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The Genes for White Skin Didn’t Develop in Europe, UPenn Study Finds
Before this, little was known about the genetic basis for the variety in human skin tone.
I'm a cat owner. I marvel at Selena's agility and shake my head at the inanities of her behavior, like not allowing me to go to the bathroom for five minutes by myself. If I shut her out, she meows at the door. The truth is, there's only about a 10% genetic difference between me and her. That's mind-blowing, considering that there are 3 billion base pairs in the human genetic code.
Between humans and chimpanzees, the genetic difference is only 4%. From one human to the next, it's minute, just 0.1%. Now, researchers at the University of Pennsylvania, have a better grasp on the science behind race and why we have different skin tones. The results were published in the journal Science.
We actually know very little about the genetics behind race. Although we may think of Africans as all having a similar pigmentation, there's a wide variety of skin tones on the continent. Some studies have isolated a few genes responsible for skin color. Yet, these were only identified among white populations, until now.
A collage of people included in the study. Credit: Alessia Ranciaro and Simon Thompson. The University of Pennsylvania.
Looking at genomes from different populations all over the African continent, researchers found the genetic variants responsible for skin pigmentation namely: SLC24A5, MFSD12, DDB1, TMEM138, OCA2, and HERC2. Geneticist Sarah Tishkoff was the senior author on this study. She said that in their paper, she and colleagues “show that mutations influencing light and dark skin have been around for a long time, since before the origin of modern humans."
Our ancient ancestor Australopithecus, which lived in Eastern Africa between 3.85 and 2.95 million years ago, probably had light skin underneath dark fur. Chimps, one of our closest living relatives, are the same way. Since their fur protects them from the sun, there's no need for more melanin.
At some point, an ancestor of ours was born without all that tremendous body hair. It was thought that shortly after, this hominin developed dark skin to protect it against harsh UV rays. So our oldest hairless ancestor may have had white skin, but only for a brief period.
Model of Lucy (Australopithecus afarensis). Credit: Getty Images.
Tishkoff and colleagues took a color meter and used it to reflect the light off the skin of over 2,000 Africans. Those with the lightest skin tone were the San people of southern Africa. While the darkest tone was found among the Nilo-Saharan pastoralists of eastern Africa, particularly the Mursi and Surma peoples.
Researchers collected genetic material from 1,570 Africans. They studied their genomes, examining 4 million single nucleotide polymorphisms (SNPs) in all. These are areas along the genome where a gene has been altered. From there, they identified the four key areas responsible for the variation in skin pigmentation. What surprised researchers most was that the gene SLC24A5—responsible for light skin, thought to have developed in Europe, is actually very common in Africa.
Genes HERC2 and OCA2, a close neighbor of SLC24A5, is associated with light eyes and skin. It was found common among the San, bearers of humanity's oldest genetic lineages. But this gene is also associated with a condition called vitiligo, which is where a depigmentation occurs on certain areas of the skin. This was an exciting find for the team. It gave greater weight to their findings.
The genes for light skin can be found not only in Europe and Africa, but Southeast Asia and the Middle East as well. “Most predate modern humans," Tishkoff said. “They've been variable for tens of thousands, if not hundreds of thousands of years in Africa. Everyone had the alleles for light skin."
San children. Credit: Nicolas M. Perrault. Wikimedia Commons.
The prevailing story of human migration is that modern humans traveled out of Africa somewhere between 80,000 and 60,000 years ago, reached Asia and later on, advanced into Astralo-Melanesia. Then, a second wave populated other regions of Eurasia.
According to Dr. Tishkoff, as a result of this study, “it is also possible that there was a single African source population that contained genetic variants associated with both light and dark skin and that the variants associated with dark pigmentation were maintained only in South Asians and Australo-Melanesians and lost in other Eurasians due to natural selection."
Those areas of highest ultraviolet intensity are where populations seem to have darker skin tones. Also, Africans are far less likely to develop melanoma. The researchers also identified gene variants for dark skin in south Asian Indian and Australo-Melanesian populations. Outside of Africa, these groups are the most likely to have dark skin. They had the same genes as dark-skinned Africans. So dark-skinned populations may have naturally selected for darker skin in regions where it's advantageous for survival, whereas Europeans did the same for lighter skin, since it allowed them to absorb more vitamin D.
To learn more about race from a genetic point of view, click here:
All this from a wad of gum?
- Researchers recently uncovered a piece of chewed-on birch pitch in an archaeological dig in Denmark.
- Conducting a genetic analysis of the material left in the birch pitch offered a plethora of insights into the individual who last chewed it.
- The gum-chewer has been dubbed Lola. She lived 5,700 years ago; and she had dark skin, dark hair, and blue eyes.
