Keeping upright: How much gravity is enough?

The experimental setup. (A) Participants lay on a human centrifuge with their feet out so that centripetal force from the centrifuge produced a centripetal force simulating gravity along the long axis of the body. (B) They viewed a screen mounted above their heads which presented a scene tilted at 112° relative to their bodies. The direction signaled by each cue to upright is indicated by arrow: red, vision; green, simulated gravity and blue, the body. (C) Thus, the three vectors involved in determining the perceptual upright (body, gravity and vision) could be dissociated.
 Credit: Harris et al; doi:10.1371/journal.pone.0106207.g001

Keeping upright in a low-gravity environment is not easy, and NASA documents abound with examples of astronauts falling on the lunar surface. Now, a new study by an international team of researchers led by York University professors Laurence Harris and Michael Jenkin, published today in PLOS ONE, suggests that the reason for all these moon mishaps might be because its gravity isn't sufficient to provide astronauts with unambiguous information on which way is "up."

"The perception of the relative orientation of oneself and the world is important not only to balance, but also for many other aspects of perception including recognizing faces and objects and predicting how objects are going to behave when dropped or thrown," says Harris. "Misinterpreting which way is up can lead to perceptual errors and threaten balance if a person uses an incorrect reference point to stabilize themselves."

Using a short-arm centrifuge provided by the European Space Agency, the international team simulated gravitational fields of different strengths, and used a York-invented perceptual test to measure the effectiveness of gravity in determining the perception of up. 

The team found that the threshold level of gravity needed to just influence a person's orientation judgment was about 15 per cent of the level found on Earth -- very close to that on the moon.

The team also found that Martian gravity, at 38 per cent of that on Earth, should be sufficient for astronauts to orient themselves and maintain balance on any future manned missions to Mars.

"If the brain does not sense enough gravity to determine which way is up, astronauts may get disoriented, which can lead to errors like flipping switches the wrong way or moving the wrong way in an emergency," says Jenkin. "Therefore, it's crucial to understand how the direction of up is established and to establish the relative contribution of gravity to this direction before journeying to environments with gravity levels different to that of Earth."

This work builds upon results obtained in long-duration microgravity by Harris and Jenkin and other members of York's Centre for Vision Research on board the International Space Station during the Bodies in the Space Environment project, funded by the Canadian Space Agency.

Source: York University

Human faces are so variable because we evolved to look unique

The amazing variety of human faces -- far greater than that of most other animals -- is the result of evolutionary pressure to make each of us unique and easily recognizable. Credit: UC Berkeley

The amazing variety of human faces -- far greater than that of most other animals -- is the result of evolutionary pressure to make each of us unique and easily recognizable, according to a new study by University of California, Berkeley, scientists.

Our highly visual social interactions are almost certainly the driver of this evolutionary trend, said behavioral ecologist Michael J. Sheehan, a postdoctoral fellow in UC Berkeley's Museum of Vertebrate Zoology. Many animals use smell or vocalization to identify individuals, making distinctive facial features unimportant, especially for animals that roam after dark, he said. But humans are different.

"Humans are phenomenally good at recognizing faces; there is a part of the brain specialized for that," Sheehan said. "Our study now shows that humans have been selected to be unique and easily recognizable. It is clearly beneficial for me to recognize others, but also beneficial for me to be recognizable. Otherwise, we would all look more similar."

"The idea that social interaction may have facilitated or led to selection for us to be individually recognizable implies that human social structure has driven the evolution of how we look," said coauthor Michael Nachman, a population geneticist, professor of integrative biology and director of the UC Berkeley Museum of Vertebrate Zoology.

The study will appear Sept. 16 in the online journal Nature Communications.

In the study, Sheehan said, "we asked, 'Are traits such as distance between the eyes or width of the nose variable just by chance, or has there been evolutionary selection to be more variable than they would be otherwise; more distinctive and more unique?'"

As predicted, the researchers found that facial traits are much more variable than other bodily traits, such as the length of the hand, and that facial traits are independent of other facial traits, unlike most body measures. People with longer arms, for example, typically have longer legs, while people with wider noses or widely spaced eyes don't have longer noses. Both findings suggest that facial variation has been enhanced through evolution.

