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If the parents are both right-handed, in dizygotic and monozygotic twins there is a 21% chance of one being left-handed. If one parent is left-handed, in DZ and MZ twins there is a 57% chance of one being left-handed. If both parents are left-handed, it is almost certain one twin will be left-handed. [citation needed]
Handedness displays a complex inheritance pattern. For example, if both parents of a child are left-handed, there is a 26% chance of that child being left-handed. [23] A large study of twins from 25,732 families by Medland et al. (2006) indicates that the heritability of handedness is roughly 24%. [24]
Handedness in and of itself tends to be a grey area. The requirements for someone to be right- as opposed to left-handed have been debated, and because individuals who identify as left-handed may also use their right hand for a large number of tasks, identifying two clearcut groups of subjects is a challenging task.
One theory, known as the acoustic laterality theory, the physical properties of certain speech sounds are what determine laterality to the left hemisphere. Stop consonants , for example t, p, or k, leave a defined silent period at the end of words that can easily be distinguished.
Also, naturally left-handed musicians have to play with right-handed-only instruments (violin, viola, cello). Kurt Cobain, frontman of Nirvana, was naturally ambidextrous. He grew up having a slight preference for his left-hand (as can be seen in many of his childhood photographies), but as an adult he wrote right-handed.
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Cross-dominance, also known as mixed-handedness, hand confusion, or mixed dominance, is a motor skill manifestation in which a person favors one hand for some tasks and the other hand for others, or a hand and the contralateral leg. For example, a cross-dominant person might write with the left hand and do everything else with the right one, or ...
Lombroso's theories were likely accepted due to the pre-existing regional stigma against left-handedness, and greatly influenced the reception of left-handedness in the 20th century. His hypothesis even manifested in a new way during the 1980s and 1990s with a series of research studies grouping left-handedness with psychiatric disorders and ...