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Extended Project Qualification

Why females live longer than

males (In both the human and animal world)

Georgina Baker September 2014- March 2015

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Abstract

In society many seem to accept the fact that, on average, women live longer than men. Few, however, are aware that there is an underlying and consistent pattern of factors contributing to the sex mortality differential. In this report, I discuss the various reasons as to why men’s life span is shorter than women.

Hypothesis: There is much anecdotal evidence that females outlive males across most (mammalian) species mainly due to their differences in lifestyle. However there are other factors – biological, environmental and behavioural which impact on this differential. In my research I have explored and analysed evidence that contributes towards longevity.

But as Martin Luther King once said it is “The quality, not the longevity, of one's life is what is important”. This suggests that it's what you do with your life i.e. work, family etc. that counts over how old you grow to become. (Quotes, 2001)

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Table of Contents

1.0 – Introduction .................................................................................................................................. 1

2.0 - Review of Literature and Discussion .......................................................................................... 2

2.1 – Immune System ......................................................................................................................... 2

2.2 – DNA and Chromosomes ............................................................................................................ 3

2.3 – Lifestyle and Disease ................................................................................................................. 4

2.4 – Hormones and Health ................................................................................................................ 7

2.5 – Child Bearing and Menopause ................................................................................................... 8

2.6 - Animal World ........................................................................................................................... 10

3.0 – Conclusion .................................................................................................................................. 12

4.0 – Evaluation & Challenges ........................................................................................................... 14

References ............................................................................................................................................ 15

 

 

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1.0  – Introduction Throughout human history, it is quite clear that men relish their physical advantages over women; they are stronger, faster, taller and less likely to be obese. However, when it comes to lifespan why can’t men be more like women?

The misogynistic response as to why women live longer than men is “women don’t have wives”. There is also some supposition that male foetuses are more likely to be miscarried than female foetuses   implying that females are inherently healthier than men, perhaps due to their child rearing function. Others say that women “are the ones that do the child bearing therefore they must be fully equipped with energy for the foetus growth inside the mother’s womb, and also once born, the baby is breastfed by the mother”. Therefore if the female’s body is harmed or damaged, there is a real threat to her chances of making a healthy offspring. The man’s reproductive role, on the other hand, is less directly dependent on his continued good health.   The conclusion therefore is that females are hard wired through millions of years of evolution, to be healthier.

However “opinions” regarding the causes of the sex mortality differences are sometimes not supported by evidence. Therefore the reasons women live longer than men require deeper exploration.

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2.0 - Review of Literature and Discussion

2.1 – Immune System

A study conducted by some Japanese scientists proposed that “women outlive their male counterparts by several years because their immune systems age more slowly.” (Briggs, 2013)  As the defence system in the body weaken over time, men become more vulnerable to disease and this contributes to their overall life expectancy being more decreased in comparison to women.

Professor Katsuiku Hirokawa and his colleagues of the Tokyo Medical and Dental University carried out an investigation where they analysed blood samples from 356 healthy men and women aged between 20 and 90. Levels of white blood cells and molecules called cytokines which interact with cells of the immune system to regulate the body's response to disease were measured and recorded. (Briggs, 2013)

In both genders, the number of white blood cells per person reduced with age as expected from previous studies. Nonetheless, some further examination they took revealed differences between men and women in two key components of the immune system; T-cells which are known to protect the body from infection and B-cells which secrete antibodies.

