'Family on All Fours' Not an Evolutionary Throwback
Evolution Before Your Eyes
Charles Darwin wasn't always right. Take his position on the speed of evolution. Darwin invoked the Latin phrase: "Natura non facit saltum," which means, "Nature doesn't make jumps." What he meant is that evolution happens very gradually with lots of transitional steps along the way. Evolutionary lineages created a densely branched tree of life. But as paleontologists started to realize a couple of decades ago - and biologists have started to see in the real world in recent years - Nature can be as jumpy as a toad. Some species can evolve in a matter of decades or even less. That makes for a tree of life with a lot of right-angle branches - more like a massive, complicated saguaro cactus than a tree. Credit: Public Domain
The Jumping Evolution of a Jumper
The most infamous case of a species evolving before our eyes is the toxic cane toad of Australia. The Cane toads were imported from South America in the 1930s to eat pests from sugar cane fields. Instead they escaped and have been leaping across large parts of northeastern Australia ever since. A few years ago, Australian researchers monitoring the toad invasion discovered that the hind legs of toads at the forefront of the invasion, "the pioneers," had been getting longer over the last seven decades, compared to those cane toads in more settled areas. Apparently there's a big fat pay off for the first toads to reach virgin territories: more offspring. So over the toad generations, the toads with the longest, strongest legs have been rewarded, while those with shorter legs have lost out or just stayed behind. Nature has been selecting longer-legged pioneers. Viola! Evolution in action. Credit: FrogWatch.org
Warmer Weather Wood Frogs
Wood frogs can be found from Georgia to Hudson Bay to Alaska's North Slope. "They are the most broadly distributed amphibian in the world," says Yale University evolutionary biologist David Skelly. But can they adapt to a warmer planet? Skelly and his colleagues have conducted experiments with frogs in cooler, shaded pond versus warmer, unshaded ponds and found that wood frogs can evolve relatively quickly to live in very different temperature regimes. This bodes well for the frogs if global warming heats up their ponds across North America. Credit: USGS
Slippery Sockeye Salmon
A case of human-induced evolution may be the sockeye salmon of Lake Washington, east of Seattle. Researcher Andrew Hendry of McGill University and his colleagues have found genetic evidence that sockeyes, introduced by humans decades ago, have since branched into separate distinct populations - the first small steps in speciation. "They provide concrete examples that evolution is occurring all around us all the time," said Hendry of the sockeyes. "Without such examples, contemporary evolution is just theoretical. Better examples exist than sockeye salmon though: Darwin's finches, big horn sheep, red squirrels, guppies, etc." Credit: NOAA
Dance or Die to Evolution's Beat
This everyday lizard has recently made the news by making a radical change in its behavior to deal with invasive fire ants. When threatened, the Eastern fence lizard normally holds still so it can't be easily spotted by predators. Around fire ants, however, the tactic means the ants can more easily attack and kill the lizard. So what's a lizard to do? Those who are oddly and fortunately wired to jiggle, jerk and escape fire ant attacks rather than sit there and be bitten to death are surviving and passing that ability on to their offspring. Oh, and some lizards are also growing longer legs, which makes it harder for the ants to get to them. Our prediction? More and more lizards will turn up with longer legs. Credit: Virginia Tech
Darwin's Unfaithful Finches
Yep, you read correctly. One of Darwin's finches has been caught in the act of contradicting its namesake and evolving very quickly in recent years. Drought conditions over the last 20 years and competition from another finch has caused the "medium ground finch," G. fortis, of Daphne Island, to evolve a smaller beak. What's more, the change may have happened in a single bird generation, according to Princeton University biologists Peter and Rosemary Grant. First some larger finches, G. magnirostris, were blown over from another island during the El Niño of 1982. The bigger birds promptly began eating up the larger seeds, pushing the smaller finches to specialize on smaller seeds, and requiring smaller beaks to do so. What would Darwin think? Credit: Larry O'Hanlon
Dog Evolution by Human Hand
None of this will seem particularly surprising to anyone familiar with domestic animal breeding. In something like 10,000 years we have artificially selected traits we prefer in what were once wolves to make an amazingly diverse range of what is called "dog." If all we had to go by was their skeletons, no paleontologist would ever suspect the bone of a dachshund and those of a Great Dane were the same species. "You can go from a dachshund to a Great Dane within human history," said Skelly. "But Darwin thought nature works at a slower pace. That's where he was wrong." We've done similar things with chickens, cows and pigs, not to mention the intensive breeding of plants â€“- many of which can not survive without human assistance. Interestingly, this "artificial selection" was exactly one of the arguments Darwin employed to explain natural selection in his book "On the Origin of Species." The only difference was that nature has had vastly more time to carry on its breeding programs. Credit: Larry O'Hanlon
Making New Species
Humans are also causing evolution to happen in other ways. With roads, shopping centers, housing tracts and other developments, we're splitting up habitats and creating isolated populations of the same species of plants and many animals. "We're cutting the world up," says Skelly. Over time, these newly separated populations can drift apart genetically and become separate species. They could also face difference pressures in their separated habitats, which can accelerate evolution and their divergence. "We're deflecting these trajectories of evolution," Skelly says. That's assuming these newly split species survive the human interference in the first place, which isn't guaranteed. Credit: Andrew Hendry
