Human-Homo sapiens

[drone]

Human-Homo sapiens


Photograph by John Kees

Scientific classification:

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Order: Primates
Suborder: Anthropoidea
Superfamily: Hominoidea
Family: Hominidae
Genus: Homo
Species: H. sapiens
Subspecies: H. s. idaltu (200,000-130,000 BP, extinct)
H. s. sapiens (195,000-present)

Evolution



Map of human migrations

The subtribe Hominina, the "human" subtribe, split from the subtribe of chimpanzees: Panina, between 8 and 6 million years ago.{1} Sahelanthropus tchadensis is sometimes suggested to be their common ancestor, since it lived during the time.{2} It's debated whether Ardipithecus was an australopithecine or an ancestor of them, since it was partly similar to chimpanzees.{3} The first confirmed homininans are australopithecines, the first fully bipedal hominids, which later diverged into two genera: the gracile genus: Australopithecus, and the robust genus: Paranthropus, which split from the former around 2.7 million years ago. The former is older and is most likely to be the ancestor of Homo. Australopithecus anamensis emerged in eastern Africa around 4 million years ago. From this species evolved Australopithecus afarensis, which lived between 3.9 and 2.9 million years ago. A. africanus evolved and lived between 3.03 and 2.04 million years ago in southern Africa and is the ancestor of A. sediba, which lived between 1.97 and 2 million years ago. A. garhi lived between 2.6 and 2.5 million years ago.{4} It's still debated on which Australopithecus is the direct ancestor of Homo. The first remains of a Homo species was a 2.8 million year old jawbone found at Ethiopia, which probably lived between 3 million and 2 million years ago, along with another Homo species.{5} Homo habilis appeared later. It's unknown whether H. rudolfensis is the same species as Homo habilis or a separate but similar species. The former lived between 2.8 and 1.5 million years ago and made and used advanced stone tools for its time. This species probably indirectly caused the extinction of the australopithecines, due to its more advanced intelligence, adaptability, social structure, and technology.{6}

H. erectus appeared in Africa at around 1.9 million years ago, it was the first hominin to probably control fire, starting from 1 million years ago.{7} It was also the first hominin to spread out of Africa and reached southern Eurasia. This species involved into H. heidelbergensis at 600,000 years ago. The latter spread out of Africa 300,000 and 400,000 years ago, evolving into H. neanderthalensis and Denisovans in Eurasia.{8} It later evolved into H. sapiens between 200,000 and 130,000 years ago in Africa. H. erectus became extinct in 143,000 BP.{7}

H. s. sapiens populations migrated out of Africa between 125,000 and 60,000 years ago, gradually replacing Neanderthals and Denisovans on the way. They reached the Near East by 125,000 BP. Ancestors of Melanesians interbred with Denisovans, putting in 3-5% of Denisovan DNA to modern Melanesians.{8} Asians and Native Americans also have around 0.2%.{9} Ancestors of Eurasians minimally interbred with Neanderthals, inputting between 1 and 4 percent of Neanderthal DNA into modern Eurasians.{10} Neanderthals and Denisovans also minimally interbred, inputting at least 0.5% of Neanderthal genes into Denisovans. The Neanderthals became extinct by 40,000 BP and Denisovans also became extinct.{11}

Ancestors of aboriginal Australians migrated to Australia from eastern Africa, since Aborigines are genetically closer to East Africans than to modern Asians, via India and Indonesia between 45,000 and 80,000 years ago, when glaciation lowered sea levels and expanded reachable landmasses.{12} Humans entered the Americas between 40,000 and 16,000 years ago, either across Beringia and through Yukon in an ice-free corridor or by sea.{13}

Description

Humans are bipedal, being able to stand and move on two legs full-time. An average adult female stands straight at 158 cm and weighs between 54 and 64 kg, while an average adult male stands straight at 172 cm weighs 76–83 kg.{14} They grow more rapidly than other primates and live longer. Due to modern technology, many people in developed countries are able to live past 60 years. Though many people in developing countries still live in poverty. Humans are highly creative and are able to create a variety of tools that no other species can do.

