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Several authors agree to the fact that August Weismann was the first to propose an explanation to biological aging (Kirkwood and Cremer, 1982; Gems and Partridge, 2013).

A lot of hallmarks (and some contradictory) are pointed out about Weismann along his life, which I am reflecting only in these

  1. When he suggested that group selection was the answer of aging;

August Weismann and Alfred Russel Wallace proposed that aging has evolved to remove worn-out older individuals, thereby reducing competition for scarce resources and resulting in benefits for the species. However, such an evolutionary mechanism would require group selection of a sort that makes this an untenable scenario. (Gems and Partridge, 2013)

the reason suggested by Weismann for the evolution of ageing was an adaptive one, namely that ageing is beneficial in ridding a species of old and decrepit individuals which would otherwise compete for resources with younger ones. Thus, by natural selection the somatic cells of the organism would have come to lose their capacity for unlimited survival, and ageing of the organism as a whole would have appeared. (Kirkwood and Cremer, 1982)

I don't understand how any of those arguments can justify the evolution of aging

they claim that group selection was responsible for the evolution of aging but it doesn't explain how older individuals get old.. they are just removed from the population because they got old, it doesn't seem to explain the evolution of ageing.

  1. When he developed the concept of panmixia to reshape his nonadaptive theory (or neutral) of biological aging.

The central component of Weismann's non-adaptive theory of ageing was the principle of panmixia which he developed [...] In brief, this principle states that as soon as any character becomes useless to an organism, natural selection ceases to operate upon it and it begins to disappear. (Kirkwood and Cremer, 1982)

How the concept of panmixia is related to the evolution of aging?

is that because since post-reproductive period does not contribute to the evolution of the species, the potential of immortality of somatic cells desapear? It doesn't make much sense..

References

  • Gems, D. and Partridge, L. (2013) ‘Genetics of longevity in model organisms: Debates and paradigm shifts’, Annual Review of Physiology, 75, pp. 621–644. doi: 10.1146/annurev-physiol-030212-183712
  • Kirkwood, T. B. L., & Cremer, T. (1982). Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress. Human Genetics, 60(2), pp. 101–121. https://doi.org/10.1007/BF00569695
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think I got it..

if I may I would like to answer this question since it could be helpful to anyone who's interested in this field of research.

Regarding the first question: " how any of those arguments can justify the evolution of aging "

Weismann presented a notion of group selection as a possible answer to biological aging, proposing that such mechanism becomes advantageous for the species by removing the most geriatric individuals.

how those arguments can justify the evolution of aging: on the hypothesis that if all individuals were immortal, they would be competing with the younger ones for the available resources.

if individuals did not die they would soon multiply inordinately and would interfere with each other's healthy existence. (Weismann, 1891)

Thus, by natural selection the somatic cells of the organism would have come to lose their capacity for unlimited survival, and ageing of the organism as a whole would have appeared. (Kirkwood and Cremer, 1982)

Regarding the second question: " How the concept of panmixia is related to the evolution of aging? "

essentially it is used to justify the aforementioned concerning somatic immortality, that is, the cause of cellular aging.

when applying this concept of panmixia to the post-reproductive period, aging can arise, as this is a period that does not contribute to the evolution of the species. Thus it can be considered as an inert physiological interval, such that the potential of somatic immortality starts to disappear.

[Weismann speaking about reproduction] As soon as the individual has performed it’s share in this work of compensation, it ceases to be of any value to the species, it has fulfilled its duty and may die. (Weismann, 1891; p. 10)

As soon as natural selection ceases to operate upon any character, structural or functional, it begins to disappear. As soon, therefore, as the immortality of somatic cells became useless they would begin to lose this attribute. (Weismann, 1891; p. 141)

it's also important to mention, as a side note, that for Weismann, natural death arises due to the absence of cell renewal, which causes the wear of the histological tissue and thus the concept of panmixia justifies the limited number of cell division.

References

Kirkwood, T. B. L., & Cremer, T. (1982). Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress. Human Genetics, 60(2), pp. 101–121. https://doi.org/10.1007/BF00569695

Weismann, A. (1891). Essays upon heredity and kindred biological problems. Volume I. Oxford: Clarendon Press.

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