Cambridge Natural Sciences Interview: Heel on a Shoe

Kyle F. · Biological Natural Sciences (Cambridge)

Hi everyone, I'm Kyle, and I've just finished my second year studying Biological Natural Sciences at Cambridge. I want to talk you through one of the interview questions I was asked a couple of years ago. It's a bit of a bizarre question, and it doesn't really require any hard biological knowledge, but I hope that by talking it through you'll come to see that it actually underpins a lot of biology.

The question: why do we have a heel on our shoe?

That was it. Why do we have a heel on our shoe? I know it sounds strange, and there are lots of ways you could approach it. An artist could say it's something that's pleasing to the eye. A philosopher could argue about whether the shoe even exists at all. But as a biologist, I think the important thing is to argue from efficiency, and, underneath that, fitness.

Thinking like a biologist: efficiency and fitness

According to Darwinian evolution, every trait is optimised to give the maximum lifetime reproductive success. That sounds a little jargony, but it basically means that everything has evolved to be as fit as possible. The real skill in an interview is taking a principle like that and asking how it applies to whatever's in front of you, even something as everyday as a shoe.

Applying it to the walking motion

To get there, you have to think about the walking motion. During stepping, the heel lifts off the floor, and to do that the muscles in the leg have to contract. By having a heel on the shoe, the foot is already off the floor slightly, so that minimises the amount of work the muscles have to do to lift the foot up. As a result, over time there's less strain on the muscles, less need for ATP, and altogether you save a lot of energy.

That saving might be negligible in a single step. But over a lifetime, it may add up to something a bit more meaningful. That chain of reasoning, from a piece of rubber to muscle work to ATP to energy saved to fitness, is exactly the kind of answer a biologist should be building.

Extending the argument: from shoes to proteins

Once you have the principle, you can stretch it, and that's what impresses. The same argument could be used for something like proteins. Why does a protein have 155 amino acids as opposed to 157, if they're both working at the same rate? Because it's more efficient for the cell, it's easier to make a protein of 155 amino acids than one of 157. From there the discussion could go on, into how ATP is made, or what the implications are of saving so much energy in the muscles. Showing that one idea generalises across completely different scales is a large part of what they're looking for.

Why interviewers ask questions like this

I'll be honest, the question confused me at first during my interview, and it took me a while to work it out. But the interviewers helped me through. They gave me lots of support and guidance, and they really aren't as scary as you might think. A question like this is there to see how you think and how you rationalise your decisions, not to test what you've memorised. With a question like this, there isn't really a wrong answer, which should take some of the fear out of it.

The key skill: think out loud

If there's one thing to take from this, it's what I see as the key interview skill: thinking out loud. The interviewers can't know what's going on inside your head unless you tell them. The moment you start narrating your reasoning, a scary curveball turns into a conversation, and they can nudge you when you drift or reward you when you're on the right track. Here's what that looks like in practice:

• start by choosing a lens, as a scientist, efficiency and fitness are powerful ones
• connect the specific thing in front of you to a bigger principle
• then show the principle generalises to another example
• narrate every step, including the uncertain ones

Common mistakes to avoid

The traps are worth naming. Don't freeze because the question sounds silly or has no obvious biological "answer". Don't give a one-line response and stop, unpack why it matters in terms of energy and fitness. And don't go quiet while you think, because the interviewers need to hear the thinking, that's the thing they're actually assessing.

Final thoughts

Before your interview, practise taking ordinary objects and everyday observations, a door hinge, a spider's web, the shape of an egg, and explaining them through evolution and energy, ideally with a friend who'll interrupt and push you. That's the muscle you're really building. Thanks for reading, and good luck. If you'd like support preparing for a Cambridge Natural Sciences interview, Oxbridge Solution can help.