Distribution and population

Map of distribution of permanent settlements with populations, image created by DLommes

Humans have permanent settlement everywhere on Earth except for the most remote, arid, or hazardous regions. Almost everywhere on the surface of Earth has been explored by humans. There are currently more than 7.2 billion people,{15} there are currently more people in eastern and southern Asia than the rest of the world combined.

Diet

Pasta is one of the most popular foods in the world; photograph by CSIRO

Before 12,000 years ago, humans do not eat a significant amount of starch and dairy, but instead eat on what they can find nearby, either by hunting or gathering, and their diet varies from different locations. Although contrary to popular belief, there is no such thing as a universal Paleolithic diet, and some Upper Paleolithic peoples did actually included some starch in their diet.{16} Agriculture and the population exploded after the 12,000 BP Neolithic Revolution, which people switched from hunting and gathering to farming, including domesticating animals and parts, which incorporated a large percentage of calories as starch (grains) in most peoples' diet around the world, with many parts of the world also including a significant portion of dairy in their diet.{17} Pasta is said to be the most popular food in the world.{18}

References

(Titles are clickable!)

1. Genetic evidence for complex speciation of humans and chimpanzees; Nature 441, 1103-1108 (29 June 2006) | doi:10.1038/nature04789

2. Sahelanthropus tchadensis; Smithsonian National Museum of Natural History

3. Ardipithecus kadabba; Smithsonian National Museum of Natural History

4. Evolution of the Australopithecines; Tree of Life

5. Ethiopian jawbone may mark dawn of humankind; Nature 04 March 2015

6. Homo habilis; Smithsonian National Museum of Natural History

7. Homo erectus; Smithsonian National Museum of Natural History

8. Why Am I Denisovan?; National Genographic Project

9. The complete genome sequence of a Neanderthal from the Altai Mountains; Nature 505, 43–49 (02 January 2014) doi:10.1038/nature12886

10. Why Am I Neanderthal?; National Genographic Project

11. Humans Did Not Wipe Out the Neanderthals, New Research Suggests; livescience

12. Migration to Australia; National Genographic Project

13. Ancient migration: Coming to America; Nature 485, 30–32 (03 May 2012) doi:10.1038/485030a

14. Human weight; articleworld.org

15. U.S. and World Population Clock; United States Census Bureau

16. Processing of wild cereal grains in the Upper Palaeolithic revealed by starch grain analysis; Nature 430, 670-673 (5 August 2004) | doi:10.1038/nature02734

17. What the World Eats; National Geographic

18. How pasta became the world's favourite food; BBC

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Theoretical and Methodological Approaches to Ecological Changes, Social Behaviour and Human Intergroup Tolerance 300,000 to 30,000 BP

Archaeological evidence suggests that important shifts were taking place in the character of human social behaviours 300,000 to 30,000 years ago. New artefact types appear and are disseminated with greater frequency. Transfers of both raw materials and finished artefacts take place over increasing distances, implying larger scales of regional mobility and more frequent and friendlier interactions between different communities. Whilst these changes occur during a period of increasing environmental variability, the relationship between ecological changes and transformations in social behaviours is elusive. Here, we explore a possible theoretical approach and methodology for understanding how ecological contexts can influence selection pressures acting on intergroup social behaviours. We focus on the relative advantages and disadvantages of intergroup tolerance in different ecological contexts using agent-based modelling (ABM). We assess the relative costs and benefits of different ‘tolerance’ levels in between-group interactions on survival and resource exploitation in different environments. The results enable us to infer a potential relationship between ecological changes and proposed changes in between-group behavioural dynamics. We conclude that increasingly harsh environments may have driven changes in hormonal and emotional responses in humans leading to increasing intergroup tolerance, i.e. transformations in social behaviour associated with ‘self-domestication’. We argue that changes in intergroup tolerance is a more parsimonious explanation for the emergence of what has been seen as ‘modern human behaviour’ than changes in hard aspects of cognition or other factors such as cognitive adaptability or population size.

