Charles Darwin must have thought the very foundation of his theory of evolution was in danger when he wrote a note to his friend Joseph Hooker in 1879, two decades after publication of his seminal work, "On the Origin of Species." The great scientist was besieged with questions about a problem that had haunted him for years.
The problem was flowers: So many kinds, flourishing in every corner of the earth, ranging from breathtakingly beautiful to simply weird, expanding their reach so rapidly that they seemed to mock natural selection, the cornerstone of his work.
Evolution, he knew, was a very slow process, so slow that it had taken nearly four billion years for life on earth to evolve from microorganisms to towering trees and intelligent life. Yet the fossil record of the mid 19th century told a story that seemed impossible.
The first flowering plants appeared around 130-140 million years ago. Yet it took only about 45 million years -- an incredibly short period of time, geologically speaking -- for flowering plants to dominate the planet, with possibly as many as 400,000 species, far eclipsing the pines and non-flowering trees and bushes that blanketed the landscape during the time of the dinosaurs.
In his letter to Hooker, Darwin famously described the story of flowers as "an abominable mystery." So it remained for the generations of scientists who followed in Darwin's tracks, and the answer today is still not as definitive as many would like. But ever so slowly, clues are emerging as scholars use new tools to help unravel the mystery.
The fossil record is much richer today than it was in Darwin's time, and it tells a different – though still incomplete – story. Flowering plants, or angiosperms, may have emerged much earlier than had been thought. Some experts believe the ancestors of flowering plants were around more than 100 million years before the first flowers appeared, and possibly even longer. And for the most part it was a gradual process, just as Darwin would have expected, with a few stunning exceptions.
Scientists from a wide range of institutions have been delving into the genetic history of flowering plants in the Ancestral Angiosperm Genome Project, based at Pennsylvania State University, and they have found two "major upheavals" leading up to the first appearance of flowers. Penn State's Claude dePamphilis calls them the "'Big Bangs' for flowering plants."
They are known as "polyploidy events," mutations in which an organism gets a double dose of genetic material. The duplication of genes has been documented in vertebrates as well as plants, and it can be fatal, but sometimes it results in an evolutionary advantage. DePamphilis thinks that in these two cases, at least, the duplication launched a "genomic renaissance," enabling the ancestors of flowering plants to evolve new and better functions.
All flowering plants probably benefited from large-scale duplications of the genome, he has suggested. That genetic diversity may help explain why today we can find flowers in full bloom in areas where common sense would suggest nothing could survive.
Once they were here, they expanded rapidly, aided by the co-evolution of insects that accelerated the spread of genetic material through cross pollination, according to Indiana University botanist David Dilcher. Dilcher has studied the evolution of flowering plants for decades.