The results indicated that the rate of decline of most T-cell and B-cell lymphocytes was faster in men. Men also showed a more rapid age-related decline in two cytokines. The two specific types of immune system cells that attack pathogens which include CD4 T-cells and natural killer cells increased in number with age, with a higher rate of increase in women than in men. (Briggs, 2013)

Figure  1:  .Source:  TurkStat  

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For instance, Figure 1 shows that Turkey’s elderly population consists mainly of women. There are 126,553 more females than males in Turkey, even though there are more males born in the country. The male population declines more rapidly with age and out of 60,176 people in the 90 age range, there is over twice as many women as there are men. This is mainly due to some of the biological reasons explained earlier - i.e. the fact that males showed a more rapid age-related decline in two cytokines and also the rate of decline of most T-cell and B-cell lymphocytes was faster in men in comparison to women. This means that there is a link between our immune system and aging however there will always be some other factors involved and not solely our immune system and its response to disease. (Today Zaman, 2009)

2.2 – DNA and Chromosomes

Women are thought to live longer than men due to chromosomal differences. The chromosomes in our gametes can carry genetic mutations that cause a number of life-threatening diseases, such as haemophilia. As women have two X chromosomes, a female with an abnormal gene on one of her X chromosomes can rely on the normal gene on the other and therefore will avoid showing expression of disease even if she is still a carrier of the defect. However a man has one X chromosome and one Y chromosome, and so they cannot depend on an alternative chromosome if a gene on one of the sex chromosomes is faulty. (Burrows, et al., 2012)

In 1985, researchers at Stanford University informed the world on the discovery on the X chromosome of a gene, critical to DNA repair and this became worrying to scientists. If a man has a defect in this gene, his body's ability to repair the mutations that arise during cell division could be severely affected. The accumulation of such mutations is thought to contribute to aging and disease in men in most cases.   However, we must bear in mind that genetics is still a science in its infancy and we are still learning a great deal about the human genome. So even though this evidence seems startlingly worrying, firm conclusions cannot be drawn until more evidence has been collected and peer reviewing of these evidences have been conducted.

Moreover it is understood by some scientists involved in genetic research that women's second X chromosome is a longevity factor in and of itself. Although one of the two X’s is randomly inactivated early in life, the second X seems to become more active with increasing age. It may be that genes on the second X "kick in" and compensate for genes on the first X that have been lost or damaged with age.  (Lancaster university, 2012)

According to research led by Dr Damian Dowling and Florencia Camus of Monash University in Australia, together with Dr David Clancy of Lancaster University in the UK shows that a set of DNA inherited solely from the mother can be harmful to males and speed up male aging however fascinatingly, these same mutations have no effects on patterns of aging in females. Mitochondria have their own DNA which is separate from the DNA that resides in the nucleus of the cell. Their research titled the Mother’s Curse confirms that Mitochondrial DNA, which is found in every cell in a woman’s body except red blood cells,

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converts the energy of food molecules into energy. This contains mutations which will generally cause faster male aging across all species. (Lancaster university, 2012)

Dr. Vincent Giampapa of Cell Health Institute said that “women live longer than men in general because they’re born with longer telomeres.” These are components at the end of chromosomes that act as an index of cell age. Research shows that if born with longer telomeres, you tend to live longer because the cells that produce the immune system can function healthier and survive for a longer period of time depending on how often the immune system is exposed to factors that challenges it.

2.3 – Lifestyle and Disease

In general, men are exposed to immunological challenges, injuries, stress and surgeries as men have tended to operate dangerous and higher risks occupations and this can affect the immune system and run it down (MSN, 2013).

Men have historically been exposed to more violence as they were the ones to fight in the world wars. Careers in construction, armed forces and rugby and other extreme sports are riskier diversions and it is clear in both today’s society and in the past that men are more involved in these occupations than women.

As soldiers are mostly males we can expect a high death rate amongst men and this might be a contributing factor as to why women live longer than men. .   For example there were 400,000 US military deaths in World War II, of which only 543 deaths were attributed to female service personnel. (Small & Singer, no date). It could be said that women are also victims in the sense that they have to live with the pain however men are those who suffer such tragedy.  

The roles men part take in child care and helping in household tasks has increased considerably over the past decades, but traditionally women’s roles as caregivers may contribute to their greater prolonged existence throughout evolution. Females nurse in times of illness, boost each other’s confidence, laugh and cry together. Whiles their non-stop chatter is criticised by men, it actually helps support female well-being, improves mental health and helps release stress. Men often internalize their stress and depression. Studies show that elderly men commit suicide than women, who have stronger social networks and better means of coping. (LeDuc, no date) Stress reduction through activities such as meditation and good personal relationships which are often practiced by women than men all have a positive impact on the lifespan of women.