Five thousand and seven hundred years ago, "Lola" — a blue-eyed woman with dark skin and hair — was chewing on a piece of pitch derived from heating birch bark. Then, this women spit her chewing gum out into the mud on an island in Denmark that we call Syltholm today, where it was unearthed by archaeologists thousands of years later. A genetic analysis of the chewing gum has provided us with a wealth of information on this nearly six-thousand-year-old Violet Beauregarde.
This represents the first time that the human genome has been extracted from material such as this. "It is amazing to have gotten a complete ancient human genome from anything other than bone," said lead researcher Hannes Schroeder in a statement.
"What is more," he added, "we also retrieved DNA from oral microbes and several important human pathogens, which makes this a very valuable source of ancient DNA, especially for time periods where we have no human remains."
In the pitch, researchers identified the DNA of the Epstein-Barr virus, which infects about 90 percent of adults. They also found DNA belonging to hazelnuts and mallards, which were likely the most recent meal that Lola had eaten before spitting out her chewing gum.
Insights into ancient peoples
The birch pitch was found on the island of Lolland (the inspiration for Lola's name) at a site called Syltholm. "Syltholm is completely unique," said Theis Jensen, who worked on the study for his PhD. "Almost everything is sealed in mud, which means that the preservation of organic remains is absolutely phenomenal.
"It is the biggest Stone Age site in Denmark and the archaeological finds suggest that the people who occupied the site were heavily exploiting wild resources well into the Neolithic, which is the period when farming and domesticated animals were first introduced into southern Scandinavia."
Since Lola's genome doesn't show any of the markers associated with the agricultural populations that had begun to appear in this region around her time, she provides evidence for a growing idea that hunter-gatherers persisted alongside agricultural communities in northern Europe longer than previously thought.
Her genome supports additional theories on northern European peoples. For example, her dark skin bolsters the idea that northern populations only recently acquired their light-skinned adaptation to the low sunlight in the winter months. She was also lactose intolerant, which researchers believe was the norm for most humans prior to the agricultural revolution. Most mammals lose their tolerance for lactose once they've weaned off of their mother's milk, but once humans began keeping cows, goats, and other dairy animals, their tolerance for lactose persisted into adulthood. As a descendent of hunter-gatherers, Lola wouldn't have needed this adaptation.
A hardworking piece of gum
A photo of the birch pitch used as chewing gum.
These findings are encouraging for researchers focusing on ancient peoples from this part of the world. Before this study, ancient genomes were really only ever recovered from human remains, but now, scientists have another tool in their kit. Birch pitch is commonly found in archaeological sites, often with tooth imprints.
Ancient peoples used and chewed on birch pitch for a variety of reasons. It was commonly heated up to make it pliable, enabling it to be molded as an adhesive or hafting agent before it settled. Chewing the pitch may have kept it pliable as it cooled down. It also contains a natural antiseptic, and so chewing birch pitch may have been a folk medicine for dental issues. And, considering that we chew gum today for no other reason than to pass the time, it may be that ancient peoples chewed pitch for fun.
Whatever their reasons, chewed and discarded pieces of birch pitch offer us the mind-boggling option of learning what someone several thousands of years ago ate for lunch, or what the color of their hair was, their health, where their ancestors came from, and more. It's an unlikely treasure trove of information to be found in a mere piece of gum.
The non-contact technique could someday be used to lift much heavier objects — maybe even humans.
- Since the 1980s, researchers have been using sound waves to move matter through a technique called acoustic trapping.
- Acoustic trapping devices move bits of matter by emitting strategically designed sound waves, which interact in such a way that the matter becomes "trapped" in areas of particular velocity and pressure.
- Acoustic and optical trapping devices are already used in various fields, including medicine, nanotechnology, and biological research.
Sound can have powerful effects on matter. After all, sound strikes our world in waves — vibrations of air molecules that bounce off of, get absorbed by, or pass through matter around us. Sound waves from a trained opera singer can shatter a wine glass. From a jet, they can collapse a stone wall. But sound can also be harnessed for delicate interactions with matter.
Since the 1980s, researchers have been using sound to move matter through a phenomenon called acoustic trapping. The method is based on the fact that sound waves produce an acoustic radiation force.
"When an acoustic wave interacts with a particle, it exerts both an oscillatory force and a much smaller steady-state 'radiation' force," wrote the American Physical Society. "This latter force is the one used for trapping and manipulation. Radiation forces are generated by the scattering of a traveling sound wave, or by energy gradients within the sound field."
When tiny particles encounter this radiation, they tend to be drawn toward regions of certain pressure and velocity within the sound field. Researchers can exploit this tendency by engineering sound waves that "trap" — or suspend — tiny particles in the air. Devices that do this are often called "acoustic tweezers."
Building a better tweezer
A study recently published in the Japanese Journal of Applied Physics describes how researchers created a new type of acoustic tweezer that was able to lift a small polystyrene ball into the air.
