Human longevity at the cost of reproductive success

Tying It Together

Rudi Westendorp, a Dutch physician-scientist known for his love of bow ties, seeks elegant solutions in his work as a clinical epidemiologist, geriatrician, and gerontologist at Leiden University Medical Center in the Netherlands. After completing his residency training and earning a Ph.D., in 1993 he made a detour into clinical epidemiology, studying patient populations to identify underlying risk factors for disease. He now supervises the long-running Leiden 85-plus study, which tracks cognitive decline, heart disease, and other illnesses in very old people. To round out his knowledge, Westendorp spent 1998 studying the biology of aging at the University of Manchester, U.K. His quest to test the evolutionary theory of the tradeoff between fertility and longevity has led him into the genealogical archives of British aristocrats and, more recently, to Ghana.

Genealogical data and the biodemography of human longevity

Biodemography of human longevity is an emerging interdisciplinary field of sociobiological research with deep historical roots. Two research questions are examined in this article: (1) What evidence is there for the familial transmission of human longevity?, and (2) what are the effects of parental age at reproduction on offspring longevity, and in particular, are there long-term adverse health consequences associated with the trend toward delayed reproduction? The ability of scientists to conduct biodemographic studies depends not only on merging theoretical and methodological elements from the biological and demographic/actuarial sciences, but unique sources of data and statistical methods must also be developed. In this article we describe how gencalogical data have been used for over a century to explore basic questions about human longevity, and how similar kinds of data now being developed are driving the formation of new testable research hypotheses in the field of biodemography.

Are we becoming less disposable?

Evolution has programmed us for early survival and reproduction but has left us vulnerable to disease in old age. In our present affluent environment, we are better adapting to these improved conditions.

Lay eggs, live longer: division of labor and life span in a clonal ant species

Due to a trade-off between reproduction and life span, highly fertile individuals often live shorter lives than nonreproductive conspecifics. Perennial eusocial insects are exceptional in that reproductive queens live considerably longer than the nonreproductive workers. The two female castes may differ strongly in morphology, ontogeny, physiology, diet, behavior, and mating, and all these differences could be responsible for life span differences. In the ponerine ant Platythyrea punctata, morphological and ontogenetic caste differences do not exist. Instead, all workers are capable of producing diploid offspring through thelytokous parthenogenesis, and colonies are essentially clones. Here, we show that reproductives live significantly longer than nonreproductive workers. Reproductives stay in the nest during their whole life, whereas nonreproductives switch from intranidal tasks to foraging when they get older. Different work load and different hormone titers might proximately underlie the different life span of reproductives and nonreproductives in this ant.

Exceptional Longevity in Pet Dogs Is Accompanied by Cancer Resistance and Delayed Onset of Major Diseases

To characterize extreme aged pet dogs as a first step in developing an animal model of exceptional longevity, we constructed lifetime medical histories for 345 Rottweiler dogs using information collected from owners and veterinarians. Extreme aged dogs (alive at the 95th percentile age at death for the study population, > or =13.3 years) were compared with a usual longevity group (9-10 years). Exceptional longevity in Rottweiler dogs was accompanied by a significant delay in the onset of major life-threatening diseases; 76% of extreme aged dogs remained free of all major diseases during the first 9 years of life. Only 19% of extreme aged dogs died of cancer versus 82% of dogs with usual longevity (p <.0001). The reduction in cancer mortality in oldest-old pet dogs mimics that seen in human centenarians and provides strong rationale for using this animal model to study comparative mechanisms of cancer resistance in the extreme aged.

Ageing purpose: another thrifty genotype

For evolutionary biology, ageing is a non-adaptive process. The 'disposable soma' theory proposes that senescence is the consequence of a reduction in the energy invested in the processes of cell maintenance and repair due to the fact that it is more beneficial to invest it in reproduction. Recently, various genes have been identified whose mutations modify the life span of certain animals. Most of these genes are related to energy metabolism, especially insulin, IGF-1 and their receptors. Furthermore, it has also been demonstrated that there is a modification in metabolic pathways during ageing. As a result, the energy-storing pathways are strengthened and there is a reduction in the pathways that use energy. All these findings suggest that ageing is a strategy designed by natural selection to save energy, in accordance with other saving strategies. This way the energy that is not used can be dedicated to offspring to improve their pre-reproductive survival.

