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 I’m struckEvolution of facial muscle anatomy in dogs Edited by Brian Hare, Duke University, Durham, NC, and accepted by Editorial Board Member C. O. Lovejoy May 10, 2019 (received for review December 5, 2018) Significance Dogs were shaped during the course of domestication both in their behavior and in their anatomical features. Here we show that domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. A muscle responsible for raising the inner eyebrow intensely is uniformly present in dogs but not in wolves. Behavioral data show that dogs also produce the eyebrow movement significantly more often and with higher intensity than wolves do, with highest-intensity movements produced exclusively by dogs. Interestingly, this movement increases paedomorphism and resembles an expression humans produce when sad, so its production in dogs may trigger a nurturing response. We hypothesize that dogs’ expressive eyebrows are the result of selection based on humans’ preferences. Abstract Domestication shaped wolves into dogs and transformed both their behavior and their anatomy. Here we show that, in only 33,000 y, domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. Based on dissections of dog and wolf heads, we show that the levator anguli oculi medialis, a muscle responsible for raising the inner eyebrow intensely, is uniformly present in dogs but not in wolves. Behavioral data, collected from dogs and wolves, show that dogs produce the eyebrow movement significantly more often and with higher intensity than wolves do, with highest-intensity movements produced exclusively by dogs. Interestingly, this movement increases paedomorphism and resembles an expression that humans produce when sad, so its production in dogs may trigger a nurturing response in humans. We hypothesize that dogs with expressive eyebrows had a selection advantage and that “puppy dog eyes” are the result of selection based on humans’ preferences. The dog−human bond is unique and diagnostic of the evolution of human cultures. Dogs were domesticated over 33,000 y ago (1), and, during that time, selection processes have shaped both their anatomy and behavior and turned them into human’s best friend (2). The most remarkable among dogs’ behavioral adaptations, as a result of selection during domestication, is their ability to read and use human communication in ways that other animals cannot (3, 4). Dogs are more skillful in using human communicative cues, like pointing gestures or gaze direction, even than human’s closest living relative, chimpanzees, and also than their own closest living relatives, wolves, or other domesticated species (5). Recent research suggests that eye contact between humans and dogs is crucial for dog−human social interaction. Dogs, but not wolves, establish eye contact with humans when they cannot solve a problem on their own (6, 7). Eye contact also helps dogs to know when communication is relevant and directed at them, as dogs tend to ignore human pointing gestures when the human’s eyes are not visible (8, 9). Dogs, but not wolves, seem to be motivated to establish eye contact with humans from an early age (10, 11), and dogs’ motivation to establish eye contact with humans seems to be an indicator of the level of attachment between humans and dogs (12). Thus, mutual gaze between dogs and humans seems to be a hallmark of the unique relationship between both species during human cultural evolution. Nagasawa et al. (13) showed that, between dogs and humans (but not wolves and humans), mutual gaze seems to lead to an oxytocin feedback loop analogous to the one that exists between human mothers and infants. Oxytocin has a fundamental role during affiliative behaviors in mammals and during the onset of maternal behavior and mother−infant attachment (14). Similarly, mutual gaze between dogs and humans seems to trigger an increase of oxytocin in both species, which then increases the motivation to establish eye contact (13). As this cross-species oxytocin loop can be found in dogs and humans, but not between dogs’ closest living relative (the wolf) and humans, selection processes during domestication must have played an important role whereby dogs hijacked the human caregiving response (15). The most likely evolutionary scenario is that dogs’ ancestor must have, to some extent, expressed characteristics that elicited a caregiving response from humans. Humans then consciously or unconsciously favored and therefore selected for those characteristics, leading to the analogous adaptations we see in dogs today. Selection for traits that facilitate eye contact between dogs and humans might have, therefore, led to 1) anatomical differences in the facial musculature around the eyes between dogs and wolves and 2) behavioral differences between the species in terms of how they use these muscles to promote eye contact. We know that humans favor dogs that show paedomorphic (infant-like) anatomical features like a large forehead, large eyes, and so on; in studies asking people to select pictures presenting dog (or cat) faces, people prefer the faces that present paedomorphic features over others (16). Importantly, paedomorphic facial features can be even further exaggerated by facial muscle movements, which act to enhance the appearance of specific facial features (particularly the eyes). Waller et al. (17) showed that a specific facial muscle movement around the eyes (which they termed AU101: inner eyebrow