This document provides an overview of left-handedness, including its definition, theories around its development and inheritance, myths and facts, and issues faced by left-handed individuals. It discusses definitions of handedness and theories such as environmental, developmental, evolutionary, and genetic factors. It also addresses myths such as left-handed individuals having shorter lifespans or lower incomes, as well as issues like tools and social situations being designed for right-handedness. Famous left-handed historical and current figures are also listed.

1. History of “left handedness“..!
Dr. Tejas

2. Scheme of presentation
• Introduction & Definition
• Assessment
• Theories
• Myths and Facts
• Issues
• References

3. Definition
• Handedness:
– Handedness is a better (faster or more precise)
performance or individual preference for use of
a hand.

4. Definition
• Right-handedness 70–90%
• Left-handedness 10%
• Mixed handedness 30%
• Ambidexterity exceptionally rare,
– Can be learned.
• Ambilevous or ambisinister

5. Testing for Handedness
• Asking Questions or Physical Tests
• The “Big Three” tasks are writing, eating and
throwing.
• Computer mouse
• Purdue Pegboard Test

6. Edinburgh Handedness Inventory

7. Theories
• Environmental
• Developmental
• Evolutionary
• Genetic

8. ENVIRONMENTAL THEORIES
• Plato was convinced that the limbs are
naturally of equal strength and ability, and
that any handedness is culturally imparted.
• In fact, he went so far as to blame left-handedness
on inept mothers and nurses who
failed to adequately school their children in
the correct way of doing things.

9. "Sword and Shield" theory
• Thomas Carlyle claimed
– Combatants who held their sword in the right hand
and shield in their left (and therefore better
protected their heart) were more likely to survive in
battle.
– The greater mortality of the left-handers in battle,
then, is proposed as the mechanism driving the
higher prevalence of right-handedness today.

10. "Mother with Baby" Theory

11. Developmental theories

12. Bakan's "Birth Stress" Theory (1973)
• That minor brain insults early in development
caused left-handedness.
• Only partly accepted.
• There are just too many lefties for brain
damage to be the major culprit.

13. Geschwind and Galaburda's
"Testosterone" theory(1987)
• Prenatal hormone exposure
• Another study in 2003 determined that males
with in-utero exposure
to Diethylstibestrol were more likely to be
left-handed over the clinical control group.

14. Previc's "Vestibular-Monoaminergic"
theory. (1991; 1996)
• The position of the foetus in the final trimester
and a baby's subsequent birth position can
affect handedness.
• This partly explains why prematurity results in
a decrease in right-handedness.
• Previc argues that asymmetric prenatal
positioning creates asymmetric stimulation of
the vestibular system, which is involved in the
development of handedness.

15. Evolutionary theories

16. MacNeilage's (1991) "Postural Origin"
• The first evolutionary step in hemispheric
specialization was a left-hand, right-hemispheric
visuospatial specialization for
unimanual predation.
• Then it lead to a right-side, left-hemispheric
specialization for postural support.

17. MacNeilage's (1991) "Postural Origin"
• Because the respiratory and phonatory
components of language production are
influenced by postural factors, and facial and
whole-body communicative gestures played a
principal role in early communication, the left
hemisphere may have been predisposed for
language functions (MacNeilage, 1991).

18. Division of labour(Corballis ;1991)
• Handedness and language -same hemisphere
because they both require similar fine motor
control.

19. Genetic theories
• Charles Darwin who, although right-handed
himself, was puzzled by his left-handed son,
noting that his brother, mother and
grandfather were all also left-handed.

20. McManus and Mckeever studies.
Parents of the Child McManus Study McKeever Study
Both Right Handed 9% 16%
One Right handed 19% 20%
Both Left handed 26% 40%

21. Right shift Theory
• Marian Annett back in 1972. A
hypothetical RS+ gene (a “right shift”).
• According to this theory, then, left-handers do
not inherit their hand preference per se, they
merely inherit a lack of neurological bias
towards a dominant left hemisphere.

22. Dextral/Chance Theory
• Chris McManus hypothesized a “dextral” (D) allele,
which strongly biases handednes in favour of the
right hand along with an alternative “chance” (C)
allele, which is presumed directionally neutral.
• DD genotype
• CC genotype
• Heterozygotic DC genotype
• What is being inherited is not left-handedness as
such, but rather an absence of handedness, so
that handedness is then determined by chance.