God's Immutable 'Types'
At this point the anti-evolution crowd usually shouts, "But none of this is really evolution! A dog is still a dog! A cow still a cow. A rose still a rose!" These folks assert that there can be plenty of variation allowed within a species, but they never become new species. In other words, they assert, species were created directly by God and they cannot be changed beyond certain boundaries. It's a nice idea, but there isn't a shred of evidence to back it up. Quite the contrary... Credit: State of Utah
Fossils, Genes and Common Sense
Earth herself has offered up ample evidence that species are not immutable. The fossil record is filled with transitional forms that make it very clear that new species arise from older species. Whales, for instance, were not always whales, according to the fossils. They evolved from dog-like land animals. What's more, fossils don't lie. Then there is the genetic evidence. Genomes carry with them a lot of evolutionary baggage. Comparing that baggage between species allows scientists to see how closely related they are. For instance, our genome is 98 percent identical to the chimpanzee's because we share a common ancestor which itself went extinct several million years ago. The bottom line: Neither the fossils nor the genomes make sense unless they are seen through the lens of evolution. Credit: John Atkinson, Ocean Alliance
Climate Change and Extinction
Finally, there is the matter of whether all this fast-paced evolution will help spare any species from extinction from climate change. Skelly and Hendry think it will help and that estimates of how many species will be pushed to extinction are probably too high. "...
ew conservation biologists have focused on what may be the most pervasive effect of climate change: as species evolve in a changing world, genetic responses may render them forever different," they concluded in a 2007 paper in the journal Conservation Biology. "Such within-species changes in biodiversity remain deserving of close study if we are to fully comprehend and accurately communicate the consequences global change." Credit: NOAA Article posted March 2, 2009
When Turkish evolutionary biologist Uner Tan introduced the world to a Turkish family with some members who could walk only on all fours, in a "bear crawl," he and other scientists speculated this odd gait was the resurgence of a trait lost during human evolution.
Not so, a new study finds.
The family and other people with Uner Tan syndrome do not represent "a backward stage in human evolution," as Tan wrote in a 2006 paper in the International Journal of Neuroscience, said Liza Shapiro, a professor of anthropology at the University of Texas at Austin. In new research, Shapiro and her colleagues compared videos of the family's gait with the gaits of nonhuman primates, such as chimpanzees or gorillas. They found the gait patterns did not match. Instead of recreating ape walks, people with Uner Tan are simply adapting to their disorder, Shapiro and her colleagues reported July 16 in the journal PLOS ONE.
Tan first noticed the syndrome that now bears his name in a family of 19 living in rural southern Turkey. Five of the family members walk using their feet and hands, and also have cognitive disabilities. The family was the subject of the 2006 BBC2 documentary, "The Family That Walks on All Fours."
Research has since revealed that the disorder is caused by a genetic mutation on chromosome 17, which affects the cerebellum, part of the brain responsible for movement and balance. From the beginning, Tan's statements about the evolutionary nature of the affected family's walking patterns were controversial. The affected children never had physical therapy or adaptive technology such as wheelchairs, making their gait a necessity. (See a video of walking on all fours)
But no one ever challenged the primary claim: that the affected children walked like nonhuman primates. Primates that walk on all fours do so differently than most other mammals, Shapiro told Live Science. Primates walk in a diagonal sequence, putting down a hind limb and then the opposite front limb: left foot, right hand, right foot, left hand.
Most other mammals walk in a lateral sequence, with the same-side limbs following each other: left foot, left hand, right foot, right hand. Human babies and adults asked to "bear crawl" on hands and feet typically walk in a lateral sequence, too, Shapiro said.
Shapiro said she became interested in studying the gait of people with Uner Tan Syndrome in 2006 after seeing the documentary on the Turkish family.
"It was all about whether or not it was evolutionary reversal, which kind of horrified me," she said. Immediately, though, she could see that the family was not using the primate diagonal gait.
Shapiro did not have access to good video of the family's walking patterns until recently, when one of her co-authors told her he had footage from the BBC. From that video, she and her colleagues were able to analyze more than 500 strides made by the five family members with the disorder.
About 99 percent of the strides were lateral, not diagonal — a blow against the notion that the family members had "rediscovered" an ancestral primate way of walking. Instead, they were walking like any typical adult would if asked to move on hands and feet.
A lateral gait is handy for long-limbed animals (such as humans) when walking on all fours, she said, because it helps keep the limbs from bumping into one another.
"They're doing what any human does in that situation where they can't stand up," Shapiro said.
Shapiro emphasized that even if the family had moved with a diagonal gait, the pattern would not prove anything about human evolution or the origins of bipedalism.
"Bipedalism requires a lot of changes, physical and anatomical changes in the body," she said. "Neurological changes. Motor changes. It's not just one thing."
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