Human Evolution Driven By Changing Environment

Human Evolution Driven By Changing Environment

  9:46:00 AM    Science Lover

---

A series of rapid environmental changes in East Africa roughly 2 million years ago may be responsible for driving human evolution, according to researchers at Penn State and Rutgers University.

The researchers examined lake sediments from Olduvai Gorge in northern Tanzania, looking for biomarkers -- fossil molecules -- from ancient trees and grasses. (Credit: Gail Ashley)

"The landscape early humans were inhabiting transitioned rapidly back and forth between a closed woodland and an open grassland about five to six times during a period of 200,000 years," said Clayton Magill, graduate student in geosciences at Penn State. "These changes happened very abruptly, with each transition occurring over hundreds to just a few thousand years."

According to Katherine Freeman, professor of geosciences, Penn State, the current leading hypothesis suggests that evolutionary changes among humans during the period the team investigated were related to a long, steady environmental change or even one big change in climate.

"There is a view this time in Africa was the 'Great Drying,' when the environment slowly dried out over 3 million years," she said. "But our data show that it was not a grand progression towards dry; the environment was highly variable."

According to Magill, many anthropologists believe that variability of experience can trigger cognitive development.

"Early humans went from having trees available to having only grasses available in just 10 to 100 generations, and their diets would have had to change in response," he said. "Changes in food availability, food type, or the way you get food can trigger evolutionary mechanisms to deal with those changes. The result can be increased brain size and cognition, changes in locomotion and even social changes -- how you interact with others in a group. Our data are consistent with these hypotheses. We show that the environment changed dramatically over a short time, and this variability coincides with an important period in our human evolution when the genus Homo was first established and when there was first evidence of tool use."

The researchers -- including Gail Ashley, professor of earth and planetary sciences, Rutgers University -- examined lake sediments from Olduvai Gorge in northern Tanzania. They removed the organic matter that had either washed or was blown into the lake from the surrounding vegetation, microbes and other organisms 2 million years ago from the sediments. In particular, they looked at biomarkers -- fossil molecules from ancient organisms -- from the waxy coating on plant leaves.

"We looked at leaf waxes because they're tough, they survive well in the sediment," said Freeman.

The team used gas chromatography and mass spectrometry to determine the relative abundances of different leaf waxes and the abundance of carbon isotopes for different leaf waxes. The data enabled them to reconstruct the types of vegetation present in the Olduvai Gorge area at very specific time intervals.

The results showed that the environment transitioned rapidly back and forth between a closed woodland and an open grassland.

To find out what caused this rapid transitioning, the researchers used statistical and mathematical models to correlate the changes they saw in the environment with other things that may have been happening at the time, including changes in the Earth's movement and changes in sea-surface temperatures.

"The orbit of the Earth around the sun slowly changes with time," said Freeman. "These changes were tied to the local climate at Olduvai Gorge through changes in the monsoon system in Africa. Slight changes in the amount of sunshine changed the intensity of atmospheric circulation and the supply of water. The rain patterns that drive the plant patterns follow this monsoon circulation. We found a correlation between changes in the environment and planetary movement."

The team also found a correlation between changes in the environment and sea-surface temperature in the tropics.

"We find complementary forcing mechanisms: one is the way Earth orbits, and the other is variation in ocean temperatures surrounding Africa," Freeman said. The researchers recently published their results in the Proceedings of the National Academy of Sciences along with another paper in the same issue that builds on these findings. The second paper shows that rainfall was greater when there were trees around and less when there was a grassland.

"The research points to the importance of water in an arid landscape like Africa," said Magill. "The plants are so intimately tied to the water that if you have water shortages, they usually lead to food insecurity.

"Together, these two papers shine light on human evolution because we now have an adaptive perspective. We understand, at least to a first approximation, what kinds of conditions were prevalent in that area and we show that changes in food and water were linked to major evolutionary changes."

The National Science Foundation funded this research.

