Shift in human ancestors’ diet earlier than previously thought

Key move to grass-based foods was 400,000 years earlier than previously known

September 15, 2015
Johns Hopkins University
Pre-humans’ shift toward a grass-based diet took place about 400,000 years earlier than experts previously thought, providing a clearer picture of a time of rapid change in conditions that shaped human evolution.

Millions of years ago, our primate ancestors turned from trees and shrubs to search for food on the ground. In human evolution, that has made all the difference.

The shift toward a grass-based diet marked a significant step toward the diverse eating habits that became a key human characteristic, and would have made these early humans more mobile and adaptable to their environment.

New evidence just published by a research team led by a Johns Hopkins University scientist shows that this significant shift took place about 400,000 years earlier than experts previously thought, providing a clearer picture of a time of rapid change in conditions that shaped human evolution.

Naomi E. Levin, the lead author of the report just published in Proceedings of the National Academy of Sciences, said the diet shift is one of an array of changes that took place during the Pliocene era — 2.6 million to 5.3 million years ago — when the fossil record indicates human ancestor species were starting to spend more time on the ground walking on two feet. Understanding the timing of these events can help show how one change related to another.

“A refined sense for when the dietary changes took place among early humans, in relation to changes in our ability to be bipedal and terrestrial, will help us understand our evolutionary story,” said Levin, an assistant professor in the Department of Earth and Planetary Sciences.

The paper reports on an analysis of fossil teeth found in Ethiopia that shows the shift from a diet based on trees and shrubs to one that included grass-based foods took place about 3.8 million years ago — roughly 400,000 years earlier than the date supported by previous research. (Grass-based foods could include not only grasses and their roots, but also insects or animals that ate grass.)

The shift in eating habits would have broadened our ancestors’ horizons and improved their species’ capacity for survival, Levin said.

“You can then range wider,” Levin said of the human precursors, species including Australopithecus afarensis, extinct some 3 million years ago and represented most famously in the fossil informally known as “Lucy.” “You can be in more places, more resilient to habitat change.”

“This research reveals surprising insights into the interactions between morphology and behavior among Pliocene primates,” said co-author Yohannes Haile-Selassie of the Cleveland Museum of Natural History. “The results not only show an earlier start to grass-based food consumption among hominins and baboons but also indicate that form does not always precede function. In the earliest baboons, dietary shift toward grass occurred before its teeth were specialized for grazing.”

Researchers analyzed 152 fossil teeth from an array of animals including pigs, antelopes, giraffes and human ancestors gathered from a roughly 100 square-mile area of what is now the Afar region of Ethiopia. Among the samples were teeth from hominins — including contemporary humans and our extinct ancestors — believed to represent 16 different individuals, said Levin, one of four co-authors of the paper. Her collaborators were Haile-Selassie, Stephen R. Frost of the University of Oregon and Beverly Z. Saylor of Case Western Reserve University.

The teeth were examined for carbon isotope distribution, a marker that can distinguish the types of foods the animals ate. The data showed that both human ancestors and members of a now-extinct, large species of baboon were eating large amounts of grass-based foods as early as 3.76 million years ago. Previous research dated the earliest evidence for grass-based foods in early human diets to about 3.4 million years ago.

The researchers could not firmly establish a link between external environmental change and the diet of hominins and baboons, but instead attribute the dietary expansion to changes in relations among members of the African primate communities, such as the appearance of new species of primates.

“Timing is critical to understanding the context for this dietary expansion among early humans in relationship to what’s happening in global climate, in vegetation communities in Africa, among other mammals, and in terms of the other evolutionary changes that are happening among early humans,” she said. “If we know the timing of events we can start to relate them to one another.”

Story Source:

The above post is reprinted from materials provided by Johns Hopkins University. Note: Materials may be edited for content and length.

Journal Reference:

  1. Naomi E. Levin, Yohannes Haile-Selassie, Stephen R. Frost, Beverly Z. Saylor. Dietary change among hominins and cercopithecids in Ethiopia during the early Pliocene. Proceedings of the National Academy of Sciences, 2015; 201424982 DOI: 10.1073/pnas.1424982112

Controlling brain cells with sound waves

Date:September 15, 2015

Source:Salk Institute

Summary:A new technique to selectively and noninvasively turn on groups of neurons in worms could be boon to science and medicine.

Salk scientists have developed a new way to selectively activate brain, heart, muscle and other cells using ultrasonic waves. The new technique, dubbed sonogenetics, has some similarities to the burgeoning use of light to activate cells in order to better understand the brain.

This new method–which uses the same type of waves used in medical sonograms–may have advantages over the light-based approach–known as optogenetics–particularly when it comes to adapting the technology to human therapeutics. It was described September 15, 2015 in the journal Nature Communications.

“Light-based techniques are great for some uses and I think we’re going to continue to see developments on that front,” says Sreekanth Chalasani, an assistant professor in Salk’s Molecular Neurobiology Laboratory and senior author of the study. “But this is a new, additional tool to manipulate neurons and other cells in the body.”

