Plant Evolution: Wheres the Root?
To Darwin, the origin of flowering plants was an “abominable mystery.” Recently, some entries on Science magazine’s blog Origins have claimed the mystery has been solved, at least partially, and a full solution is near at hand. Here is a great test case for evolution. Angiosperms comprise a huge, diverse population of organisms. There should be an ample fossil record, and many genes to decipher. Let’s see if the optimistic claims are rooted in evidence.
- Beginning to make sense: Elizabeth Pennisi wrote for the April 2 blog entry that recent discoveries are “beginning to make sense” of the fossil record of plants, and evolutionists are finding out “how, and when, flowers got started—and from which ancestor.” The blog entry is a summary of her lengthier essay in Science.1 In the short version, Pennisi concluded with a taste of doubt: “Questions still remain, particularly about the nature and identity of the angiosperm ancestor itself,” she said. But hope reigns eternal after 150 years: “modern botanists are hopeful that the abominable mystery is well on its way to being solved.”
- Good news, bad news: In the lengthier article,1 Pennisi began with a praise for the fantastic angiosperm family that so colors our world. Almost 9 in 10 plants are angiosperms. They do a world of good:
In 1879, Charles Darwin penned a letter to British botanist Joseph Dalton Hooker, lamenting an “abominable mystery” that threw a wrench into his theory of evolution: How did flowering plants diversify and spread so rapidly across the globe? From rice paddies to orange groves, alpine meadows to formal gardens, prairies to oak-hickory forests, the 300,000 species of angiosperms alive today shape most terrestrial landscapes and much of human life and culture. Their blooms color and scent our world; their fruits, roots, and seeds feed us; and their biomass provides clothing, building materials, and fuel.
Then came the hard news:
And yet this takeover, which took place about 100 million years ago, apparently happened in a blink of geological time, just a few tens of millions of years.
The father of evolution couldn’t quite fathom it. Darwin had an “abhorrence that evolution could be both rapid and potentially even saltational,” writes William Friedman in the January American Journal of Botany, which is devoted to this “abominable mystery.” Throughout his life, Darwin pestered botanists for their thoughts on the matter, but they couldn’t give him much help.
Now, 130 years later, evolutionary biologists are still pestering botanists for clues about what has made this plant group so successful, as well as when, where, and how flowers got started–and from which ancestor….
How can Pennisi bounce back to optimism after that? She did. She claims new analytical tools, more fossils, and genomic data are converging on the answer, providing “insights that Darwin could never have imagined,” diluting the abominality quotient of his mystery. After this buildup of hope, though, better prepare for another letdown.
But one of Darwin’s mysteries remains: the nature and identity of the angiosperm ancestor itself. When flowering plants show up in the fossil record, they appear with a bang, with no obvious series of intermediates, as Darwin noted. Researchers still don’t know which seed- and pollen-bearing organs eventually evolved into the comparable flower parts. “We’re a bit mystified,” says botanist Michael Donoghue of Yale University. “It doesn’t appear that we can locate a close relative of the flowering plants.”
It seems the major abominations remain: no ancestor, and no intermediates. How can Pennisi call this progress? She investigated some candidate ancestors: magnolias, Amborella trichopoda, water lilies, and Archaefructus (05/03/2002, 02/21/2003). Each of these, however, had the basic flower-and-seed equipment down. The only differences were in petals, sepals, and subjective judgments about morphology, such as one species said to have “a primitive look about it.” And, woe for Archaefructus, it turned out to be too young to be grandpa. For all the candidates, “These fossils often spark debate because specimens tend to be imperfectly preserved and leave room for interpretation,” she said. But new techniques with synchrotron radiation are at least bringing the ambiguity into better focus.
