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In the thymus, na\u00efve T cells capable of recognizing specific antigens are generated through random gene rearrangement, ensuring a diverse immune repertoire. However, the production rate of na\u00efve T cells declines with age, typically following an exponential or power-law function\u2014a phenomenon known as thymic involution, which is often regarded as a deterioration of biological function (immunosenescence). In this paper, we propose a novel theory suggesting that thymic involution may represent an adaptive strategy. As individuals age, repeated exposure to diverse pathogens leads to the accumulation of memory T cells, thereby reducing the need for newly generated na\u00efve T cells to combat infections. Moreover, na\u00efve T cells can persist in the periphery and retain the capacity to initiate immune responses against novel antigens. Using Pontryagin\u2019s Maximum Principle, we calculate the optimal schedule of na\u00efve T cell production. The results show that the production rate peaks during a brief period shortly after birth, followed by an exponential decline throughout life, eventually reaching a phase in which na\u00efve T cell production ceases. If peripheral na\u00efve T cells decay very slowly, the optimal strategy may consist of producing all cohorts at birth, with no subsequent production.<\/jats:p>","DOI":"10.1007\/s11538-025-01569-0","type":"journal-article","created":{"date-parts":[[2026,1,17]],"date-time":"2026-01-17T18:12:57Z","timestamp":1768673577000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Is Thymic Involution Truly a Deterioration or an Adaptation?"],"prefix":"10.1007","volume":"88","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0691-1852","authenticated-orcid":false,"given":"Yoh","family":"Iwasa","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4192-3317","authenticated-orcid":false,"given":"Rena","family":"Hayashi","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2483-6489","authenticated-orcid":false,"given":"Akane","family":"Hara","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kosei","family":"Matsuo","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"297","published-online":{"date-parts":[[2026,1,17]]},"reference":[{"key":"1569_CR1","doi-asserted-by":"publisher","first-page":"90","DOI":"10.1016\/j.exger.2014.01.003","volume":"54","author":"V Appay","year":"2014","unstructured":"Appay V, Sauce D (2014) Na\u00efve T cells: The crux of cellular immune aging? 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