raise) seems to be particularly attractive to humans. The movement makes the eyes appear bigger, hence more infant-like and potentially more appealing to humans. This inner brow raise also resembles a facial movement humans produce when they are sad, potentially eliciting a nurturing response from humans (17, 18). The study showed that dogs that produce this facial movement more were rehomed from a shelter more quickly than those that produced the movement less often, suggesting that the production of this eye movement gives dogs a potential selection advantage. No other facial movement had the same effect (17). However, thus far, it has been unknown whether domestication has shaped this phenomenon, and whether dogs show marked differences from wolves in anatomy and behavior in relation to this facial movement. Results To determine whether domestication has shaped facial muscles to facilitate dog−human communication in this way, we 1) conducted a detailed comparative facial dissections of gray wolves (Canis lupus, n = 4) and domestic dogs (Canis familiaris, n = 6) and 2) quantified wolves’ and dogs’ AU101 facial movements in their frequency and intensity during social interactions with humans in both wolves (C. lupus, n = 9) and domestic dogs (C. familiaris, n = 27). The main finding is that facial musculature between domestic dogs and gray wolves was relatively uniform and differed only around the eye (Fig. 1 and Table 1). While the levator anguli oculi medialis muscle (LAOM) was routinely present in dogs, in the gray wolves, it was typically represented only by scant muscle fibers surrounded by a high quantity of connective tissue. In the wolves, a tendon was sometimes observed that blended with the medial aspect of the fibers of the orbicularis occuli muscle, near the region where an LAOM would normally be expected (Fig. 2). Thus, wolves have less ability to raise the inner corner of their brows independent of eye squinting relaxation—the anatomical basis for the difference in expression of the AU101 movement. The rest is here… worth reading www.pnas.org. |
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stalhandske 29-Apr-23, 09:08 |
Actually, cousins to all living organisms - although the 'cousin distance' can be very long.... |
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Stal We are related to mammals, insects, bacteria, fungus and viruses - as you say, all living things…. Although perhaps not living things on other planets. |
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stalhandske 29-Apr-23, 10:09 |
Zorro |
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Stal But there’s no real evidence that viruses evolved separately from the rest of us either. Lacking evidence to the contrary, I tend towards thinking we’re all related. Always willing to revise my views given evidence, of course. |
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stalhandske 29-Apr-23, 10:15 |
Zorro |
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Viruses? Does this still have any credibility, or has it been discarded? |
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stalhandske 29-Apr-23, 20:49 |
Bob |
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stalhandske 29-Apr-23, 22:12 |
Comparison between Chimp and Human DNA structure |
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Stal 1. The chimpanzee and human genomes are strikingly similar and encode very similar proteins. The DNA sequence that can be directly compared between the two genomes is almost 99 percent identical. When DNA insertions and deletions are taken into account, humans and chimpanzees still share 96 percent sequence identity. At the protein level, 29 percent of genes code for the same amino sequences in chimpanzees and humans. In fact, the typical human protein has accumulated just one unique change since chimpanzees and humans diverged from a common ancestor about 6 million years ago. 2. A few classes of genes are changing unusually quickly in both humans and chimpanzees compared with other mammals. These classes include genes involved in perception of sound, transmission of nerve signals, production of sperm and cellular transport of ions. The rapid evolution of these genes may have contributed to the special characteristics of primates. 3. Humans and chimpanzees have accumulated more potentially deleterious mutations in their genomes over the course of evolution than have mice, rats and other rodents. While such mutations can cause diseases that may erode a species' overall fitness, they may have also made primates more adaptable to rapid environmental changes and enabled them to achieve unique evolutionary adaptations. 4. About 35 million DNA base pairs differ between the shared portions of the two genomes. In addition, there are another 5 million sites that differ because of an insertion or deletion in one of the lineages, along with a much smaller number of chromosomal rearrangements. Most of these differences lie in what is believed to be DNA of little or no function. However, as many as 3 million of the differences are found in crucial protein-coding genes or other functional areas of the genome. Somewhere in these relatively few differences lies the biological basis for the unique characteristics of the human species, including human-specific diseases such as Alzheimer's disease, certain cancers, and HIV/AIDS. 5. Although the statistical signals are relatively weak, a few classes of genes appear to be evolving more rapidly in humans than in chimpanzees. The single strongest outlier involves genes that code for transcription factors, molecules that regulate the activity of other genes and that play key roles in embryonic development. 