According to UCLA neuroscientist Shelley Taylor,

women are much more social in the way they cope with stress, men are more likely to

deal with stress with a 'fight or flight' reaction; with aggression or withdrawal. But

aggression and withdrawal can take a physiological toll and friendship brings

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comfort that diminishes the effects of stress. That difference alone contributes to the

gender difference in longevity”

(LeDuc, no date)

Some say the lifestyle of men differs to women however others argue that they are not that much different. Whether the average person drinks, smokes or exercises, adds or subtracts five to ten years to or from his or her life. Generally, men tend to smoke, eat (especially food high in saturated fat) and drink excessively more than women and this can result in increased blood pressure and heart disease risk, which cause men to die sooner.

However, times are changing and the Institute of Alcohol Studies (IAS) (Studies, 2013) reports that women have been consuming more alcohol steadily since the 1980s. This has been labelled “ladette” culture by the media which is suggestive of youthful misdemeanours (of 18-24 year olds) but there are many factors (both environmental and socio-economic) are proposed to contribute to this rise. An example of this socio-economic factor is that legislation from the 2003 Licensing Act granted businesses 24-hour licences to sell alcohol and the youthful group has taken advantage of this to drink all the time exacerbating the drinking culture especially amongst women who tend to socialise a lot more than men.

Furthermore, the IAS reports that women in professional occupations, who are exposed to greater levels of stress, are also drinking more and drinking more frequently. It will be of great scientific importance to monitor this group of women as they age to determine whether excessive drinking will affect their longevity. (Studies, 2013) However,   even though this is only becoming a scientific matter in recent years, Non-Governmental Organisations (NGO’s) working in the field of alcohol policy are trying to help protect women from alcohol harm as alcohol can take great toll on women longevity and lifestyle as well as men’s.

Overall, men’s mortality rate from cancer is about 30% to 50% higher than women’s with much of this difference driven by more lung cancer among men as smoking has traditionally been a male activity. Also research shows that cardiovascular diseases kill five of every 1,000 men in the 55 to 64 year old range as at that age men tend to socially drink together.  (Robinson, 2007).Japan has a higher life expectancy than UK,   as shown in figure 2a, yet UK women outlive longer than Japanese males by average of about 2 to 3 years.

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A longer life doesn't necessarily mean a healthier life, however while men succumb to fatal illnesses like heart disease, stroke, and cancer, women live on with non-fatal but chronic conditions such as arthritis, osteoporosis, and diabetes. While men tend to die from their diseases, women live with them.

As stated by Centres for Disease Control and Prevention (CDC) of the USA, older women utilize more home health care and long-term care than older men. For example, in the year 2000, the rate of home health care discharges for any service was 1,521 per 10,000 for women aged 65 years and over, compared with 1,230 per 10,000 for men. Likewise, in 2004, there were almost 1 million women aged 65 years and over living in nursing homes compared with fewer than 400,000 men that lived in care homes. This means that women are seeking out for the help they require whereas men tend to be dismissive of interference as they want to take care of themselves even if they might not necessarily be capable of doing so. As older men tend to stay at home than the women, this might imply that they also die at home because they don’t get the medical services they need. (Robinson, 2007)

Another possible medical interpretation of life span difference lies in iron levels. It has been proven that women are relatively iron-deficient compared to men. This is rather common with younger women, those in their late teens and early twenties because of menstruation. Iron plays a very important part in the reactions in our cells that produce damaging free radicals, which glom onto cell membranes and DNA, and may translate into aging the cell. In fact, in our diets, red meat is the main source of iron, and lack of iron is probably one major reason that being vegetarian is healthy for you. There was a very good study looking at the intake of red meat and heart disease in Leiden in the Netherlands. In regions where people didn't eat red meat, those populations had half the rate of heart attack and stroke compared to

Figure  2:  (a)  Life  expectancy  between  males  and  females  in  different  countries  (b)  Overall  life  expectancy  at  birth  vs.  healthy  life  expectancy  at  birth  in  selected  countries.    