In optogenetics, researchers add light-sensitive channel proteins to neurons they wish to study. By shining a focused laser on the cells, they can selectively open these channels, either activating or silencing the target neurons. But using an optogenetics approach on cells deep in the brain is difficult: typically, researchers have to perform surgery to implant a fiber optic cable that can reach the cells. Plus, light is scattered by the brain and by other tissues in the body.

Chalasani and his group decided to see if they could develop an approach that instead relied on ultrasound waves for the activation. “In contrast to light, low-frequency ultrasound can travel through the body without any scattering,” he says. “This could be a big advantage when you want to stimulate a region deep in the brain without affecting other regions,” adds Stuart Ibsen, a postdoctoral fellow in the Chalasani lab and first author of the new work.

Chalasani and his colleagues first showed that, in the nematode Caenorhabditis elegans, microbubbles of gas outside of the worm were necessary to amplify the low-intensity ultrasound waves. “The microbubbles grow and shrink in tune with the ultrasound pressure waves,” Ibsen says. “These oscillations can then propagate noninvasively into the worm.”

Next, they found a membrane ion channel, TRP-4, which can respond to these waves. When mechanical deformations from the ultrasound hitting gas bubbles propagate into the worm, they cause TRP-4 channels to open up and activate the cell. Armed with that knowledge, the team tried adding the TRP-4 channel to neurons that don’t normally have it. With this approach, they successfully activated neurons that don’t usually react to ultrasound.

So far, sonogenetics has only been applied to C. elegans neurons. But TRP-4 could be added to any calcium-sensitive cell type in any organism including humans, Chalasani says. Then, microbubbles could be injected into the bloodstream, and distributed throughout the body–an approach already used in some human imaging techniques. Ultrasound could then noninvasively reach any tissue of interest, including the brain, be amplified by the microbubbles, and activate the cells of interest through TRP-4. And many cells in the human body, he points out, can respond to the influxes of calcium caused by TRP-4.

“The real prize will be to see whether this could work in a mammalian brain,” Chalasani says. His group has already begun testing the approach in mice. “When we make the leap into therapies for humans, I think we have a better shot with noninvasive sonogenetics approaches than with optogenetics.”

Both optogenetics and sonogenetics approaches, he adds, hold promise in basic research by letting scientists study the effect of cell activation. And they also may be useful in therapeutics through the activation of cells affected by disease. However, for either technique to be used in humans, researchers first need to develop safe ways to deliver the light or ultrasound-sensitive channels to target cells.

Other researchers on the study were Stuart Ibsen and Ada Tong of the Salk Institute, and Carolyn Schutt and Sadik Esener of the University of California, San Diego.

The work and the researchers involved were supported by a Salk Institute Pioneer Fund Postdoctoral Fellowship, a Salk Institute Innovation Grant, the Rita Allen Foundation, the W.M. Keck Foundation and the National Institutes of Health.

Story Source:

The above post is reprinted from materials provided by Salk Institute. Note: Materials may be edited for content and length.

Journal Reference:

  1. Stuart Ibsen, Ada Tong, Carolyn Schutt, Sadik Esener, Sreekanth H. Chalasani. Sonogenetics is a non-invasive approach to activating neurons in Caenorhabditis elegans. Nature Communications, 2015; 6: 8264 DOI: 10.1038/ncomms9264

Evidence of emotional ‘load sharing’ in close relationships

Date:September 14, 2015

Source:Queen’s University

Summary:Evidence of emotional load sharing between partners in a close relationship has bee uncovered by researchers. Their new study found that a strong relationship with a loved one can help ease stress when placed in difficult situations.

“We wanted to test a new evolutionary theory in psychology called Social Baseline Theory which suggests that humans adapted to be close to other humans,” says Ms. Lougheed. “The idea is that individuals function at a relative deficit when they are farther away from people they trust.”

In their study, Ms. Lougheed and co-authors measured the stress levels of 66 adolescent girls during a spontaneous speech task. Before the speech performance, the participants and their mothers rated the quality of their relationship. During the speeches, researchers tracked the participants’ level of stress via galvanic skin response (measuring the level of skin perspiration). To account for the effect of physical — rather than purely emotional — closeness, the participants’ mothers were instructed either to hold or not hold their daughters’ hand.

The researchers found that physical closeness allowed the participants to manage their stress more efficiently, regardless of how close the mother-daughter pair reported being. However, when physical contact was removed from the equation, only the participants who reported higher relationship quality showed signs of load sharing.

“Our results suggest that we are better equipped to overcome challenging situations when we are closer — either physically or in terms of how we feel in our relationships — to people we trust,” says Ms. Lougheed.

Participants who had reported the lowest level of mother-daughter relationship closeness and lacked physical contact during the task were the least efficient in managing emotional stress.

