Ageing
Other than the evidence which supports the programmed theory, there are also some contradictory concepts. One argument against programmed ageing was the long-held belief 7 that in the untamed, only a negligible proportion of a population dies from ageing-related causes. The absence of significant senescence in the wild would speak against the evolution of a programme for ageing by removing any potential advantage of actively destroying aged individuals (which would not normally be observed) and making it difficult to imagine how a programme to drive a process that was not actually realized could have evolved. 8 Recent field studies have shown, however, that ageing is also observable in natural populations of a wide variety of species. 9
Firstly, the programmed theory states that the functioning of organs and cells decreases as the organism reaches nearer the end of its lifespan. But the truth is that not all organisms follow a similar trend. There are organisms which die immediately after they have reached the peak of their
physiological abilities. A typical example is the male Argiope spider; they die shortly after copulation
by a programmed stop of the heartbeat and are then eaten by the female. This example shows that either the programmed theory does not apply to all organisms or it is not right. Secondly, there is a dramatic increase in the average life expectancy of human beings from 30 years in 1900 to around 70 years in 2000, which opposes the idea that each species has a similar lifespan. This enormous rise is caused by improved living conditions and the health care system. As the economy grew extremely fast in the last centuries, the incidence of famine and lack of medical care decreased. In the past, people were more likely to get sick from contaminated food and water due to poor hygiene, and this number decreased a lot due to the boost in the economy. The fact that environmental factors can play an essential part in the ageing of people is opposed to the idea of the process of ageing being programmed by our genes. 10
7 Medawar, P. (1952) An Unsolved Problem of Biology . London; Lack, D. (1954) The natural regulation of animal numbers. Oxford; Berry, R. & Bronson, F. (1992) ‘Life history and bioeconomy of the house mouse’, Biological Reviews of the Cambridge Philosophical Society 67.4:519-50. 8 Kowald A, Kirkwood TBL. Can aging be programmed? A critical literature review. Aging Cell . 2016;15(6):986- 998. doi:10.1111/acel.12510. 9 Brunet- Rossinni, A. & Austad,S. (2004) ‘Ageing studies on bats’, Biogerontology 5.4: 211-22; Bouwhuis, S. et al. (2012) ‘The forms and fitness cost of senescence’, The American Naturalist 179.1: E15-E27; Nussey, D. et al. (2013) ‘Senescence in natural populations of animals’, Ageing Research Reviews 12.1: 214-25. 10 Prinzinger, R. (20 05) ‘Programmed ageing: the theory of maximal metabolic scope. How does the biological clock tick?’ EMBO Rep . 6 (Suppl 1): S14- 9. doi:10.1038/sj.embor.7400425; Bezruchka, S. (2009) ‘The effect of economic recession on population health’, Can Med Assoc J . 181.5:281-285. doi:10.1503/cmaj.090553.
64
Made with FlippingBook - PDF hosting