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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 ...
[19] [18] [note 2] Thus, if a male with no older brothers has a 2% chance of being homosexual and the fraternal birth order effect increases those chances by 33% for each older brother, then a male with one older brother has a 2.6% chance of being homosexual; a male with two older brothers has a 3.5% chance, and males with three and four older ...
Multiple birth. A multiple birth is the culmination of one multiple pregnancy, wherein the mother gives birth to two or more babies. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such births are often named according to the number of offspring, as in twins and triplets.
Identical twin studies are a useful mechanism for assessing the role of genes and environment. Twin studies have also found that among twins with differing sexual orientations, homosexual twins were significantly more gender nonconforming than their heterosexual co-twin, and that this was noticeable from a young age. [29] Bailey states:
MTFS is a twin study established in June 1989 with 1300 same-gendered twin pairs age 11 or 17, with an additional cohort of 500 such pairs recruited around 2004. Twins were born between 1972 and 2000. [1] All twins born in Minnesota at that time were eligible to participate using birth registry data. Both identical and fraternal twins share ...
The paternal age effect is the statistical relationship between the father's age at conception and biological effects on the child. [1] Such effects can relate to birthweight, congenital disorders, life expectancy and psychological outcomes. [2] A 2017 review found that while severe health effects are associated with higher paternal age, the ...
The power of twin designs arises from the fact that twins may be either identical (monozygotic (MZ), i.e. developing from a single fertilized egg and therefore sharing all of their polymorphic alleles) or fraternal (dizygotic (DZ), i.e. developing from two fertilized eggs and therefore sharing on average 50% of their alleles, the same level of genetic similarity found in non-twin siblings).
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. [96] The family was the subject of a reality television show, Table for 12, on TLC in the U.S. [97]