“We were somewhat surprised to find that mothers’ stress did not vary by physical closeness — after all, it can be stressful for parents to watch their children perform, but being able to offer physical comfort might have lessened the mothers’ stress,” says Ms. Lougheed.

“Thus, emotional load sharing in this context was not a function of the mothers’ stress level, and we expect that it occurred instead through the daughters’ perceptions of how stressful it was to give a speech. That is, higher physical and/or relationship closeness helped the daughters feel like they could overcome the challenging situation.”

The results suggest that physical contact can overcome some difficulties associated with relatively low relationship quality, or that being in a high-quality relationship is helpful for managing emotions in the same way as the physical comfort of a loved one. Lougheed does, however, note that the general level of relationship quality was relatively high in their sample, and that physical contact may function very differently in distressed families. She also cautions against generalizing these results to other partnerships — such as a relationship between romantic partners, platonic friends and other family members — and suggest that more research be done to determine the effect of socioeconomic status and gender, amongst other factors.

The study, “Sharing the burden: the interpersonal regulation of emotional arousal in mother-daughter dyads,” was published in the journal Emotion.

Story Source:

The above post is reprinted from materials provided by Queen’s University. Note: Materials may be edited for content and length.

Journal Reference:

  1. Jessica P. Lougheed, Peter Koval, Tom Hollenstein. Sharing the Burden: The Interpersonal Regulation of Emotional Arousal in Mother−Daughter Dyads.. Emotion, 2015; DOI: 10.1037/emo0000105

Birds reveal the evolutionary importance of love

Date: September 14, 2015

Source: PLOS

Summary: Humans are extremely choosy when it comes to mating, only settling down after a long screening process involving nervous flirtations, awkward dates, humiliating rejections and the occasional lucky strike. But evolution is an unforgiving force — isn’t this choosiness rather a costly waste of time and energy when we should just be ‘going forth and multiplying?’ What, if anything, is the evolutionary point of it all? A new study may have the answer.

Doing a cost/benefit analysis of love is a challenging business, with many potential confounds, and — in the case of humans — some ethical limitations on doing experiments. A new study publishing on September 14th in the Open Access journal PLOS Biology by Malika Ihle, Bart Kempenaers, and Wolfgang Forstmeier from the Max Planck Institute for Ornithology, Seewiesen, Germany, describes an elegant experiment designed to tease apart the consequences of mate choice.

The authors took advantage of the fact that the zebra finch shares many characteristics with humans, mating monogamously for life, and sharing the burden of parental care. Female finches choose mates in a way that is specific to the individual, and there is little consensus among females as to who the cutest male is.

Using a population of 160 birds, the authors set up a speed-dating session, leaving groups of 20 females to choose freely between 20 males. Once the birds had paired off, half of the couples were allowed to go off into a life of wedded bliss. For the other half, however, the authors intervened like overbearing Victorian parents, splitting up the happy pair, and forcibly pairing them with other broken-hearted individuals.

Bird couples, whether happy or somewhat disgruntled, were then left to breed in aviaries, and the authors assessed couples’ behavior and the number and paternity of dead embryos, dead chicks and surviving offspring.

Strikingly, the final number of surviving chicks was 37% higher for individuals in chosen pairs than those in non-chosen pairs. The nests of non-chosen pairs had almost three times as many unfertilized eggs as the chosen ones, a greater number of eggs were either buried or lost, and markedly more chicks died after hatching. Most deaths occurred within the chicks’ first 48 hours, a critical period for parental care during which non-chosen fathers were markedly less diligent in their nest-care duties.

Watching the couples’ courtship showed some noticeable differences — although non-chosen males paid the same amount of attention to their mates as the chosen ones did, the non-chosen females were far less receptive to their advances, and tended to copulate less often. An analysis of harmonious behavior revealed that non-chosen couples were generally significantly less lovey-dovey than the chosen ones. There was also a higher level of infidelity in birds from non-chosen pairs — interestingly the straying of male birds increased as time went by while females roamed less.

Overall the authors conclude that birds vary rather idiosyncratically in their tastes, and choose mates on the basis that they find them stimulating in some way that isn’t necessarily obvious to an outside observer. This stimulation “turns on” the females to increase the likelihood of successful copulation and encourages paternal commitment for the time needed to raise young; together these maximize the couple’s likelihood of perpetuating their genes through their thriving offspring.

Sounds familiar? This is presumably what the human dating game is about, the need perhaps exacerbated by the extended phase of dependence during which our children need parental support. Indeed, these authors’ results are consistent with some studies on the differences between love-based and arranged marriages in human society.

Story Source:

The above post is reprinted from materials provided by PLOS. Note: Materials may be edited for content and length.

Journal Reference:

  1. Malika Ihle, Bart Kempenaers, Wolfgang Forstmeier. Fitness Benefits of Mate Choice for Compatibility in a Socially Monogamous Species. PLOS Biology, 2015; 13 (9): e1002248 DOI: 10.1371/journal.pbio.1002248