What do the companies in these three groups have in common?
Group A. American Motors, Studebaker, Detroit Steel, Maytag and National Sugar Refining.
Group B. Boeing, Campbell Soup, Deere, IBM and Whirlpool.
Group C. Cisco, eBay, McDonald's, Microsoft and Yahoo.
All the companies in Group A were in the Fortune 500 in 1955, but not in 2011.
All the companies in Group B were in the Fortune 500 in both 1955 and 2011.
All the companies in Group C were in the Fortune 500 in 2011, but not 1955.
Comparing the Fortune 500 companies in 1955 and 2011, there are only 67 companies that appear in both lists. In other words, only 13.4% of the Fortune 500 companies in 1955 were still on the list 56 years later in 2011, and almost 87% of the companies have either gone bankrupt, merged, gone private, or still exist but have fallen from the top Fortune 500 companies (ranked by gross revenue). Most of the companies on the list in 1955 are unrecognizable, forgotten companies today. That's a lot of churning and creative destruction, and it's probably safe to say that many of today's Fortune 500 companies will be replaced by new companies in new industries over the next 56 years.
Update: Here's a related article from Steve Denning in Forbes, featuring some insights from Steve Jobs about what causes great companies to decline (power gradually shifts from engineers and designers to the sales staff) and how the life expectancy of firms in the Fortune 500 and S&P500 has been declining over time.