link.springer.com/article/10.1007%2Fs10816-020-09503-5

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An early cell shape transition drives evolutionary expansion of the human forebrain

Summary

The human brain has undergone rapid expansion since humans diverged from other great apes, but the mechanism of this human-specific enlargement is still unknown. Here, we use cerebral organoids derived from human, gorilla, and chimpanzee cells to study developmental mechanisms driving evolutionary brain expansion. We find that neuroepithelial differentiation is a protracted process in apes, involving a previously unrecognized transition state characterized by a change in cell shape. Furthermore, we show that human organoids are larger due to a delay in this transition, associated with differences in interkinetic nuclear migration and cell cycle length. Comparative RNA sequencing (RNA-seq) reveals differences in expression dynamics of cell morphogenesis factors, including ZEB2, a known epithelial-mesenchymal transition regulator. We show that ZEB2 promotes neuroepithelial transition, and its manipulation and downstream signaling leads to acquisition of nonhuman ape architecture in the human context and vice versa, establishing an important role for neuroepithelial cell shape in human brain expansion.

www.cell.com/cell/fulltext/S0092-8674(21)00239-7?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867421002397%3Fshowall%3Dtrue

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This is currently the oldest modern human genome.

A genome sequence from a modern human skull over 45,000 years old from Zlatý kůň in Czechia

Modern humans expanded into Eurasia more than 40,000 years ago following their dispersal out of Africa. These Eurasians carried ~2–3% Neanderthal ancestry in their genomes, originating from admixture with Neanderthals that took place sometime between 50,000 and 60,000 years ago, probably in the Middle East. In Europe, the modern human expansion preceded the disappearance of Neanderthals from the fossil record by 3,000–5,000 years. The genetic makeup of the first Europeans who colonized the continent more than 40,000 years ago remains poorly understood since few specimens have been studied. Here, we analyse a genome generated from the skull of a female individual from Zlatý kůň, Czechia. We found that she belonged to a population that appears to have contributed genetically neither to later Europeans nor to Asians. Her genome carries ~3% Neanderthal ancestry, similar to those of other Upper Palaeolithic hunter-gatherers. However, the lengths of the Neanderthal segments are longer than those observed in the currently oldest modern human genome of the ~45,000-year-old Ust’-Ishim individual from Siberia, suggesting that this individual from Zlatý kůň is one of the earliest Eurasian inhabitants following the expansion out of Africa.

www.nature.com/articles/s41559-021-01443-x

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The evolution and changing ecology of the African hominid oral microbiome

The oral microbiome plays key roles in human biology, health, and disease, but little is known about the global diversity, variation, or evolution of this microbial community. To better understand the evolution and changing ecology of the human oral microbiome, we analyzed 124 dental biofilm metagenomes from humans, including Neanderthals and Late Pleistocene to present-day modern humans, chimpanzees, and gorillas, as well as New World howler monkeys for comparison. We find that a core microbiome of primarily biofilm structural taxa has been maintained throughout African hominid evolution, and these microbial groups are also shared with howler monkeys, suggesting that they have been important oral members since before the catarrhine–platyrrhine split ca. 40 Mya. However, community structure and individual microbial phylogenies do not closely reflect host relationships, and the dental biofilms of Homo and chimpanzees are distinguished by major taxonomic and functional differences. Reconstructing oral metagenomes from up to 100 thousand years ago, we show that the microbial profiles of both Neanderthals and modern humans are highly similar, sharing functional adaptations in nutrient metabolism. These include an apparent Homo-specific acquisition of salivary amylase-binding capability by oral streptococci, suggesting microbial coadaptation with host diet. We additionally find evidence of shared genetic diversity in the oral bacteria of Neanderthal and Upper Paleolithic modern humans that is not observed in later modern human populations. Differences in the oral microbiomes of African hominids provide insights into human evolution, the ancestral state of the human microbiome, and a temporal framework for understanding microbial health and disease.