Longevity after early surgical menopause-the long-term effect of a permanent cessation of reproductive function and female sex hormone loss

OBJECTIVE

To investigate longevity in women after bilateral salpingo-oophorectomy (BSOE), not given hormonal replacement therapy (HRT) post-operatively, as compared to the national mean.

STUDY DESIGN

Long-term follow-up study of a historical cohort of young women undergoing BSOE in the early 20th century at the General Hospital, Malmö, Sweden. Comparison was made with mean life expectancy in corresponding birth cohorts.

RESULTS

No difference in life expectancy was recorded in 152 women with an early menopause caused by BSOE and not substituted with HRT, as compared to national statistics of contemporary women. Half of the operated women died of cardiovascular disease and a minority of cancer, none of which was a breast cancer.

CONCLUSION

Permanent loss of female sex hormones and reproductive function in early life does not seem to influence longevity but may change patterns of morbidity and mortality.

Longevity cost of reproduction for males but no longevity cost of mating or courtship for females in the male-dimorphic dung beetle Onthophagus binodis

Life history theory predicts a trade-off between current and future reproduction. Despite a wealth of research on the cost of reproduction for females, there have been very few studies that have looked at the cost of reproduction for males. Longevity is closely related to the opportunity for future reproduction, and thus decreased longevity in response to current reproductive effort has been used as a measure of the cost of reproduction. Here we examine the cost of reproduction for males and females in the dung beetle Onthophagus binodis. Like many onthophagines, O. binodis exhibit dimorphic male morphology; major males develop a large pronotal horn while minor males remain hornless. Alternative morphologies are associated with alternative reproductive tactics. Thus, we ask whether major and minor males pay different costs of reproduction. We found that in contrast to previous work on Diptera, mating is not costly in terms of reduced longevity for female dung beetles. Despite a longevity cost of reproduction for males, we found no evidence for differential longevity costs associated with alternative reproductive tactics.

Reproduction and longevity among the British peerage: the effect of frailty and health selection

Whether a cost of reproduction exists among humans is still questionable. A major study of aristocratic British families finds a significant positive correlation between parity and late-life mortality, which indicates a trade-off between reproduction and longevity. This result is supported by four other studies, while earlier studies have not found a relationship or came to the opposite conclusion. We show that in natural fertility populations the relationship between fertility and late-life mortality cannot be studied correctly without considering the effects of differences in health and of mortality selection during childbearing ages because these two effects lead to a dampening of the true relationship. If these effects are controlled in Hollingsworth's genealogy of the British peerage a significant trade-off between reproduction and longevity exists for females but not for males.

Age of ovary determines remaining life expectancy in old ovariectomized mice

We investigated the capacity of young ovaries, transplanted into old ovariectomized CBA mice, to improve remaining life expectancy of the hosts. Donor females were sexually mature 2-month-olds; recipients were prepubertally ovariectomized at 3 weeks and received transplants at 5, 8 or 11 months of age. Relative to ovariectomized control females, life expectancy at 11 months was increased by 60% in 11-month recipient females and by 40% relative to intact control females. Only 20% of the 11-month transplant females died in the 300-day period following ovarian transplantation, whereas nearly 65% of the ovariectomized control females died during this same period. The 11-month-old recipient females resumed oestrus and continued to cycle up to several months beyond the age of control female reproductive senescence. Across the three recipient age groups, transplantation of young ovaries increased life expectancy in proportion to the relative youth of the ovary. Our results relate to recent findings on the gonadal input upon aging in Caenorhabditis elegans and may suggest how the mammalian gonad, including that of humans, could regulate aging and determine longevity.

Grandmothers and the evolution of human longevity

Great apes, our closest living relatives, live longer and mature later than most other mammals and modern humans are even later-maturing and potentially longer-lived. Evolutionary life-history theory seeks to explain cross-species differences in these variables and the covariation between them. That provides the foundation for a hypothesis that a novel role for grandmothers underlies the shift from an ape-like ancestral pattern to one more like our own in the first widely successful members of genus Homo. This hypothesis links four distinctive features of human life histories: 1). our potential longevity, 2). our late maturity, 3). our midlife menopause, and 4). our early weaning with next offspring produced before the previous infant can feed itself. I discuss the problem, then, using modern humans and chimpanzees to represent, respectively, genus Homo and australopithecines, I focus on two corollaries of this grandmother hypothesis: 1). that ancestral age-specific fertility declines persisted in our genus, while 2). senescence in other aspects of physiological performance slowed down. The data are scanty but they illustrate similarities in age-specific fertility decline and differences in somatic durability that are consistent with the hypothesis that increased longevity in our genus is a legacy of the "reproductive" role of ancestral grandmothers.

