subject: Landward Crept The Pioneers [print this page] In the Upper Cambrian mollusks were abundant, and a few well-developed and going snails were living in the Lower Cambrian-five hundred million years back. Now look at our snail with renewed respect; his ancestors with shell, muscles, movement and life closely similar to his, were alive when the earth itself was only three-quarters evolved. We are reasonably certain that the higher evolution had little impetus in the deep sea; conditions there were too stable and unchanging, competition was hardly felt: not until the hard rock and the shifting sands of the shore were encountered, the crash and drag of waves, the submersion and exposure of varying tides, enemies in pool and air- these demanded change, adaptation, extermination, and progress.
As yet we know nothing definitely about the very early ancestors of our snail, but, as we have seen, even in the early eons of the sea he had achieved a shell, and when he crawled shoreward and out upon primeval mud-flats, it was as if he dragged with him a bit of the unchanging deeps. As long as food was at hand and no danger threatened he crept slowly along, peering safely from a narrow crevice between earth and shell, and at the first hint of trouble withdrew within his mineral castle. Such a procedure made for individual safety, but cramped the style of progress.
In the course of time the architecture might vary-spines and pillars, furrows and cones might be added, pigment of the whole spectrum, a hutlike home which was its own door, or an elaborate hinged entrance; a mere flattened scale or an embossed superstructure of jointed armor-to such unimportant lengths of variation, but no farther, might a mollusk go without endangering precedent.
No wonder we find these creatures dominant as fossils-when in life they are little else, born in a ready-made, rocky sarcophagus, with interior decoration and reinforced concrete construction as their chief indoor sports throughout life. With the slogan of "eternally conservative" the ancient snails spread along all the shores of the sea, clambering to the furthest spray of high tide. While they were content to munch old fragments of algae and cringe to all the cosmos, their neighbors fought and died, and through their changed offspring lived again.
Landward crept the pioneers, fish, crabs, worms, and even lowly single-cellers, all changing, altering every portion of their beings to meet and cope with the new conditions. And along with this host quietly glided the same old snails, outstripping their other neighbors of the dawn of life-sponges, jelly-fish, and sea-urchins-which were fated forever to remain prisoners of the denser medium, and hastening in the foot-steps of their betters.
