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Posts Tagged ‘Evolution’

A surefire way to suck the romance out of any kiss is to envision it as free shipping for germs. Recent research by British scientists sheds light on why that is actually a good thing.

Writing in the journal Medical Hypotheses, researcher Dr Colin Hendrie from the University of Leeds said: ‘Female inoculation with a specific male’s cytomegalovirus is most efficiently achieved through mouth-to-mouth contact and saliva exchange, particularly where the flow of saliva is from the male to the typically shorter female.’

Cytomegalovirus is likely to be only one of many germs which take advantage of kissing as a transfer system and which can confer benefits rather than harm to the recipient.

Cytomegalovirus, which lurks in saliva, normally causes no problems. But it can be extremely dangerous if caught while pregnant and can kill unborn babies or cause birth defects.

These can include problems ranging from deafness to cerebral palsy.

Kissing, over the course of several months and increasing in intensity, transfers small amounts of the virus each time. The result is a built up immunity to the virus, thereby cutting the risk of infection and potential damage to the fetus tremendously. Previous research had hypothesized that kissing was important because it conveyed fitness information about the individual through saliva. Given this new data and given that there are many other methods for determining fitness, kissing is not likely to have evolved as a means of determining fitness from an evolutionary perspective.

Dr Hendrie said: ‘Information concerning body tone, smell, reproductive condition, disease state and, of course, personal physical and oral hygiene can all be gained solely from close physical proximity.’

‘The small amount of additional information from kissing is an unlikely pressure for its development.’

People have subconsciously understood for a long time that germs can be transferred via kissing, hence that use of copious amounts of alcohol when strangers kiss. Clearly, it is being used as an antiseptic.

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QaliaSoup has a great video which addresses some misconceptions and explains some of the basics of evolution.

See the evolution video on YouTube here.

If you enjoyed that one we think you will also enjoy one of their other videos, Skewed views of science.

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To be more precise, 60% of adults cease producing the enzyme lactase which is responsible for the digestion of lactose, the primary sugar in milk.

No other species has adult members capable of digesting milk, including cats. It is not advisable to feed an adult cat milk, popular images to the contrary notwithstanding. Some may tolerate the milk and merely suffer from gas, while others will get diarrhea and/or throw up. That’s one kind of hot mess you do not want running around your house.

The 40% or so of the human adult population carrying a genetic variant which continues to produce lactase into adulthood is not evenly distributed.

The numbers are often given as close to 0% of Native Americans, 5% of Asians, 25% of African and Caribbean peoples, 50% of Mediterranean peoples and 90% of northern Europeans. Sweden has one of the world’s highest percentages of lactase tolerant people.

The old theory about the origin of this unusual ability was that humans living in the colder, less sunny parts of Northern Europe had difficulty getting sufficient vitamin D and individuals who could tolerate milk into adulthood were at a great advantage.

Actually, vitamin D isn’t really a vitamin. It’s a hormone.

Here’s the new theory, published in PLoS Computational Biology:

Using data on −13,910*T allele frequency and farming arrival dates across Europe, and approximate Bayesian computation to estimate parameters of interest, we infer that the −13,910*T allele first underwent selection among dairying farmers around 7,500 years ago in a region between the central Balkans and central Europe, possibly in association with the dissemination of the Neolithic Linearbandkeramik culture over Central Europe. Furthermore, our results suggest that natural selection favouring a lactase persistence allele was not higher in northern latitudes through an increased requirement for dietary vitamin D. Our results provide a coherent and spatially explicit picture of the coevolution of lactase persistence and dairying in Europe.

In other words, the lactose tolerance began with dairy farmers in Central Europe and gradually spread outwards, rather than spontaneously appearing in Northern Europe.

The remarkable part is that the ancient Europeans were not the only ones to develop that type of mutation.

The European mutation is different from several lactase persistence genes associated with small populations of African peoples who historically have been cattle herders.

Researchers at the University of Maryland identified one such mutation among Nilo-Saharan-speaking peoples in Kenya and Tanzania. That mutation seems to have arisen between 2,700 to 6,800 years ago. Two other mutations have been found among the Beja people of northeastern Sudan and tribes of the same language family in northern Kenya.

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Carl Zimmer has a new brief article up discussing an interesting point which was raised during his research for On The Origin Of Eukaryotes.

No living eukaryote, whether animal, plant, fungus, or protozoan, has completely lost its mitochondria since that symbiotic milestone some 2 billion years ago. It wasn’t the only time that two species merged, however. Plants, for example, descend from algae that engulfed a species of photosynthesizing bacteria. Many protozoans have swallowed up photosynthetic partners as well.

Absorbing an external organism through a cellular membrane and safely enclosing it in a bubble takes complex molecular machinery. One theory is that such a system evolved in eukaryotes, not prokaryotes, which gave them an advantage in integrating mitochondria.

But today, there’s a provocative new alternative to consider. Maybe a lot of today’s prokaryotes are also the result of an ancient merger. The idea comes from James Lake of the University of California, Los Angeles, a veteran researcher on the early history of life. In my essay, I describe how Lake first proposed in the early 1980s that the host cell that gave rise to eukaryotes belonged to a lineage of prokaryotes he dubbed eocytes. Now, a quarter of a century later, new studies on genomes are strongly supporting his eocyte hypothesis.

It is still not clear how prokaryotes handled fusion, but there is evidence that it happened. The double membrane of gram negative bacteria seem to be one indication of a bacteria swallowing another at some point in the ancient past.