Human life histories and the demographic transition: a case study from Finland, 1870-1949

The life histories of humans who were engaged in reproduction during the demographic transition were investigated. It was discovered that these life histories were subject to great changes during the period involving the birth cohorts from the years 1870-1949. Although the number of all and surviving children decreased during this period, the individual fitness values (lambda) of females remained quite even. The lambda values are sensitive not only to reproductive quantity but also to the timing of reproduction. Therefore, the effective change in female fitness during the demographic transition may not be as dramatic as previously thought. When studying the level of selection (or rather the opportunity for selection), it was found that mortality selection steadily decreased to a very low level. However, fertility selection and total selection, which were relatively low for the cohorts 1870-1889, increased before the steep decrease that was detected for the cohorts 1930-1949. The situation reflects the presence of considerable variance in fertility for the cohorts 1890-1929, when the mean fertility was decreasing. A previously found trade-off between female longevity and reproductive success appeared less significant, apparently due to the presence of more plentiful resources and voluntary limitation of reproduction. The deviation from the potential fitness maximization and the presence of subfertility have become prevalent in human populations.

Cessation of reproduction: an analytic view of menopause

While there is evidence for genetic control of ovarian and follicular development, only recently have reports appeared on genetic components involved in ovarian failure. Unlike predictions of a stable population, age at menarche is decreasing, while female life span is increasing. This leads to examination of genotype-environment interactions. Evolution of the large human brain size has been accompanied by a reduction in size of the gastrointestinal tract. Consequences, in terms of altered diet and effects on menarche/menstruation/menopause were discussed. In the earliest days of human evolution, genotoxic agents and marginal diets could have produced heritable changes in cessation of menstruation. Toxic alterations may still be apparent, such as epidemiological studies on the effects of smoking on age at menopause. Attempts to reconstruct some of the recent past history, from coprolites to findings in frozen human specimens, have to be extended still further into the past.

The genetics of aging-- implications for pharmacogenomics

Lifespan experiments of lower organisms and mammals along with recent studies of centenarians are making inroads into delineating genetic factors that determine the ability to achieve exceptional longevity. These models may be helpful for the discovery of both longevity-enabling genes as well as genes associated with increased propensity to develop specific diseases. Both academic and commercial laboratories are putting substantial resources into discovering such genes in order to better understand the genetic and environmental underpinnings of how some people age more slowly than others and markedly delay or even escape age-associated diseases.

The Institute for Ageing and Health, University of Newcastle, UK

The Institute For Ageing And Health (IAH) is the largest cross-disciplinary research grouping within Newcastle University's Faculty of Medicine, which recently obtained the highest 5 or 5* ratings in all fields evaluated in the UK Research Assessment Exercise 2001. The IAH was set up in 1994 to bring together clinical, basic and social scientists in partnership with colleagues in the National Health Service. It builds upon a long tradition of outstanding clinical research on age-related disorders, particularly in the field of dementia where the pioneering studies of Tomlinson and Roth in the 1960s first showed Alzheimer's disease to be the commonest cause of cognitive decline in later life. The clinical research of the IAH now extends to both neurodegenerative and vascular dementia in a joint Medical Research Council-University Development for Clinical Brain Ageing, and to studies in many other areas including depression in later life, falls and neurovascular instability, stroke and ischaemic brain disease, and health services research on the medical and social care of older people. These diverse areas of clinical investigation are now complemented by strong research on the basic biology of ageing within the new Department of Gerontology with its programmes on the genetics of ageing and longevity; molecular mechanisms of cellular ageing, including oxidative stress, DNA damage and genomic instability, telomere reduction and regulation, mitochondrial DNA mutations, and accumulation of aberrant proteins; and theoretical models of the ageing process. An ambitious strategy for future research on ageing and age-related disorders is based on the synergy between these complementary approaches.

