The new biology of ageing

Human life expectancy in developed countries has increased steadily for over 150 years, through improvements in public health and lifestyle. More people are hence living long enough to suffer age-related loss of function and disease, and there is a need to improve the health of older people. Ageing is a complex process of damage accumulation, and has been viewed as experimentally and medically intractable. This view has been reinforced by the realization that ageing is a disadvantageous trait that evolves as a side effect of mutation accumulation or a benefit to the young, because of the decline in the force of natural selection at later ages. However, important recent discoveries are that mutations in single genes can extend lifespan of laboratory model organisms and that the mechanisms involved are conserved across large evolutionary distances, including to mammals. These mutations keep the animals functional and pathology-free to later ages, and they can protect against specific ageing-related diseases, including neurodegenerative disease and cancer. Preliminary indications suggest that these new findings from the laboratory may well also apply to humans. Translating these discoveries into medical treatments poses new challenges, including changing clinical thinking towards broad-spectrum, preventative medicine and finding novel routes to drug development

The co‐evolution of longevity and social life

Living in social groups could influence the evolution of senescence and longevity by affecting key life‐history parameters such as extrinsic mortality and the cost of reproduction. For example, a decrease in extrinsic mortality as a result of social life is predicted to lead to the evolution of increased longevity. We argue that benefits of social life in terms of increased survival are common only in species in which life in large groups is already the norm, most likely because these species have adapted to depend on social groups. By contrast, species with smaller social groups tend to show no clear association between survival and social group size. This lack of a consistent benefit of social life on survival casts doubt on the idea that extended longevity should follow the evolution of sociality. In line with this, most rigorous cross‐taxonomic studies failed to find an association between sociality and longevity, suggesting that a social mode of life does not systematically lead to the evolution of extended longevity. The only effect of sociality on longevity that has been convincingly demonstrated is increased longevity in high‐ranking individuals from cooperatively breeding vertebrates and social insects, who benefit from the protection and support of their non‐breeding helpers. In contrast, helpers in these species usually do not show evidence of increased longevity, with the exception of naked mole rats where both breeders and helpers live much longer than related solitary species. Where long‐lived phenotypes exist in highly social species, such as social insect queens and naked mole rats, the scale of longevity increase is often striking. The means by which increased longevity is achieved are still poorly understood, but both social and physiological mechanisms are involved in reducing the burden of disease, including cancer, thus increasing the chances of surviving to old age

Time evolution of the Partridge-Barton Model

The time evolution of the Partridge-Barton model in the presence of the pleiotropic constraint and deleterious somatic mutations is exactly solved for arbitrary fecundity in the context of a matricial formalism. Analytical expressions for the time dependence of the mean survival probabilities are derived. Using the fact that the asymptotic behavior for large time $t$ is controlled by the largest matrix eigenvalue, we obtain the steady state values for the mean survival probabilities and the Malthusian growth exponent. The mean age of the population exhibits a $t^{-1}$ power law decayment. Some Monte Carlo simulations were also performed and they corroborated our theoretical results.Comment: 10 pages, Latex, 1 postscript figure, published in Phys. Rev. E 61, 5664 (2000

Exact Solution of an Evolutionary Model without Ageing

We introduce an age-structured asexual population model containing all the relevant features of evolutionary ageing theories. Beneficial as well as deleterious mutations, heredity and arbitrary fecundity are present and managed by natural selection. An exact solution without ageing is found. We show that fertility is associated with generalized forms of the Fibonacci sequence, while mutations and natural selection are merged into an integral equation which is solved by Fourier series. Average survival probabilities and Malthusian growth exponents are calculated indicating that the system may exhibit mutational meltdown. The relevance of the model in the context of fissile reproduction groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.

Population position along the fast–slow life‐history continuum predicts intraspecific variation in actuarial senescence

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Why Y chromosome is shorter and women live longer?

We have used the Penna ageing model to analyze how the differences in evolution of sex chromosomes depend on the strategy of reproduction. In panmictic populations, when females (XX) can freely choose the male partner (XY) for reproduction from the whole population, the Y chromosome accumulates defects and eventually the only information it brings is a male sex determination. As a result of shrinking Y chromosome the males become hemizygous in respect to the X chromosome content and are characterized by higher mortality, observed also in the human populations. If it is assumed in the model that the presence of the male is indispensable at least during the pregnancy of his female partner and he cannot be seduced by another female at least during the one reproduction cycle - the Y chromosome preserves its content, does not shrink and the lifespan of females and males is the same. Thus, Y chromosome shrinks not because of existing in one copy, without the possibility of recombination, but because it stays under weaker selection pressure; in panmictic populations without the necessity of being faithful, a considerable fraction of males is dispensable and they can be eliminated from the population without reducing its reproduction potential.Comment: 8 pages, 5 figure

Age, state, environment, and season dependence of senescence in body mass

Funded by Natural Environment Research Council National Geographic Society UCLA (Faculty Senate and the Division of Life Sciences) Rocky Mountain Biological Laboratory research. Grant Numbers: DBI 0242960, 0731346 NSF. Grant Numbers: IDBR-0754247, DEB-1119660, DEB-1557130Peer reviewedPublisher PD

Human factors and missed solutions to Enigma design weaknesses

The German World War II Enigma suffered from design weaknesses that facilitated its large-scale decryption by the British throughout the war. The author shows that the main technical weaknesses (self-coding and reciprocal coding) could have been avoided using simple contemporary technology, and therefore the true cause of the weaknesses is not technological but must be sought elsewhere. Specifically, human factors issues resulted in the persistent failure to seek out more effective designs. Similar limitations seem to beset the literature on the period, which misunderstands the Enigma weaknesses and therefore inhibits broader thinking about design or realising the critical role of human factors engineering in cryptography

Linking the subcultures of physics: Virtual empiricism and the bonding role of trust

This article draws on empirical material concerning the communication and use of knowledge in experimental physics and their relations to the culture of theoretical physics. The role that trust plays in these interactions is used to create a model of social distance between interacting theoretical and experimental cultures. This article thus seeks to reintroduce trust as a fundamental element in answering the problem of disunity in the sociology of knowledge