 Complete the following phrase:  The central argument in Principles was that the present is the key to the past  a concept of the Scottish Enlightenment which David Hume had stated as all inferences from experience suppose ... that the future will resemble the past, and James Hutton had described when he wrote in 1788 that from what has actually been, we have data for concluding with regard to that which is to happen thereafter. Geological remains from the distant past can, and should, be explained by reference to geological processes now in operation and thus directly observable. Lyells interpretation of geological change as the steady accumulation of minute changes over enormously long spans of time was a powerful influence on the young Charles Darwin. Lyell asked Robert FitzRoy, captain of HMS Beagle, to search for erratic boulders on the 