Division of labour influences the rate of ageing in weaver ant workers

The evolutionary theory of ageing predicts that the timing of senescence has been primarily shaped by the extrinsic mortality rate, which causes selection intensity to decline over time. One difficulty in testing the evolutionary theory of ageing is that extrinsic mortality risk is often confounded with body size and fecundity, which may also directly affect lifespan. Social insects with a pronounced division of labour between worker castes provide a unique opportunity to study the direct effect of extrinsic mortality on the evolution of ageing rates independently of body size, reproductive effort and genetic configuration. In the weaver ant, Oecophylla smaragdina, the major (large) workers perform the risky tasks outside the nest, while the minor (small) workers stay within the highly protected arboreal nest. Hence, this pronounced division of labour is associated with high differences in extrinsic mortality risks. The evolutionary theory of ageing predicts that the minor workers should have a longer intrinsic lifespan than the major workers. In line with this prediction, we found that in a protected environment the minor workers lived significantly longer than the major workers did. Hence, the ageing rate appears to have been moulded by variation in the extrinsic mortality rate independently of size, reproductive effort and genetic configuration.

Fertility and life span: late children enhance female longevity

The relation between fertility and postmenopausal longevity is investigated for a sample of 1635 women from a historical (17th to 18th century) French-Canadian cohort who lived past the age of 50 years. We find that increased fertility is linked to increased rather than decreased postreproductive survival. Postreproductive life expectancy extension is found to be tied to late births. This finding sheds new light on the cost of reproduction and may be viewed as supporting a new paradigm that states that reproductive potential drives remaining longevity. The emerging reproductive potential concept complements the well-established cost of reproduction hypothesis. Alternative explanations for the observed association are also explored. A specific finding is that the degree to which mortality increases for 50-year-old mothers as a result of senescence is closely tied to the logarithm of the age of their youngest child. For example, 50-year-old mothers experience a mortality decrease of 38% and an increase of remaining lifetime of 3.93 years for every 10-fold decrease in the age of their youngest child. This amount of gain in remaining life expectancy would apply to a mother with a two-year-old child as compared with a mother with a 20-year-old offspring. We also find evidence for the existence of vulnerable periods in human life history that are characterized by phases of heightened mortality and are found to be tied to reproduction and senescence.

Leiden research program on ageing

Research into ageing is among the priorities of the Leiden University Medical Center. Several tight collaborations between basic and clinical departments are the basis of this program. Our focus is to identify determinants of human longevity and disease at old age with an emphasis on inflammation, atherosclerosis, and cognitive decline. To this end we enroll a large series of long-lived families for genetic screening, prospectively follow large cohorts of old people dependent on various genetic and environmental risk factors, and perform randomized controlled trials in the general population testing plausible hypotheses how interventions can maximize rewarding lifespans.

Evolution of ageing

Explaining why ageing occurs is a solution to the longstanding enigma of the role of senescence in nature. Even after half a century of progress, this solution continues to unfold. Evolution theory argues strongly against programmed ageing, suggesting instead that organisms are programmed for survival, not death. In the current view, ageing results from the twin principles that (i) the force of natural selection declines with age, and (ii) longevity requires investments in somatic maintenance and repair that must compete against investments in growth, reproduction and activities that might enhance fitness. In addition to explaining why ageing occurs, the evolutionary theory also provides insight into the mechanisms underlying the complex cellular and molecular changes that contribute to senescence, as well as an array of testable predictions. Some of the most interesting current problems are to understand how the genetic factors influencing ageing and longevity are predicted to respond to fluctuating environments, such as temporary periods of famine, as well as to other kinds of spatial and/or temporal heterogeneity. Rapid progress in human genomics raises the prospect of greatly increasing our knowledge of the determinants of human longevity. To make progress in understanding the role and evolution of genetic and non-genetic factors in human longevity, we need more detailed theoretical studies of how intra-population variables, such as socio-economic status, influence the selection forces that shape the life history.

Living longer--but better?

The highest attained age has increased by about 20 years since the beginning of the 19th century. In the course of the 1990s, more than ten individuals reached 115 years or more, including Jeanne Calment who attained the age of 122 years. In low-mortality countries, the number of centenarians has doubled every decade since 1950. This dramatic increase was mainly due to periodical effects related to the drastic fall in mortality among the elderly. The fact that centenarians are survivors does not mean that they are healthy. A high prevalence of comorbidity is found, and many centenarians have survived major diseases thanks to medical treatment and surgery. It is, however, possible that the comorbidity is less serious than in younger elderly. Certain personality traits may also be important in surviving health-threatening conditions. Furthermore, a number of biological and cognitive functions seem to be well-preserved in several centenarians. The influence of the apoE-gene and other genes involved in fundamental mechanisms illustrates that with advancing age and increasing mortality even small risks may have a substantial effect on survival to 100 years. A small proportion of long-livers may be considered as relatively autonomous, and this proportion will probably increase in the future. We are living longer and seem to postpone the terminal dependent phase to higher ages. Longevity may thus be perceived as part of our postmodern condition with its mix of pleasure and suffering.

