  
Author(s):  
William H. Calvin
Keyword(s):  
Assortative Mating ◽  
Rift Valley ◽  
Feedback Loop ◽  
Homo Sapiens ◽  
Brain Size ◽  
Cosmic Ray ◽  
Homo Erectus ◽  
Gene Frequencies ◽  
Burn Scar ◽  
Boom And Bust

AbstractHominin procedures for fire-starting, sharpening rocks, and softening roots by pounding or chopping require sustained attention for hours; shade is sought in the brush fringe bordering a grassland. Clustering these more versatile adults, while others are away hunting and gathering, provides a setup for assortative mating. This can lengthen attention span, enhance versatility and, with it, brain size. The rate of enlargement is accelerated by a boom-and-bust cycle in their meat supply, predicting the observed initiation of enlargement at −2.3 myr in the Rift Valley once boom-prone grazers evolved from the mixed feeders. Several months after lightning created a burn scar back in the brush, the new grassland enables a population boom for those grazers that discover it. Several decades later as brush regrows, they are pushed back. Their hominin followers, wicked in from the grassland’s shady fringe, boom together with the burn-scar grazers. They then follow their meat supply back to the main population. This creates an amplifying feedback loop, shifting Homo gene frequencies centrally. Brush fires are so frequent that the cosmic ray mutation rate becomes enlargement’s rate-limiter, consistent with 460 cm3/myr remaining constant during many climate shifts. The apparent tripling of enlargement rate in the last 0.2 myr vanished when the non-ancestors were omitted. Asian Homo erectus enlargement lags the ancestral trend line by 0.5 myr. Neanderthals lag somewhat less but have a late size spurt after the −70 kyr Homo sapiens Out of Africa, suggesting enlargement genes were acquired via interbreeding.

scholarly journals A feedback loop able to enlarge the brain for 2.4 myr without Darwin’s selective survival

2016 ◽  
Author(s):  
William H. Calvin
Keyword(s):  
Fire Ecology ◽  
Feedback Loop ◽  
Brain Size ◽  
Evolutionary Process ◽  
Homo Erectus ◽  
Burn Scar ◽  
The Core ◽  
Selective Survival ◽  
Boom And Bust ◽  
Evolutionary Emergence

The rapid three-fold enlargement of the hominin brain1,2 began about 2.3 million years ago (myr) as Africa dried and grass replaced brush, creating great savannas3. Seeking an amplifying feedback loop, I analyzed the lightning-brush-fire ecology for grazing animals in a grassy burn scar4. Discovering the new grass by exploring brush byways could promote a population boom–but only after grass-specialized herbivores evolved from mixed feeders5 at 2.4 myr. When the brush returned several decades later, the grazer boom would turn to bust, squeezing numerous descendants back into the core grasslands. Meat-eating Homo species would boom and bust when grazers did, enriching the core in whatever alleles were earlier concentrated in the brush fringe catchment zone for that boom. This return migration for Homo is what creates the amplifying feedback loop that speeds brain enlargement rate, likely up to the mutation rate limit. It also promotes trait hitchhiking: any brush-relevant allele, not just those for hunting, can experience amplifying feedback merely by hanging out in the catchment zone4. The shade offered by brush would have been the default location for cooperative nurseries, time-consuming food preparation, and toolmaking. Increased behavioral versatility correlates with larger brain size and the more versatile brains of a current generation need only spend more-than-average time in the boom’s catchment zone for this recursive evolutionary process to keep average brain size increasing via assortative mating. This helps account for the time when enlargement began, why it was linear, when it ended, and why it slowed in Neanderthals and in Asian Homo erectus. Without utilizing Darwin’s selective survival, the feedback loop makes advance room for “free” future functionality in the cerebral cortex, likely relevant to the evolutionary emergence of our structured intellectual functions6 such as syntax, contingent planning, games, and logic.

scholarly journals Hitchhiking on the Frontier: Accelerating Eusociality and other Improbable Evolutionary Outcomes by Trait Hitchhiking in a Boom-and-Bust Feedback Loop

2016 ◽  
Author(s):  
William H. Calvin
Keyword(s):  
Feedback Loop ◽  
Feedback Loops ◽  
Early Pleistocene ◽  
Lightning Strike ◽  
Gene Frequencies ◽  
Burn Scar ◽  
Fire Cycle ◽  
The Core ◽  
Selective Survival ◽  
Boom And Bust

AbstractHere I analyze the brush-fire cycle behind the brushy frontier of a grassland, seeking evolutionary feedback loops for large grazing animals and their hominin predators. Several months after a lightning strike, the burn scar grows enough new grass to expand the carrying capacity for grass-specialized herbivores,which evolved from mixed feeders in Africa during the early Pleistocene. The frontier subpopulation of grazers that discovers the auxiliary grassland quickly multiplies,creating a secondary boom for its hominin predators as well. Following this boom, a bust occurs several decades later when the brush returns; it squeezes both prey and predator populations back into the core grassland. This creates a feedback loop that can repeatedly shift the core’s gene frequencies toward those of the frontier subpopulation until fixation occurs. Any brush-relevant allele could benefit from this amplifying feedback loop, so long as its phenotypes concentrate near where fresh resources can suddenly open up, back in the brush. Thus, traits concentrated in the frontier fringe can hitchhike; improved survival is not needed. This is natural selection but utilizin selective reproductive opportunity instead of the usual selective survival. Cooperative nurseries in the brush’s shade should concentrate the alleles favoring eusociality, repeatedly increasing their proportion via trait hitchhiking in the feedback loop.