23. • Annett’s RS+ and RS- genes and McManus’ D
and C genes all remain hypothetical
• In 2007, Oxford University researchers
LRRTM1 (Leucine-Rich Repeat Trans-Membrane
1), a variant of which also slightly increases the
risk of psychotic mental illnesses.
• In 2010 , PCSK6 and handedness in children
with language-related disorders like dyslexia.

24. HANDEDNESS, THINKING AND
HEMISPHERIC DOMINANCE

25. Handedness and Thinking
• One theory divides left- and right-handed
thinkers into two camps: Linear Sequential vs.
Visual Simultaneous
• Ex.Popcorn

26. Handedness and Thinking

27. • Right-handed people process information
using "analysis", which is the method of
solving a problem by breaking it down to its
pieces and analysing the pieces one at a time.
• Left-handed people process information using
"synthesis", which is the method of solving a
problem by looking at the whole and trying to
use pattern-matching to solve the problem.

28. • Ultimately, being left handed is not an all or
nothing situation. The processing styles
operate on a continuum

29. Intelligence
• It’s a common belief that left-handed people
are more intelligent or creative than right-handed
people.
• While there is an unresolved debate within the
scientific community on how to operationalize
both intelligence and creativity, some studies
have demonstrated a small positive
correlation

30. • Marian Annett indicated significantly more
left-handers among mathematics
students than among students of other
subjects, arguing that this is consistent with
her genetic right shift theory of left-handedness.
• John Santrock's 2008 study, also suggested
that more mathematicians, architects,
musicians and artists - all of whom, it is
argued, require good visual-spatial skills - are
left-handed than the population as a whole.

31. FACT
• Contrary to earlier assumptions, only about
20% of left-handers have right-hemisphere
language dominance.
• Thus, while left-handers may be largely right-brain
dominant in terms of motor control, this
may or may not be associated with any of the
commonly-claimed right-brain attributes (such
as intuition, creativity, imagination, etc).

32. MYTH
• Studies in the late
1980s, showed left-handers
tend to die
early. In one study,
(1991), they claimed
that left-handers may
die up to nine years
earlier than right-handers.
FACT
• Studies were seriously
flawed and conclusions
erroneous.
• The findings were
roundly refuted by
more than a dozen
studies in the 1990s.

33. MYTHS & FACTS
• FACT
– Interactive sports such as table tennis, badminton,
cricket, and tennis have an overrepresentation of
left-handedness, while non-interactive sports such
as swimming show no overrepresentation.

34. MYTHS & FACTS
• The advantage to players in one-on-one sports,
such as tennis, boxing, fencing or judo, is that, in
a population containing perhaps 10% left-handers
and 90% right-handers, the left-hander plays 90%
of his or her games against right-handed
opponents and is well-practiced at dealing with
this asymmetry. Right-handers play 90% of their
games against other right-handers. Thus, when
confronted with left-handers, they are less
practiced.

35. MYTH
• Heterosexual
individuals are
somewhat more likely
to be right-handed than
homosexual individuals.
FACT
• Handedness and sexual
orientation may be
linked to the faternal
birth order and there s
no definite increased
incidence of
homsexuality in left
handers..

36. MYTH
• Left-handers earn lower
wages than their right-handed
counterparts
FACT
• In a study published
in Laterality, it was
found that lefties earn
slightly more money
than their right-handed
peers who work at the
same jobs.

37. FACT
• An intresting report in Current Surgery says
“One out of every 10 left handed surgeons is
uncomfortable with the idea of being
operated on by a left handed surgeon”
• Six per cent also reported concerns by
patients about their laterality .

38. FACT
• Left-handers might have the advantage in
careers like piloting a jet fighter or talking and
driving at the same time.
• A study published in the journal
Neuropsychology in 2006 suggests that left-handed
people are faster at processing
multiple stimuli than righties.

39. MYTHS & FACTS
• The Romans were responsible for a lot of anti-left
customs. They were the most militantly
right-handed people in history. Romans
invented the right handed handshake, the
fascist salute, and that right to left alphabet
that still creates a lot of trouble for lefties

40. Myths and Facts
• It was no coincidence that the fourth finger of
the left-hand was chosen for the wedding
finger in 300BC.
• Doctors at that time believed a nerve from
this finger ran directly to the heart

41. MYTHS & FACTS
• Handshakes Whilst Julius Caesar was left-handed
it was he who instructed all of his
Roman subjects to adopt the right-handed
handshake. Maybe this was because it left his
weapon hand free whether greeting either
friend or foe.