6. A small number of other genes have undergone even more dramatic changes. More than 50 genes present in the human genome are missing or partially deleted from the chimpanzee genome. The corresponding number of gene deletions in the human genome is not yet precisely known. For example, three key genes involved in inflammation appear to be deleted in the chimpanzee genome, possibly explaining some of the known differences between chimpanzees and humans in respect to immune and inflammatory response. On the other hand, humans appear to have lost the function of the caspase-12 gene, which produces an enzyme that may affect the progression of Alzheimer's disease. 7. There are six regions in the human genome that have strong signatures of selective sweeps over the past 250,000 years (selective sweeps occur when a mutation arises in a population and is so advantageous that it spreads throughout the population within a few hundred generations and eventually becomes "normal.") One region contains more than 50 genes, while another contains no known genes and lies in an area that scientists refer to as a "gene desert." Intriguingly, this gene desert may contain elements regulating the expression of a nearby protocadherin gene, which has been implicated in patterning of the nervous system. A seventh region with moderately strong signals contains the FOXP2 and CFTR genes. FOXP2 has been implicated in the acquisition of speech in humans. CFTR, which codes for a protein involved in ion transport and, if mutated, can cause the fatal disease cystic fibrosis, is thought to be the target of positive selection in European populations. The initial complete sequence of the chimpanzee genome and comparison to the human genome is an important milestone in what will be several years of intensive work at understanding human evolutionary history and applying these data to biomedical research. The fact that these data, and all future data from the Consortium, are being placed in the public domain means that scientists worldwide can contribute to this work. The 67 researchers who took part in the Chimpanzee Sequencing and Analysis Consortium share authorship of the Nature paper. The sequencing and assembly of the chimpanzee genome was done at the Broad Institute and at the Washington University School of Medicine in Saint Louis, MO. In addition to those centers, the consortium included researchers from institutions elsewhere in the United States, as well as Israel, Italy, Germany and Spain. The work of the Chimpanzee Sequencing and Analysis Consortium is funded in part by the National Human Genome Research Institute (NHGRI) of the National Institutes of Health. The team was co-led by Lander, Richard Wilson of the Washington University School of Medicine in Saint Louis, MO and Robert Waterston of the University of Washington, Seattle WA. |
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stalhandske 01-May-23, 01:20 |
Zorro |
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Stal 01:20 If someone is convinced that Life, the Universe, and Everything (including eternal damnation or ecstasy) all depends on believing something, is wrong, then NOTHING will convince them otherwise. It takes an enormous chunk of courage for someone from that background to look at facts dispassionately. |
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Yeah |
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stalhandske 01-May-23, 06:45 |
That's just it - I do! |
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Stal I think it's best to accept that many choose to remain ignorant, cling to their dogma/mythology, and reject science. Focus your energies on places where you can make a difference.... Universe, "grant me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference." |
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God Being Lazy (or Efficient) If there were no other primates or primate fossils, it would be super easy for us to dismiss human evolution as a pipe dream. It is impossible for any rational person to do so in light of what we have found. Beyond the genetic similarities in functional genes we have endogenous retro viral genetic insertions. It is like God builds a car. That car get involved in a wreck, but can still be driven. So God builds a new car (humans), incorporating all the dings and scratches from the wrecked vehicle. That don’t make a lick of sense. How do creationists explain this? God is malevolent? Psychotic? A human engineer building a better automobile that included the defects of a damaged version would be regarded as a fool. Do creationists worship the architect of the universe, or a bumbling oaf? Then there is the chromosome count. We see humans have 23 pairs while other primates have twenty four. It was easy to identify which pair fused to reduce the count, and the presence of telomeres at the fusion locus cements this evolutionary event. Telomeres are repeated DNA sequences marking the ends of chromosomes. In the battle between evolution and creationism, God saw fit to equip evolutionists with armored helicopter gunships and night vision goggles, whereas the evidence provided creationists is the equivalent of damp pea shooters and dirty loin cloths. It is a David and Goliath tale, but with David going to the garden to fetch peas instead of heading out to the river for nice round stones. And the loincloth bears target circles and a homing beacon for the laser sights, if you see where this is going. David is going to require some transgender corrective surgery after Goliath unleashes a barrage. |
