SUMMARY

This sixth, BIOLOGICAL EPOCH has outlined the salient features of life and its meandering drift through ages so long as to be measured in millions of millennia. For the first few billion years it remained starkly unicellular, resembling the simple blue-green algae found today in lakes, streams, and wetlands everywhere on Earth. Eventually, ~1 billion years ago, some cells began clustering into groups, coordinating their activities, and thus becoming multicellular organisms. Not long thereafter, the fossil record documents what must have been a virtual explosion in the number and diversity of species.

Change was rampant as life forms multiplied and speciated rapidly. Legions of fish swam in the seas little more than 0.5 billion years ago. Plants came ashore ~400 million years ago and amphibians quickly thereafter, doubtless in search of food. Early animals mastered the land ~200 million years ago, while birds, mammals, and flowers flourished for not quite half that time. By contrast, hominids—the subject of the seventh, CULTURAL EPOCH—have endured for only the past few million years, a span so brief that if we were to imagine all of cosmic history compressed into a single year, then earthly humans would have existed for only the past hour or so. In this analogy, our specific species, Homo sapiens, would not have emerged until some ten minutes ago.

Darwin was basically right. The fossil record leaves little doubt that biological evolution by natural selection has occurred and is continuing. The rate at which evolution works, however, remains unresolved, as does the possibility that other mechanisms of change are also operative in Nature. Cosmic rays, chemical drugs, intense radiation, or just plain DNA copying errors enable mutations to accelerate the motor of evolution, altering life’s genetic structure and causing some organisms to adapt to new niches in ever-changing environments. In thermodynamic terms, microbes, plants, and animals evolve far-from-equilibrium systems with combinations of properties that are unpredictable in detail. But the outcome isn’t all chance, for evolution does have a deterministic component as well; natural selection prunes, edits, and decides who is optimally fit for a given set of environmental conditions, and it non-randomly eliminates the rest. Changes, most notably selection and adaptation to those changes, are the keys to the genesis—and destiny—of all living things.

Admittedly, gaps in the fossil record currently hinder a complete understanding of life’s history, just as missing links hamper our present knowledge of galaxies, stars, and planets. It’s not easy squeezing evidence from stones and, in any case, genome mapping is now filling in the fossil gaps. To be sure, each day brings new ideas, new tests, new discoveries, and further refinement of our modern conception of biological evolution. And with these advances come greater objectivity, and progress too, while searching the sands of time to decipher erstwhile reality.

The BIOLOGICAL EPOCH has sketched the traditional view of evolution, namely, Darwinian evolution via natural selection. Yet, life is but a small, albeit important, part of the grander cosmic-evolutionary worldview. This Web site suggests that evolution, universally considered, pertains to much more than mere life on Earth. The word “evolution” has been intentionally used in a broad, provocative way, attempting to capture the process of change on all spatial and temporal scales by means surely including, but not restricted to, biological Darwinism. Within the expansive, all-inclusive scenario of cosmic evolution, general trends are identifiable among Nature’s myriad, persistent changes over the course of an impressively long span of deep natural history, from the origin of time to intelligent life on Earth. In the next CULTURAL EPOCH, we shall extend the narrative to include our technological selves, for humankind, too, is most assuredly part of this unfolding and unifying epic-class story.

FOR FURTHER READING

Conway Morris, S., The Crucible of Creation, 1998, Oxford University Press, Oxford.

Carroll, S., Endless Forms Most Beautiful, 2006, W.W.Norton, New York.

Fortey, R., Life, 1998, Knopf, New York.

Gould, S.J., Wonderful Life, 1989, W.W.Norton, New York.

Knoll, A., Life on a Young Planet, 2003, Princeton University Press, Princeton.

Margulis, L. and Sagan, D., What is Life?, 1995, Univ. of Calif., Berkeley.

Mayr, E., This is Biology, 1997, Harvard University Press, Cambridge.

Mayr, E., What Evolution Is, 2001, Basic Books, New York.

Schopf, J.W., Major Events in the History of Life, 1992, Jones and Bartlett, Boston.

Wilson, E.O., The Diversity of Life, 1992, W.W.Norton, New York.

FURTHER WEB SITES

Biological Evolution:
http://evolution.berkeley.edu

Genetics Primer:
http://www.genome.gov/Pages/EducationKit

Paleonotology Network:
http://www.paleontologynetwork.com

Map of Life:
http://www.mapoflife.org


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