Finally, they compared the genomes of people from around the world and found 

more genetic variation in the genomic regions that control facial characteristics than in other areas of the genome, a sign that variation is evolutionarily advantageous.

"All three predictions were met: facial traits are more variable and less correlated than other traits, and the genes that underlie them show higher levels of variation," Nachman said. "Lots of regions of the genome contribute to facial features, so you would expect the genetic variation to be subtle, and it is. But it is consistent and statistically significant."

Using Army data

Sheehan was able to assess human facial variability thanks to a U.S. Army database of body measurements compiled from male and female personnel in 1988. The Army Anthropometric Survey (ANSUR) data are used to design and size everything from uniforms and protective clothing to vehicles and workstations.

A statistical comparison of facial traits of European Americans and African Americans -- forehead-chin distance, ear height, nose width and distance between pupils, for example -- with other body traits -- forearm length, height at waist, etc. -- showed that facial traits are, on average, more varied than the others. The most variable traits are situated within the triangle of the eyes, mouth and nose.

Sheehan and Nachman also had access to data collected by the 1000 Genome project, which has sequenced more than 1,000 human genomes since 2008 and catalogued nearly 40 million genetic variations among humans worldwide. Looking at regions of the human genome that have been identified as determining the shape of the face, they found a much higher number of variants than for traits, such as height, not involving the face.

Prehistoric origins

"Genetic variation tends to be weeded out by natural selection in the case of traits that are essential to survival," Nachman said. "Here it is the opposite; selection is maintaining variation. All of this is consistent with the idea that there has been selection for variation to facilitate recognition of individuals."

They also compared the human genomes with recently sequenced genomes of Neanderthals and Denisovans and found similar genetic variation, which indicates that the facial variation in modern humans must have originated prior to the split between these different lineages.

"Clearly, we recognize people by many traits -- for example their height or their gait -- but our findings argue that the face is the predominant way we recognize people," Sheehan said.

Source: University of California - Berkeley

Dogs hear our words and how we say them

The results from this study support the idea that our canine companions are paying attention "not only to who we are and how we say things, but also to what we say," authors say. Credit: © Uros Petrovic / Fotolia

 When people hear another person talking to them, they respond not only to what is being said--those consonants and vowels strung together into words and sentences--but also to other features of that speech--the emotional tone and the speaker's gender, for instance. Now, a report in the Cell Press journal Current Biology on November 26 provides some of the first evidence of how dogs also differentiate and process those various components of human speech.

"Although we cannot say how much or in what way dogs understand information in speech from our study, we can say that dogs react to both verbal and speaker-related information and that these components appear to be processed in different areas of the dog's brain," says Victoria Ratcliffe of the School of Psychology at the University of Sussex.

Previous studies showed that dogs have hemispheric biases--left brain versus right--when they process the vocalization sounds of other dogs. Ratcliffe and her supervisor David Reby say it was a logical next step to investigate whether dogs show similar biases in response to the information transmitted in human speech. They played speech from either side of the dog so that the sounds entered each of their ears at the same time and with the same amplitude.

"The input from each ear is mainly transmitted to the opposite hemisphere of the brain," Ratcliffe explains. "If one hemisphere is more specialized in processing certain information in the sound, then that information is perceived as coming from the opposite ear."
If the dog turned to its left, that showed that the information in the sound being played was heard more prominently by the left ear, suggesting that the right hemisphere is more specialized in processing that kind of information.

The researchers did observe general biases in dogs' responses to particular aspects of human speech. When presented with familiar spoken commands in which the meaningful components of words were made more obvious, dogs showed a left-hemisphere processing bias, as indicated by turning to the right. When the intonation or speaker-related vocal cues were exaggerated instead, dogs showed a significant right-hemisphere bias.

"This is particularly interesting because our results suggest that the processing of speech components in the dog's brain is divided between the two hemispheres in a way that is actually very similar to the way it is separated in the human brain," Reby says.
Of course, it doesn't mean that dogs actually understand everything that we humans might say or that they have a human-like ability of language--far from it. But, says Ratcliffe, these results support the idea that our canine companions are paying attention "not only to who we are and how we say things, but also to what we say."