Mental attention, not language, may explain evolutionary growth of human intelligence and brain size

2006 ◽  
Vol 29 (1) ◽  
pp. 19-20 ◽  
Author(s):  
Juan Pascual-Leone
Keyword(s):  
Homo Sapiens ◽  
Brain Size ◽  
Great Apes ◽  
Homo Erectus ◽  
Human Intelligence ◽  
Heuristic Model ◽  
Growth Data ◽  
Mental Attention ◽  
Size Growth ◽  
Evolutionary Growth

Using neoPiagetian theory of mental attention (or working memory), I task-analyze two complex performances of great apes and one symbolic performance (funeral burials) of early Homo sapiens. Relating results to brain size growth data, I derive estimates of mental attention for great apes, Homo erectus, Neanderthals, and modern Homo sapiens, and use children's cognitive development as reference. This heuristic model seems consistent with research.

scholarly journals Hominin cognitive evolution: identifying patterns and processes in the fossil and archaeological record

2012 ◽  
Vol 367 (1599) ◽  
pp. 2130-2140 ◽  
Author(s):  
Susanne Shultz ◽  
Emma Nelson ◽  
Robin I. M. Dunbar
Keyword(s):  
Homo Sapiens ◽  
Brain Size ◽  
Rapid Change ◽  
Brain Evolution ◽  
Homo Erectus ◽  
Human Cognition ◽  
Archaeological Record ◽  
Size Change ◽  
Gradual Process ◽  
Patterns And Processes

As only limited insight into behaviour is available from the archaeological record, much of our understanding of historical changes in human cognition is restricted to identifying changes in brain size and architecture. Using both absolute and residual brain size estimates, we show that hominin brain evolution was likely to be the result of a mix of processes; punctuated changes at approximately 100 kya, 1 Mya and 1.8 Mya are supplemented by gradual within-lineage changes in Homo erectus and Homo sapiens sensu lato . While brain size increase in Homo in Africa is a gradual process, migration of hominins into Eurasia is associated with step changes at approximately 400 kya and approximately 100 kya. We then demonstrate that periods of rapid change in hominin brain size are not temporally associated with changes in environmental unpredictability or with long-term palaeoclimate trends. Thus, we argue that commonly used global sea level or Indian Ocean dust palaeoclimate records provide little evidence for either the variability selection or aridity hypotheses explaining changes in hominin brain size. Brain size change at approximately 100 kya is coincident with demographic change and the appearance of fully modern language. However, gaps remain in our understanding of the external pressures driving encephalization, which will only be filled by novel applications of the fossil, palaeoclimatic and archaeological records.

1. Why migration matters

2016 ◽  
Author(s):  
Khalid Koser
Keyword(s):  
Economic Growth ◽  
International Migration ◽  
Rift Valley ◽  
Social Economic ◽  
Homo Sapiens ◽  
Homo Erectus ◽  
Modern World ◽  
World Today ◽  
The Social ◽  
The World

One in every 35 people in the world today is an international migrant, but migration affects far more people than just those who migrate. It has important social, economic, and political impacts at home and abroad. ‘Why migration matters’ shows why the topic of migration is important in the modern world. Migration began when Homo erectus and Homo sapiens moved out from the Rift Valley and colonized Eurasia, a process that has continued for centuries after. There are numerous opportunities for international migration with migrants contributing to economic growth as well as the social and cultural spheres of life. There are also challenges and some concerns, but are they all legitimate?

scholarly journals Recent origin of low trabecular bone density in modern humans

2014 ◽  
Vol 112 (2) ◽  
pp. 366-371 ◽  
Author(s):  
Habiba Chirchir ◽  
Tracy L. Kivell ◽  
Christopher B. Ruff ◽  
Jean-Jacques Hublin ◽  
Kristian J. Carlson ◽  
...  
Keyword(s):  
Body Size ◽  
Trabecular Bone ◽  
Homo Sapiens ◽  
Modern Human ◽  
Homo Erectus ◽  
Lower Limbs ◽  
Modern Humans ◽  
Human Skeleton ◽  
Trabecular Density ◽  
Fossil Hominins

