"There has been more material progress in the United States in the 20th century than there was in the entire world in all the previous centuries combined." -- Stephen Moore and Julian Simon, Cato Institute, December 1999

Given the success of the 20th century, those of us living in the 21st century have come to expect constant improvements in technology. We expect to need a new computer now that Microsoft's Vista is here. We expect our cell phones will soon also be our camera, personal organizer, and portable music player. And we expect that we'll be able to download any movie we want within the next year.

But this culture of constant expectations is a relatively new phenomenon in human history. In terms of technology, your great-great-grandfather's life in the 19th century wasn't that much different than his great-great-grandfather's before him. In fact, the two could have switched times and places and still functioned with relative ease. But try putting one of them here in the 21st century. Talk about a fish out of water! Things we accept as commonplace today -- commercial airplanes, televisions, and microwaves -- would be downright perplexing to them.

And to think, all of these world-changing advances took place in the 20th century. Heck, in just 66 years we went from the Wright brothers' first flight to Neil Armstrong setting foot on the moon. That's absolutely incredible when you think about it in the context of human history.

So, what's next?
If the first six years of this century are any indication, 21st-century innovation will prove to be even more prolific than the 20th. Consider the social and cultural changes brought about by camera phones manufactured by Nokia (NYSE:NOK), Motorola (NYSE:MOT), and Sony (NYSE:SNE). Suddenly, everyone with a cell phone can be a freelance paparazzo or news reporter. Indeed, there are quite a few of them out there these days -- camera phone sales totaled 348 million mark in 2006, and are expected to be over 490 million this year.

A recurring topic that will be addressed and re-addressed in the 21st century is the need for renewable energy sources. Integrated oil companies are getting into the renewable energy game. BP has stakes in solar, geothermal, wind, and hydrogen power technology. Then there are the ethanol producers like Pacific Ethanol (NASDAQ:PEIX), Archer-Daniels-Midland (NYSE:ADM), and Verasun Energy (NYSE:VSE) that are ramping up production to capitalize on the growing demand for ethanol-based products.

Clearly, whether the eventual solution is wind energy, ethanol, nuclear energy, a more efficient use of current fossil fuels, or solar energy, a lot of money will be spent and made to solve our world's growing energy needs. At our Motley Fool Rule Breakers growth investing service, one company we've recommended is Suntech Power, a Chinese company that designs, manufactures, and sells photovoltaic cells, which are used to generate power in solar panels. Currently, solar power accounts for a fractional percentage of energy use, so there's huge growth potential here. Moreover, because Suntech is aiming to be the world's low-cost producer of solar technology, our team thinks the company is in a good position to meet both consumer and environmental demands.

How to profit from change
More world-changing technology will come about in the 21st century than in any previous period. The Cato Institute's report noted that "the progress of the 20th century is not a mere historical blip but rather the start of a long-term trend of improved life on earth." Indeed, science and engineering have already reshaped the world we knew just 10 years ago.

This is great news for investors. Such innovation presents unparalleled opportunities to capitalize on the pioneering companies that will change our world -- but which of these companies is worthy of your investing dollars?

Fool co-founder David Gardner and his Rule Breakers team are always keeping their eyes out for ground-breaking companies that also happen to have great business models. For example, in April 2005, the team noticed Intuitive Surgical's tremendous sales growth and near-monopoly in robotic technology that allows for minimally invasive surgery. The pick has since returned 530% for subscribers.

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This article was originally published on Oct. 16, 2006. It has been updated.

Fool contributor Todd Wenning does not own shares of any company mentioned. The Motley Fool is investors writing for investors.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.