Archive for the ‘Evolution’ Category
It’s amazing what evolution can produce given enough time. Derek Mead reports at Motherboard:
A funny-looking moth has more in common with fighter jets than most of us would ever have guessed: The luna moth’s long, fluttering tail acts like radar-distracting chafffor bats’ echolocation signals, effectively misdirecting the flying mammals to an expendable part of their body. It’s a scene seemingly better suited to Top Gun than the night skies of North America, but hey, the animal kingdom is no stranger to a good arms race.
If you’re a flying insect, having a bat show up on your tail is assuredly more terrifying than a fighter plane. Bats’ echolocation abilities have evolved over millions of years to become incredibly effective at locating and tracking prey, like the relatively noisy fluttering of a moth.
Moths aren’t entirely helpless, however. Many, such as noctuid moths, have simple ears that are tuned to the sonar frequencies of the bats that prey on them. Yet closeto half of nocturnal moth species don’t have those bat-tracking ears. According to new research, the luna moth (Actias luna, family Saturniidae) has evolved a different defense entirely: Its swallow-like tails flap and spin in its wake, creating a confusing mess that bats end up targeting, much like a heat-seeking missile getting misdirected by aerial flares. . .
Continue reading. Video at the link.
Robert Axelrod’s book The Evolution of Cooperation suggested that (in the context of the Prisoner’s Dilemma) cooperation is a winning strategy. (It’s a very interesting book, BTW. It describes a competition of algorithms for playing Prisoner’s Dilemma. One algorithm (by Anatol Rapoport) won the first competition easily. Axelrod (who created the tournament) published the results, including the various algorithms used, then launched a second tournament. Anatol Rapoport was again the winner, using the same algorithm. His book Operational Philosophy had a big impact on me in high school.)
But perhaps cooperation’s victory then was less decisive than we thought. Emily Singer writes in Quanta:
en the manuscript crossed his desk, Joshua Plotkin, a theoretical biologist at the University of Pennsylvania, was immediately intrigued. The physicist Freeman Dyson and the computer scientist William Press, both highly accomplished in their fields, had found a new solution to a famous, decades-old game theory scenario called the prisoner’s dilemma, in which players must decide whether to cheat or cooperate with a partner. The prisoner’s dilemma has long been used to help explain how cooperation might endure in nature. After all, natural selection is ruled by the survival of the fittest, so one might expect that selfish strategies benefiting the individual would be most likely to persist. But careful study of the prisoner’s dilemma revealed that organisms could act entirely in their own self-interest and still create a cooperative community.
Press and Dyson’s new solution to the problem, however, threw that rosy perspective into question. It suggested the best strategies were selfish ones that led to extortion, not cooperation.
Plotkin found the duo’s math remarkable in its elegance. But the outcome troubled him. Nature includes numerous examples of cooperative behavior. For example, vampire bats donate some of their blood meal to community members that fail to find prey. Some species of birds and social insects routinely help raise another’s brood. Even bacteria can cooperate, sticking to each other so that some may survive poison. If extortion reigns, what drives these and other acts of selflessness?
Press and Dyson’s paper looked at a classic game theory scenario — a pair of players engaged in repeated confrontation. Plotkin wanted to know if generosity could be revived if the same math was applied to a situation that more closely resembled nature. So he recast their approach in a population, allowing individuals to play a series of games with every other member of their group. The outcome of his experiments, the most recent of which was publishedin December in the Proceedings of the National Academy of Sciences, suggests that generosity and selfishness walk a precarious line. In some cases, cooperation triumphs. But shift just one variable, and extortion takes over once again. “We now have a very general explanation for when cooperation is expected, or not expected, to evolve in populations,” Plotkin said.
The work is entirely theoretical at this point. But the findings could potentially have broad-reaching implications, explaining phenomena ranging from cooperation among complex organisms to the evolution of multicellularity — a form of cooperation among individual cells.
Plotkin and others say that Press and Dyson’s work could provide a new framework for studying the evolution of cooperation using game theory, allowing researchers to tease out the parameters that permit cooperation to exist. “It has basically revived this field,” said Martin Nowak, a biologist and mathematician at Harvard University.
