The origin of menopause

Abstract

The origin of menopause is mysterious and difficult to explain in terms of evolutionary theory. Menopause is described in humans and in four cetacean species. Natural selection cannot act on a trait that appears after the end of reproduction; therefore, it cannot be formed by the classical selection mechanism. All the proposed theories of the onset of menopause, adaptive and non-adaptive, can explain the benefits of menopause, but are completely untenable from the point of view of the theory of evolution and do not answer the main question - how did it arise. We propose a hypothesis based on the assertion that menopause is a byproduct of the rapid increase in the size of the cerebral cortex during the formation of Homo sapiens. Genes associated with the development of congenital microcephaly, which are responsible for the development of the cerebral cortex, were identified, and clear traces of natural selection were found in them, and a powerful evolutionary process continues up to the present. Most products of these genes are associated with the process of formation of the cell division spindle, both in the process of mitosis and meiosis. We hypothesize that the rapid evolutionary process that led to the growth of the cerebral cortex in humans, as a side effect, led to the formation of a high frequency of aneuploidy in oocytes. A similar process has also led to the formation of menopause in cetaceans.