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Shiva “It is impossible for any rational person to do so in light of what we have found.” Rational is the key here |
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Octopi This is cool. Curiouser and Curiouser--Octopus's Evolution Is Even Stranger Than Thought Cephalopods adapt to changing water temperatures by altering their RNA more often than their DNA, according to a new study Bret StetkaApril 6, 2017 Advertisement As if octopuses, squids and other cephalopods were not already strange enough, they may have found a way to evolve that is foreign to practically all other multicellular organisms on the planet. For most animals, changes that might prove beneficial to the organism primarily occur at the beginning of their molecular production process. Mutations occur in DNA that are then transcribed into RNA; the RNA is then translated into an altered protein. Not so for cephalopods—at least not entirely. A new study published in Cell reports these aquarium oddities can modify the proteins found in their bodies without having to change the basic sequence of their DNA blueprint. As a result, it looks as if cephalopods have changed very slowly over the eons of their existence. The findings also suggest that octopuses and their tentacled cousins may be a lot older than previously thought. Advertisement The new paper reports on a process called “RNA editing,” which involves enzymes swapping out one RNA base (or nitrogen-based “letter” in the RNA/DNA alphabet) for another, presumably in the interest of an organism adapting to its environment. RNA editing is rarely employed in most animals. Among the 20,000 or so genes found in humans, for example, only a few dozen sites are thought to change their RNA so that it no longer matches the original DNA template. Yet previous work, in part by the same authors, suggested the process is employed rather frequently by octopuses and squid to respond to changes in ocean water temperature. The new study looked at DNA sequences, RNA sequences and proteomes—meaning all of the proteins encoded in a particularly cell or tissue—of multiple cephalopod species to determine how common RNA editing really is. Very, it turns out. Squid also have around 20,000 genes, a whopping 11,000 of which code for RNA that in some cases undergoes editing. A similar degree of editing was found in two species of octopus and the common cuttlefish. Far lower levels of RNA-editing were seen in the nautilus—a more primitive cephalopod—and in a non-cephalopod control, a mollusk called a sea hare. RNA editing was especially high in the cephalopod nervous system, including in genes coding for ion channels that facilitate electrical communication between neurons. What’s more, such extensive RNA editing seems to have helped to minimize changes in the cephalopod DNA over the eons that they have been around. Unlike most animal species, whose genomes are riddled with millions of years of mutations that have helped them adapt to a volatile world, cephalopod adaption appears to have been more a result of RNA editing. Heavy reliance on RNA editing, however it first evolved, practically would have guaranteed the need for cephalopod DNA to remain fairly stable over millennia. The proteins used for editing RNA would, after all, need to recognize various complexes of RNA, says paper co-author Joshua Rosenthal, a cephalopod neurobiologist at the Marine Biological Laboratory. Hence, the DNA coding for the RNA that generates those particular proteins would have to stay consistent. In other words, in an animal reliant on RNA-editing for survival, any mutations that interfered with that process would probably not have survived into the next generation. “If a squid and octopus want to edit a base, they must preserve the underlying RNA structure,” Rosenthal says, “This means that the RNA structure can’t evolve. If it collects mutations as a result of DNA mutations, it would no longer be recognized by the editing enzymes. We normally think of mutations as the currency of evolution. But in this case their accumulation is suppressed.” Advertisement In 2015 University of Chicago neurobiologist Clifton Ragsdale and his team published the first cephalopod genome, that of an octopus. Clifton also noticed an unusually high degree of RNA editing. “We saw the same thing,” he recalls. “But this new paper provides much more information and raises interesting ideas—instead of just using regular old genome evolution, RNA editing might have been a way to produce molecular diversity, particularly in their nervous systems. You could imagine that it’s an alternative engine for cephalopod evolution.” Why Edit RNA? No one knows why cephalopods are so keen on RNA editing. Perhaps it is a faster, easier way to adapt to their environment than waiting for a random mutation to occur. Or maybe it better suits their relatively short life spans. Cephalopods grow up fast and die young . Most live only for a few years and they only breed once. Ragsdale feels RNA editing may help them navigate what are often lonesome, fleeting lives. “This may explain why they’re such good problem solvers. No one’s around to show them how to figure out the