Developing an integrated algorithm to support autism diagnostic decisions: Model performance and statistical fairness.

In 18th- and 19th-century Finland, having living siblings was linked to marriage and childbearing – not always positively. An individual’s total fitness is the combination of their personal fitness and the fitness of their genetic relatives (Hamilton, ). This inclusive fitness theory has been used to explain, for example, cooperative breeding, meaning allomaternal help in rearing offspring (Hrdy, ). Alloparental help has been suggested to be essential in past human populations (Hrdy, ). The more closely related the helper is, the greater indirect fitness benefits they can gain from helping (Hamilton, ). The most common helpers in human societies are pre-reproductive siblings, often called helpers-at-the-nest, and post-reproductive grandmothers, who both gain fitness benefits from helping as they do not reproduce themselves (Emlen, ; Sear & Coall, ; Sear & Mace, ). Due to paternity uncertainty, relatives on the maternal side are expected to invest more in helping (Queller, ). Even unrelated individuals, especially pre-reproductive individuals, can sometimes benefit from helping, as the experience of caretaking may improve the survival of their own future offspring (Hrdy, ). However, individuals will likely maximize their own fitness even to the detriment of relatives (Hamilton, ). As inclusive fitness theory predicts, some studies have discovered that the presence of kin increases fertility (realized reproduction) in humans (Mathews & Sear, ; Sear & Coall, ), although some show contrasting results. For example, some studies have discovered that the fertility of couples is positively influenced by their parents (Chapman et al., ; Dillon et al., ; Okun & Stecklov, ; Sear, ; Sear et al., ; Snopkowski & Sear, ; Tymicki, , ). The presence of parents-in-law has similarly been associated with higher fertility in women (Dillon et al., ; Hacker et al., ; Sear & Coall, ; Sear et al., ; Willführ et al., ), whereas a woman’s own parents may decrease fertility due to concerns about maternal well-being (Hacker et al., ; Sear & Coall, ). In contrast, siblings have been previously mostly associated with lower fertility (Borgerhoff Mulder, ; Gibson & Gurmu, ; Low, ; Mace, ; Yang & Spencer, , but see Rotering & Bras, ).