(a) (b)

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the populations that did eat red meat. These heart attacks and stroke cases were higher in men than women as men are known to consume a lot of meat than women. (Blue, 2008)

The death of a loved one is a normal part of life, but this at first sight may not be an obvious topic for scientific investigation. However, through case studies we can say that counsellors and therapists typically encounter a larger proportion of widows needing support than widowers. This suggests that there are more men dying than women nonetheless, it might be that men do not see a need to go for therapy after the loss of their female partner. Also, it would seem fair to conclude from this that widows are more vulnerable and in need of counselling than widowers, on the loss of a partner.   Another possible medical interpretation of life span difference lies in iron levels.

2.4 – Hormones and Health

The influence of sex hormones is a contributor to the gender difference in life span. In women, the female hormone oestrogen lowers harmful cholesterol and raises the high-density lipoprotein which is the healthy cholesterol. Oestrogen makes the inner lining of the coronary arteries more flexible, so it’s less prone to injury and inflammation related to plaque formation and atherosclerosis (Cromie, 1998)

On the other hand, the testosterone hormone in men can increase their aggressiveness and competitive behaviour and this sometimes leads to unlawful venture which sometimes causes death. Testosterone can also increase levels of low-density lipoprotein which is the harmful cholesterol in the human body. Therefore cardiovascular diseases and stroke can become a risk factor in males. For instance, between ages 15 and 24 years, men are four to five times more likely to die than women. This time frame coincides with the onset of puberty and an increase in recklessness and violent behaviour in males as described earlier. Researchers tend to refer to it as a "testosterone storm." Most deaths in males that fall into this group come from motor vehicle accidents, followed by homicide, suicide, cancer, and drowning. However this mortality gap varies during other stages of life (Cromie, 1998)

However even though high levels of testosterone may seem to increase death rates there are also problems associated with low levels of this hormone. An American team of researchers found that older males with relatively low testosterone had an 88 per cent increased risk of death compared with their counterparts with normal testosterone levels.   As men age, their testosterone levels gradually decline. After 30 years of age, levels decrease by about 1.5 per cent per year. Low testosterone levels can result in decreased muscle mass and bone density, insulin resistance and low sex drive, as well as less energy, more irritability and feelings of depression, the researchers noted.   It's not yet clear whether low testosterone helps cause illness and death however, men who have chronic illnesses typically have low testosterone levels. So, it may be that men who are ill have a low testosterone level and then they have a higher death rate (Reinberg, 2006) .

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Women also have testosterone. The ovaries produce both testosterone and oestrogen. Relatively small quantities of testosterone are released into a female’s bloodstream by the ovaries and adrenal glands. Even though men with low testosterone levels could be facing low energy, low sex drive, and changes in sleep patterns, women don’t face the same dire effects as the benefits of oestrogen outweighs this risks provided by the testosterone hormone. However, testosterone in women is said to become important after menopause especially in helping women maintain sex drive and preserve cognitive health. (Madeline R Vann, 2015)

2.5 – Child Bearing and Menopause

The biological function of females is to reproduce however they eventually became so feeble that bearing children involves a high risk of death.   . Menopause has been said to protect women from this danger providing them with a survival advantage. This is a common opinion shared among traditional gerontologists; people who learn about the  study of aging and older adults.    

