Science Current Events | Science News |

Beyond a 'speed limit' on mutations, species risk extinction

October 02, 2007

Genomes of various organisms lose stability with more than 6 mutations per generation

CAMBRIDGE, Mass. -- Harvard University scientists have identified a virtual "speed limit" on the rate of molecular evolution in organisms, and the magic number appears to be 6 mutations per genome per generation -- a level beyond which species run the strong risk of extinction as their genomes lose stability.

By modeling the stability of proteins required for an organism's survival, Eugene Shakhnovich and his colleagues have discovered this essential thermodynamic limit on a species's rate of evolution. Their discovery, published this week in the Proceedings of the National Academy of Sciences, draws a crucial connection between the physical properties of genetic material and the survival fitness of an entire organism.

"While mathematical genetics research has brought about some remarkable discoveries over the years, these approaches always failed to connect the dots between the reproductive fitness of organisms and the molecular properties of the proteins encoded by their genomes," says Shakhnovich, professor of chemistry and chemical biology in Harvard's Faculty of Arts and Sciences. "We've made an important step toward finally bridging the gap between macroscopic and microscopic biology."

According to Shakhnovich, crucial aspects of an organism's evolutionary fitness can be directly inferred by inspecting its DNA sequences and analyzing how the proteins encoded by those sequences fold. DNA sequences encode the order of amino acids in a protein, and amino acids act as the protein's basic building blocks by arranging themselves into a structure that allows the protein to perform its biological function.

The research was inspired in part by the longstanding recognition that knocking out essential genes, making them inactive, produces a lethal phenotype, or a physiologically unviable organism.

"From there, we made the simple assumption that in order for an organism to be viable, all of its essential genes -- those that support basic cell operations -- have to encode at least minimally stable proteins," says Shakhnovich. "What occurs over the long process of evolution is that random mutations can either encode slightly more or less stable proteins."

If enough mutations push an essential protein towards an unstable, non-functional structure, the organism will die. Shakhnovich's group found that for most organisms, including viruses and bacteria, an organism's rate of genome mutation must stay below 6 mutations per genome per generation to prevent the accumulation of too many potentially lethal changes in genetic material.

The existence of a mutation limit for viruses helps explain how the immune system can perform its function. Because viral replication and survival can only occur at a limited rate, the body has a window of time to develop antibodies against infectious agents. Furthermore, if the mutation rate is high, the size of the genome in question must be small to stay within the bounds of the speed limit -- thus organisms that tend to mutate quickly are those with concise genomes, such as viruses and bacteria.

The Shakhnovich speed limit also offers an explanation for observed differences in genome sizes between organisms with genome error correction -- such as bacteria, mammals, birds, and reptiles - and those without, such as RNA viruses: In more complex organisms, cells have evolved correction systems to detect and fix errors in DNA replication. These systems drastically reduce the number of mutations per replication, increasing the mutational stability of the genome and allowing more intricate and delicate biological systems to develop without the risk of interruptive mutations.

"It's an interesting corollary because it suggests that there is a fundamental tradeoff between evolutionary security and adaptive flexibility: Larger, more complex organisms have to have error correction to protect organismic viability, but this means the rate of evolution slows down significantly," Shakhnovich says. "As organisms become more complex, they have more to lose and can't be as radically experimental with their genomes as some viruses and bacteria."

Harvard University

Related Extinction Current Events and Extinction News Articles

Climate study finds evidence of global shift in the 1980s
Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.

Half of all Amazonian tree species may be globally threatened
Forests in the Amazon have been declining since the 1950s, but scientists still have a poor understanding of how this has affected populations of individual species.

Ecological extinction explains how turbulence dies
As anyone who has experienced turbulence knows, its onset and departure are abrupt, and how long it lasts seems to be unpredictable.

Modeling the promise and peril of gene drive
What if we could eradicate malaria by engineering a mosquito population that doesn't transmit the disease?

Mass extinctions don't favor large vertebrates
A new study finds that, similar to the mass extinction that's underway now, the end-Devonian extinction resulted in the loss of most large-bodied vertebrates.

