Why We Sigh (It's a Human Reset Button)
Sighing is critical for keeping our breathing systems flexible, new research shows.
Humans Vs. Neanderthals: How Did We Win?
Aug. 9, 2011 --
Up until about 30,000 years ago, humans shared the planet with Neanderthals, a relative so close to humans that our species interbred. In fact, some Neanderthal lives on in some of our DNA to this day. But around then, Homo sapiens were already well into the process of displacing Neanderthals, an undertaking that had been some 20,000 to 40,000 years in the making. How humans outpaced their relatives remains a mystery, but fossil evidence has left some clues about the scenarios that may have led to the downfall of Neanderthals. No single smoking gun is likely responsible for the disappearance of Homo neanderthalensis. Here, we explore some of the factors that likely contributed to their decline.
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In the end, Neanderthals may have been wiped out because they simply lost the numbers game. As Homo sapiens moved from Africa into areas of southern Europe where Neanderthals had already been settled, the two species were placed in direct competition with one another. Eventually outnumbered 10 to one, Neanderthals were pushed to less favorable areas where food and shelter were more difficult to find, according to a study published last month in the journal Science. Resource competition and interbreeding wiped out the Neanderthals in this scenario.
Forced into Cannibalism?
With Homo sapiens pushing Neanderthals to fringe settlements, it’s possible that resource competition between Neanderthal groups forced them to turn to cannibalism. Fossil evidence suggests that may have been the case. Bones discovered in a cave in France show a group of Neanderthals defleshed the bones of others within their species for sustenance. They even ate humans. As grisly as the practice was, cannibalism also took a hidden toll on those who hunted and consumed their own species: a fatal epidemic similar to mad cow disease that caused severe mental impairments and wiped out thousands. These series of events could have contributed to the disappearance of Homo neanderthalensis.
The Fitter Specimen
In a battle of the brawn, Neanderthals would surely come out ahead. But in a footrace over a long distance, humans had the advantage. Humans were built for long-distance running, which allowed for hunting in hotter climates. Neanderthals, on the other hand, were strong and sturdy. They could run faster than humans, but only over a short sprint. As such, Homo neanderthalensis was better equipped for cooler climates. Distance-running and endurance could have given prehistoric Homo sapiens an edge when they entered Neanderthal strongholds in Asia and Europe, and came into direct competition with their cousins.
The Big Bang Theory
Neanderthals may not have quietly faded away so much as they went out with a bang, according to a study published last September in Current Anthropology. Around 40,000 years ago, a sequence of three major volcanic eruptions devastated Neanderthal homelands in Europe and Asia, speeding the demise of this species. Homo sapiens, by contrast, lived on the fringes beyond the range of the volcanic ash clouds. In other words, simple geographic luck could have led early humans to overtake Neanderthals.
Neaderthals had brawn, but early humans had a leg up on brains. Starting at birth, human and Neanderthal brains are similar. During the first year of life, however, the human brain begins more activity in neural circuitry. Although this doesn't mean that Neanderthals weren't as intelligent as humans, the brains of Homo sapiens developed to support higher-order functions, such as creativity and communication. Traces of Neanderthal creativity have been found, but no evidence has yet emerged to show they had a complex language of their own. However, according to one study published in the journal Medical Hypotheses, this lack of cognitive complexity also may have meant that Neanderthals didn't suffer from the same mental disorders as humans. This distinction, however, proved to be a net gain for humans and may have "helped early Homo sapiens survive in the process of natural selection," according to one report.
Humans Weren't to Blame
Neanderthals and humans were not in direct competition for too long, because Neanderthals disappeared earlier than once thought, according to one study published in May of this year in the Proceedings of the National Academy of Sciences, In this scenario, Neanderthals disappeared around 39,700 years ago -- 10,000 years earlier than is commonly believed. Since Homo sapiens arrived in the northern Caucasus region a few hundred years earlier, that didn't leave too much time for the two species to interact. This theory discounts any human intervention in the decline of Neanderthal populations, but still leaves open the possibility of other extinction scenarios.
- Sighing is an essential part of an inherently chaotic system: breathing.
- Researchers find that breathing before and after sighs fits the "re-setter hypothesis" for sighs.
- Sighs help people on ventilators, but too much sighing can be trouble for anyone.
Scientists studying breathing patterns think they have found the reason we sigh: To reset breathing patterns that are getting out of whack and keep our respiratory system flexible.
The study entailed rigging up eight men and 34 women with sensor-equipped shirts that record their breathing, heart rates and blood carbon dioxide levels over 20 minutes of quiet sitting.
What the researchers at the University of Leuven in Belgium were looking for were specific changes over one-minute periods encompassing sighs that could confirm or contradict the "re-setter hypothesis" for the function of sighing. And they think they found it.
"Our results show that the respiratory dynamics are different before and after a sigh," writes Elke Vlemincx and her co-authors in the latest issue of the journal Biological Psychology. "We hypothesize that a sigh acts as a general re-setter of the respiratory system."
The re-setter hypothesis is based on the idea that breathing is an inherently dynamic and rather chaotic system, with all sorts of internal and external factors changing how much oxygen we need and keeping our lungs healthy and ready for action.
This sort of system requires a balance of meaningful signals and random noise to operate correctly.
Occasional noise in a physiological system -- like the respiratory system -- is essential because it enables the body to learn how to respond flexibly to the unexpected, Vlemincx said.
"A sigh can be considered a noise factor because it has a respiratory volume out of range," said Vlemincx.
In this experiment, a sigh was defined as at least two times as large as the mean breath volume.
"A breath is defined by a specific volume (depth), the amount of air we breathe in and out, and a specific timing, the time it takes to breathe in and out," Vlemincx told Discovery News. "Both these characteristics vary: from one moment to the next we breathe slower, faster, shallower, deeper."Vlemincx explained that when breathing is in one state for too long, the lungs deteriorate. They become more stiff and less efficient in gas exchange.
Sighing is critical for keeping our breathing systems flexible, new research shows.Getty Images
So in times of stress, when breathing is less variable, a sigh can reset the respiratory system and loosen the lung's air sacs, or alveoli, which may be accompanied by a sensation of relief, Vlemincx said.
Knowing this, it would seem logical then to add some sighs to the breathing regimes of people on mechanical, ventilators. As it turns out, it has been tried.
"If you put in a few sigh breaths, people feel better," said Frank Wilhelm a clinical psychologist at the Universität Basel in Switzerland.
Wilhelm has studied the role of breathing in psychological disorders extensively.
On the other hand, too much sighing can add too much noise to the system and can also throw the system out of whack. This appears to be what happens to people experiencing panic attacks, said Wilhelm.
"Panic victims don't recover from sighing," said Wilhelm.
In fact, people experiencing panic attacks have been long observed to involve a great deal of sighing, and show all the symptoms of hyperventilation: dizziness, numbness in the extremities, etc., he said.
For that reason a training program involving biofeedback was developed to help panic disorder victims get control of their sighing. It works, said Wilhelm, and further confirms the re-setter hypothesis for sighs.
"It's like a miracle cure, when you think about it," said Wilhelm.