www.pnas.org/content/118/20/e2021655118

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When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants


Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced positive rate changes at 2.1 and 1.5 million years ago, coincident with the early evolution of Homo and technological innovations evident in the archeological record. But we also find that human brain size reduction was surprisingly recent, occurring in the last 3,000 years. Our dating does not support hypotheses concerning brain size reduction as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest our analysis supports the hypothesis that the recent decrease in brain size may instead result from the externalization of knowledge and advantages of group-level decision-making due in part to the advent of social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the deep history of Homo, the impacts of group size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of labor, and collective cognition. Ants provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction and aid in interpreting patterns of brain evolution identified in humans. Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can broadly inform us of the selective forces that influence brain size.

www.frontiersin.org/articles/10.3389/fevo.2021.742639/full

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A cis-acting structural variation at the ZNF558 locus controls a gene regulatory network in human brain development

The human forebrain has expanded in size and complexity compared to chimpanzees despite limited changes in protein-coding genes, suggesting that gene expression regulation is an important driver of brain evolution. Here, we identify a KRAB-ZFP transcription factor, ZNF558, that is expressed in human but not chimpanzee forebrain neural progenitor cells. ZNF558 evolved as a suppressor of LINE-1 transposons but has been co-opted to regulate a single target, the mitophagy gene SPATA18. ZNF558 plays a role in mitochondrial homeostasis, and loss-of-function experiments in cerebral organoids suggests that ZNF558 influences developmental timing during early human brain development. Expression of ZNF558 is controlled by the size of a variable number tandem repeat that is longer in chimpanzees compared to humans, and variable in the human population. Thus, this work provides mechanistic insight into how a cis-acting structural variation establishes a regulatory network that affects human brain evolution.

www.sciencedirect.com/science/article/pii/S1934590921003842

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Human Neurons are Strikingly Different from Those of Other Mammals, Study Says

Human neurons have a much smaller number of channels that control the flow of ions (such as potassium and sodium) than expected, compared to the neurons of other mammals, according to new research led by MIT neuroscientists; and this reduction in channel density may have helped the human brain evolve to operate more efficiently, allowing it to divert resources to other energy-intensive processes that are required to perform complex cognitive tasks.

Neurons in the mammalian brain can receive electrical signals from thousands of other cells, and that input determines whether or not they will fire an electrical impulse called an action potential.

In 2018, MIT researcher Mark Harnett and colleagues discovered that human and rat neurons differ in some of their electrical properties, primarily in parts of the neuron called dendrites — tree-like antennas that receive and process input from other cells.

One of the findings from that study was that human neurons had a lower density of ion channels than neurons in the rat brain.

The researchers were surprised by this observation, as ion channel density was generally assumed to be constant across species.

In their new study, the scientists decided to compare neurons from several different mammalian species to see if they could find any patterns that governed the expression of ion channels.

They studied two types of voltage-gated potassium channels and the HCN channel, which conducts both potassium and sodium, in layer 5 pyramidal neurons, a type of excitatory neurons found in the brain’s cortex.

They were able to obtain brain tissue from 10 mammalian species: Etruscan shrews (one of the smallest known mammals), gerbils, mice, rats, Guinea pigs, ferrets, rabbits, marmosets, and macaques, as well as human tissue removed from patients with epilepsy during brain surgery.

This variety allowed the team to cover a range of cortical thicknesses and neuron sizes across the mammalian kingdom.

The authors found that in nearly every mammalian species they looked at, the density of ion channels increased as the size of the neurons went up.

The one exception to this pattern was in human neurons, which had a much lower density of ion channels than expected.

“The increase in channel density across species was surprising, because the more channels there are, the more energy is required to pump ions in and out of the cell,” Dr. Harnett said.

“However, it started to make sense once we began thinking about the number of channels in the overall volume of the cortex.”

In the tiny brain of the Etruscan shrew, which is packed with very small neurons, there are more neurons in a given volume of tissue than in the same volume of tissue from the rabbit brain, which has much larger neurons.

