What percent of humanity is left handed, and why isn't it 50 percent?

Kainantu

There have been many different numbers put forth, with the most common numbers we have seen being in the area of 13 percent. However, we have seen numbers as high as 30 percent, when you allow a very loose definition of left-handedness. http://www.cs.uu.nl/wais/html/na-dir/lefty-faq.html The percentage of left-handedness (8.3%) in neonates coincided with adult left-handedness (6.3-9.2%). The percentage of consistent right-hand preference in adults coincided with percentage of right-handedness in neonates (25.7%). http://cogprints.org/135/ Only about 10% of the population is left handed ... http://www.holidayinsights.com/other/lefthand.htm ... while in humans that percentage hovers around 10. http://www.discover.com/jan_02/featbiology.html Why not 50%? It's all to do with genes... One theory on the causes of left-handedness states that in some cases a left-hander is actually born with a brain that is different in structure from that of a right-hander. http://www.angelfire.com/oh/gluegirl/leftyfact.htm (Interesting website for lefties) Thinks: 'If the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body, left-handed people are the only ones in their right mind!' Oct 16 02, 5:21 AM

Ladymacb29

From what I understand, left-handedness is a recessive trait, meaning that there should be no more than 25% of the population with it at any time. Say the gene for being right-handed is H and the gene for left-handed is h, the only combinations you can have are HH, Hh (twice), and hh. Only one quarter of the time is left-handedness expected. Now, add into factors that in many places, it's taboo to favour the left hand (considered dirty, immoral, etc.) and in many places lefties are forced to switch their preference to the right hand. So if that happens to half of the lefties, the percentage of lefties in the world is actually 12.5% - exactly as someone else pointed out. Oct 17 02, 3:32 AM

little lady

Left-handedness is a recessive trait. Right-handed people can be homozygous, (RR) or heterozygous, (Rr) to be left handed you must be homozygous, (rr). To work out what chances your child would have hypothetically of being left-handed, you can work it out on a punnett square. eg., if both parents were homozygous right-handed, the offspring would be 100% right handed. If there was one homozygous right-handed parent and one heterozygous parent, the offspring would be also 100% right handed, but may be either hetero or homozygous right-handed. If both parents were heterozygous the child would have 25% chance of being left-handed (homozygous-rr), 50% heterozygous right-handed and 25% chance of being homozygous right-handed. And finally, if both parents were left-handed, the child would have 100% chance of being left-handed. Hope that clears things up. Oct 18 02, 4:55 AM