To many people, it may seem far-fetched that the thousands of different species of microbes that live within our bodies could influence such conditions as depression and autism. But when it comes to the human microbiome - the garden of bacteria within our gut - the implications are near endless, and science has barely scratched the surface. Science reporter Jamie Morton talked with renowned Stanford University microbiologist Professor David Relman, who is visiting New Zealand for Queenstown Research Week.

So what exactly is the human microbiome, and how long have humans had these resident bugs?

The microbiome is essentially these microbes that come together, form communities and make the human body their home.

Our histories go back to the very beginning - we evolved along with them and they evolved along with us.

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But the microbes that live on and within human bodies are not random members of the microbes that we find in the world - they're a particular set of organisms that have adapted to us, and us to them.

So the microbes of the human gut are particularly dedicated to life in the human gut.

The benefits that we derive from them include things like nutrition, development of the immune system and a whole variety of physiological traits that we often used to think of as our own.

For how long have we understood this?

I would date it right back to a guy named Antonie van Leeuwenhoek, in the 1680s.

He was the first to use the microscope and turn it on samples from the world around him, and he was the first to recognise these small little animals, as he called them, that came from the human body.

So he first described them visually, and then there was a period of time before the technology of cultivation arose - that came in the late 1800s.

That allowed a lot of people to grow microbes in humans and understand them much better, because now, you had a lot of them to study.

And then the third phase of renewed understanding and appreciation came with the development of molecular technologies like DNA sequencing.

That allowed people to realise that there were microbes in the world that hadn't been able to be grown by us in our labs, but were there nonetheless, and it was their sequences that allowed us to recognise who they were and what they might be doing.

This happened only 20 years ago.

So what kind of possibilities did this open up?

I think there are lots of kinds of questions.

One is just, what makes them special, and why have they chosen humans to live in?

And for us as clinicians, there are questions about what are they doing exactly that we might understand better, so we can either maintain it or restore it if it's lost.

From an intervention point of view, there are questions about whether we can alter these communities to do things better or more to our advantage, especially when these properties are being lost as a function of modern life.

We've seen a lot of stories in the media about eating certain foods to 'cleanse' our microbiome and keeping our gut bacteria healthy, as it were. Has there been too much hype?

I think it has been pushed a little too hard.

There are glimpses of what we might be able to understand and exploit, but there's not yet a plan about what we ought to do, exactly.

A big part of the challenge is one size doesn't fit all - we each have our own microbiome, but the measures that might benefit one person quite well may have no effect on someone else, simply because they are walking around with a different kind of community.

So the effort to find commonalities across all peoples' microbiomes, that's the big thing.

A lot of questions are being asked, in part, because the functional diversity of the microbiome is immense.

There is almost untold kinds of things that might be happening with us - and compounds being made through all sorts of activities.

The other reason is that, because we have so much human disease we can't explain right now with what we already know elsewhere, there is a natural tendency to say, ah-ha, we have this new lot of interesting insights, and maybe we can apply it to all of those things we don't understand.

In many cases, I think the bottom line will be that, if it does apply, it will only explain so much - it will be an answer, but not the answer.

I would just urge people to have a little patience - science takes time, and this is so much more complex than the human genome was, because we're talking about thousands of genomes, all intertwined and operating within us.

It's going to take some years before we really understand it well enough to make predictive interventions, but this will come, I think.