15 billion years, X 365 days, X 24 hours, X 60 minutes, X 60 seconds = 473,040,000,000,000,000. 473 to the 15th power, but evolution requires 104,000th power for the simplest ammino acid, let alone mammals. There simply has not been enough time for evolution to have worked, given one POSITIVE change per second. See Unshakable Foundations, by Norman Giesler.