A parable to illustrate the limits and progress of science and human knowledge.

There is a community of intelligent beings who live in a place they call Cognita.  It's made up of two islands: Prima and Segunda.  Collectively, they call themselves the Cognitians.  Their world is composed of a variety of natural environments, full of life in a multitude of forms.  All the life on the two islands (and the waters surrounding them) evolved from a single common ancestor.  The Cognitians themselves descended from a single ancestor (the Proto-Cognitian) who was herself born of an earlier species of beings (the Pre-Proto-Cognitians or Precognitians).  All Cognitians were born on either Prima or Segunda and none has ever ventured beyond them. 

The theory of natural selection has application beyond speciation and biological morphology, it can describe cultural and social institutions as well.  Take for example, the Roy Rogers restaurant chain.  Their fixin's bar is one of the great achievements of American fast food.  At one time, there were some 650 locations primarily in the mid-Atlantic region of the east coast.  Today, there are 52.  Almost half are located in a kind of commercial archipelago--the expressway service area.  Just as marsupials in Australia (the island continent) were shielded from the rise of placental mammals by the oceans, so Roy Rogers have only been able to survive in an economic niche.

Part Two: The Present

In our causally deterministic universe, all time can be divided into three categories: the unitary past, the unitary present and the unitary future.  The present is the most interesting of the three.  All moments spend some time as the past and future, but only one moment as the present.  J. M. E. McTaggart proposed this view of time as the A-Series theory of time (as opposed to the B-Series which breaks time into two categories: the past and present).

Part One: The Past

IF we live in a casually deterministic universe, then everything in the past that gave rise to the present really existed.  The past must be perfectly preserved as a record of what has come before the present.  Every event, all objects and all energy were actually there when the present swept past them.  In an infinitesimally small moment, the then-present became a part of history stored in a subsequent present in an ongoing process.  Our memories appear to mimic this process--imperfectly.  We live in the present, as does the universe.  We recall the past, as the universe does.  And we predict the future, which the universe also appears to do.

What is the Present?  The apparent motion of time in one direction, apart from an apparent asymmetry, leads us to the obvious question of how do we describe the past, present and future in a meaningful way.  Do these different "times" actually exist as separate things or are they an illusion created by our minds.  The best evidence is that the present does exist as an independent physical entity.  It must, otherwise there would be no way for our our minds to differentiate between it and other times. 

But if it does, what is it?  It is the forward edge of the time component of space-time.  It contains a perfect record of all past and present events and objects and it constructs the future based on that record.  In that sense, the future, while determinable by the present, does not actually exist until it becomes part of the present and then part of the past.

UPDATE October 14, 2009: In honor of his 200th birthday, a "missing link" of flying dinosaurs, which filled in a gap, millions of years long, between the earliest, primitive pterosaurs and those that followed has been named after him.  The gap was known in Darwin's time and the features of Darwinopterus reveal much about how these creatures evolved.