Despite this evolutionary advantage, child birth was a major killer for women for centuries. Mary Wollstonecraft, the 18th Century crusader of women’s rights, who wrote “A Vindication of Women’s Rights” in 1792, tragically died 10 days after giving birth to her daughter Mary Shelley, the Frankenstein author. The most common causes of maternal death in the past were post-partum bleeding, unsafe abortion, hypertensive disorders, infections, obstructed labour, blood clots and effects of pre-existing conditions. It was clear in the 17th and 18th Centuries that the medical industry did not really understand the concept of hygiene as they had rejected the idea of medical professionals washing their hands in between child births. It was up to the likes of Ignaz Semmelweis and Thomas Watson who ensured that the staff in their wards practised this act even though they weren’t aware of the remarkable results this would bring. This practice began to reduce the rate of puerperal fever, a deadly disease women faced during child labour in those days. Presently, vast improved health care and technology, particularly in gynaecology, has put women ahead of men in the survival struggle, as well as raising life expectancy for both sexes. (Cellania, 2013)

Maternal mortality has declined drastically over time due to thorough researching leading to the emergence of modern obstetric care. In the Netherlands, Norway, and Sweden low maternal mortality rates were reported in the late 19th/early 20th century and were believed to be a result of an extensive collaboration between physicians and highly competent, locally available midwives. In the year 1900, Sweden had an annual maternal mortality of 230 per 100 000 live births, while the rate for England and Wales was almost double at 440 per 100 000. (Högberg, 2004)

However, the United States of America reported 520 to 850 maternal deaths per 100 000 live births. This very high maternal mortality rate, especially when compared with the lower rates achieved in other European countries. This caused some American obstetricians to express concern and this began to raise awareness for maternal mortality worldwide. Also they

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provided delivery assistance to poor women by also offering them the option of having a safe and inexpensive home delivery helped reduced the death rates of females especially through pregnancy. This was carefully supervised under a strict system of midwifery instruction and practice. Furthermore, health reform brought new regulations authorizing midwives, after an extended training period, to use forceps, sharp hooks, and perforators, in addition to their ability to perform manual removal of the placenta and extraction in breech presentation. This reform was opposed by contemporary international medical societies but was motivated by the long tradition of community midwives who assisted at home deliveries. (Högberg, 2004)

The tremendous decline in the Maternal Mortality Ratios (MMR) starting in the 1940s in all Western countries in Figure 3 is primarily due to the introduction of new technology (oxytosics, sulphonamides and later penicillin) and better access to blood transfusion but better emergency obstetric care in most healthcare organisations has also impacted on these figures. The rapid decline in Sri Lanka (Figure 3) is explained by malaria control, then introduction of midwifery care with consequent rollout to rural areas. Continuous quality improvement in lifestyle   has also played a part in the lowering of MMR. In Malaysia improved access to midwifery care and later increased institutional deliveries might be the decisive factors for the reduction of MMR (Hanson, 2010)

The longevity of women is apparent when looking at the sex ratio of centenarians, where women outnumber men by about nine to one. The 10 oldest people in the world whose birth records were fully documented are women. Some biologists have suggested that the gender differences in longevity might be linked to the female menopause which is proposed to have evolved so that older women can help to bring up their grandchildren but this is still only a theory. (Connor, 2012)  

On the other hand, other gerontologists have claimed menopause might not be the sole survival feature in helping women endure more years on earth than men. The “grandmother

Figure  3:  Historical  decline  in  MMR  in  selected  countries  Source:  Gapminder

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hypothesis" - that menopause frees older women to help their daughters to raise grandchildren, is a sort of group-selection hypothesis. Group selection refers to one mechanism of evolution in which natural selection acts at the level of the group instead of level of the individual. However this poses contradictory questions which, to some extent, decrease the validity of the hypothesis:

•   “why do daughters not delay reproduction just in order to help their mothers raise siblings?”

•   •“what is the biological sense to stop reproduction, if a woman has no grandchildren living with her?”

Unfortunately evolution is such a slow process, making it very difficult to collect sufficient evidence to support or discount this hypothesis. There is value is discussing this theory but once must not attach too much weight to this argument for female longevity.