Read More

Leaping Lizards and Dinosaurs Inspire Robot Design

Leaping Lizards and Dinosaurs Inspire Robot Design

  10:48:00 PM    Science Lover

---

Leaping lizards have a message for robots: Get a tail! University of California, Berkeley, biologists and engineers -- including undergraduate and graduate students -- studied how lizards manage to leap successfully even when they slip and stumble. They found that lizards swing their tails upward to prevent them from pitching head-over-heels into a rock.

An Agama lizard next to Tailbot, a toy car with an attached tail 
and a toy figure. Sensors detect Tailbot's orientation and swing 
the tail upward to keep the robot from pitching forward, similar 
to the way the lizard uses its tail. 
(Credit: Photo by Robert Full lab, UC Berkeley.)

But after the team added a tail to a robotic car named Tailbot, they discovered that counteracting the effect of a slip is not as simple as throwing your tail in the air. Instead, robots and lizards must actively adjust the angle of their tails just right to remain upright.

"We showed for the first time that lizards swing their tail up or down to counteract the rotation of their body, keeping them stable," said team leader Robert J. Full, UC Berkeley professor of integrative biology. "Inspiration from lizard tails will likely lead to far more agile search-and-rescue robots, as well as ones having greater capability to more rapidly detect chemical, biological or nuclear hazards."

Agile therapod dinosaurs like the velociraptor depicted in the movie Jurassic Park may also have used their tails as stabilizers to prevent forward pitch, Full said. Their tail movement is illustrated in a prescient chase sequence from the 1993 movie in which the animated animal leaps from a balcony onto a T. rex skeleton.

"Muscles willing, the dinosaur could be even more effective with a swing of its tail in controlling body attitude than the lizards," Full said.

Student involvement crucial to research

Full and his laboratory colleagues, including both engineering and biology students, will report their discoveries online on Jan. 5 in advance of publication in the Jan. 12 print edition of the journal Nature. The paper's first author, mechanical engineering graduate student Thomas Libby, also will report the results on Jan. 7 at the annual meeting of the Society for Integrative and Comparative Biology in Charleston, S.C.

Full is enthusiastic about the interplay fostered at UC Berkeley between biologists and engineers in the Center for Interdisciplinary Bio-inspiration in Education and Research (CiBER) lab, within which he offers a research-based teaching lab that provides dozens of undergraduate students with an opportunity to conduct cutting-edge research in teams with graduate students. Each team experiences the benefits of how biologists and engineers approach a problem.

"Learning in the context of original discovery, finding out something that no one has ever know before, really motivated me," said former UC Berkeley integrative biology undergraduate Talia Moore, now a graduate student in the Department of Organismic and Evolutionary Biology at Harvard University. "This research-based lab course … showed me how biologists and engineers can work together to benefit both fields."

"This paper shows that research-based teaching leads to better learning and simultaneously can lead to cutting-edge research," added Full, who last year briefed the U.S. House of Representative's Science, Technology, Engineering and Mathematics (STEM) Education Caucus on this topic. "It also shows the competitive advantage of interdisciplinary approaches and how involvement of undergraduates in research can lead to innovation."

From gecko toe hairs to tails

Full's research over the past 20 years has revealed how the toe hairs of geckos assist them in climbing smooth vertical surfaces and, more recently, how their tails help to keep them from falling when they slip and to right themselves in mid-air.

The new research tested a 40-year-old hypothesis that the two-legged theropod dinosaurs ‑ the ancestors of birds ‑ used their tails as stabilizers while running or dodging obstacles or predators. In Full's teaching laboratory, students noticed a lizard's recovery after slipping during a leap and thought a study of stumbling would be a perfect way to test the value of a tail.

In the CiBER lab, Full and six of his students used high-speed videography and motion capture to record how a red-headed African Agama lizard handled leaps from a platform with different degrees of traction, from slippery to easily-gripped.

They coaxed the lizards to run down a track, vault off a low platform and land on a vertical surface with a shelter on top. When the friction on the platform was reduced, lizards slipped, causing their bodies to potentially spin out of control.