world!” Ragsdale says, “How to make their dens. How to camouflage themselves and attack prey. They’re on their own, and fortunately for them they have big brains and can sort matters out.” newsletter promo Sign up for Scientific American’s free newsletters. Rosenthal feels RNA editing provides cephalopods with another means of environmental flexibility and is planning follow-up research to test his theory: “It can turn certain RNA on and off. We want to see which environmental variables influence the RNA editing process—things like variation in temperature…maybe something more complex like experiences.” Lore around cephalopods goes back millennia. Aristotle wrote of various forms of “calamari”; seaside cultures have long feared mythic, tentacled beasts like the Norse kraken; Jules Verne, of course, entrenched in us images of a giant squid battling Captain Nemo’s steampunk submarine. And more recently, the squid lent its effort to neuroscience. Much of what we know about how neurons communicate with one another began with experiments in the 1940s and ‘50s on the exceedingly long neuron that runs through the squid body. So perhaps it is fitting that Rosenthal’s new findings suggest cephalopods may hold a unique honor among Earthly species. Advertisement Along with fossil records, species are typically dated by analyzing the number of mutations they have accumulated—in most species these genetic blips occur at a steady rate, creating a sort of “molecular clock” that can be used to calculate evolutionary time lines. If RNA editing allows changes in the cephalopod's DNA to occur at a markedly slower rate than is normally assumed, the animals most likely arose many millions of years earlier than current time lines suggest. In other words, the DNA mutations they do harbor would have taken a lot longer to crop up. “This may mean that our molecular clock estimates of when different cephalopod lineages arose and diverged might be too recent,” Ragsdale says. “The Nobel Prize–winning biologist Sydney Brenner once said that octopi were the first intelligent beings on Earth. This could prove he was right.” www.scientificamerican.com |
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stalhandske 01-May-23, 21:02 |
Zorro |
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bobspringett; 29-Apr-23, 04:51: I just want to make a point here: I am no scientist either, far from it in fact, but I tend towards a similar description as zorroloco when someone is willfully daft. I have no formal training as any kind of scientist, but I read, I learn, and I can stand objective and evaluate. I don't need to understand complex mathematical equations, or even the difficult to understand terms that I came across in the two papers by stalhandske that I read, to catch the gist of a topic and the direction facts and evidence leads us in. Ignoring evidence and facts and punting sheer stupidity has no excuse. I have read books by Paul Davies in which the applied mathematics of astrophysics are explained. Even the explanation made no sense to me; but I got the drift of the surrounding facts and the context, and still came away enriched with knowledge that I didn't posses before. I have caught up with the thread, and found the post by zorroloco; 29-Apr-23, 09:07 interesting. I have read some of this before, but not as well explained. I suspect I read a summary. Thanks for that. |
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stalhandske 02-May-23, 05:50 |
Riaan The genetic evidence from Neanderthal DNA is definite: H.sapiens definitely got offspring with Neanderthals, and also with Denisovians (a Homo representative more common in the east). It seems clear that all humans today have a few per cent of Neanderthal 'influence', except for some groups in Africa where such mixing did not occur (but that doesn't include you ). Yes, just get in front of that mirror and check.... |
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stalhandske 02-May-23, 06:01 |
Evolution and the Bible But if that is a mistake on my part, then I don't understand how these fanatic Bible interpreters explain Neanderthals and Denisovans, which dies out dome 30,000 years ago, but 'mixed' with our ancestors. I am for sure no Bible expert, but I don't know of any passage where this would have been described. |
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Stal You forget …. It’s all a plot by 98% of the world’s scientists to excise god and promote an atheistic, communist workers paradise. Once you understand that, it all falls into place. Obviously! 🤣🤣🤣 |
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How chimps and humans How Are Chimpanzees and Humans Similar? Chimpanzees and humans share a number of similar characteristics: They’re both hominids. Humans and chimps are primates (and mammals) and members of the Hominidae family (also known as hominids). Some common characteristics of primates include flat faces, clavicles, larger brain sizes, flexible shoulders and hips, and front-facing eyes. Like humans, chimpanzee mothers take care of their young after birth, providing food, warmth, and protection, and teaching them the necessary skills to survive. These non-human primates also use tools to accomplish tasks. They’re both terrestrial. Chimps and humans typically move around on the ground, rather than through the trees like monkeys. Though some species of primates have adaptations to allow them to climb trees for eating or sleeping, most spend much of their day on the