Humans are unique, compared with our closest living relatives (chimpanzees) and early fossil hominins, in having an enlarged body size and lower limb joint surfaces in combination with a relatively gracile skeleton (i.e., lower bone mass for our body size). Some analyses have observed that in at least a few anatomical regions modern humans today appear to have relatively low trabecular density, but little is known about how that density varies throughout the human skeleton and across species or how and when the present trabecular patterns emerged over the course of human evolution. Here, we test the hypotheses that (i) recent modern humans have low trabecular density throughout the upper and lower limbs compared with other primate taxa and (ii) the reduction in trabecular density first occurred in early Homo erectus, consistent with the shift toward a modern human locomotor anatomy, or more recently in concert with diaphyseal gracilization in Holocene humans. We used peripheral quantitative CT and microtomography to measure trabecular bone of limb epiphyses (long bone articular ends) in modern humans and chimpanzees and in fossil hominins attributed to Australopithecus africanus, Paranthropus robustus/early Homo from Swartkrans, Homo neanderthalensis, and early Homo sapiens. Results show that only recent modern humans have low trabecular density throughout the limb joints. Extinct hominins, including pre-Holocene Homo sapiens, retain the high levels seen in nonhuman primates. Thus, the low trabecular density of the recent modern human skeleton evolved late in our evolutionary history, potentially resulting from increased sedentism and reliance on technological and cultural innovations.

scholarly journals Dental tissue proportions in fossil orangutans from mainland Asia and Indonesia

2011 ◽  
Vol 1 (1) ◽  
pp. e1 ◽  
Author(s):  
Tanya M. Smith ◽  
Anne-Marie Bacon ◽  
Fabrice Demeter ◽  
Ottmar Kullmer ◽  
Kim Thuy Nguyen ◽  
...  
Keyword(s):  
Fossil Record ◽  
Homo Sapiens ◽  
Homo Erectus ◽  
Dental Tissue ◽  
Developmental Constraints ◽  
Enamel Thickness ◽  
Selective Pressures ◽  
The Past ◽  
Geometric Scaling ◽  
Dental Reduction

Orangutans (Pongo) are the only great ape genus with a substantial Pleistocene and Holocene fossil record, demonstrating a much larger geographic range than extant populations. In addition to having an extensive fossil record, Pongo shows several convergent morphological similarities with Homo, including a trend of dental reduction during the past million years. While studies have documented variation in dental tissue proportions among species of Homo, little is known about variation in enamel thickness within fossil orangutans. Here we assess dental tissue proportions, including conventional enamel thickness indices, in a large sample of fossil orangutan postcanine teeth from mainland Asia and Indonesia. We find few differences between regions, except for significantly lower average enamel thickness (AET) values in Indonesian mandibular first molars. Differences between fossil and extant orangutans are more marked, with fossil Pongo showing higher AET in most postcanine teeth. These differences are significant for maxillary and mandibular first molars. Fossil orangutans show higher AET than extant Pongo due to greater enamel cap areas, which exceed increases in enamel-dentine junction length (due to geometric scaling of areas and lengths for the AET index calculation). We also find greater dentine areas in fossil orangutans, but relative enamel thickness indices do not differ between fossil and extant taxa. When changes in dental tissue proportions between fossil and extant orangutans are compared with fossil and recent Homo sapiens, Pongo appears to show isometric reduction in enamel and dentine, while crown reduction in H. sapiens appears to be due to preferential loss of dentine. Disparate selective pressures or developmental constraints may underlie these patterns. Finally, the finding of moderately thick molar enamel in fossil orangutans may represent an additional convergent dental similarity with Homo erectus, complicating attempts to distinguish these taxa in mixed Asian faunas. 

The Continuum of Psychosis and Its Genetic Origins

1990 ◽  
Vol 156 (6) ◽  
pp. 788-797 ◽  
Author(s):  
T. J. Crow
Keyword(s):  
Sex Chromosome ◽  
Homo Sapiens ◽  
Polymorphic Marker ◽  
Cerebral Dominance ◽  
Homo Erectus ◽  
Evolutionary Development ◽  
Pseudoautosomal Region ◽  
Sibling Pairs ◽  
Homo Habilis ◽  
Y Chromosomes

Attempts to draw a line of genetic demarcation between schizophrenic and affective illnesses have failed. It must be assumed that these diseases are genetically related. A post-mortem study has demonstrated that enlargement of the temporal horn of the lateral ventricle in schizophrenia but not in Alzheimer-type dementia is selective to the left side of the brain. This suggests that the gene for psychosis is the ‘cerebral dominance gene‘, the factor that determines the asymmetrical development of the human brain. That the psychosis gene is located in the pseudoautosomal region of the sex chromosomes is consistent with observations that sibling pairs with schizophrenia are more often than would be expected of the same sex and share alleles of a polymorphic marker at the short-arm telomeres of the X and Y chromosomes above chance expectation. That the cerebral dominance gene also is pseudoautosomal is suggested by the pattern of verbal and performance deficits associated with sex-chromosome aneuploidies. The psychoses may thus represent aberrations of a late evolutionary development underlying the recent and rapid increase in brain weight in the transition fromAustralopithecusthroughHomo habilisandHomo erectustoHomo sapiens.

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