Tit for Tat
Vervet monkeys are known for their alarm calls. A monkey will scream to warn its neighbors when a predator is nearby. But in doing so, it draws dangerous attention to itself. Scientists going back to Darwin have struggled to explain how this kind of altruistic behavior evolved. If a high enough percentage of screaming monkeys gets picked off by predators, natural selection would be expected to snuff out the screamers in the gene pool. Yet it does not, and speculation as to why has led to decades of (sometimes heated) debate.
Researchers have proposed different possible mechanisms to explain cooperation. Kin selection suggests that helping family members ultimately helps the individual. Group selection proposes that cooperative groups may be more likely to survive than uncooperative ones. And direct reciprocity posits that individuals benefit from helping someone who has helped them in the past.
The prisoner’s dilemma helps researchers understand . . .
And, to provide balance, an example of non-meme evolution: “New class of antibiotic found in dirt could prove resistant to resistance”
And now provide an example of a meme analogue…
And, BTW, how on earth can people deny evolution? I don’t get it.
Emily Singer writes in Quanta magazine:
For 30 years, Gerald Joyce has been trying to create life. As a graduate student in the 1980s, he studied how the first RNA molecules — chemical cousins to DNA that can both store and transmit genetic information — might have assembled themselves out of simpler units, a process that many scientists believe led to the first living things.
Unfortunately, he had a problem. At a chemical level, a deep bias permeates all of biology. The molecules that make up DNA and other nucleic acids such as RNA have an inherent “handedness.” These molecules can exist in two mirror image forms, but only the right-handed version is found in living organisms. Handedness serves an essential function in living beings; many of the chemical reactions that drive our cells only work with molecules of the correct handedness. But the pre-biological building blocks of life didn’t exhibit such an overwhelming bias. Some were left-handed and some right. So how did right-handed RNA emerge from a mix of molecules?
Joyce was able to build RNA out of right-handed building blocks, as others had done before him. But when he added in left-handed molecules, mimicking the conditions on the early Earth, everything came to a halt. “Our paper said if you have [both] forms in the same place at the same time, you can’t even get started,” Joyce said.
His findings, published in Nature in 1984, suggested that in order for life to emerge, something first had to crack the symmetry between left-handed and right-handed molecules, an event biochemists call “breaking the mirror.” Since then, scientists have largely focused their search for the origin of life’s handedness in the prebiotic worlds of physics and chemistry, not biology.
Three decades later, Joyce’s latest research has shown that perhaps life came first after all. Joyce, now at the Scripps Research Institute in La Jolla, Calif., and Jonathan Sczepanski, a postdoctoral researcher, created an RNA enzyme — a substance that copies RNA — that can function in a soup of left- and right-handed building blocks, providing a potential mechanism for how some of the first biological molecules might have evolved in a symmetrical world. The new experiment, published in the November 20 issue of Nature, is reinvigorating the discussion over how life first arose. “They have really opened up a new realm of possible roads,” said Niles Lehman, a biochemist at Portland State University in Oregon who wasn’t involved in the study.
Even more intriguing, Joyce and Sczepanski’s enzyme works differently from other RNA-copying molecules, a discovery that may have profound implications for how life originated. The enzyme is much more efficient and flexible than other RNA-based enzymes developed to date, and it may provide the key to Joyce’s ultimate goal — making life from scratch.
A Crack in the Mirror
Louis Pasteur, the famous 19th-century French chemist, was the first to describe chemical handedness, or “chirality.” He was puzzled by the fact that crystals derived from the dregs of wine twisted light in a specific direction, but the same crystal synthesized in the lab did not. Examining the crystals under a microscope, he discovered that the synthetic chemical came in two mirror-image forms, which canceled out the polarizing effect. The crystal derived from wine had only one.
Scientists later discovered that this bias encompasses the entire living world. Synthetic chemical processes will generate both left- and right-handed molecules. But when nature makes a molecule, the product is either left- or right-handed. For example, all amino acids that are used to make proteins twist light to the left.
Indeed, chirality is an essential component of biochemistry. “It provides a form of molecular recognition,” said Donna Blackmond, a chemical engineer at Scripps and a colleague of Joyce’s. The chirality of a molecule affects how it interacts with other components of the cell. Molecular locks can only be opened with a key of the correct handedness.