Idea of slow climate change in the Earth's past misleading
In order to predict how today's ecosystems will react to increasing temperatures over the course of global warming, palaeobiologists study how climate change happened in the earth's history and what the consequences were.

Declining snowpacks may cut many nations' water
Gradual melting of winter snow helps feed water to farms, cities and ecosystems across much of the world, but this resource may soon be critically imperiled.

New findings rock long-held assumptions about ancient mass extinction
New evidence gathered from the Karoo Basin in South Africa sheds light on a catastrophic extinction event that occurred more than 250 million years ago and wiped out more than 90 percent of life in Earth's oceans and about 70 percent of animal species on land.

Ice-age lesson: Large mammals need room to roam
A study of life and extinctions among woolly mammoths and other ice-age animals suggests that interconnected habitats can help Arctic mammal species survive environmental changes.

Large igneous provinces linked to extinction events
Mass extinction events are sometimes portrayed in illustrations of volcanic eruptions causing widespread destruction.
More Extinction Current Events and Extinction News Articles

Extinction Evolution (Extinction Cycle) (Volume 4)

Extinction Evolution (Extinction Cycle) (Volume 4)
by Nicholas Sansbury Smith (Author)

 Book 4 in Nicholas Sansbury Smith's bestselling & top-rated Extinction Cycle series____________________________There's a storm on the horizon...  Central Command is gone, the military is fractured, and the surviving members of Team Ghost, led by Master Sergeant Reed Beckham, have been pushed to the breaking point. While the strong return to the battlefield, the wounded are forced to stay behind on Plum Island and fight their inner demons.  Betrayed by the country they swore to defend and surrounded by enemies on all sides, Team Ghost has one mission left: protect Dr. Kate Lovato and Dr. Pat Ellis while they develop a weapon to defeat the Variants once and for all. But after a grisly discovery in Atlanta, Kate and Ellis realize their weapon might not be able to stop the evolution of...

The Sixth Extinction: An Unnatural History

The Sixth Extinction: An Unnatural History
by Elizabeth Kolbert (Author)

A NATIONAL BOOK CRITICS CIRCLE AWARD FINALISTA major book about the future of the world, blending intellectual and natural history and field reporting into a powerful account of the mass extinction unfolding before our eyes

Over the last half-billion years, there have been Five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us. In prose that is at once frank, entertaining, and deeply...

Extinction: Star Force Series #2

Extinction: Star Force Series #2
by B. V. Larson (Author)

Earth's Star Force Marines invade an alien world!

In the second book of the Star Force series, Kyle Riggs has another bad year. The Nano ships have a new mission--one that sentences their pilots to death. Meanwhile, the governments of Earth want to steal Star Force's Nano technology for their own. Worst of all, Earth has made a promise to the Macros, and the machines are coming to collect.

EXTINCTION is the story of Earth's entry into an interstellar war between living creatures and machines. To buy the peace, we've signed up with the machines.... EXTINCTION is an 111,000 word novel of science fiction by bestselling author B. V. Larson.

(To find the first book in the series, search for SWARM, by B. V. Larson)

Extinction Horizon (The Extinction Cycle) (Volume 1)

Extinction Horizon (The Extinction Cycle) (Volume 1)
by Nicholas Sansbury Smith (Author)

Book 1 in Nicholas Sansbury Smith's bestselling & top-rated Extinction Cycle Series ____________________________________________________________________ The worst of nature and the worst of science will bring the human race to the brink of extinction...  Master Sergeant Reed Beckham has led his Delta Force Team, codenamed Ghost, through every kind of hell imaginable and never lost a man. When a top secret Medical Corps research facility goes dark, Team Ghost is called in to face their deadliest enemy yet--a variant strain of Ebola that turns men into monsters. After barely escaping with his life, Beckham returns to Fort Bragg in the midst of a new type of war. The virus is already spreading... As cities fall, Team Ghost is ordered to keep CDC virologist Dr. Kate Lovato alive long...

Extinction End (Extinction Cycle Book 5)

Extinction End (Extinction Cycle Book 5)
by Nicholas Sansbury Smith; 1st Edition

*Special Pre-order Price*_____________________ The fifth and thrilling conclusion of the Extinction Cycle main storyline. Will Team Ghost and Dr. Kate Lovato save the human race from extinction, or will humanity fade to dust?