The genetics of exceptional human longevity

There is a substantial distinction to be made between the genetics of aging and the genetics of exceptional longevity. Twin studies suggest that the average set of genetic variations facilitates the average human's ability to live well into their octogenarian years. Other studies indicate that taking full advantage of this average set results in spending the majority of those years in good health. However, many people counteract such genetic endowment with poor health habits, resulting in a substantially lower average life expectancy and relatively more time spent in poor health. To live beyond the octogenarian years, life-span experiments in lower organisms and mammals and population and molecular genetic studies of centenarian sibships suggest that genetic factors play an important role in exceptional longevity. These factors are likely to influence basic mechanisms of aging, which in turn broadly influence susceptibility to age-related illnesses. Lacking genetic variations that predispose to disease, and having variations that confer disease resistance (longevity enabling genes), are probably both important to such a remarkable survival advantage. Recent studies indicate the likelihood that such factors will be elucidated in the near future.

Evolution of germ-line signals that regulate growth and aging in nematodes

We show that a signal from the germ line represses growth in the nematode Caenorhabditis elegans. Laser-microbeam ablation of cells that give rise to the germ line causes adults to become giant. Ablation of these cells in self-sterile mutant worms also causes gigantism, suggesting that the germ line represses growth because it is the source of a growth-antagonizing signal rather than because of a sink of resources required for reproduction. The C. elegans germ line also emits a signal that represses longevity. This longevity-repressing signal requires the activity of DAF-16, a forkhead/winged-helix transcription factor, but we find that that the growth-repressing signal does not. The growth-repressing signal also does not require the activity of DBL-1, a transforming growth factor beta-related protein that promotes growth in worms. By ablating the germ-line precursors of other species of free-living nematodes, we also found that both the growth-repressing and longevity-repressing signals are evolutionarily variable. Some species have both signals; others have just one or the other. We suggest that variation in germ-line signaling contributes to body size and life-history diversity in the nematodes.

Y chromosome binary markers to study the high prevalence of males in Sardinian centenarians and the genetic structure of the Sardinian population

We have analyzed a sample of 40 centenarians and 116 young controls from Sardinia, with a set of new Y chromosome binary markers, to evaluate if Y chromosome genes are involved in the high prevalence of males among centenarian Sardinians (1/2 vs. 1/4 in other populations studied). The results indicate that none of the seven lineages that account for >97% of the Y chromosome diversity in Sardinia provide an advantage with respect to the extreme longevity. However, our results, although based on the male-specific Y chromosome polymorphisms, give a clear profile of the pattern of genetic variability in Sardinia. Indeed they indicate that the Sardinian population had two main founder populations that have evolved in isolation for at least the last 5,000 years. These findings set the stage for future studies on longevity and other complex traits in Sardinia.

What does it take to live to 100?

Centenarians disprove the ageist myth "the older you get, the sicker you get"; they live 90-95% of their very long lives in excellent health, only to experience illnesses in the very last few years of their lives. Thus, it appears that in order to live to 100, one must age relatively slowly and markedly delay and/or escape age-associated diseases. How they achieve such a survival advantage is still a mystery though it is becoming increasingly clear that a substantial genetic advantage plays a role in their ability to live 20-25 years beyond average life expectancy. Current genetic studies of centenarian sibships may yield the identity of some of these genes in the near future. Identifying such genes may yield new information about how people age differently and what modulates differences in susceptibilities to various diseases associated with aging.

Fertility and post-reproductive longevity

We examine the effects of reproduction on longevity among mothers and fathers after age 60. This study is motivated by evolutionary theories of aging and theories predicting social benefits and costs of children to older parents. We use the Utah Population Database, that includes a large genealogical database from the Utah Family History Library. Cox proportional hazard models based on 13,987 couples married between 1860-1899 indicate that women with fewer children as well as those bearing children late in life live longer post-reproductive lives. As the burdens of motherhood increase, the relative gains in longevity of late fertile women increase compared to their non-late fertile counterparts. Husbands' longevity is less sensitive to reproductive history, although husbands have effects that are similar to those of their wives during the latter marriage cohort. We find some support for predictions based on evolutionary principles, but we also find evidence that implicates a role for shared marital environments.