But because the rabbit neurons have a higher density of ion channels, the density of channels in a given volume of tissue is the same in both species, or any of the nonhuman species the researchers analyzed.

“This building plan is consistent across nine different mammalian species,” Dr. Harnett said.

“What it looks like the cortex is trying to do is keep the numbers of ion channels per unit volume the same across all the species. This means that for a given volume of cortex, the energetic cost is the same, at least for ion channels.”

The human brain represents a striking deviation from this building plan, however.

Instead of increased density of ion channels, the authors found a dramatic decrease in the expected density of ion channels for a given volume of brain tissue.

They believe this lower density may have evolved as a way to expend less energy on pumping ions, which allows the brain to use that energy for something else, like creating more complicated synaptic connections between neurons or firing action potentials at a higher rate.

“We think that humans have evolved out of this building plan that was previously restricting the size of cortex, and they figured out a way to become more energetically efficient, so you spend less ATP per volume compared to other species,” Dr. Harnett said.

The study was published in the journal Nature.

www.sci-news.com/biology/human-neurons-10262.html

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Allometric rules for mammalian cortical layer 5 neuron biophysics

The biophysical properties of neurons are the foundation for computation in the brain. Neuronal size is a key determinant of single neuron input–output features and varies substantially across species. However, it is unknown whether different species adapt neuronal properties to conserve how single neurons process information. Here we characterize layer 5 cortical pyramidal neurons across 10 mammalian species to identify the allometric relationships that govern how neuronal biophysics change with cell size. In 9 of the 10 species, we observe conserved rules that control the conductance of voltage-gated potassium and HCN channels. Species with larger neurons, and therefore a decreased surface-to-volume ratio, exhibit higher membrane ionic conductances. This relationship produces a conserved conductance per unit brain volume. These size-dependent rules result in large but predictable changes in somatic and dendritic integrative properties. Human neurons do not follow these allometric relationships, exhibiting much lower voltage-gated potassium and HCN conductances. Together, our results in layer 5 neurons identify conserved evolutionary principles for neuronal biophysics in mammals as well as notable features of the human cortex.

www.nature.com/articles/s41586-021-04072-3

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Apparently our desire to be in nature and how we experience it are partially heritable.

journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001500

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New type of human lung cell discovered.

Human distal airways contain a multipotent secretory cell that can regenerate alveoli

The human lung differs substantially from its mouse counterpart, resulting in a distinct distal airway architecture affected by disease pathology in chronic obstructive pulmonary disease. In humans, the distal branches of the airway interweave with the alveolar gas-exchange niche, forming an anatomical structure known as the respiratory bronchioles. Owing to the lack of a counterpart in mouse, the cellular and molecular mechanisms that govern respiratory bronchioles in the human lung remain uncharacterized. Here we show that human respiratory bronchioles contain a unique secretory cell population that is distinct from cells in larger proximal airways. Organoid modelling reveals that these respiratory airway secretory (RAS) cells act as unidirectional progenitors for alveolar type 2 cells, which are essential for maintaining and regenerating the alveolar niche. RAS cell lineage differentiation into alveolar type 2 cells is regulated by Notch and Wnt signalling. In chronic obstructive pulmonary disease, RAS cells are altered transcriptionally, corresponding to abnormal alveolar type 2 cell states, which are associated with smoking exposure in both humans and ferrets. These data identify a distinct progenitor in a region of the human lung that is not found in mouse that has a critical role in maintaining the gas-exchange compartment and is altered in chronic lung disease.

www.nature.com/articles/s41586-022-04552-0

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This is how the skeleton is modified in habitually quadrupedal humans.

onlinelibrary.wiley.com/doi/10.1111/joa.13693

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Unfolding the evolution of human cognition

Recent findings spanning fields, from braincases in paleoneurobiology to in vivo measurements in cognitive neuroscience, provide insights into the evolution of cognition. Here, we integrate these findings and propose that studying small, evolutionarily new cortical structures has significant implications for identifying new links between neuroanatomical substrates and human-specific aspects of cognition.

