Book 2 Listening (1108796), страница 20
Текст из файла (страница 20)
As a result, between 1979 and 2009 male smokingrelated deaths fell by 64% and the male-to-female ratio of such deaths fell from 2.1 to 1.7.Deaths from cancers of the lung, trachea and bronchus in particular fell by 39% between1991 and 2005 among Englishmen over 49. For women the comparable figure was 3%.A further fifth of the longevity gap between the sexes is explained by alcohol.
In thiscase, however, the gap is widening. In 1979 two men died from alcohol-related causes forevery woman who succumbed. In 2009 it was 2.4.A third important factor is obesity - or, rather, the physiological complications obesitybrings, such as high blood pressure and type 2 diabetes. On the face of things, there is littledifference between the sexes in this area: 15.6% of women in the EU are obese, comparedwith 15.4% of men.
But obesity may have a greater impact on women because it increasesthe risks of both hypertension and diabetes in their sex more than it does in men. And menare also closing the gap in another area related to obesity and high blood pressure: coronaryheart disease. In England, deaths from this fell more than 90% between 1991 and 2005 forboth men and women. But, because heart disease kills twice as many men as it doeswomen, the reduction in the male mortality rate has been greater.All of which is good news if you are male.
Men do, nevertheless, have the deck stackedagainst them by biology. One way the cards are marked is that female mammals (womenincluded) have two X chromosomcs, whereas males have an X and a Y, the latter being arunty little thing with only a small complement of genes. Females' "spare" X chromosomeprotects them from genetic mutations on the other one. Males have no such protection.Women are thus carriers of, but rarely suffer from, diseases like haemophilia which arecaused by the mutation of X-chromosomc genes.
In birds, by contrast, it is the males who72have matched chromosomes while females sport the runt. As a result, male birds tend tooutlive their mates.A further biological difference between the sexes is in the lengths of their telomeres.These are sections of DNA that protect the ends of chromosomes from decay. Men'stelomeres are shorter than those of women, and also degrade more quickly. Both of theseattributes have been linked to reduced lifespans.But some are more equal than othersThe biggest biological difference between health of the sexes, however, can besummed up in a single word: testosterone. Testosterone is the hormone that more or lessdefines maleness (though women have it too, in lesser quantities). It promotes bothaggression and risky behaviour. It also suppresses the immune system, which is whycastrated tomcats and rams live longer than those that have not been neutered.
The sameapplies to people. A study on eunuchs found they livу 13.5 years longer than men who areintact.Testosterone-driven behaviour means that men are more likely than women to die inaccidents, and more likely to die from the violence of others. They are also more likely to killthemselves. These things are particularly true of young adults. Men are two-and-a-half timesmore likely to die in their 20s than women are.
Testosterone may also explain the differencesbetween the sexes in risky behaviours like smoking and drinking.But blaming testosterone for male risk-taking explains only the "how", not the "why". Forthat, you must turn to evolutionary biology. It is no coincidence that the gap between thesexes' mortality is widest in people's 20s. This is the peak period for reproduction. Men arefighting each other, and showing off to the girls, in a competition whose prize is, in anevolutionary sense, immortality itself - the passage of their genes to the next generation.To stake a claim in the afterlife, as any religion will tell you, you must make sacrifices inthe present one.
In actuarial terms, therefore, the Longevity Science Advisory Panel reckonsthat even if men adopt healthy lifestyles, women will continue to outlive them. A gap ofbetween one and two years of life expectancy (at age 65) will persist indefinitely. That, if youare a man, might seem unfair. But if it does, then think of it as the price of eternity. (From TheEconomist, January 12, 2013)Script 40. Prehistoric reptilesA loving motherFamily life in plesiosaursThe Mesozoic land was dominated by dinosaurs. At sea, though, the most abundantreptiles were the ichthyosaurs and plesiosaurs.
Roughly speaking, these animals filled theecological niches now occupied by toothed cetaceans such as dolphins and killer whales.Ichthyosaurs, indeed, looked somewhat like dolphins, though plesiosaurs - with their longnecks and diamond-shaped paddles were unlike anything now alive.Ichthyosaurs also resembled cetaceans in another way: unlike most living reptiles,which lay eggs, they gave birth to live young. For years, palaeontologists have wondered ifthe same was true of plesiosaurs.