Complex adaptive systems, aging and longevity

Mortality and reproduction are intimately entwined in the study of aging and longevity. I apply the modern theory of complex adaptive systems (nonlinear, stochastic, dynamic methods) to questions of aging and longevity. I begin by highlighting major questions that must be answered in order to obtain a deeper understanding of aging. These are: (i) What should (in an evolutionary sense) mortality trajectories look like? (ii) Why does caloric restriction slow aging? (iii) Why does reproduction cause delayed mortality? (iv) Why does compensatory growth cause delayed mortality? I show how dynamic state variable models based on stochastic dynamic programming (Clark & Mangel, 2000) can be used to embed genetic theories of senescence (either mutation accumulation or antagonistic pleiotropy) in the somatic environment, as George Williams called for in 1957, and how they make the disposable soma theory of aging operational. Such models will allow unification of genetic and phenotypic theories of aging.

Bridging epidemiology and demography: theories and themes

Epidemiology and demography, although both encumbering several theoretical constructs, are generally applied, problem-solving disciplines concerned with the nature and trajectories of defined groups. There are differences between the two disciplines in substantive interests and methodological traditions, however both have comprehensive perspectives and both are deeply concerned with the health, social, and economic well-being of human populations. One way to promote productive interdisciplinary research is to apply or develop scientific theories that exploit the complementary interests and methods of the two disciplines. Several candidate theories and themes are suggested here, including (1) the life course approach as applied to the biology of longevity; (2) the "modernized" Malthusian dilemma; (3) the demographic transition within developing countries; (4) the theory of evolution and its social and biological implications; (5) reciprocal effects of ecological and environmental characteristics on population health and well-being; and (6) systems theory as an approach to population complexity. Other approaches to fostering interdisciplinary investigation between these disciplines include joint course work, specifically targeted research funding initiatives and collaborative development of new population theory. The latter may be particularly important from several perspectives: uniting disciplines to jointly approach common and important scientific problems, providing existing frameworks with which to generate new scientific questions, and promoting enhanced scientific rigor by more tightly linking methods with hypotheses.

Does functional depletion of stem cells drive aging?

The regenerative power of stem cells has raised issues about their relation to aging. We focus on the question of whether a decline in the function of stem cells may itself be a significant feature of aging. The question is implicitly two-fold: does functional depletion of stem cells affect the accumulation of aging-related deficits, and--whether or not depletion is significant--can activation of stem cells alleviate deficits? Two types of system are considered: 1) the exhaustible pool of ovarian follicles. The depletion of follicles leads to the aging-related phenomenon of menopause; and 2) the reserve of hematopoietic stem cells. Substantial numbers are sustained throughout life, but in mouse models, endogenous replicative activity has been shown to decline sharply with age. We discuss the possible implications of these observations for the rate of aging and the prospects for intervention.

Biological ageing research in the Netherlands

After an introduction on the development of biological ageing research in the Netherlands during the past decades, 606 papers on aging published by Dutch institutes in the period 1991-2000, collected from PubMed, were analysed for their relevance to research into biological ageing. For the period 1996-2000, the total number of research papers on biological ageing amounted to 142, which accounts for 23% of all publications on ageing in that period. The number of publications per year did not change. On the basis of these papers and additional information provided by research groups a comprehensive overview of biological ageing research in the Netherlands is presented, together with an extensive literature list. Ageing of the central nervous system (CNS), of the endocrinological system and of the cardiovascular system are the topics most studied. It is concluded that general biological ageing research has not increased in the Netherlands over the last ten years, and that the infrastructure for basic biological ageing research in the Netherlands is weak.

A critique of the grandmother hypotheses: old and new

The singularity of reproductive senescence in human females has led many investigators to consider menopause an adaptation permitting increased maternal investment in existing progeny. Much of the focus has been on the grandmother hypothesis-the notion that aging women gain an inclusive fitness advantage from investing in their grandchildren. This hypothesis has evolved from an explanation for menopause into an explanation for the exceptionally long postreproductive lifespan in human females. In the old grandmother hypothesis, menopause is an adaptation facilitating grandmothering; it is about stopping early in order to create a postreproductive lifespan. In the new grandmother hypothesis, grandmothering is an adaptation facilitating increased longevity, and menopause is a byproduct. This paper reviews and critically evaluates the evidence for and against both hypotheses, focusing on key predictions of each. If menopause is the result of selection for increased maternal investment, this involved mainly mothers, not grandmothers.