Tweezers of Sound: Acoustic Manipulation off a Reflective Surface youtu.be
It is not the first example of a successful "acoustic tweezer" device, but the new method is likely the first to overcome a common problem in acoustic trapping: sound waves bouncing off reflective surfaces, which disrupts acoustic traps.
To minimize the problems of reflectivity, the team behind the recent study configured ultrasonic transducers such that the sound waves that they produce overlap in a strategic way that is able to lift a small bit of polystyrene from a reflective surface. By changing how the transducers emit sound waves, the team can move the acoustic trap through space, which moves the bit of matter.
Move, but don't touch
So far, the device is only able to move millimeter-sized pieces of matter with varying degrees of success. "When we move a particle, it sometimes scatters away," the team noted. Still, improved acoustic trapping and other no-contact lifting technologies — like optical tweezers, commonly used in medicine — could prove useful in many future applications, including cell separation, nanotechnologies, and biological research.
Could future acoustic-trapping devices lift large and heavy objects, maybe even humans? It seems possible. In 2018, researchers from the University of Bristol managed to acoustically trap particles whose diameters were larger than the sound wavelength, which was a breakthrough because it surpassed "the classical Rayleigh scattering limit that has previously restricted stable acoustic particle trapping," the researchers wrote in their study.
In other words, the technique — which involved suspending matter in tornado-like acoustic traps — showed that it is possible to scale up acoustic trapping.
"Acoustic tractor beams have huge potential in many applications," Bruce Drinkwater, co-author of the 2018 study, said in a statement. "I'm particularly excited by the idea of contactless production lines where delicate objects are assembled without touching them."
Australian parrots have worked out how to open trash bins, and the trick is spreading across Sydney.
- If sharing learned knowledge is a form of culture, Australian cockatoos are one cultured bunch of birds.
- A cockatoo trick for opening trash bins to get at food has been spreading rapidly through Sydney's neighborhoods.
- But not all cockatoos open the bins; some just stay close to those that do.
Dumpster-diving trash parrots
In a study about these smart birds just published in Science, researchers define animal culture as "population-specific behaviors acquired via social learning from knowledgeable individuals."
Co-lead author of the study Barbara Klump of the Max Planck Institute of Animal Behavior in Konstanz, Germany says, "[C]ompared to humans, there are few known examples of animals learning from each other. Demonstrating that food scavenging behavior is not due to genetics is a challenge."
An opportunity presented itself in a video that co-author Richard Major of the Australian Museum shared with Klump and the other co-authors. In the video, a sulphur-crested cockatoo used its beak to pull up the handle of a closed garbage bin — using its foot as a wedge — and then walked back the lid sufficiently to flip it open, exposing the bin's edible contents.
Major has been studying Cacatua galerita for 20 years and says, "Like many Australian birds, sulphur-crested cockatoos are loud and aggressive." The study describes them as a "large-brained, long-lived, and highly social parrot." Says Major, "They are also incredibly smart, persistent, and have adapted brilliantly to living with humans."(Research regarding some of the ways in which wild animals adapt to the presence of humans has already produced some fascinating results and is ongoing.)
Clever cockie opens bin - 01 youtu.be
The researchers became curious about how widespread this behavior might be and saw a research opportunity. After all, says John Martin, a researcher at Taronga Conservation Society, "Australian garbage bins have a uniform design across the country, and sulphur-crested cockatoos are common across the entire east coast."
Martin continues, "In 2018, we launched an online survey in various areas across Sydney and Australia with questions such as, 'What area are you from, have you seen this behavior before, and if so, when?'"
Word gets around
Credit: magspace/Adobe Stock
Although the cockatoos' maneuver was reported in only three suburbs before 2018, by the end of 2019, people in 44 areas reported observing the behavior. Clearly, more and more cockatoos were learning how to successfully dumpster dive.
As further proof, says Klump, "We observed that the birds do not open the garbage bins in the same way, but rather used different opening techniques in different suburbs, suggesting that the behavior is learned by observing others." One individual bird in north Sydney invented its own method, and the scientists saw it grow in popularity throughout the local population.
To track individual birds, the researchers marked 500 cockatoos with small red dots. Subsequent observations revealed that not all cockatoos are bin-openers. Only about 10 percent of them are, and they are mostly males. The other cockatoos apparently restrict their education to a different lesson: hang around with a bin-opener, and you will get supper.
Thanks to the surveys, the researchers consider the entire project to be a valuable citizen-science experiment. "By studying this behavior with the help of local residents, we are uncovering the unique and complex cultures of their neighborhood birds."
The few seconds of nuclear explosion opening shots in Godzilla alone required more than 6.5 times the entire budget of the monster movie they ended up in.