Time and Change by John Burroughs — Read

Bergson, the new French philosopher, thinks we all had a narrow escape, back in geologic time, of having our eggs spoiled before they were hatched, or, rather, rendered incapable of hatching by too thick a shell. This was owing to the voracity of the early organisms. As they became more and more mobile, they began to take on thick armors and breastplates and shells and calcareous skins to protect themselves from one another. This tendency resulted, he thinks, in the arrest of the entire animal world in its evolution toward higher and higher forms. These shells and armors begat a kind of torpor and immobility which has continued down to our day with the echinoderms and mollusks, but the arthropods and vertebrates escaped it by some lucky stroke. Now you and I are here without imprisoning shells on our backs; but how or why did we escape? Bergson does not say. Was it a matter of luck or chance? Was there ever a time when the stream of life tended to harden and become fixed in its own forms like a stream of cooling lava, or has the innate plasticity of life been easily equal to its own ends? True, the clam remains a clam, and the starfish remains a starfish; some other forms have carried the evolutionary impulse forward till it flowered in man. Was this impulse ever really checked or endangered? Was the golden secret ever intrusted to the keeping of any single form? and, had that form been cut off, would the earth have been still without its man? These are puzzling questions.

Thus, when we have come to look upon life and nature in the light of evolution, what vistas are opened to us where before were only blank walls! The geologic ages take on a new interest to us. We know that in some form we were even there. The systems of sedimentary rocks which the geologist portrays, piled one upon the other to a depth of fifty miles or more, seem like the stairway by which we have ascended, taking on some new and more developed form at each rise. What we were at the first step in Cambrian times only the Lord knows, but whatever we were, we crept up or floated up to the next rise. In the Silurian seas we may have been a trilobite for aught we know; at any rate, we were the outcome of the life impulse that begat the trilobites, but our fate was not bound up with theirs, as their race came to an end in those early geologic ages, and our stem form did not. Whether or not we were a fish in the Devonian seas, there is little doubt that we had gills, because we have the gill slits yet in our early foetal life, and it is quite certain that in some way we owe our backbones to the fishes.