When the researchers saw how the lizard used its tail to counteract the spin, they created a mathematical model as well as Tailbot -- a toy car equipped with a tail and small gyroscope to sense body position ‑ to better understand the animal's skills. With a tail but no feedback from sensors about body position, Tailbot took a nose dive when driven off a ramp, mimicking a lizard's take-off. When body position was sensed and fed back to the tail motor, however, Tailbot was able to stabilize its body in midair. The actively controlled tail effectively redirected the angular momentum of the body into the tail's swing, as happens with leaping lizards, Full said.

Inertial assisted robotics

Tailbot's design pushed the boundaries of control in robotics in an area researchers call inertial assisted robotics, an attention-grabber at last October's meeting of the International Conference on Intelligent Robots and Systems. The UC Berkeley researchers' paper, presented by Libby and fellow mechanical engineering graduate student Evan Chang-Siu, was one of five finalists there among more than 2,000 robot studies.

"Engineers quickly understood the value of a tail," Libby said, noting that when he dropped Tailbot nose-down, it was able to right itself before it had dropped a foot. "Robots are not nearly as agile as animals, so anything that can make a robot more stable is an advancement, which is why this work is so exciting."

Full and his students are now investigating the role of the tail in controlling pitch, roll and yaw while running.

UC Berkeley coauthors include Full and students Moore, Libby and Chang-Siu, along with Department of Integrative Biology undergraduate Deborah Li and graduate students Ardian Jusufi in the Department of Integrative Biology and Daniel Cohen in the Department of Bioengineering.

The work was funded by the National Science Foundation, including the NSF's Integrative Graduate Education and Research Traineeship (IGERT) program, and the Micro Autonomous Systems Technologies (MAST) consortium, a large group of researchers funded in part by the U.S. Army Research Laboratory that is focused on creating autonomous sensing robots.

Read More

Sex (As We Know It) Works Thanks to Ever-Evolving Host-Parasite Relationships, Biologists Find

Sex (As We Know It) Works Thanks to Ever-Evolving Host-Parasite Relationships, Biologists Find

  1:55:00 PM    Science Lover

---

It seems we may have parasites to thank for the existence of sex as we know it. Indiana University biologists have found that, although sexual reproduction between two individuals is costly from an evolutionary perspective, it is favored over self-fertilization in the presence of coevolving parasites. Sex allows parents to produce offspring that are more resistant to the parasites, while self-fertilization dooms populations to extinction at the hands of their biological enemies.

The relationship between the roundworm Caenorhabditis 
elegans and the pathogenic bacteria Serratia marcescens, 
pictured here together in a Petri dish, is helping scientists 
understand why sexual reproduction occurs as it does. 
(Credit: Image courtesy of Indiana University)

The July 8 report in Science, "Running with the Red Queen: Host-Parasite Coevolution Selects for Biparental Sex," affirms the Red Queen hypothesis, an evolutionary theory who's name comes from Lewis Carroll's Alice in Wonderland text: "It takes all the running you can do, to keep in the same place." The idea is that sexual reproduction via cross-fertilization keeps host populations one evolutionary step ahead of the parasites, which are coevolving to infect them. It is within this coevolutionary context that both hosts and parasites are running (evolving) as fast as they can just to stay in the same place.

"The widespread existence of sex has been a major problem for evolutionary biology since the time of Charles Darwin," said lead author Levi T. Morran. Sex does not make evolutionary sense, because it often involves the production of males. This is very inefficient, because males don't directly produce any offspring. Self-fertilization is a far more efficient means of reproduction, and as such, evolutionary theory predicts that self-fertilization should be widespread in nature and sex should be rare. However, as we all know, this is not the case.

The Red Queen Hypothesis provides one possible explanation for the existence of sex.

"The Red Queen Hypothesis predicts that sex should allow hosts to evade infection from their parasites, whereas self-fertilization may increase the risk of infection," said co-author Curtis M. Lively.

By combining the DNA of two parents, sex allows parents to produce offspring that are genetically diverse and different from their parents. Parasites that have adapted to infect one generation may have difficulty infecting the next generation. However, offspring produced through self-fertilization inherit the DNA of their single parent, thus any parasites adapted to infect the parent should also be capable of infecting the offspring.