It will be interesting to see if Lake’s new hypothesis fares as well as his eocyte hypothesis is doing. If he’s right, this symbiosis had an impact on the history of life on par with the origin of eukaryotes. Gram-negative bacteria were the first photosynthesizers, for example, and were then swallowed up by the ancestors of plants. And the same lineage also gave rise to the bacteria that became our own mitochondria. Our cells, in other words, are not just microbes within microbes; they are microbes within microbes within microbes: a true Russian doll of evolution.

Carl Zimmer is the author of Evolution: The Triumph of an Idea and Parasite Rex : Inside the Bizarre World of Nature’s Most Dangerous Creatures among others. We highly recommend these books.

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So… Why Sleep?

Jerome Siegel, UCLA professor of psychiatry and director of the Center for Sleep Research at the Semel Institute for Neuroscience and Human Behavior at UCLA and the Sepulveda Veterans Affairs Medical Center is one scientist who is delving into the reasons behind our need for sleep.

It was thought that sleep has to provide a neurological benefit which cannot be attained during an awake state because sleep puts an animal in a vulnerable state, and prevents other functions from being carried out, such as a searching for food. Different species have varying requirements as far as sleep duration and patterns. Migrating birds can be awake for days at a time, whereas bears go into hibernation in the winter.

Siegel’s lab conducted a new survey of the sleep times of a broad range of animals, examining everything from the platypus and the walrus to the echidna, a small, burrowing, egg-laying mammal covered in spines. The researchers concluded that sleep itself is highly adaptive, much like the inactive states seen in a wide range of species, starting with plants and simple microorganisms; these species have dormant states — as opposed to sleep — even though in many cases they do not have nervous systems. That challenges the idea that sleep is for the brain, said Siegel.

Animals, including humans, have a selective system which can shift from a sleeping state to an awake state in milliseconds if the right stimulus occurs. The answer then has to do with metabolism and energy conservation.

In humans, the brain constitutes, on average, just 2 percent of total body weight but consumes 20 percent of the energy used during quiet waking, so these savings have considerable adaptive significance. Besides conserving energy, sleep invokes survival benefits for humans too — “for example,” said Siegel, “a reduced risk of injury, reduced resource consumption and, from an evolutionary standpoint, reduced risk of detection by predators.”

“This Darwinian perspective can explain age-related changes in human sleep patterns as well,” he said. “We sleep more deeply when we are young, because we have a high metabolic rate that is greatly reduced during sleep, but also because there are people to protect us. Our sleep patterns change when we are older, though, because that metabolic rate reduces and we are now the ones doing the alerting and protecting from dangers.”

It is an interesting hypothesis, but it still remains to be seen if it is in fact correct. If you are interested in this subject and would like a more in depth analysis, we recommend reading The Neural Control of Sleep and Waking.

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An article posted about “Women Are Getting More Beautiful” at Times Online which we wrote about earlier apparently misrepresented the research of Markus Jokela. (You can read his original article here [PDF].) Here’s what he has to say about it:

Having your study publicized by the media is nice. Having your study misrepresented and misinterpreted in the process is not. The media coverage of my paper on physical attractiveness and having children had a bad start and even worse follow-up. The origin of the problem: Times Online news article sexing up the finding a bit too much (I wasn’t interviewed for this article at all and heard about it only after it had been published).

He goes on to make several clarifications and corrections to the misrepresentations of his research published in the press. We will list a summary here, but the reader is encouraged to read all the details for a complete understanding of the issues.

  • The main point of the study was to see whether attractiveness predicts fertility in a contemporary American population, not whether people are becoming more or less attractive over time. Such a slow process would be observed only over several generations, say, at least 5-10 generations to get an observable effect. In other words, the finding says nothing of comparison of people’s attractiveness in the 1950s vs. the 1970s vs. the 2000s!
  • The association between attractiveness and fertility was observed in women and men. Most stories have mentioned only women or have even claimed that there wasn’t an association in men (“Women more beautiful but men remain Neanderthal, study finds”). This is incorrect!
  • According to some news reports, my study found that attractive women were more likely to have daughters than sons. This is not true! TimesOnline presented the earlier work of Satoshi Kanazawa together with my study and it was Kanazawa’s study which found evidence for such an association. No, I am not Satoshi Kanazawa and this study was not carried out by Kanazawa.
  • Several commentators have dismissed the study because they think that the standards of beauty vary so much over time and across cultures. However, there is substantial agreement between individuals and between different cultures on some aspects of attractiveness, e.g., facial attractiveness (which was the measure of attractiveness in the present study).


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Women Are Getting More Beautiful

UPDATE: See the clarifications and corrections from Markus Jokela, the author of the original research cited in the Times Online article.

The evolutionary power behind this is straightforward: more attractive women tend to have greater numbers of children, and the most attractive are less likely to have sons.

In a study released last week, Markus Jokela, a researcher at the University of Helsinki, found beautiful women had up to 16% more children than their plainer counterparts.

One finding was that women were generally regarded by both sexes as more aesthetically appealing than men. The other was that the most attractive parents were 26% less likely to have sons.

Physical appearance is highly heritable, so it follows that the daughter of an attractive woman will have greater odds of being attractive herself and thus carry a reproductive advantage.

However, what about the men?

“For women, looks are much less important in a man than his ability to look after her when she is pregnant and nursing, periods when women are vulnerable to predators. Historically this has meant rich men tend to have more wives and many children. So the pressure is on men to be successful.”

As with many human traits, such as skin color or height, the distribution follows a bell curve. A shift in the curve as indicated by this research means that a comparison of two women who are average for their respective times, would place the more modern woman as the more attractive one.

A factor acting as a brake on overall attractiveness is male appearance. For example, an attractive woman may have children with an attractive man but their daughter may look like the father and therefore have an unattractive, masculine appearance. Other similar scenarios are why the majority of people are neither very attractive or very ugly, but somewhere in between.

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