Long telomeres, the protective caps of eukaryotic chromosomes, which erode during aging, have been the symbol of youth and regenerative potential. It therefore came as a surprise, when several cross-sectional studies reported that telomeres in sperm cells of old men are longer than in young men and that paternal age is positively linked to telomere length of children. To explain the puzzling data, several theories have been put forward, from Darwinian selection to high telomerase activity or alternative telomere lengthening in sperms of geriatrics. Unfortunately, the idea of a birth-cohort effect has been ignored, despite existing theoretical models and despite findings of progressive telomere erosion between human generations. The old theoretical model of progressive telomere erosion in the female germline is discussed here and updated with the hypothesis that progressive telomere erosion is tied to the monogametic sex in all higher animals. Longitudinal studies of germline telomere length in humans are much needed, since a limited regenerative capacity of somatic tissues will most likely result in an increase in and earlier onset of the so-called age-associated diseases.
Keywords: Birth-cohort effect; Germline; Paternal age at conception; Telomere erosion; Telomeres; Transgenerational.