Evolution
Downard, James, Secular Global Institute Communicator 7/31/2014
The scientific concept that all life on earth is related by common descent, and has come to be the way it is through natural processes observable today and open to experimental investigation, is one of the major unifying discoveries of human thought. Charles Darwin and Alfred Wallace independently recognized the role natural selection played in this, but even had they never lived, others would have followed to connect the same evidence.
In the century since Darwin and Wallace a mountain of discoveries have built on their initial insight. Paleontologists recovered fossil after fossil of ancient life (such as the vertebrate mammals, birds and dinosaurs) that filled in the blank spaces of Deep Time. In the middle of the 20th century the genetic mechanism of natural inheritance (DNA) was also discovered, and in the decades to follow geneticists and developmental biologists have converged on the deep dynamics of natural variation and evolutionary change.
Every living thing carries the traces of that heritage.
The vital power pack mitochondria in our cells came to us by an “endosymbiotic” cellular fusion among bacteria billions of years ago. A similar merger with the oxygen-producing cyanobacteria produced the chloroplasts found in plants today.
The way we use our jaws to speak and ears to hear developed from an extraordinary repurposing of the bones of the reptile jaw, morphing over millions of years of descent with modification, visible not only in the fossil record, but corroborated by the developmental biology and genetics of all living mammals. Such “exaptations” pervade the history of life.
Closer to home, we have one fewer pair of chromosomes than our primate cousins due to a fusion event that left telltale genetic fossil traces of the old separate pieces (the centromeres and end tag telomeres) buried inside. And sometimes the tiniest of mutations can have momentous effects. Many of us can’t stand eating broccoli because we have inherited the basic primate bitter reaction to some plants (useful to discourage eating anything over ripe). But just as many of us have a single DNA change disabling that function, broadening the human range when it comes to appreciating a leafy green vegetable salad.
In recent years the experimental exploration of our evolutionary history has expanded to the new field of “paleogenomics,” where scientists retro-engineer ancestral biological molecules to test out how the earlier system functioned and enhance our understanding of why the living counterparts operate as they do. The practical utility of such research are improved medical strategies to keep abreast of an ever-evolving natural world.