ground. They both have complex emotions. Chimps, like humans, are capable of complex cognitive thoughts and feelings. Chimps are social creatures who experience joy, grief, jealousy, affection, and compassion. Like humans, chimps can feel depression and isolation and have expressive faces to communicate different emotions and reactions. Neither have tails. Humans and chimpanzees, including gorillas, gibbons, bonobos, and orangutans, do not have tails. This is also the most significant distinguishing feature between chimps and monkeys. How Are Chimpanzees and Humans Different? Chimp and human genomes share about 99 percent of the same DNA sequencing and a common ancestor—the chimpanzee-human last common ancestor (CHLCA). However, there are a few genetic differences between human-chimpanzee genomes that separate us, such as: Chimps walk on all fours. Chimpanzees mainly move around on all four limbs, much like gorillas and monkeys, though they can move bipedally. Chimpanzees can’t swim. Chimps have a low ratio of body fat and a top-heavy composition that makes it impossible for them to swim. While they’ll splash around in shallow waters, they can’t float or swim well in deeper waters. However, most humans with different body compositions can learn to swim or tread water. Chimps have shorter lifespans. Most chimpanzees only live in the wild for 40 to 50 years (potentially 50 to 60 in captivity), while humans can live past 100 years of age. Humans have bigger brains. Even though chimpanzees have larger brains than most mammals, human evolution has helped the human brain grow three times as large as their non-human counterparts. The human brain’s cerebral cortex contains twice as many cell types as a chimpanzee, affecting processes like memory and attention. In the early phase of brain development, human brain cells spend more time in the metaphase of cell division, possibly contributing to the differences in primate evolution. Chimps have an extra chromosome. While human genomic makeup only consists of 23 pairs of chromosomes, other great apes have 24. Research projects aimed at the study of chimpanzee genomes have revealed the possibility that during the evolution of human lineage, two ape chromosomes fused to create what is known as early human origin. Over time, nucleotide variability and altered transcription factor binding led to the evolution of human-specific genes, allowing humans to develop verbal communication and other language behavior, excelling past primate evolution. |
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Honestly |
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Smarter m.youtube.com |
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Why mosquitoes love you Evolution explains mosquitoes’ taste for human blood September 2020 This summer the coronavirus pandemic forced many residents of the northern hemisphere out of air-conditioned spaces and into the great outdoors for socially distanced get-togethers, barbecues, playdates, drive-in movies, and dining. There, we became the de facto buffet for biting insects. While we balanced our drinks, mosquitoes also had a sip … of human blood. New research published this summer explains why some mosquitoes just can’t leave humans alone, while others prefer a nice, juicy guinea pig. The answer, of course, comes down to evolution… Where's the evolution? First, mosquitoes are not all the same. Though it might feel otherwise when you are fighting off a swarm, most of the world’s 3,500 mosquito species feed on a wide variety of vertebrates and don’t particularly like human blood. Only a few, like the mosquito Aedes aegypti, which spreads Zika, dengue fever, and other scourges, evolved to specialize on humans. And even within the species that prefer human blood, there is variation. For example, some populations of A. aegypti in Africa don’t fit the mold: some seem to be more tempted by the scent of a non-human animal than by human odor. To find out what could cause a mosquito lineage to evolve a narrow preference for human blood, researchers first needed to learn more about how preference varies. So they collected A. aegypti eggs from a variety of sites in sub-Saharan Africa, including large cities, open savannahs, and dense forests. They then used these eggs to establish separate colonies of mosquitoes in a lab and presented individual insects with a choice: head towards the guinea pig or head towards the exposed human arm? The mosquitoes did not choose randomly. Instead, mosquitoes from the same colony had similar preferences. Insects from some colonies nearly always chose the human arm; others strongly preferred guinea pig. Since all the mosquitoes were raised in the same lab in the same way and yet behaved differently, the finding suggests that odor preference is influenced by the individual mosquito’s genes. In order for a trait to evolve by natural selection, three conditions must be met: (1) it must have variation, (2) this variation must have a genetic basis, and (3) there must be selection (i.e., a difference in an organisms’ ability to survive to reproduce) because of that trait. Based on these results, it was clear that there is variation in host preference among the mosquitoes (i.e., insects from some areas prefer humans; others prefer non-human animals) and that this variation can be chalked up to genetic differences among the populations. But was there a selective advantage to specializing on humans, and if so, what was it? To investigate that