If you would live long, choose your parents well

Human longevity appears to have a modest but significant heritable component. A recent study in Iceland has added to this evidence by making a unique assessment based on records for an entire population. Although the evidence for inheritance of human lifespans appears robust, there remains considerable uncertainty about the extent of the genetic versus the nongenetic contribution and about the importance of gene-environment interactions. Sex-specific patterns of transmission of lifespan between parents and offspring might provide clues to the basis of lifespan heritability, but the reported patterns are neither conclusive nor consistent.

The evolution of menopause and human life span

Noteworthy data is emerging to support the existence of longevity-enabling genes. Our observations of the relationship between reproductive fitness and longevity among centenarians support theories that posit strong selective forces in the determination of how fast humans age and their susceptibility to diseases associated with ageing. Current data support the idea that there is no selective advantage for humans to have a lifespan of approximately 100 years. Rather, getting to such a very old age may be a by-product of longevity-enabling genes that maximize the length of time during which women can bear children, and during which they can increase the survival probabilities of their children and grandchildren. We thus review the literature pertaining to the relationship between reproductive fitness and longevity.

Hypothesis: pulse pressure and human longevity

In exploration of the association between pulse pressure and longevity in humans, 3 hypotheses are briefly discussed: the fetal origin hypothesis, antagonistic pleiotropy, and the telomere hypothesis of cellular aging. The implications of these hypotheses serve to draw a critical distinction between biologic age (aging) and chronological age and, thereby, offer an answer to a question that presently matters most in the field of hypertension: Why has it been so difficult to disentangle the genetic components of essential hypertension and to identify the variant genes responsible for elevated blood pressure in a large segment of the human population?

Reproductive potential predicts longevity of female Mediterranean fruitflies

Reproduction exacts a price in terms of decreased survival. Our analysis of the interplay between age patterns of fecundity and mortality for individual female medflies (Ceratitis capitata) revealed that individual mortality is associated with the time-dynamics of the egg-laying trajectory. In a sample of 531 medflies, we found that each individual has a characteristic rate of decline in egg laying with age. This defines an individual's rate of reproductive exhaustion. This rate was shown to predict subsequent mortality The larger the remaining reproductive potential, the lower the subsequent mortality An increased mortality risk was seen in flies for which egg production declined rapidly early on, irrespective of the level of egg production. Thus, reproductive potential and lifetime are coupled in such a way that those flies which are able to profit most from an extended life span in terms of increased egg output are indeed likely to live longer.

Sex and ageing

Sex and ageing are often linked, particularly in the context of the evolutionary theories of ageing, which suggest that senescence may be the price for investing in offspring at the expense of somatic maintenance and repair. Considerable evidence supports this concept although, strictly, it is not sex per se but the existence of the soma/germ-line distinction that appears to hold the key. Other aspects of the sex-ageing axis seeing exciting new developments are the evolution of the human life history, particularly with respect to menopause, and the molecular mechanisms that sustain the immortality of the germ-line in contrast to the cumulative damage that appears to underlie the ageing of somatic cells.

A study of French centenarians: are ACE and APOE associated with longevity?

Association study is the method of choice to identify genes involved in complex processes that result from the interaction of environmental and genetic factors. However, because of biases that increase the risk of false positive reports, preliminary positive conclusions have to be reproduced on other populations to be validated as firm conclusions. In 1994, certain alleles of two genes, APOE (Apolipoprotein E) and ACE (angiotensin converting enzyme), were reported to be more frequent in French centenarians, suggesting an association with such a complex polyfactorial process as longevity. Enlargement of the French centenarian cohort allows a new assessment of this hypothesis on 563 centenarians. In contrast to APOE, the ACE association was not confirmed. Retrospective analysis of the initial study revealed discrepancies that may in part explain this observation. Risk of reporting false positive associations is discussed and recommendations to set up a rigorous experimental design are proposed.

Optimizing offspring: the quantity-quality tradeoff in agropastoral Kipsigis

The tradeoff between offspring quantity and offspring quality is at the heart of most evolutionary approaches to the fertility transition, as it is for demographers oriented towards economic explanations for this transition. To date, however, there have been few empirical tests of the key idea that humans trade offspring quantity for quality, and no strictly comparative work designed to identify the specific environmental conditions that favor such a tradeoff. This study suggests that in an East African community where the principal form of intergenerational inheritance is land, intermediate levels of offspring production are favored for women but not men. Women produce approximately the optimal number of surviving children, whereas men produce far fewer than the optimal number. The result highlights the significance of inheritable extrasomatic capital, in conjunction with evolved psychological mechanisms, in shaping fertility strategies that emphasize quality over quantity.

