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The fraternal birth order effect has been described by one of its proponents as "the most consistent biodemographic correlate of sexual orientation in men". [5] In 1958, it was reported that homosexual men tend to have a greater number of older siblings (i.e., a 'later/higher birth order') than comparable heterosexual men and in 1962, these findings were published in detail. [6]
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.
Since the 1990s, a large volume of research has demonstrated that each older biological brother a man has from the same mother increases his odds of being gay by 28–48%. This phenomenon is known as the fraternal birth order effect. The correlation is not found in those with older adoptive or step brothers, leading scientists to attribute this ...
The Hayes also have two sets of twins, Kevin and Kyle (eight years old at the time of the sextuplets' birth) and Kieran and Meghan (five years old). They are the only family in the United States to have two sets of twins and a set of sextuplets. [93] The family was the subject of a reality television show, Table for 12, on TLC in the U.S. [94]
Most, [12] but not all, studies have been able to reproduce the fraternal birth order effect. Some did not find any statistically significant difference in either the sibling composition or rate of older brothers of gay and straight men, [ 13 ] [ 14 ] including large, nationally representative studies in the US and Denmark.
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]
José’s death comes as the couple — whose whirlwind romance was quickly followed by the birth of their twins in the summer of 2023 — were settling into their newfound family life.
Identical or monozygotic twins share their genes, while fraternal or dizygotic twins are only as genetically similar as any other sibling pair. When twins both share a trait, they are concordant for this trait; and when they differ they are discordant. If identical twins have a higher rate of concordance for a trait than fraternal twins, it ...