Evolution of Evolution — Text-only | Flash Special Report
Evolution: Past, Present and Future
Scientific knowledge may permit humans to guide future evolution
By Richard Lenski
Most of us think about evolution in the past tense. After all, we were first exposed to the concept of evolution when we saw dinosaurs and other fossils at museums. But evolution has not stopped; it is an on-going process. Charles Darwin emphasized this point when he closed On the Origin of Species by saying: “… from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.”
With patience and skill, one can even watch evolution in action in some organisms. Peter and Rosemary Grant have spent decades in the Galápagos Islands observing the evolution of beak shape in certain birds, known as Darwin’s finches, in response to changes in seed availability caused by a fluctuating climate and competition. Microbiologists, too, observe evolution in action, including bacteria that become resistant to antibiotics.
Because bacteria reproduce so quickly, we use them in experiments to test evolutionary hypotheses. For over 20 years and 45,000 bacterial generations, my students and I have maintained twelve populations of E. coli in small flasks of sugar water. We measure the process that Darwin discovered – adaptation by natural selection – by competing ‘modern’ bacteria against their ancestors, which we store frozen and then revive for the tests. Imagine if we could bring Homo erectus back to life, and challenge them to games of football and chess! In our flasks, the modern bacteria outscore their ancestors in the struggle for existence.
You might wonder if the twelve lineages improved in the same or in different ways. Just how repeatable would evolution be if, in the metaphor of Stephen Jay Gould, we could replay the tape of life? On the one hand, mutations are random, so the lineages would tend to diverge. On the other hand, selection would favor the same adaptations because they live in identical environments. We have seen many cases of parallel evolution. The individual cells in all twelve lineages are larger than their ancestors, and all are more efficient at using the glucose in the culture medium we grow them in. Also, all twelve lines have similar mutations in several genes. In other ways, however, they have diverged, including a striking case where a single lineage evolved the ability to consume citrate, another source of energy in the medium, but one the ancestors could not exploit. In fact, a characteristic feature of E. coli as a species is that it cannot grow on citrate. We are now investigating the series of mutations that enabled this transcendent change.
What does evolution hold for the future? First, we humans have changed landscapes and climates, causing some species to go extinct, allowing others to colonize new habitats, and altering the selective pressures on those that survive. We have left a profound mark on the future evolution of life. Second, the increased density and mobility of our species provides new opportunities for pathogens to gain a foothold and evolve to exploit us. We ignore evolution at our peril. Third, we humans have acquired the scientific knowledge and technological tools to guide evolution in potentially useful ways. Researchers today can combine genes from distantly related species that cannot interbreed, synthesize genes that have never existed in nature, and evolve molecules in novel contexts. Moreover, and remarkably, the processes that allow evolution have been transported from nature into artificial realms. Self-replication, mutation, recombination and competition have been introduced into computer programs – ‘digital organisms’ – that can then evolve to solve computational problems. Similar approaches allow electronic circuits and even robots to evolve complex and interesting functions.
Darwin would be amazed to see where his ideas have led. Not only do we understand the history of life on Earth and the mechanisms of evolution far better than anyone in his day, we can directly observe the process of evolution and harness its power toward new ends.
Richard Lenski is the Hannah Distinguished Professor of Microbial Ecology at Michigan State University. His research attracts world-wide recognition and focuses on the genetic mechanisms and ecological processes that drive evolutionary change. Lenski is a Member of the National Academy of Sciences and a Fellow of the American Academy of Arts and Sciences. The National Science Foundation supports his long-term evolution experiment with E. coli.
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