All of this should come as good news to many of us dog-loving humans, as we spend considerable time talking to our respective pups already. They might not always understand you, but they really are listening.

Source: Cell Press

A clear, molecular view of how human color vision evolved

Mountain Gorilla - Bwindi Uganda. “Gorillas and chimpanzees have human color vision,” Yokoyama says. “Or perhaps we should say that humans have gorilla and chimpanzee vision.” Credit: © Alexander / Fotolia

Many genetic mutations in visual pigments, spread over millions of years, were required for humans to evolve from a primitive mammal with a dim, shadowy view of the world into a greater ape able to see all the colors in a rainbow.

Now, after more than two decades of painstaking research, scientists have finished a detailed and complete picture of the evolution of human color vision. PLOS Genetics published the final pieces of this picture: The process for how humans switched from ultraviolet (UV) vision to violet vision, or the ability to see blue light.

"We have now traced all of the evolutionary pathways, going back 90 million years, that led to human color vision," says lead author Shozo Yokoyama, a biologist at Emory University. 

"We've clarified these molecular pathways at the chemical level, the genetic level and the functional level."

Co-authors of the PLOS Genetics paper include Emory biologists Jinyi Xing, Yang Liu and Davide Faggionato; Syracuse University biologist William Starmer; and Ahmet Altun, a chemist and former post-doc at Emory who is now at Fatih University in Istanbul, Turkey.

Yokoyama and various collaborators over the years have teased out secrets of the adaptive evolution of vision in humans and other vertebrates by studying ancestral molecules. The lengthy process involves first estimating and synthesizing ancestral proteins and pigments of a species, then conducting experiments on them. The technique combines microbiology with theoretical computation, biophysics, quantum chemistry and genetic engineering.

Five classes of opsin genes encode visual pigments for dim-light and color vision. Bits and pieces of the opsin genes change and vision adapts as the environment of a species changes.

Around 90 million years ago, our primitive mammalian ancestors were nocturnal and had UV-sensitive and red-sensitive color, giving them a bi-chromatic view of the world. By around 30 million years ago, our ancestors had evolved four classes of opsin genes, giving them the ability to see the full-color spectrum of visible light, except for UV.

"Gorillas and chimpanzees have human color vision," Yokoyama says. "Or perhaps we should say that humans have gorilla and chimpanzee vision."

For the PLOS Genetics paper, the researchers focused on the seven genetic mutations involved in losing UV vision and achieving the current function of a blue-sensitive pigment. 

They traced this progression from 90-to-30 million years ago.

The researchers identified 5,040 possible pathways for the amino acid changes required to bring about the genetic changes. "We did experiments for every one of these 5,040 possibilities," Yokoyama says. "We found that of the seven genetic changes required, each of them individually has no effect. It is only when several of the changes combine in a particular order that the evolutionary pathway can be completed."

In other words, just as an animal's external environment drives natural selection, so do changes in the animal's molecular environment.

In previous research, Yokoyama showed how the scabbardfish, which today spends much of its life at depths of 25 to 100 meters, needed just one genetic mutation to switch from UV to blue-light vision. Human ancestors, however, needed seven changes and these changes were spread over millions of years. "The evolution for our ancestors' vision was very slow, compared to this fish, probably because their environment changed much more slowly," 
Yokoyama says.

About 80 percent of the 5,040 pathways the researchers traced stopped in the middle, because a protein became non-functional. Chemist Ahmet Altun solved the mystery of why the protein got knocked out. It needs water to function, and if one mutation occurs before the other, it blocks the two water channels extending through the vision pigment's membrane.

"The remaining 20 percent of the pathways remained possible pathways, but our ancestors used only one," Yokoyama says. "We identified that path."

In 1990, Yokoyama identified the three specific amino acid changes that led to human ancestors developing a green-sensitive pigment. In 2008, he led an effort to construct the most extensive evolutionary tree for dim-light vision, including animals from eels to humans. At key branches of the tree, Yokoyama's lab engineered ancestral gene functions, in order to connect changes in the living environment to the molecular changes.

The PLOS Genetics paper completes the project for the evolution of human color vision. "We have no more ambiguities, down to the level of the expression of amino acids, for the mechanisms involved in this evolutionary pathway," Yokoyama says.

Source: Emory Health Sciences