Some scientists look to the heavens to explain how this biological bias first arose. . .
Interesting: those ancient little microbes, working away and continuing to evolve for millions of years underground. Maddie Stone writes in Motherboard:
Earth’s “deep biosphere”—the vast, subterranean world that’s home to as many single-celled organisms as our planet’s surface—has a rep for being a stark and lonely place. But a new study finds that deep oil reservoirs, miles beneath the ocean floor, are anything but solitary. Here, bacteria are social critters that have been swapping genetic material back and forth for eons.
What’s more, rapid DNA swapping between oil-dwelling bacteria could hold clues to how life survived on early Earth—and, perhaps, on extraterrestrial worlds.
Oil reservoirs, formed over millions of years as carbon-rich sediments are compressed and cooked, are scattered like islands across Earth’s subsurface. Like other deep biosphere habitats, we know they harbor life, but we aren’t really sure how or when life got there.
“There’s a hypothesis that these bacteria were buried, then continued to live on in complete isolation,” study author Olga Zhaxybayeva told me.
To test that hypothesis, the team of researchers, hailing from Dartmouth College, the University of Alberta, and the University of Oslo, analyzed 11 genomes of the heat-loving bacterium Thermotoga. The bacteria was taken from oil reservoirs in the North Sea and Japan, and marine sites near the Kuril Islands, Italy and the Azores. They compared their results with publicly available Thermotoga genomes from North America and Australia.
Their analysis revealed . . .
Interesting article by Amy Amos in Pacific Standard:
I hadn’t thought much about bird sex in a long time—30 years. But as I stood on a dirt road in the Canaan Valley National Wildlife Refuge in West Virginia this past summer, instinct (or perhaps muscle memory) took over. I lifted my binoculars to my eyes, listened for a distinctive bubbly song, and scanned the fence posts in the adjacent field. Sure enough, two male bobolinks were perched a few posts apart singing like mad to keep the other away from his territory.
Typical male behavior, I thought.
Years ago, as a wildlife biology major at Cornell University, I spent an entire summer watching a field of bobolinks do their thing. Males fiercely guarded their territories and females chose mates based on some mysterious combination of alluring song and impressive real estate. The mated pairs built nests and raised their broods together in seemingly monogamous bliss. On the surface, it was a Father Knows Best kind of scenario straight out of the Eisenhower era. But all of us on the research team watching knew that some of those daddies were fooling around on the side. We called the mistresses “secondary” and “tertiary” females. They raised their young on father’s territory, but he never acknowledged their existence. Instead, he doted faithfully on his “primary” female and helped her feed the brood.
As I watched a few bobolinks posture again this past summer for the first time since then, I suddenly saw things a bit differently. The fence posts morphed into bar stools and the bobolinks became men in some rowdy roadhouse. And I wondered: How did our research on bobolink sex influence thinking about human sex? This wasn’t a random question. Thirty years earlier, our team discovered something just beginning to be recognized: The mommy birds were fooling around on the side too.
Ever since Charles Darwin put his ideas about sexual selection down on paper in 1871 (in The Descent of Man and Selection in Relation to Sex) biologists had been reinforcing conventional thinking about female sexuality. Namely, that males of most species compete for as many females as they can get, that their “investment” in mating is low (sperm and copulation are energetically cheap compared with eggs and pregnancy), and therefore it’s to their advantage to seek out as many sexual partners as possible. Females, the thinking went, would gain no such advantage from having more than one sexual partner. Instead, it made evolutionary sense for females to choose one really good mate and put her eggs in one basket (figuratively and literally).
Scientists quibbled over the details and tweaked these ideas over the decades, but didn’t challenge them much. A.J. Bateman seemed to prove this point in 1948 with his classic study of fruit flies: Male fruit flies that mated with many females had more offspring that those who mated with few. But he found no such advantage for female fruit flies. Robert Trivers added consideration of parental investment to the discussion in 1972, noting that the sex that invests more in raising offspring would be choosy about mates, and the sex that invests less would compete with others of their gender for partners. But since females of most species—including humans—typically invest more time and energy in their offspring than males, scientific thinking didn’t change all that much.
Until DNA analysis.
By the mid-1980s, . . .