Doing the math: Study shows chicks count from left to right


Photo courtesy of Rosa Rugani/University of Padova

Editor’s Note: This article is from our Science for Kids series, aimed at children in grades 4-8.

By Rachel Zamzow

Do you think baby chickens are very smart? Chicks can’t play computer games or even talk like we do. They just peep. But scientists recently found out chicks know more than we thought. Not only can they count, they prefer to count from left to right, just like humans.

When we count, we usually think of numbers in order from left to right. This is called a number line. For example, rulers start with zero inches on the left and go to twelve inches on the right. And calendars list dates increasing from left to right. We even have an imaginary number line in our head. Think about the numbers “two” and “five.” Out of habit, you probably thought of “two” on the left and “five” on the right in your mind.

Until recently, scientists thought humans were the only creatures who had a mental number line. They had assumed we count from left to right because of the way we learn to read from left to right.

But a new study led by Rosa Rugani, a researcher at the University of Padova in Italy, shows that chicks also count from left to right – and they can do this within days after hatching.

This is the first time anyone has shown the use of a mental number line in a species other than humans, said Charles Gallistel, a professor at Rutgers University who studies how animals think. Directly observing this behavior in chicks is surprising, he said.

In their study, Rugani and her team taught three-day-old chicks to find a tasty, crunchy mealworm behind a plastic panel with five red squares on the front. Then they removed this panel and showed the fluffy subjects two new, identical panels – each with two red squares – one on the left and the other on the right.


Where did the chicks search for their treat first? Almost three-quarters of the time, they poked their beaks behind the panel on the left. This shows that the chicks noticed that two is less than five, and that they thought of smaller numbers being on the left. And when the chicks were later shown panels that each had eight squares – more than five – they looked for food behind the right panel, again almost three-quarters of the time.

Rugani’s experiment shows us that chicks tend to think of smaller numbers on the left and larger numbers on the right. In other words, they seem to have an imaginary number line just like we do. These findings, published in the journal Science, not only reveal that chicks are far less bird-brained than we thought, but they also teach us something about ourselves.

“This is an experiment that can make us understand better how numbers are processed,” Rugani said. She thinks an imaginary number line from left to right is prewired in the brains of chicks and probably in humans, too. That’s because the right half of our brain typically handles numbers, Rugani said. Things we see on the left are actually sent to the right side of the brain, so it makes sense that we would first look left when ordering numbers.

We may start life with a left-to-right number sense, but it’s not permanent. People who grow up in a culture that reads in the opposite direction – from right to left, such as in the Middle East – can learn to flip their mental number line later.

This study also shows us how simple experiments can answer big questions. Cleverly using chicks and some colored squares, Rugani was able to explain how animals and maybe even humans think about numbers. Science doesn’t have to be complicated to add to our understanding of the world around us.


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