Do you have ideas, or do ideas have you? What exactly are ideas? Are they divine sparks of inspiration, the accidental by-products of our weird ape brains, neuronal fireworks displays that find meaning in our lives – or are they more than all these things?

One idea that I've spent the past three years of my life investigating is that ideas are, to a very real extent, 'alive' in their own right – surviving, reproducing, evolving, going extinct, just like living things.

It sounds a harmless proposition, but the implications are quite startling. If ideas are just like living things, then they are subject to Darwinian rules – inherently selfish entities, doing anything and everything they must to survive and propagate. And in this scenario, what are we? Little more than their hosts, their habitats? Vehicles to carry them from one parasitic generation to the next, coerced accomplices to their wild ambitions? If this idea has any substance at all, it will upset a lot of people.

It's not my idea, you understand. 'Meme theory', as it has been labelled, evolved in the minds of people including biologist Richard Dawkins, philosopher Daniel Dennett and psychologist Susan Blackmore, years before it entered mine. But at some point I, too, became infected and, in 2009, I decided to do what every good vehicle should do and take its passenger for a ride.

Like Darwin, I ventured abroad, into the cultural wilderness of America, to search out first-hand evidence that ideas are subject to natural selection. As I crossed the prairies, I classified the changing moustaches of farmers, plotted the evolution of the cowboy hat, dated American barns, and charted a taxonomy of tepees. In doing so, I found the evidence I needed to suggest that ideas do evolve just like the finches and tortoises that Darwin discovered in the Galapagos.

What's more, I found that viewing our world through 'meme goggles' is like suddenly spotting that vase in the optical illusion with the two faces. Your focus shifts from the human beings to the things in between – the countless living ideas that skip through our seven billion brains, each one competing for space in our cerebrums and the chance to procreate through our tongue and wrist movements. The mêlée of a new form of life is revealed. It's quite a view! Let me give you a few glimpses, with examples from my notebook.

Jonnie Hughes' book 'On the Origin of Tepees' (One World) can be ordered at the special price of £9.89 (usually £10.99), including p&p; call Independent Books Direct on 0843 0600 030

The cowboy hat

A great demonstration of the logic of meme theory comes when you ask the question "Where did the idea for the cowboy hat come from?". There are three answers to this question, each more provocative than the last.

The textbook answer is that John Batterson Stetson invented the cowboy hat in the 1860s after joining the gold rush to Colorado. The son of a hatter, Stetson noticed the Wild West was short of bespoke headwear. At that time, cowboys had a choice of floppy felt hats, raccoon skins or Derbies. None were perfect for a life in which the rain, wind, dust, sun and cold took turns to torment. So Stetson stitched together fur felts to make a wide-brimmed hat with a tall crown. It looked ridiculous, but it was stiff, waterproof, and cool. He marketed it as 'The Boss of the Plains' and it took the West by storm.

Answer number two: the fact is, The Boss of the Plains didn't look anything like the cowboy hat we know today. The crown was a uniform dome, with no peaks or dents. The brim was flat, no rolled edges. So Stetson didn't invent the cowboy hat – the cowboys must have.

The crucial factor is that The Boss was a pricey hat, so each cowboy only ever bought one. They were worn until they fell apart – each night under the stars, rolling the brim, each "yee-haw" denting the crown. Soon enough, in the railhead towns, all the true cowboys wore battered hats, so an aesthetic was born that represented the untamed West – the pursed, rolled cowboy hat. Anyone wanting to blend in had to have one. Stetson and other manufacturers obliged, evolving their ranges over the years to reflect this desire. What we regard today as the cowboy hat is a product of the climate, the hard Western life and the purchasing selections of a hundred thousand cowboys.

Answer number three: who invented the tiger? No one. The environment, by acting upon thousands of generations of proto-tigers, selecting some and not others, for whatever reasons, created the tiger we know today. That's how meme goggles see the invention of the cowboy hat.

Upon production, Stetson's hat entered a design journey through the selections of a century of cowboys. But it would be wrong to think that the cowboys collectively planned the route. They chose their hats for 'whatever reasons' – practical considerations, aesthetic judgements, unfathomable yearnings – no two selections alike. The hat simply bounced through this environment, its form changing subtly for forgotten reasons with each generation. End result: a mindless, unplanned ascent to the hat we know today.

Through meme goggles, no one invented the cowboy hat. If anything, it invented itself.

The American barn

The history of the cowboy hat suggests how idea selection comes about, but what about idea variation, the second vital ingredient of Darwinian evolution. Without variation, after all, there is nothing to select.

