Peter and rosemary grant how are they related to Darwins theory?

Peter and Rosemary Grant, how are they related to Darwins theory?


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Peter and rosemary grant how are they related to Darwins theory?
This is from Wikipedia:





"Peter R. Grant and B. Rosemary Grant, a married couple, are both evolutionary biologists at Princeton University. They are noted for their work on Darwin's Finches on the Galapagos Island named Daphne Major. The Grants spent six months of the year each year since 1973 capturing, tagging, taking blood samples, and releasing finches from the islands. Peter Grant also helped to discover that natural selection by itself is not evolution but a mechanism within the complex process."