The crucial assumption of ‘grandmother' hypothesis is that menopause occurs only in humans. This isn’t exactly true as menopause was documented in non-human primates such as rodents, whales, dogs, elephants and many more. It was shown, for instance, that mice eventually undergo ovarian changes similar to menopause in humans. In an investigation, it was found that grandmothers may promote survival of their maternal grandchildren in Gambia. Grandmothers are useful but menopause may not be as equally useful. Menopause is known to sometimes accelerate age-related diseases such as atherosclerosis, osteoporosis and cancer. (Blagosklonny, 2010)  

Therefore it is evident that menopause in some arguments can affect the longevity of women in both positive and negative ways however there isn’t very strong evidence to support either claim

2.6 - Animal World

It is important to consider as many variables as possible when conducting scientific research therefore it is important to consider animal based research Even though Professor Tom Kirkwood of Newcastle University claims that fruit flies offer DNA clue to why females live longer, he certainly thinks that doesn’t explain why women outlive their male counterparts. However mitochondria, the animal power storage of a cell are inherited only from mothers therefore we can’t set aside any mutations that damage a male's prospects.

Research carried out by experts from Australia's Monash University and the Lancaster University by analysing the mitochondria of 13 different groups of male and female fruit flies showed that the results point to numerous mutations within mitochondrial DNA that affect how long males live, and the speed at which they age. Interestingly, these same mutations have no effects on patterns of ageing in females. This result suggests that the mitochondrial mutations the scientists have uncovered will generally cause faster male ageing across the animal kingdom and this might be common to many different species. (Anon., 2012 )

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Also another investigation showed that male flies die earlier than their female counterparts when forced to evolve with the pressures of mate competition and juvenile survival. The flies were subjected to elevated or relaxed sexual groups or were left in elevated or relaxed natural selection conditions. To elevate sexual selection groups of males were housed with single females. A stressful temperature was used to elevate natural selection. Males court females by singing, dancing and smelling good but their efforts come at considerable cost and this cost is amplified when they also have to cope with stressful temperatures. The results of the study showed that under relaxed sexual and natural selection, male and female flies had very similar lifespans -- around 35 days. However males that evolved under elevated sexual selection and elevated natural selection had a much shorter lifespan -- just 24 days -- and died seven days earlier than females under the same conditions. Both sexual selection and natural selection were found to affect lifespan but their effects were greatest on males.

It is unfortunate that our pets' life spans aren't as long as ours. Not all dogs have the same life expectancy and different factors influence how long a dog can live. Female dogs tend to live longer than male dogs – two to three years longer on the average as shown in Figure 4. Other influencing factors can include lifestyle; how much exercise the dog gets, whether or not the dog has been spayed or neutered, and also regular health care checks or the lack of it. (Elle Di Jensen, 2014). Another supposed reason for longevity is the female body is made for pregnancy so it's able to withstand more stress, -even in animals.

Figure  4.    Source: Wild  Mammals  of  North  America:  Biology,  Management,  and  Conservation  Page  239

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3.0 – Conclusion Although the reasons women live longer than men having been changing as years go by, history suggests that women have been outliving men for centuries. It appears that women have out survived men at least since the 1500s, when the first reliable mortality data was kept. Sweden was the first country to collect data on death rates nationally; in their earliest records, between 1751 and 1790, the average life expectancy at birth was 36.6 years for women and 33.7 years for men.

It can be seen in figure 5 above how the death rates differ for U.S. men and women over nearly a century. Mortality has been consistently higher for men than women at all ages for a long period of time. The mortality ratio is its highest in the year 1990 in comparison to 1900 when technology and good medical care was less readily available

The average life expectancy for women in the UK is 82.1 compared with 78.1 in men. Nonetheless, recent official data shows that the gender mortality gap appears to be closing. It is not so much that men are narrowing the gap, but that women in the general population are adopting the more harmful “male” way of life. More women have been entering the workforce, experiencing the stress that can come with professional jobs and taking up the habits men use to cope, such as drinking and smoking.

Today, males have greater mortality than females throughout the world. The very few exceptions are in southern Asia where it has been demonstrated that females receive less food and health care than males. Males experience lower mortality than females in these countries. An example of this is Bangladesh; a country with a high population density and high birth rate but has more males in comparison to females.

