Left-handed, left-footed, left-kissing? | Science| In-depth reporting on science and technology | DW | 13.08.2019
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Left-handed, left-footed, left-kissing?

Handedness is not the only asymmetry of our bodies. Whether hugging, kissing or listening, we usually prefer one side over the other. And so do animals.

In the past, scientists believed that a single gene was responsible for our handedness. Today we know that in addition to many different genes, the environment also has an influence on our dexterity.

Sebastian Ocklenburg from the Ruhr University Bochum investigates the handedness and cognitive asymmetries in humans and animals. On International Lefthanders Day we interviewed the biopsychologist about cats, kisses and Leonardo da Vinci.

DW: About 85 to 90 percent of all people are right-handed. Does this preference for the right side also apply to other body parts or activities? 

Sebastian Ocklenburg: Yes, there are many such asymmetries - even if the right side is not always preferred. A nice example is kissing. When kissing, everyone has to turn their head to one side. When you turn your head to the other side than the one you usually use for kissing, it feels very strange. Give it a try! 

That's right. I always turn my head to the right. Luckily my boyfriend does, too, or we'd probably be in trouble. Are there other examples?

The feet. With football players, you can always see that most people clearly prefer a foot when they shoot at the goal. There are a few people, for example Lionel Messi, who can shoot equally well with both feet.

These players often have a big advantage. Beyond these motor asymmetries, there are also sensory asymmetries. For example, when people look through a telescope with their eyes, almost everyone uses just one particular eye. When people use their ears to listen at the door, almost everyone prefers to use one particular ear - even if they have the same hearing ability in both ears.

Prince William and Duchess Catherine kissing at the wedding ceremony. (picture-alliance/dpa/P. Kneffel)

Prince William and Duchess Catherine like to turn their head to the right side - like 65 percent of all humans.

Are these preferences related to handedness - are left-handed people also left-footed?

Partly. The motor asymmetries are strongly related. If I am left-handed, I am usually also left-footed and prefer to kiss with the left side of my head turned in. However, this is independent of the sensory asymmetries in hearing or seeing. Although they are interrelated, they are independent of handedness.

Do we see the same asymmetries in animals?

Yes, it's also true of animals. For example, we have just submitted a study on the "laziness" of cats and dogs. In contrast to humans, however, the distribution here is more 50 to 50, so there are about the same number of left- and right-handed animals.

How do you test the 'pawedness' on animals?

Usually the animal is given a task in which it has to reach for food. Everyone can replay this at home with their own pet. Take an empty toilet roll, cover one side and put some food inside. The tube must be narrow enough that the animal cannot fit it's snout inside, but has to grab the food with its paw.

If you give your pet the roll ten times and it uses the same paw ten times to get the food, then you know that the animal is right- or left-pawed.

A cat (picture-alliance/dpa/P. Pleul)

Cats and dogs prefer to use one specific paw.

Why do these preferences even exist?  Why are some people left-handed and others right-handed?

The handedness has very little to do with our hands - the brain is decisive. In humans, it is divided into two halves, the right and the left side. Whether you are left-handed or right-handed depends on which half of the brain is particularly good at performing fine motor skills.

In right-handed people, that's the left side of the brain, in left-handed people, the right side. This lateral displacement is due to the nerve tracts crossing in the spinal cord. The left side of the brain always controls the right side of the body and vice versa.

Does this make the brains of right-handed and left-handed people function differently? Are left-handed people really smarter or more creative than right-handed people?

No, I'm afraid I have to disappoint you. In the 1970s there were a few small, poorly controlled studies that came to this conclusion. Since then, however, this has been refuted several times. Left-handed people are neither smarter nor more creative than right-handed people. Unfortunately, however, this result is much less interesting, which is why many people still refer to the studies from the 1970s.

And to a whole series of famous personalities who were allegedly all left-handed.

Yes, for example Leonardo da Vinci, who was also supposed to be left-handed. But if you look at the scientific literature on the subject, it becomes clear that this statement is based on a single portrait, on which da Vinci paints with his left hand. That he wears the right arm in a bandage on this portrait and paints with the right hand on other portraits is concealed.

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