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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 ...
Intersex people have been treated in different ways by different cultures. Whether or not they were socially tolerated or accepted by any particular culture, the existence of intersex people was known to many ancient and pre-modern cultures and legal systems, and numerous historical accounts exist.
He named the human species as Homo sapiens in 1758, as the only member species of the genus Homo, divided into several subspecies corresponding to the great races. The Latin noun homÅ (genitive hominis) means "human being". The systematic name Hominidae for the family of the great apes was introduced by John Edward Gray (1825). [8]
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. In non-humans, the whole group may also be referred to as a litter, and multiple births may be more common than single births ...
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:
Androgyny is the possession of both masculine and feminine characteristics. [1] Androgyny may be expressed with regard to biological sex or gender expression.. When androgyny refers to mixed biological sex characteristics in humans, it often refers to conditions in which characteristics of both sexes are expressed in a single individual.
In humans and many other species of animals, the father determines the sex of the child. In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.
The term gonochorism is most often used for animal species, an estimated 95% of which are gonochoric. [17] It is very common in vertebrate species, 99% of which are gonochoric. [18] [19] Ninety-eight percent of fishes are gonochoric. [20] Mammals (including humans [21] [22]) and birds are solely gonochoric. [23] and Tardigrades are almost ...