As I drove across the plains, a perfect case of idea variation materialised on the side of the highway, with examples every few miles – the American barn. American barns are icons of the West – big, often red, their doors at the gable end, their roofs crooked in cross-section, like a broken stick. It's an ingenious design because the roof maximises the volume of storage space available for crops to overwinter. Where did it come from? The American barn is a composite of the barns the Germans and English built on the east coast, with a crooked roof borrowed from Dutch houses for good measure.

But although the mongrel barns on the highway are clearly now the same 'species', no two are exactly alike. They have differing door designs, roof lengths, window heights, build materials. What causes this variation? The normal response is to say they vary because the farmers wanted them to vary. But, once again, these goggles question that assumption.

Most of the barns I see are pre-industrial, 'raised' by a community, rather than designed by an architect. Picture the scene at one of these barn-raisings: dozens of men and women, some with experience, others without; plenty with strong opinions on what to do when. As the barn goes up, these opinions will be voiced, discussions entertained, decisions made. The availability of funds and building materials, the lie of the land, the wind direction will all play their part.

Ultimately, the barn will come together only upon the negotiation of all these opinions and contributing factors – a unique barn realised imperfectly: the result of a never-to-be-repeated interplay between competing instructions, the peculiarities of the environment and a pinch of good old-fashioned randomness – just like you or I.

Coca-cola

Coca-Cola is perhaps even more American than apple pie, and the reason for this tells us something about the ways ideas inhabit our brains. Invented as a non-alcoholic version of a French 'coca wine' (cocaine and wine, together at last) by John Pemberton in 1886 upon the passing of a prohibition law in Georgia, its potential began to be realised only when Asa Candler founded the Coca-Cola Company in 1889 to market the product. Candler understood that the key to selling a product was not the quality of the product, but the quality of the idea of the product. He made certain that the Coca-Cola brand was visible in as many places as possible – on buildings, on ashtrays, on bumper stickers – so that Coke would become part of America's routine experience. Today, Coke now stands for America, or the idea of America.

The power of this association is revealed by MRI scanners. Measure the activity of the brain's pleasure centre as people drink different colas, and Coke comes way down the list. But measure the prefrontal cortex – the centre for self-identity – and it lights up like a candle. Coke remains number one not because it's more pleasurable, but because Candler's brand is the one we associate with our personality.

The American accent

Inheritance is the third vital ingredient of Darwin's evolution. Whenever I opened my mouth on my pilgrimage through America, a significant component of my cultural inheritance became apparent. Whereas they say "Pass the budder", I say "Pahss the butta".

We all collectively inherit accents as mindlessly as we collectively select hats or bring about variations in barns. We unthinkingly imitate the muscle movements that create the word sounds that surround us when we're young. Americans sound like Americans because they were raised among Americans.

In some ways, today's Americans sound more like yesterday's English than today's English. In the 17th century, when the American colonies were formed, almost all English accents were 'rhotic', meaning that they pronounced the letter 'r' like a pirate. It is our accent that has 'drifted' in the interim, turning mainly non-rhotic as our association with the soft-tongued Europeans grew. By the time the Antipodes was colonised, our 'r' sounds had all but disappeared, hence the Australian accent is non-rhotic too. In the States, only New England, which had a tight relationship with Britain into the 18th century, lost their 'r's with us.

The tepee

Looking at hats, barns, accents and soft drinks, it's possible to see how Darwin's evolution could be at work in the secret world of ideas. But how do they all come together to create the grand patterns that Darwin found in the biosphere? Can we discern a cultural 'tree of life'?

I reckon I've found one branch – a radiation of tepees equivalent to the radiation of Darwin's finches. Every one of the 20-plus Indian tribes on the Great Plains has a unique tepee. They vary in their arrangement of poles, their doorways, the design of their cover, the shape of their smoke flaps, and a dozen other ways. But this variation is different to the variation in American barns. The differing traits of the 20-plus tepees never intermingle – there are no mongrel tepees – they are all separate 'species'. The obvious question is, "Why so many varieties?" and "Is there no such thing as the perfect tepee?".

Again, it's tempting to suggest that, for whatever reason, the tepees were designed to be different by the Indians themselves – that human ingenuity was in the driving seat. But if ideas do evolve like living things, the isolation of the tribes alone would account for much of this radiation. Separated from each other by language, geography or distrust, the Plains tribes were scattered like an archipelago of cultural islands. As Darwin discovered, a foundation species will radiate into a cluster of daughter species in such circumstances, and so it is here.

Which is why, towards the end of my trip, I could wander the pop-up town of the Tepee Festival at Crow Reservation in Montana, spotting the tepees of different tribes. The Crow tepees reached skyward with flailing poles, their foliage intact. The Sioux tepees were squat and trim, with special pockets for their smoke flap poles. The Blackfoot tepees were broad and proud, decorated in wild dyes and flashy iconography.