New Study Looks Into Why Females Live Longer Than Males
Researchers already know that women live longer than men in all parts of the world. Scientists have largely linked the difference in life expectancy between the sexes to biological survival factors.
Now, a new study of wild mammals has found great differences in length of life and aging in many species of mammals.
The researchers found that, in humans, women live almost 8 percent longer than men. But among wild mammals, females in 60 percent of the studied species live, on average, 18.6 percent longer. The percentages are very different for different groups of mammals.
Jean-Francois Lemaitre led the study. He is from the University Lyon 1 in France. He and his research team collected information on age-related deaths for 134 groups of 101 wild species of mammals.
Lemaitre said, "It was surprising to observe that this gender gap in lifespan often exceeds the one observed in humans and is, at the same time, extremely variable across species."
Tamás Székely, from the University of Bath, was one of the writers of the study. He told VOA that female lions in the wild live at least 50 percent longer than male lions.
"We previously thought this was mostly due to sexual selection, he said. "However our data do not support this."
Scientists say the risk of death does not increase more quickly in males than in females across species. They say there must be other, more complex reasons. These include things such as environmental conditions in which the animals live, sex-specific growth, survival and reproduction through the history of the species.
Székely suggests that one reason for the differences between the sexes is that "female survival increases when males provide some or all of the parental care."
He added that "giving birth and caring for young becomes a significant health cost for females and so this cost is reduced if both parents work together to bring up their offspring."
Scientists plan to compare the data on wild mammals with the data on mammals kept in zoos. They want to measure how much biological differences between the sexes affect life expectancy. In zoos, animals do not have to fight with predators or fight for food and mates.
Scientists hope the findings will give them a better understanding of what affects length of life in humans. In the past 200 years, the average life expectancy of humans has more than doubled. The main reasons for the increase are improved living conditions and developments in the field of medicine. However, women continue to live longer than men. This suggests biological differences also play a part.
The U.S. Centers for Disease Control says the average American man will live to age 76. The average woman in America will live to age 81. Women can also expect to be healthier than men in their older years. Experts said this is because of a combination of biological and social differences.
A hormone in men called testosterone is connected to a decrease in their immune system and risk of heart-related diseases as they age. It is also connected to risky behavior, such as smoking, drinking and unhealthy eating habits.
Men are also less likely than women to follow suggestions and warnings from a doctor. And research shows that men are more likely to take life-threatening risks and to die in car accidents or gun fights.
I'm Jonathan Evans.
We've got stable labor, decreasing interest rates, low oil prices.
Caitlin was born with a life-threatening heart abnormality.
3.car accidents 车祸
I saw quite a few car accidents on the highway.
4.gun fights 枪战
The intensive gun fight honeycombed the outer walls of the building.
5.This cost is reduced if both parents work together to bring up their offspring."
work together to 合力做某事
He said they all needed to work together to put the country on its feet again.
The staff should work together to revise the school curriculum.
6.This cost is reduced if both parents work together to bring up their offspring."
bring up 提出；教育
He was brought up in North Yorkshire.
We'd been brought up to think that borrowing money was bad.
研究人员已经知道，全球各地的女性寿命都比男性长 。科学家们认为，男女预期寿命差异很大程度上与生物学上的生存因素有关 。
研究人员发现，对于人类来说女性的寿命比男性的要长近8% 。但对于野生哺乳动物来说，60%的研究物种中雌性预期寿命（比雄性）长18.6% 。不同哺乳类动物群体的比例差异也很大 。
来自法国里昂第一大学的让·弗朗索瓦·勒梅特（Jean-Francois Lemaitre）领导了这项研究 。他和他的研究小组收集了134组101种野生哺乳动物与年龄相关的死亡信息 。
巴斯大学的塔玛斯·塞凯利是该研究的作者之一 。他告诉美国之音，野生的雌狮比雄狮的寿命至少长50% 。
科学家表示，在不同的物种中，雄性的死亡风险并没有比雌性增加更快 。他们认为，肯定还有其他更复杂的原因，包括诸如动物生活的环境条件，性别特异性增长，物种生存和繁殖的历史等因素 。
科学家计划将野生哺乳动物的数据与动物园饲养的哺乳动物的数据进行比较 。他们希望借此衡量性别差异对两性之间预期寿命的影响 。在动物园，动物们无需对抗掠食者，也不必为了食物与配偶争斗 。
科学家希望，这些发现能帮助他们更好地了解影响人类寿命的因素 。在过去200年间，人类的预期寿命增长了一倍多，造成这一现象的主要原因是生活条件的改善和医学领域的发展 。然而，女性的寿命仍然比男性长，这表明生物学差异也起到了一定作用 。
美国疾病控制中心表示，美国男性的平均寿命为76岁，美国女性的平均寿命为81岁 。女性在老年阶段也会比男性更加健康 。专家表示，这是由于生物和社会的差异造成的 。
男性体内的一种叫做睾丸素的激素与他们的免疫系统下降和随着年龄增长患心脏病的风险有关 。寿命还与一些危险的行为习惯有关，如吸烟、饮酒和不良的饮食习惯 。
女性比男性更愿意听从医生的建议和警告 。研究表明，男人更愿意冒风险，更容易死于车祸或枪战 。