www.cell.com/trends/cognitive-sciences/fulltext/S1364-6613(22)00139-5?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS1364661322001395%3Fshowall%3Dtrue#.YuZ5j8gNxBk.twitter

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Evolutionary loss of complexity in human vocal anatomy as an adaptation for speech

Human speech production obeys the same acoustic principles as vocal production in other animals but has distinctive features: A stable vocal source is filtered by rapidly changing formant frequencies. To understand speech evolution, we examined a wide range of primates, combining observations of phonation with mathematical modeling. We found that source stability relies upon simplifications in laryngeal anatomy, specifically the loss of air sacs and vocal membranes. We conclude that the evolutionary loss of vocal membranes allows human speech to mostly avoid the spontaneous nonlinear phenomena and acoustic chaos common in other primate vocalizations. This loss allows our larynx to produce stable, harmonic-rich phonation, ideally highlighting formant changes that convey most phonetic information. Paradoxically, the increased complexity of human spoken language thus followed simplification of our laryngeal anatomy.

www.science.org/doi/10.1126/science.abm1574


I'm really grateful for this human profile. It means whenever I find an interesting new paper about human biology I can just dump it here. Thanks drone.

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TKTL1 implies greater neurogenesis in frontal neocortex of modern humans than Neanderthals

Neanderthal brains were similar in size to those of modern humans but differed in shape. What we cannot tell from fossils is how Neanderthal brains might have differed in function or organization of brain layers such as the neocortex. Pinson et al. have now analyzed the effect of a single amino acid change in the transketolase-like 1 (TKTL1) protein on production of basal radial glia, the workhorses that generate much of the neocortex (see the Perspective by Malgrange and Nguyen). Modern humans differ from apes and Neanderthals by this single amino acid change. When placed in organoids or overexpressed in nonhuman brains, the human variant of TKTL1 drove more generation of neuroprogenitors than did the archaic variant. The authors suggest that the modern human has more neocortex to work with than the ancient Neanderthal did.

www.science.org/doi/10.1126/science.abl6422

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A massacre of early Neolithic farmers in the high Pyrenees at Els Trocs, Spain

Violence seems deeply rooted in human nature and an endemic potential for such is today frequently associated with differing ethnic, religious or socio-economic backgrounds. Ethnic nepotism is believed to be one of the main causes of inter-group violence in multi-ethnic societies. At the site of Els Trocs in the Spanish Pyrenees, rivalling groups of either migrating early farmers or farmers and indigenous hunter-gatherers collided violently around 5300 BCE. This clash apparently resulted in a massacre of the Els Trocs farmers. The overkill reaction was possibly triggered by xenophobia or massive disputes over resources or privileges. In the present, violence and xenophobia are controlled and sanctioned through social codes of conduct and institutions. So that, rather than representing an insurmountable evolutionary inheritance, violence and ethnic nepotism can be overcome and a sustainable future achieved through mutual respect, tolerance and openness to multi-ethnic societies.

Two hypotheses can be formulated for the isolation of the perpetrator group and their motives. If the causes were territorial in nature, for example, then the perpetrators could have been indigenous hunter-gatherers who saw the Neolithic group encroaching upon their foraging territories, and who may have brutally enforced their claims. Alternatively, it may have been an altercation between two Neolithic groups in which disputes over territorial rights escalated. This reasoning considers as a motive that the terrain on which the violent event took place is a plateau offering manifold resources. The other variant for interpreting the conflict focuses on general patterns of behaviour. Common causes of disputes between local groups, regardless of time and place, origin or ethnicity, are territorial disputes, raids for acquisition of possessions (e.g. livestock, women, harvest), and conflicts over scarce resources (land, water, game). In contrast to present day interracial or inter-ethnic conflicts (“interracial clash”), however, the systematic extermination of entire communities is rather rare in the event of the recurrent use of violence between neighbouring groups, who often know each other well and may share socio-cultural roots3,24 (Supplementary Text S6).

www.nature.com/articles/s41598-020-58483-9