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Hellin's law, also called Hellin-Zeleny's law, is an empirical observation in demography that the approximate rate of multiple births is one n-tuple birth per 89 n-1 singleton births: twin births occur about once per 89 singleton births, triplets about once per 89 2, quadruplets about once per 89 3, and so on.
The equation expresses the fact that the first person has no one to share a birthday, the second person cannot have the same birthday as the first ( 364 / 365 ), the third cannot have the same birthday as either of the first two ( 363 / 365 ), and in general the n th birthday cannot be the same as any of the n − 1 preceding birthdays.
In 2019, a Chinese woman was reported to have two babies from different fathers, one of whom was her husband and the other was a man having a secret affair with her during the same time. [12] In 2022, a 19-year-old Brazilian from Mineiros gave birth to twins from two different fathers with whom she had sex on the same day. [13]
Dizygotic (fraternal) twins can be caused by a hyperovulation gene in the mother. [8] Although the father's genes do not influence the woman's chances of having twins, he could influence his children's chances of having twins by passing on a copy of the hyperovulation gene to them. Monozygotic (identical) twins do not run in families.
The chance the other child is a girl is 1 / 2 . This is a very different procedure from (1) picking a two-child family at random from all families with two children, at least one a boy, born on a Tuesday. The chance the family consists of a boy and a girl is 14 / 27 , about 0.52.
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As a result, these populations have more chances of having multiple reproductive episodes. [1] Intense fecundity selection depends on the length of breeding season (LBS). Factors that may delay LBS or the start of breeding season, are snow cover or delayed food growth, which, in turn, minimizes the chance for these populations to reproduce.
The human twin birth rate in the United States rose 76% from 1980 through 2009, from 9.4 to 16.7 twin sets (18.8 to 33.3 twins) per 1,000 births. [5] The Yoruba people have the highest rate of twinning in the world, at 45–50 twin sets (90–100 twins) per 1,000 live births, [6] [7] [8] possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may ...