Some plant and animal hybrids survive environmental threats better than their purebred parents. Here's why:
Blight Resistant Hybrid May Save American Chestnut
Plant biologists have created a strain of American chestnut trees Fagaceae (Castanea dentata) resistant to blight. Scientist have introduced Chinese Chestnut (Castanea mollissima) genes into American Chestnut Trees. While the first generation of progeny is 50% Chinese Chestnut, subsequent breeding reduces the percentage of Chinese genes to 1/16. The result is not the original American Chestnut Tree, but a hybrid that is over 90% American chestnut.
It has taken the American Chestnut Foundation over 20 years to create this blight resistant strain. By 2010, there should be enough hybrid chestnuts to start planting tests in national forests. This new hybrid is welcome news for fans of the majestic American Chestnut.
Between 1904 and 1950, Chestnut Blight Fungus (Cryphonectria parasitica) originating from Japanese and Chinese chestnut trees in the New York Botanical Gardens and Bronx Zoo killed 3.5 billion American Chestnut trees. Centuries old forests were decimated. Stumps were all that remained of immense trunks, four feet across, and sky scraping foliage reaching 120 feet (36.5 metres.)
This achievement also illustrates an important fact: Plant hybrids often have genetic advantages over their parents.
Hybrid Finches More Viable Too
Hybridization creates viable offspring in the animal kingdom too.
Perhaps the most famous example of hybridization is seen in the so-called Darwin's finches of the Galapagos Islands and Cocus Island off the coast of South America.
These fourteen species differ from each other primarily in the shapes of their beaks and their mating rituals. They are thought to have descended from a common ancestor that arrived from the mainland of South America centuries ago. Darwin's finches have often been touted as evidence of Darwin’s theory of natural selection.
But there is evidence that these species are not becoming more distinct. In fact, they may actually be merging.
At least half of the finch species on the Galapagos Islands have been observed to produce hybrids. These hybrids thrive and reproduce even better than their parents.
Even purebred finches show evidence that they are not evolving as Darwin's theory predicts. During their extensive study of finches on the Island of Daphne Major in the Galapagos, biologists Peter and Rosemary Grant did observe changes in finch morphology.
After a drought in the 1970s, survivors had beaks that were on average 5% deeper than those of the birds that perished. It appeared that the finches were giving a live demonstration of Darwin's theory of natural selection.
But the performance was short-lived.
When wetter El Nino conditions returned in the 1980s, food supply increased, and the average depth of finch beaks returned to what existed prior to the drought. Peter Grant stated in 1991 that "the population, selected to natural selection, is oscillating back and forth." Not only are the species not showing any trend toward increasing differentiation, genetic sharing continues between species of Darwin's finches.
As Jonathan Wells, Senior Fellow at the Discovery Institute , writes in Icons of Evolution: Science or Myth?, "It remains a theoretical possibility that various species of Galapagos finches originated through natural selection. But the Grants’ observations provided no direct evidence of this. And in the course of their work, they discovered that several species of Darwin's finches may now be merging rather than diverging."
Hybrids With Genetic Advantages A Problem for Darwinian Theory
Darwin's theory of natural selection requires offspring to diverge from a common ancestor to create new species. It requires genetic differences to increase, as descendants adapt to their environmental niches.
It is this "natural selection" and "adaptation" that creates species over time. And, as the newly created species continue to adapt, they should become more different over time. Following this line of thought, hybrids should be less viable than their parents.
Not only is there evidence that natural selection oscillates over time, but some hybrids, in both plant and animal kingdoms, are better suited to their environments than their parents.
In the case of Darwin's finches, even the "purebred" finch populations show little tendency to sustain changes in size or shape of their beaks over the long term. This scenario is exactly what Darwinian theory doesn't predict.