Fitness, reproduction and longevity among European aristocratic and rural Finnish families in the 1700s and 1800s

The life histories of two socio-economically different groups of humans comprising birth cohorts from the 1700s and 1800s were investigated. It was discovered that fertility selection was greater among European aristocrats and mortality selection greater among rural Finns. The life history of the rural Finns involved shorter female life spans, a considerably longer period of reproduction, higher juvenile mortality, a greater total production of offspring and slightly higher individual fitness. In a comparison of parental cohorts, it was discovered that longevity and progeny survival improved significantly from the 1700s to the 1800s. Out of the three factors investigated, longevity was found to influence reproduction and fitness more than socio-economic group or birth cohort. The reproductive efficacy and fitness of women increased along with their life span. However, reproductive success and fitness were lower among women with the longest life span (over 80 years). Among men, reproductive success improved consistently along with the increase in longevity. When birth intervals were examined, it was discovered that the sex of previous offspring did not influence the interval between births.

Differential longevity in mouse stocks selected for early life growth trajectory

Small body size is associated with superior longevity in several intraspecies comparisons, including dogs bred for specific forms of work, mice and rats fed diets low in calories, rats fed diets low in methionine, and mutant mice whose levels of growth hormone and thyroid hormone are atypically low. To further investigate the interactions among body size, genetic endowment, and longevity, we measured the life span of female mice selectively bred from Institute for Cancer Research stock for differences in rate of body weight gain. These mice were selected for differential rates of growth either early (0-10 days) or later (26-56 days) in the first 2 months of life. The data show a good correlation between the average weight of the stock and its mean longevity, with low body size associated, as predicted, with longer life span. Weight at 3, 6, and 12 months, and weight at peak body weight, are all significant predictors of longevity (among stocks) in univariate regressions; weight at 6 months has the strongest association in stepwise multiple regression. There is no significant correlation between the life span for the stock and the proportion of deaths attributable to neoplasia in this group of mice. The data provide support for the hypothesis that genetic factors that influence early life growth trajectories can have a strong influence on life span. These size-selected mice provide useful tools for analysis of the genetic factors that influence life history parameters, including maturation and aging rates.

Genetics of human aging. The search for genes contributing to human longevity and diseases of the old

An aging population of humans reflects early-onset morbidity and mortality as well as late-onset disease in the phase when the mortality rate doubles and, finally, longevity of extremely long-lived subjects. Genetic influences have been reported to be relevant for each of these three phases. A growing field in genetic research is aimed at the identification of genes involved in multifactorial diseases of the old and in longevity. Important issues in these studies include the definition of phenotype, which maximally highlights the genetic contribution, whether earlier and later onset phenotypes have loci in common, and how to rank or reject the many candidate disease loci found in different studies. These issues will be illustrated from research on cardiovascular disease and osteoarthritis.

Evidence of sex-linked effects on the inheritance of human longevity: a population-based study in the Valserine valley (French Jura), 18-20th centuries

A long-standing puzzle in gerontology is the sex dependence of human longevity and its inheritance. We have analysed the sex-linked pattern of inheritance of longevity from 643 nuclear families on the historical population register of a French valley. We have focused on mean conditional life expectancy at a minimum age of 50 years, thus, in the present study, longevity refers to late or post-reproductive survival. A comparison of parents' and offspring's longevity has shown the existence of a heritable component of late survival in this population. We have found that the heritable component was substantially larger for daughters compared to sons. Moreover, this result appeared to be specific to late survival, that is, when only post-reproductive mortality for parental and offspring generations is taken into account. The stronger resemblance of parents to their daughters was no longer observed when considering younger ages at death for the offspring. This observation explains the hitherto unaccountable diversity of data in previous studies.

Diseases of aging

By definition, diseases of aging become clinically manifested in elderly patients. However, their pathogenetic basis has to be sought earlier in life. The general thread of this presentation relies on the concept of an evolutionary-Darwinian view of the development of age-related diseases. In essence, this concept states that we may have to "pay" for genetic traits that play a beneficial role earlier in life by the later development of diseases since there is no post-reproductive selective pressure that may have eliminated the potential late onset detrimental effects of such genes. Examples for this kind of trade-off are taken from diseases involving the immune system (infections), the endocrine system (andropause), the nervous system (Alzheimer's disease), the locomoter system (osteoporosis), the cardio-vascular system (atherosclerosis) and cancer.