It was species-defining. I don't think so. The history of mankind is the story of the development of tools of increasing complexity and utility. A computer is a tool. It helps to solve problems.
Chess is a problem.
Now there are computers that help solve the problem of chess. If you prefer to solve this problem without a computer, that's OK, too. It is not the end of civilization. IBM should be applauded for providing Feng-Hsiung Hsu with the resources he needed to develop Deep Blue. It should also receive kudos for the creative World Wide Web site it ran to help chess players follow the match.