42. Left hand drive/Right hand drive
• When passing a stranger on the road, it would be
safer to walk on the left, so ensuring that your
weapon was between yourself and a possible
opponent.
• Revolutionary France was to overturn this
historic practice, as part of its social rethink.
• Also Napoleon was left handed.
• From this time any part of the world that was
colonised by the French would travel on the
right, the rest would remain travelling on the left.

43. Politics(Leftists)
• In the French parliament before the
revolution, the nobles sat in the right side of
the king, while the capitalists sat on the left.
• The right became associated with the
prevalent social order, and the left with the
subversive elements wanting to change it.

44. • It was founded by the Left-Handers Club in
1992, with the club itself having been founded
in 1990.

45. Handedness Issues

46. Handedness Issues
• Historically, the left side, and subsequently
left-handedness, was considered negative.
• The word "left" itself derives from the Anglo-
Saxon word lyft, "weak“.
• Latin adjective sinister/sinistra/sinistrum origi
nally meant "left“
• In Sanskrit, the word "वाम" (waama) stands for
both "left" and "wicked."

47. Handedness Issues
• Social stigmatization of left hand/side.
• Cleanliness.
• Especially in Islam and Hinduism
• Christianity, the right hand of God is the
favoured hand. For example, Jesus sits at
God's right side.

48. Forced use of right hand
• Can cause multiple problems - learning
disorders, dyslexias, stuttering and
other speech disorders
• Shifts from left- to right-handed are more
likely to be successful than right to left,
though neither have a high success rate to
begin with.

49. Handedness Issues
• Nearly all tools and devices are designed to be
comfortably used with the right hand.
• For example, scissors.

50. Tools and devices
• Opening Bottles
• Computer input devices; QWERTY keyboards
• Cameras
• Musical instruments
• Weapons
• Machinery

51. WRITING PROBLEMS
• Desks designs
• Sitting arrangements

52. Awkward Social situations
• Shaking hands with the non-dominant hand;
• Accidentally taking a neighbour’s drink at
the dinner table;
• Putting a belt on upside down;
• Receiving Prasadam at a temple in an
unexpected hand.
• Difficulty tying shoe laces
• Opening Bottles
• Trouble opening
or locking locks/Screws.

53. FAMOUS LEFT HANDERS
• Narendra Modi*
• Dr. Raman Singh
• Ratan Tata
• Laxmi nivas Mittal
• Sachin Tendulkar
• Ted Williams
• Frankie Albert
• Pt.Hariprasad Chaurasia
• Mahatma Gandhi
• Amitabh Bachchan
• Saurav Ganguly
• Alexander The Great
• Charlie Chaplin
• Bill Gates
• Bill Clinton
• J.K. Rowling
• James Cameron
• Gary Kasparov
• Marie Curie
• Barack Obama
• Henry Ford
• Tom Cruise
• Bruce Willis
• Oprah Winfrey
• Napoleon Bonaparte
• Julius Caesar
• Prince Charles
• Leonardo Da Vinci
• Angelina Jolie
• Diego Maradona
• Monica Seles
• Martina Navratilova
• Benjamin Franklin
• Hellen Keller
• John F. Kennedy
• Rafael Nadal
• Thomas Jefferson
• Leo Tolstoy
• Mark Twain

54. • Left Brain, Right Brain: Facts and Fantasies Michael C. Corballis mail
Published: January 21, 2014DOI: 10.1371/journal.pbio.1001767
• Corballis MC (2009) The evolution of language. Ann N Y Acad Sci
1156: 19–43. doi: 10.1111/j.1749-6632.2009.04423.x
• McManus IC, Davison A, Armour JAL (2013) Multilocus genetic
models of handedness closely resemble single-locus models in
explaining family data and are compatible with genome-wide
association studies. Ann N Y Acad Sci 1288: 48–58. doi:
10.1111/nyas.12102
• Corballis MC, Beale IL (1993) Orton revisited: dyslexia, laterality, and
left-right confusion. In: Willows DM, Kruk RS, Corcos E, editors.
Visual processes in reading and reading disabilities. Hillsdale (New
Jersey): Lawrence Erlbaum Associates. pp. 57–73.
• McManus IC, Bryden MP (1992) The genetics of handedness,
cerebral dominance and lateralization. In: Rapin I, Segalowitz SJ,
editors. Handbook of neuropsychology, Vol. 6: developmental
neuropsychology, Part 1. Amsterdam: Elsevier. pp. 115–144.
• http://www.rightleftrightwrong.com/
• http://www.lefthandersday.com
• http://en.wikipedia.org/wiki/Handedness
• http://www.encyclopedia.com/topic/handedness.aspx

55. THANK YOU