question, the researchers analyzed how a colony’s preference related to the site from which the eggs had been collected — whether it was urban or wild, and what the climate was like. They found that colonies that preferred humans were likely to come from areas with a dense human population and were especially likely to come from areas with an intense dry season. Data on how mosquitoes’ preference for humans (represented by a human hand silhouette) or non-human animals (guinea pig silhouette) relate to the human population density and climatic conditions at the collection site. Note that higher human population density and more intense dry seasons are associated with mosquito colonies that more strongly prefer humans. Credit: Current Biology, Cell.com These findings hint at a selective advantage. Mosquitoes lay their eggs in standing water. In areas with an extended dry season, the lack of water could block mosquito reproduction. But in these landscapes, humans, because they need water also, are a reliable source of standing water. Hence, mosquitoes may be forced to rely on human populations to lay eggs. So any mosquito that happened to carry genes that made it prefer human blood would have been more likely to stick around groups of humans — and so more likely to have access to water when it came time to lay eggs. Or perhaps, a mosquito that preferred human blood and was already hanging out around humans found itself with an abundant untapped resource (lots of juicy humans to bite) — and so was able to produce more eggs than other mosquitoes that had to go out looking for non-human animals to bite. In either case, those mosquitoes that preferred human blood would get more of their genes into the next generation — and so the frequency of genes that make mosquitoes like human blood would increase in that population. The hypothesis that access to water was the key factor causing some mosquitoes to evolve a preference for human blood is an old one. But this is the first time that biologists have investigated that hypothesis directly. And uncovering a link between high densities of humans (i.e., city living) and the evolution of bloodthirsty, human-loving mosquitoes has important implications for the future. Africa is currently undergoing rapid urbanization — a trend in which people move out of rural settings and into cities. The new evidence suggests that, in the past, urbanization in dry landscapes has triggered the evolution of mosquitoes that specialize on humans. The same selective pressures uncovered by the new research apply today and could favor the evolution of even more mosquito populations with a taste for human blood. For affected city-dwellers, this would be, not just be annoying, but also dangerous. Illnesses carried by mosquitoes already sicken about 100 million people per year, with increases looming if urbanization has the predicted evolutionary result. While uncovering this threat, evolutionary theory also highlights ways to combat it. For example, aggressively eliminating mosquito breeding sites within cities has a twofold benefit. Of course, it reduces the mosquito population in the near term. But it also reduces the selective advantage offered by specializing on humans. In the long term, this should slow the evolution of mosquitoes’ taste for humans… and make future summers’ outdoor gatherings a little less infested and a little more festive. evolution.berkeley.edu Q: Why did god make mosquitoes? |
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Stal 06:01 This is just my own personal speculation on the matter, but Genesis 6:1-4 might be a distant folk memory:- "When human beings began to increase in number on the earth and daughters were born to them, the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose. Then the Lord said, ‘My Spirit will not contend with humans for ever, for they are mortal; their days will be a hundred and twenty years.’ The Nephilim were on the earth in those days – and also afterwards – when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown." There are a few hints here. 1. The 'when humans began to multiply' might refer to the H.Sapiens expansion into H. Neanderthalis areas, specially in the Middle Est, where there are caves showing occupation by both breeds. 2. 'the daughters of humans were beautiful' - well, it's only natural that you think your own daughter is more attractive than the short-legged, chinless broad-faced girl next door. 3. 'The Nephilim were on the earth in those days, and afterward' implies that they have since died out. 4. 'Nephilim' is of unknown meaning, but the following description of 'heroes of old, men of renown' implies that they were powerful. It is known that Neanderthals were much stronger and more powerfully-built than Sapiens, and would have been able to wrestle the crap out of any Sapiens challenger. It is also significant that this description is part of the lead-in to the story of the Flood. Is the Flood story, at least in part, a folk memory of rising sea levels that resulted from an interglacial, or the end of the last glaciation around 10,000 B.C.? I think it is possible that this is the remnant of a long-lost folk tale that recalls Neanderthals. And of course they are portrayed as among the 'evil' who are to be destroyed; Genesis has a fair slice of 'particularism' - what we might call 'racism' - in it. Only the children of Seth (Eve's third son) and afterwards Abraham are the Chosen. |
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