Extinction Age (Extinction Cycle) (Volume 3)

Extinction Age (Extinction Cycle) (Volume 3)
by Nicholas Sansbury Smith (Author)

Book 3 in Nicholas Sansbury Smith's bestselling and top-rated Extinction Cycle Series ________________________________________________________________ On the eve of extinction all seems to be lost, but there is still one final hope... Operation Liberty has failed. Humans are losing the war. With no other option, General Kennor decides to pull back the troops and give science a second chance.  Trapped in the extensive sewer system beneath New York, Master Sergeant Reed Beckham and the survivors of 1st Platoon must battle through the tunnels--where they make a grisly discovery in their attempt to escape.  At Plum Island, Dr. Kate Lovato is working on a new bioweapon to destroy the Variants. But when a derelict Navy Destroyer crashes into the Connecticut shoreline, she is forced to...

The 6th Extinction: A Sigma Force Novel (Sigma Force Novels)

The 6th Extinction: A Sigma Force Novel (Sigma Force Novels)
by James Rollins (Author)

A remote military research station sends out a frantic distress call, ending with a chilling final command: Kill us all! Personnel from the neighboring base rush in to discover everyone already dead-and not just the scientists, but every living thing for fifty square miles is annihilated: every animal, plant, and insect, even bacteria.The land is entirely sterile-and the blight is spreading.To halt the inevitable, Commander Gray Pierce and Sigma must unravel a threat that rises out of the distant past, to a time when Antarctica was green and all life on Earth balanced upon the blade of a knife. Following clues from an ancient map rescued from the lost Library of Alexandria, Sigma will discover the truth about an ancient continent, about a new form of death buried under miles of ice.From...

The Remaining: Extinction

The Remaining: Extinction
by D.J. Molles (Author)

This is the sixth and final novel in the action-packed series following Special Forces Captain Lee Harden and a group of survivors struggling to survive while rebuilding an America devastated by a bacterium that has turned 90% of the population into a ravenous horde.

The merciless tide of infected is flooding south and time is running out to stop them.

Bolstered by new allies, Captain Lee Harden continues his struggle to establish a safe haven from which the embers of a shattered society can be rekindled.

This is the sixth and final novel in D.J. Molles's bestselling series:

Book 1: The Remaining
Book 2: The Remaining: Aftermath
Book 3: The Remaining: Refugees
Book 4: The Remaining: Fractured
Book 5: The Remaining: Allegiance
Book 6:...

Extinction Edge (Extinction Cycle) (Volume 2)

Extinction Edge (Extinction Cycle) (Volume 2)
by Nicholas Sansbury Smith (Author)

Book 2 in Nicholas Sansbury Smith's bestselling & top-rated Extinction Cycle Series______________________________________ A new threat that will bring humanity to the edge of extinction...   The dust from Dr. Kate Lovato's bioweapon has settled. Projections put death counts in the billions. Her weapon was supposed to be the endgame, but it turned a small percentage of those infected with the Hemorrhage Virus into something even worse.  Survivors call them Variants. Irreversible epigenetic changes have transformed them into predators unlike any the human race has ever seen. And they are evolving.  With the doomsday clock ticking, the fractured military plans Operation Liberty--a desperate mission designed to take back the cities and destroy the Variant threat. Master Sergeant...

The Great Extinctions: What Causes Them and How They Shape Life

The Great Extinctions: What Causes Them and How They Shape Life
by Norman MacLeod (Author)

Population sizes of vertebrate species -- mammals, birds, reptiles, amphibians, and fish -- have declined by 52 percent over the last 40 years. in other words, those populations around the globe have dropped by more than half in fewer than two human generations.
-- World Wildlife Fund Living Planet report 2014 This book straddles an awkward boundary between being a colorful popular work and a scientific literature review.... Profusely and beautifully illustrated with figures, maps, charts, and period reconstructions. Recommended.
-- Choice A good introduction to the great puzzle that is extinction study.
-- Publishers Weekly Selected by the Scientific American Book Club and now a more affordable paperback for a far-wider audience. For more than a century ...

© 2015