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Hello, this is 6 Minute English from BBC Learning English. I'm Sam.

And I'm Roy. Whether it's salmon swimming up river to lay their eggs or cheaters running faster than a car,

animals can do incredible things with their bodies.

Human bodies are no less incredible. Just think of Olympic swimmers and sprinters.

Our bodies work using just the energy provided by what we eat.

This means that the human body has to be incredibly efficient, using as little energy as possible to do what it needs to.

Yet, even with our efficient bodies, no one can run as fast as a cheater.

Not even Olympic champions. In this programme, we'll be asking, exactly how efficient is the human body?

We'll be comparing human bodies' performance against each other and against some animals too.

And of course, we'll be learning some new and useful vocabulary as well.

But before that, I have a question for you, Roy.

Efficiency involves an input and an output.

It's about the relationship between the amount of energy coming in, in other words, the food we eat,

and the amount of energy going out, the usual movements and activities of day-to-day life.

So, according to this definition, which animal is the most efficient?

Is it A, an ant? B, a whale or C, a human?

Humans are the most efficient animal.

Okay, Roy. I'll reveal the answer later in the programme.

To find out more about how the human body works, it's helpful to know how our species evolved.

Here's Herman Ponce, Professor of Evolutionary Anthropology at Duke University,

speaking with BBC World Service programme Crowd Science.

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