Morran, a post-doctoral researcher, and Lively, a distinguished professor of biology, both in the IU Bloomington College of Arts and Science's Department of Biology, authored the report with biology undergraduates Olivia G. Schmidt, Ian A. Gelarden and Raymond C. Parrish II.



The team used the microscopic roundworm Caenorhabditis elegans as a host and the pathogenic bacteria Serratia marcescens to generate a host-parasite coevolutionary system in a controlled environment, allowing them to conduct more than 70 evolution experiments testing the Red Queen Hypothesis. They genetically manipulated the mating system of C. elegans, causing populations to mate either sexually, by self-fertilization, or a mixture of both within the same population. Then they exposed those populations to the S. marcescens parasite. The parasites were either allowed to coevolve with C. elegans or were prevented from evolving. The researchers then determined which mating system gave populations an evolutionary advantage.

"We found that the self-fertilizing populations of C. elegans were rapidly driven extinct by the coevolving parasites, a result consistent with the Red Queen Hypothesis," Morran said. On the other hand, sex allowed populations to keep pace with their parasites. "Sex helped populations adapt to their coevolving parasites, allowing parents to produce offspring that were resistant to infection and ultimately avoid extinction," he noted.

In host populations where either sex or self-fertilization were possible, the evolutionary state of the parasite determined the most effective reproductive strategy. When the parasite did not coevolve, self-fertilization evolved as the dominant form of host reproduction. However, when the parasite was allowed to coevolve with the hosts, then sex became the favored reproductive strategy.

"Coevolution with the pathogen not only favored sex over self-fertilization, but also allowed sex to be maintained throughout the experiment," Morran said.

These results are consistent with the Red Queen Hypothesis and may go a long way toward explaining the widespread existence of sex.

"Coevolving parasites seem to be very common in nature," said Lively. "The experiment shows that coevolution with parasites, but not the presence of parasites per se, selects for higher levels of outcrossing. Thus the coevolutionary struggle between hosts and their parasites could explain the existence of males."

Read More

Mouse Sperm Cooperates With Its Brethren

Mouse Sperm Cooperates With Its Brethren

  11:06:00 PM    Science Lover

---

Some mouse sperm can discriminate between its brethren and competing sperm from other males, clustering with its closest relatives to swim faster in the race to the egg. But this sort of cooperation appears to be present only in certain promiscuous species, where it affords an individual's sperm a competitive advantage over that of other males.

Male deer mouse. Some mouse sperm can discriminate between its brethren and competing sperm 

from other males, clustering with its closest relatives to swim faster in the race to the egg. 

(Credit: iStockphoto/Katherine Garrenson)

The work is described January 21 in the journal Nature by biologists Heidi S. Fisher and Hopi E. Hoekstra of Harvard University.

"The race among sperm toward the egg is fierce, but never more so than when sperm of different males compete," says Fisher, a postdoctoral researcher in Harvard's Department of Organismic and Evolutionary Biology. "In some species where females mates with multiple males, groups of sperm join forces in order to outswim their uncooperative competitors. We've shown that in deer mice, cooperation only occurs among close relatives -- sperm from the same male."

Read More

Rise in Certain Disorders can be Explain by Human Evolution

Rise in Certain Disorders can be Explain by Human Evolution

  12:09:00 AM    Science Lover

---

The subtle but ongoing pressures of human evolution could explain the seeming rise of disorders such as autism, autoimmune diseases, and reproductive cancers, researchers write in the Proceedings of the National Academy of Sciences. Certain adaptations that once benefited humans may now be helping such ailments persist in spite of -- or perhaps because of -- advancements in modern culture and medicine.

New research suggests that certain adaptations that once benefited humans may now be helping such ailments persist in spite of -- or perhaps because of -- advancements in modern culture and medicine. (Credit: iStockphoto/Mads Abildgaard)

"This work points out linkages within the plethora of new information in human genetics and the implications for human biology and public health, and also illustrates how one could teach these perspectives in medical and premedical curricula," says author Peter Ellison, John Cowles Professor of Anthropology at Harvard University.

Read More