Now they have found out that it was - but with aninteresting twist.Robin O'Keefe of Marshall University in West Virginia has analysed a plesiosaur fossilfound in Kansas in1987, which palaeontologists had suspected was a pregnant female about4.7 metres (15 feet) long, but which had not been cleaned up and studied until last year. Ashe reports in Science, he found an array of tiny bones, apparently belonging to a smallspecimen of the same species, in the fossil's abdominal cavity.
lt is unlikely that these werethe remains of a meal because the bones are not broken down in the way that would beexpected if they were partly digested. Instead, Dr O'Keefe believes he has discoveredevidence that plesiosaurs, too, gave birth to live young.What is more, all the baby bones come from a single individual, estimated to have been1.5 metres long. Ichthyosaurs and other contemporary viviparous species, by contrast, gavebirth to multiple offspring. The fetus's level of development indicates that it was at most two73thirds mature. Had it survived to birth it would have been about 1.8 metres in length, andabout one and a half times as heavy (relative to parental weight) as the offspring of otherviviparous species of the time.That it was so heavy, and also alone, is of great interest.
Georges Cuvier, an earlypalaeontologist, made his reputation by predicting the anatomies of newly discovered fossilspecies from scant evidence, such as single bones. He did so by applying to fossils theprinciples of comparative anatomy, asking what light the body shapes of living animals couldcast on the shapes of creatures from the past. Many modern palaeontologists try to dosomething similar, except that what they reconstruct is behaviour.Dr O'Keefe has performed such an analysis on his find.
He starts from a fundamentalobservation about reproduction: you can go for quantity or quality. Having one child at a timeis the ultimate expression of quality. It implies huge parental investment in the offspring since,if you lose it, you lose everything. Often, too, it implies membership of a social group, withinwhich favours can be traded to spread the load of parenthood. Most speculatively, it mighteven imply a degree of intelligence - for the most intelligent mammals and birds are generallythose that live in groups.All this is a lot to load on a single fossil, of course. But it would make sense.
It wouldmean plesiosaurs not only occupied a similar ecological niche to whales, but behaved likethem, too. (From The Economist, August 13, 2011)Script 41. Genetic damage and paternal ageFather figuresA father's age has an alarming effect on his children's geneticsWomen have to get their reproducing done early.
The menopause curtails it, and evenbefore that a woman's fertility falls significantly over the years. Men - those who can findwilling partners, at least - do not suffer in quite the same way, as many stories of celebrityelder fathers testify. But perhaps such ageing Lotharios should think twice, for evidence isaccumulating that their offspring are at greater than average risk of genetic disease.The latest study to this effect has just been published in Nature by Kari Stefansson andhis colleagues at deCODE Genetics, a genetic-analysis company based in Reykjavik thatwas founded to take advantage of Iceland's excellent medical records and its uniquegenealogical history.
Recent immigrants apart, the relationship of almost everybody on theisland to everybody else is known back as far as the first census, in 1703. In many cases it isknown back to the first human settlement of the island, in 874.Dr Stefansson's study does not reach as far back as that. He and his colleaguesexamined 78 trios of father, mother and child who are all still alive. In some cases theylooked at grandchildren as well. Their goal was to examine the number of new mutations traits not found in the normal body cells of either parent - in children.The average answer is about 63.
That number, however, varies widely - and the mainfactor involved in this variation is the age of the father. Mothers transmitted an average of 14mutations to their children, regardless of age. Fathers showed a much wider range: 20-yearolds passed on an average of 29 mutations; 30-year-olds (the average age of fatherhood inDr Stefansson's sample) passed on 49; and 40-year-olds passed 69.That it is the father, rather than the mother, who causes this effect is probably becausea woman's eggs are created early on, when she is still in her mother's womb, and are thenput into what is, in effect, physiological deep-freeze until they are required for ovulation.Sperm, by contrast, are made continuously throughout life, and each division of theirprecursor cells brings risk of a misinterpretation of the DNA, and thus a mutation.Dr Stefansson's work adds to an existing body of research on the effect of paternal age.Previous studies have linked older fathers with higher rates of schizophrenia and autism intheir offspring.
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