Are Humans Still Evolving?

[RAM]

Are Humans Still Evolving?

Although advances in medical care have improved standards of living over time, humans aren't entirely sheltered from the forces of natural selection, a new study shows.
"There is this idea that because medicine has been so good at reducing mortality rates, that means that natural selection is no longer operating in humans," said Stephen Stearns of Yale University.
A recent analysis by Stearns and colleagues turns this idea on its head. As part of a working group sponsored by the National Evolutionary Synthesis Center in Durham, NC, UK the team of researchers decided to find out if natural selection — a major driving force of evolution — is still at work in humans today. The result? Human evolution hasn't ground to a halt. In fact, we're likely to evolve at roughly the same rates as other living things, findings suggest.
Taking advantage of data collected as part of a 60-year study of more than 2000 North American women in the Framingham Heart Study, the researchers analyzed a handful of traits important to human health. By measuring the effects of these traits on the number of children the women had over their lifetime, the researchers were able to estimate the strength of selection and make short-term predictions about how each trait might evolve in the future. After adjusting for factors such as education and smoking, their models predict that the descendents of these women will be slightly shorter and heavier, will have lower blood pressure and cholesterol, will have their first child at a younger age, and will reach menopause later in life.

"The take-home message is that humans are currently evolving," said Stearns. "Natural selection is still operating."

The changes may be slow and gradual, but the predicted rates of change are no different from those observed elsewhere in nature, the researchers say. "The evolution that's going on in the Framingham women is like average rates of evolution measured in other plants and animals," said Stearns. "These results place humans in the medium-to-slow end of the range of rates observed for other living things," he added. "But what that means is that humans aren't special with respect to how fast they're evolving. They're kind of average."
Additional authors on the study were Sean Byars of Yale University, Douglas Ewbank of the University of Pennsylvania, and Diddahally Govindaraju of Boston University.
The team's findings were published online in the October 19th issue of Proceedings of the National Academy of Sciences.
The National Evolutionary Synthesis Center (NESCent) is an NSF-funded collaborative research center operated by Duke University, the University of North Carolina at Chapel Hill, and North Carolina State University.

Courtsey- Guardian uk

http://www.eurekalert.org/pub_releases/2009-10/nesc-ahs101909.php

 

[tarunraju]

I'm pessimistic about human evolution. Maybe it has saturated? Clearly, with the kind of technology at our disposal, we should have colonised the moon by now. We're busy waging wars against eachother to salvage whatever natural resources that are left.

 

[Yusuf]

Don't know about evolving but humans are showing all thwarted signs of going back to barbaric ways as we see around us everyday. But then again I think that barbarism was probably always around.

 

[RAM]

There's a speed limit to the pace of evolution, Penn biologists say

Researchers at the University of Pennsylvania have developed a theoretical model that informs the understanding of evolution and determines how quickly an organism will evolve using a catalogue of "evolutionary speed limits." The model provides quantitative predictions for the speed of evolution on various "fitness landscapes," the dynamic and varied conditions under which bacteria, viruses and even humans adapt. A major conclusion of the work is that for some organisms, possibly including humans, continued evolution will not translate into ever-increasing fitness. Moreover, a population may accrue mutations at a constant rate –- a pattern long considered the hallmark of "neutral" or non-Darwinian evolution -– even when the mutations experience Darwinian selection.

While much is known about the qualitative aspects of evolutionary theory — that organisms mutate and these mutations are selected by the environment and are gradually absorbed by the entire population, very little is known about how, or how quickly, this is accomplished. Information on evolution between consecutive generations is hard to come by, and the lack of understanding has real-world implications. Public-health officials would have an easier time preparing targeted vaccinations, or combating drug resistance, if they understood the evolutionary speed limits on viruses and bacteria such as influenza and M. tuberculosis.

Penn researchers presented a theory of how the fitness of a population will increase over time, for a total of 14 types of underlying landscapes or "speed limits" that describe the consequences of available genetic mutations. These categories determine the speed and pattern of evolution, predicting how a population's overall fitness, and the number of accumulated beneficial mutations, are expected to increase over time.

Researchers compared the theory to the data from a two-decades study of E. coli to investigate how the bacterium evolves. Organisms of that simplicity and size reproduce more rapidly than larger species, providing 40,000 generations of data to study.

"We asked, quantitatively, how a population's fitness will increase over time as beneficial mutations accrue," said Joshua B. Plotkin, principal investigator and an assistant professor in the Department of Biology in Penn's School of Arts and Sciences. His research focuses on evolution at the molecular scale.

"This was an attempt to provide a theoretical framework for studying rates of molecular evolution," said first-author Sergey Kryazhimskiy, also of the Department of Biology. "We applied this theory to infer the underlying fitness landscape of bacteria, using data from a long-term bacterial experiment.".

In some theoretically conceivable landscapes, fitness levels are expected to increase exponentially forever because of an inexhaustible supply of beneficial mutations. But in more realistic landscapes the rate of adaptive substitutions (mutations that improve an organism's fitness) eventually lose steam, resulting in sub-linear fitness growth. In some of these landscapes, the fitness eventually levels out and the organism ceases to adapt, even though mutations may continue to accrue.

E. coli, for example, has been observed to increase its rate of cellular division by roughly 40 percent during the course of 40,000 generations. Initially, the bacterial fitness increased rapidly, but eventually the fitness leveled out. These data have allowed the research team to infer that early mutations, while conferring large beneficial effects, also diminish the beneficial effects of subsequent mutations.

According to the study, a population's fitness and substitution trajectories —t he mutations acquired to achieve higher fitness — depend not on the full distribution of fitness effects of available mutations but rather on the expected fixation probability and the expected fitness increment of mutations. This mathematical observation greatly simplifies the possible trajectories of evolution into 14 distinct categories.

Researchers demonstrated that linear substitution trajectories that signify a constant rate of accruing mutations, long considered the hallmark of neutral evolution, can arise even when mutations are strongly beneficial. The results provide a basis for understanding the dynamics of adaptation and for inferring properties of an organism's fitness landscape from long-term experimental data. Applying these methods to data from bacterial experiments allowed the researchers to characterize the evolutionary relationships among beneficial mutations in the E. coli genome.

Science Centric | News | There's a speed limit to the pace of evolution, Penn biologists say


There's a speed limit to the pace of evolution, Penn biologists say | Eureka! Science News

 

[Dovah]

H G wells believed biological evolution of humans has stopped. Since, evolution is a response to natural factors and human way of coping with nature is technology(now). Technological evolution is the future I think.

 

[jackprince]

Definitely evolving. It's in the nature of the nature.