Physically, Homo sapiens is not that special in the animal world. But the species has discovered ways of finding food and beating the odds of survival in every habitat from jungle to Arctic wasteland.

It has also come to obsess Alice Roberts, who started off in medicine, becoming a surgeon and an anatomist. She was captivated by the evolutionary story of the ape that walked and talked, and is now professor of public engagement in science at the University of Birmingham, UK. Her expertise spans anthropology, archaeology and palaeopathology.

She also has a huge track record of TV shows, from Digging for Britain and The Lost Scrolls of Pompeii to Witches of Essex, and a growing pile of books. Roberts was editor-in-chief of the latest, Humans: The evolution of a species, which tells the story of human evolution with illustrations and contributions from an international team, including Michael Marshall, who quizzed her about her latest work.

Michael Marshall: What’s the big idea in this latest part of your journey into the human past?

Alice Roberts: When I was working at the University of Bristol, something happened that was really important to how I think about humans. When I was a young surgeon, teaching anatomy to students, we built a dissection room in the vet school. I was roped in to teach there and remember looking at a lamb’s heart.

It was the first time I properly understood the way the heart changes from the fetus to the heart in a baby and an adult. I was thrown into a bigger department where I was forced to see humans as another mammal. And that is what we are. It really changed the way I look at us all.

How should we think about our bodies as products of evolution, about our history being written in our skeletons and our organs?

There’s biochemistry going on in our cells that goes back to these earliest single-celled creatures living in the ancient oceans. If we look at our arms and legs, they go back about 360 million years, when the first amphibians crawl onto land, and fins have become limbs. We can see that change, map the bones of our arm, and see where they’ve come from in evolutionary terms. You can do that with every bit of the body.

Can you give me some examples?

I’ve always said I could put the humerus of a female chimp in a medical students’ exam and they wouldn’t notice the difference – the bone is about the same size and shape; all the features are there. The more you look, the more similarities you start to see. Hands are really interesting: so similar and, at the same time, subtly different. The human thumb is longer and really chunky compared with the chimp thumb.

I’m always struck when palaeoanthropologists compare ape and human hands and confidently say, “obviously that one is Homo habilis“. It’s not obvious to me…

Exactly. Because if we’re saying chimp hands are quite similar to human hands, if you’re looking at other hominins, [then] they fit into the gap between the two. It’s difficult when the fossil record is fragmentary as well. I’m quite nervous about some classification. It makes me feel uncomfortable – as somebody from a medical background who likes a lot of data.

Humans do seem to have one exceptional thing – our brain. How much difference does this make?

I think it’s the biggest thing. If I characterise humans in as few words as possible, it is: walks on two legs, small teeth, big brains. Big brains are connected with walking on two legs, but I’m not sure how.

There are lots of theories linking that [bigger brains] to bipedalism: the two are happening at the same time, or bipedalism is happening and then brains are growing. People have said, it frees your hands so you can use tools and that drives brain expansion. Or you’re able to move in different ways and maybe cover greater distances, so you’ve got larger social networks. Maybe that’s driving brain expansion.

We have similar-sized bodies to other apes, yet the human brain isn’t just bigger, it’s got more folds – packing in an awful lot of cortex into an already massive brain. We tend to say, humans are over here and the rest of the natural world is over there. It totally influences the way we deal with it.

The number of human species that coexisted before us and alongside us really stands out now. How has that changed our understanding?

The first other humans we knew about were Neanderthals. We understand now there’s an overlap, that they weren’t a human ancestor that developed into modern humans. We’ve got about 20 different hominin species now, and more every year.

In 2008, I was making The Incredible Human Journey, my first landmark series for the BBC. In Jakarta, Indonesia, I went to the museum and introduced myself as a biological anthropologist, and they said, great, in that cupboard is Homo floresiensis [LB1], you can lay out this fossil. I was blown away. There I was with LB1 and the table with bubble wrap on it.

“The hobbit” – the original Homo floresiensis!

The original H. floresiensis! I laid out the skeleton and it sent shivers down my spine because it was so human and yet not, especially the skull. It has a tiny skull and a tiny brain. And yet, we know it is anatomically human. We know they were making stone tools. That was a big revelation. In the archaeological record, we’ve got brains getting bigger and stone tools appearing – we just assumed the two went together. Then you find tiny-brained individuals making stone tools on Flores.

I love it when new discoveries throw big spanners in the works. It did change my concept of what it was to be human. It’s a paradox that I hold in my head continually. I will rail against human exceptionalism while saying humans are exceptional. If we look at our culture and our tech, we are utterly exceptional. If you’re looking at individual bits of us, you can see where it has come from; it hasn’t just exploded into being. We are fundamentally, at the end of the day, animals.

Still primates. But eventually the Neanderthals, the Denisovans, they all disappeared. Why is our species left?

It’s a very hard question. You’re pushing tens of thousands of years, if not hundreds of thousands, of evolution into one question and one answer. One hypothesis, which is hard to test but it has the best evidence – and I’m cautious because I don’t think it’s one thing – is about the social networks modern humans had. The evidence is extraordinary. It seems raw material is travelling further in human networks. If you try to work out why, you’re talking about groups of people who are connected and exchange objects, raw materials and artefacts.

So you think, OK, you’ve got small bands of people, but they know others. Maybe if you fall on hard times and you aren’t managing to get enough food for your tribe, there are other people you can call on.

Like the rest of the natural world, we are evolving. Will we change over the next few hundred years?

Not much. When we see evolution happening rapidly, it’s usually because something awful has happened – a population has been reduced to just a few. Then you get profound effects based on that selection of genetic diversity.

If we remain a big global species, I think most change will be the change we’ve been able to detect in the immune system, that kind of thing. We’re not going to grow extra arms and legs, certainly not in the next 100 years.

One really interesting and very scary thing on the horizon is the ability for us to change DNA. I don’t know how that will play out. That’s a big ethical question.

Is your work feeding into the fiction you are writing?

I’ve written two children’s books set in the ice age. I was imagining what it was like when modern humans first met Neanderthals. I wanted to bring it alive as a story.

Then my first novel for adults is out in September, The Goddess Queen, the story of Cleopatra and Mark Antony. When we talk about Cleopatra, we talk about her love affairs, but politically she’s incredible. What intrigued me was the potential for things to have played out differently: there’s a lot of chance and contingency in human history, just as in evolutionary history. Different books, but with the same themes and ideas.

Overall, where is our relationship with nature? What should that be?

There are billions of us. Our culture is exceptional. But by taking this evolutionary approach, you’ve got less of a hard line between the rest of the natural world and us, you can see where this culture has actually come from, even if it makes us feel completely separate.

Today, it’s important to remember we’re not separate. I don’t believe in any supernatural phenomena. I don’t believe in any divinity. Another way of framing that is, I think nature is enough, and for me as a humanist, I draw quite a strong moral lesson from the knowledge that I am part of the natural world, that all those other species out there are close cousins, that what evolution has conferred on us is this incredible intelligence and understanding.

We understand the impacts we’re having. When we have a deleterious impact – even if it’s not happening immediately – we understand that by virtue of the lifestyles we’re living, we are impacting negatively on biodiversity. Morally, we need to limit that impact. Because however insulated we feel from the natural world, we’re part of it. If that disappears, we’re not going to be here very long.

This is an edited version of a New Scientist video interview that will be available at youtube.com/NewScientist from 10 June. Michael Marshall is a writer based in Devon, UK