Figure  5:  Comparison  of  death  rates  for  men  and  women  in  the  United  States  of  America    

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Males have greater mortality at all ages, even before birth. It is estimated that there are 105 males born for every 100 females in America yet still women outlive men. After birth the greatest difference between male and females mortality rates is around the age of 22, when the rate is more than three times greater for men that it is for women.

Two studies compared the mortality between males and females in similar circumstances. One study involved Catholic teaching orders, and the other considered kibbutz members in Israel. Both studies showed that when the roles and environments are very similar between the sexes, the sex mortality differentials are actually greater than they are in the general population. (Kalben, 2002).

For almost all of the animal species studied, the males have higher mortality than the females. These animals include roundworms, crustaceans, insects, spiders, reptiles, fish, and mammals, including primates. Greater male longevity in animals appears to be related to monogamy and greater female care of offspring.

After very thorough research, I can say my assumptions and hypothesis were right as lifestyle plays a very big role in the longevity of both women and men; however men are the ones that suffer majority of the problems.   As it is most biological studies, it is obvious that a combination of factors affect longevity with the principal contributors being lifestyle, attitudes towards mental health, genetic factors and disease.

There is very strong evidence in support of female longevity but of significant interest is how the picture is changing as women drink more and adopt more dangerous lifestyles. The role of the health care practitioner is to narrow the gaps between male and female mortality and lifestyle and stress management is clearly an area on which we, as a society, can focus.

We cannot change male DNA or make men bear children, but we can help them lead healthier lifestyles and provide better support and guidance for mental health issues. As ever, preventative measures are essential in promoting sustained female longevity and raising the life expectancy for males.

 

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4.0 – Evaluation & Challenges Prior to this report, I was only aware of the obvious reasons as to why females outlive their male counterparts such as men worked riskier jobs than women. Therefore it was interesting and surprising to find out that the reasons didn’t just stop at their physical attributes however internal and psychological reasons were involved too.

Moreover, I was stunned by the fact that socializing with friends which is most common amongst women really did have an impact on the prolonged existence of females. Also,  this  research does not only provide knowledge but a greater understanding of how some parts of the human/animal anatomy and physiology really works.

In reviewing the literature, I felt that I did not obtain all the information that I wanted to. This is down to a number of factors. Firstly, one of the limitations took the form of language barriers. There were times where the research I had accumulated was in other languages other than English. Therefore even though I had found an article of interest, the inability to read that language made it useless to me. With that being said the problem was not often because of the algorithms of search engines, and the advanced search features of online services.

Moreover, paid online subscription meant that if what I was looking for was not in the abstract shown, then I will not be able to get anything from that publishing unless I paid.

Initially, I only wanted to source information from 2005 but realised after making preliminary searches that this may limit the information I can gather. As a consequence, I decide to go as far as the year 1998. Due to this I was able to find a lot of useful data and graphs in which some has been used in this report.

For all the research, it was unclear to me who it was funded by. This is important because the conclusions of the study could be biased in favour of the person funding. Furthermore, the reliability of some findings, like those from the   Tokyo Medical and Dental University, was questionable because of the small sample groups involved.

The majority of the information I obtained was from the internet, therefore I had to use my intuition to gather what I believed to be good information and data. I only used professional looking websites or those who had an academic institution accreditation – an example of this would be the research that was conducted by the Lancaster University. In addition to this the articles I picked required a title, author and date, but in one case, the article didn’t not mention the specific author however because the article was from the BBC, I thought it will be too important to just dismiss it therefore it has been included in my report.

To organise the information I gathered, I always recorded different aspects of the data such as the title, author, time accessed etc. which is clear in my reference page. This exercise made it incredibly easy and efficient to structure my work.

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Fretts, R. & Perls, T., 1998. cmu.edu. [Online] Available at: https://www.cmu.edu/CSR/case_studies/women_live_longer.html [Accessed 18 February 2015].

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