1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
AveGali [126]
3 years ago
12

Why are there lefties (and righties)?

Biology
2 answers:
malfutka [58]3 years ago
7 0

Answer:

These changes are often brought about by environmental influences and can affect how a baby grows. These gene-expression differences could affect the right and left parts of the spinal cord differently, resulting in lefties and righties.

Explanation:

Most people — about 85 to 90% — are right-handed, and there's no population on Earth where left-handers are in the majority.

That uneven split has had some historic downsides for lefties. They've had to use scissors, desks, knives and notebooks that were designed with righties in mind. Many lefties were forced, against their natural inclination, to write with their right hands (including some famous examples like King George VI of England). They've been discriminated against and eyed with suspicion, as evidenced in the language used to describe lefties. "Right" in English obviously also means "correct." The etymology of the word "sinister" can be traced back to the Latin word for "left."

While the stigma against left-handedness has faded in most places, scientists are still confounded by the righty-lefty divide. Researchers are still trying to understand what makes people prefer one hand over the other and why righties dominate.  

On an individual level, handedness might be determined at the earliest stages of development. Scientists reported in 2005 in the journal Neuropsychologia that fetuses will show a hand preference in the womb (by sucking the thumb of one hand), a proclivity that continues after they're born.  

While there's no righty or lefty gene, DNA does seem to play a role in handedness. In a recent study published in Brain: A Journal of Neurology, researchers at the University of Oxford looked at the DNA of about 400,000 people in the U.K. and found that four regions of the genome are generally associated with left-handedness. Three out of these four regions were involved in brain development and structure. Some researchers hope that studying the biological differences between lefties and righties could shed light on how the brain develops specializations in its right and left hemispheres.  

The right stuff

Trying to answer the question of handedness from an evolutionary perspective is also complicated. Researchers can detect handedness in the archaeological record by looking for certain anatomical traits in prehistoric skeletons, such as asymmetry in the size and density of arm bones, and by examining prehistoric tools.  

"If you know how the tool was held and how it was used, then you can look at the wear traces" to determine if a lefty or righty used the tool, said Natalie Uomini, a senior scientist at the Max Planck Institute for the Science of Human History in Germany. Scientists can even look at the direction of diagonal scratches on fossilized teeth to see which hand people were using to tear off meat or animal hides in their mouths.

Righties have dominated for as far back in the archaeological record as researchers can see, about 500,000 years, Uomini said. Neanderthals, our now-extinct human cousins, were also strongly right-handed.  

That makes humans pretty strange among animals. Several nonhuman species, such as the other great apes, are individually handed, but the split between righties and lefties is typically closer to 50-50.

What caused our extreme bias toward right-handedness to evolve and persist? From an evolutionary perspective, if right-handedness evolved because it had some kind of advantage, then you might expect left-handers to disappear completely, Uomini told Live Science. She added that there are some disadvantages to being left-handed, such as higher frequencies of work accidents. Researchers also linked left-handedness to learning disabilities, in a study published in 2013 in Brain: A Journal of Neurology.  

But there's a leading theory to explain why left-handers have maintained a constant minority: the fighting hypothesis.  

"The idea is that in hand-to-hand combat, or in combat with weapons, there is an evolutionary advantage to being a minority left-hander," Uomini said. "If you're left-handed, you have a surprise advantage because most people are used to fighting against right-handers." That lefty advantage has been shown in one-on-one sports like fencing, scientists reported in 2010 in the journal Laterality.  

If that hypothesis is correct, it would mean that even though the downsides to left-handedness were significant enough to keep lefties in the minority, lefties' advantage in combat at least gave them a fighting chance against eventual extinction.

Delicious77 [7]3 years ago
5 0

Answer:

handedness is a complex trait and it's influenced by multiple factors, including genetics, environment, and chance. ... More specifically, handedness appears to be related to differences between the right and left halves (hemispheres) of the brain.

Explanation:

You might be interested in
Which two materials form igneous rocks upon cooling?
Keith_Richards [23]

Answer: B) magma and lava

Explanation:

5 0
1 year ago
Read 2 more answers
In the graph of an enzymatic reaction explain why the line begins as a straight line.
lianna [129]
Generally, the graph line will begin as a straight line when the substrate concentration is low. At very low substrate concentrations, the rate is proportional to the substrate concentration. As substrate concentration increases, it affects the enzymatic reaction, so the rate will change and the line will change.
3 0
3 years ago
8. What is a metabolic pathway? (1pt)
KengaRu [80]

Answer:

What is a metabolic pathway?

Metabolic pathways could be simply defined as ways whereby reaction occurs chemically within a cell which are carried about by enzymes called metabolites, those enzymes helps in hasten up the reaction.

Explanation:

7 0
3 years ago
Read 2 more answers
A catabolic pathway may be which of the following? a. a set of reactions that combine monomers into larger, more energy-rich pol
KiRa [710]

Answer:

The correct answer is option c. "a set of reactions that release energy that can be used to drive cellular work".

Explanation:

Catabolism is a part of metabolism at which molecules are broken down into smaller units in order to release energy that could be used in other reactions that drive cellular work. A catabolic pathway follows catabolism criteria. Catabolic pathways are the opposite of anabolic pathways, at which large molecules are synthesized with the requirement of external energy supply.

5 0
3 years ago
How does adding and removing heat energy to water affect it’s temperature?
alexandr402 [8]

Answer:

Usually, when you add energy to a bunch of atoms they move faster and get hotter. Similarly, if you remove energy from a bunch of atoms, they usually move less and get cooler. Because adding heat energy usually results in a temperature rise, people often confuse heat and temperature.

Explanation:

3 0
2 years ago
Other questions:
  • Help! Need definitions ASAP
    7·1 answer
  • What is a hominid ?
    10·2 answers
  • Which condition likely promoted the fossilization of the skeleton in the animation?
    7·1 answer
  • Alice purchased paint in a bucket with a radius of 9 in. and a height of 9.5 in. The paint cost $0.09 per in3.
    8·1 answer
  • Families of minerals are based on what
    9·2 answers
  • Match the following descriptions with the correct term or structure Cytoskeleton element that determines the cell diameter and i
    5·1 answer
  • Which characteristic of four different dinosaur fossils makes a dinosaur most similar to the present-day birds?
    11·1 answer
  • Evidence you studied in this lesson points ...... as having murdered Caesar
    15·1 answer
  • 21 POINTS
    5·2 answers
  • In some forests and parks that contain varieties of flowering trees and shrubs, there are signs that read "Take nothing but pict
    11·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!