The rest of the article presented more problems. No one has found the oldest flowers. No one can connect the gymnosperms (including conifers) with the angiosperms. Even when they try, “These groups’ perceived relevance to flower evolution and their relationships to angiosperms have ping-ponged between camps, depending on how the evolutionary trees were constructed.” Theories have waxed and waned in credibility. An evolutionary botanist admitted, “figuring out what’s homologous is quite a difficult thing.” A popular “anthophyte hypothesis” from the mid-1980s is dead. Prepare for more letdown:
And if the molecular work is correct, then the field doesn’t know in which direction to turn, because in most analyses the genetic data don’t place any living plant close to angiosperms. The angiosperms group together, the living gymnosperms group together, and there’s nothing in between. “The nonangiosperm ancestor just isn’t there,” says paleobotanist William Crepet of Cornell. “I’m starting to worry that we will never know, that it transformed without intermediates.”
Since that is tantamount to believing a miracle occurred, Pennisi didn’t want to linger on that comment. Her next paragraph turned a corner with a triumphant-sounding subheading, “Seeds of Success.” More bad news, though, was right behind it. “The exact timing of the angiosperms’ explosion and expansion is under debate, as is the cause,” she continued. The news has only gotten worse. Recent molecular clock studies push the angiosperm ancestor even farther back in time. “There appears to be a gap in the fossil record,” said one researcher. An astute observation, indeed. Bang: they appear, and bang: they diversify. Better call daddy again: “Darwin suspected that coevolution with insect pollinators helped drive diversification, though such a causal relationship is not settled.”
So far Pennisi has not presented one solid foundation for optimism. Genes didn’t help. Fossils didn’t help. Homology didn’t help. The molecular clock didn’t help. Why not just assume evolution? That would get the uncooperative data out of the way. Maybe plants were just really darn good at inventing things, the evolutionists might say. Angiosperms evolved because they evolved flexibility that could exploit new ecological niches. This “set them up for long-term evolutionary success,” Pennisi explained. She quoted Peter Crane (U of Chicago), who said, “My own view is that in the past, we have looked for one feature,”says Crane. Now, “we are realizing that this huge diversity is probably the result of one innovation piled on top of another innovation.” Assume evolution. Then evolution just happens.
The rest of the article offered nothing more of substance. A few more suggestions were offered as tentative, heuristic possibilities. Evolutionists have found that the genetic toolkit is conserved [i.e., unevolved] all the way back. Maybe there were differences in how genes were employed. Avocados, for instance, appear sloppy at differentiating between petals and carpels. Is this a sign of a less-evolved plant structure? “This sloppiness may have made development flexible enough to undergo many small changes in expression patterns and functions that helped yield the great diversity in floral forms,” she said, as if running an idea up the flagpole to see if anyone salutes.
This was the lengthiest article on angiosperm evolution this month, but it consisted of pessimism sandwiched between optimistic hope. After 29 paragraphs of despair, the only thing left was faith, hope, and love for Darwin.
In his letter to Hooker, Darwin wrote that he would like “to see this whole problem solved.” A decade ago, Crepet thought Darwin would have gotten his wish by now. That hasn’t happened, but [William] Crepet [Cornell] is optimistic that he and his colleagues are on the right track, as analyses of various kinds of data become more sophisticated. “We are less likely to go around in circles in the next 10 years,” he says. “I believe a solution to the problem is within reach…. The mystery is solvable.”
- Pennisi update: A week later, Pennisi wrote a blog entry in Origins announcing that land plant genes have been found in green algae. This pre-announced the Micromonas genome story reported here 04/13/2009. Any support here for angiosperm evolution? No; “No bigger than a bacterium, these minuscule marine eukaryotes have surprisingly sophisticated genomes,” she said. Problem: this early, “primitive” algae contains genes only found previously in leafy plants. Those supposedly evolved hundreds of millions of years later:
Overall, the Micromonas genome is about 21 million bases long, with 10,000 genes, 2000 more than its much more streamlined relative, Ostreococcus, which has already been sequenced, twice. About 20% of the genes found in Micromonas but not in Ostreococcus are genes generally thought to have evolved only in land plants, not earlier, her team reports. For example, the team finds that Micromonas has a gene called YABBY, which is missing from other green algae and even moss, and is thought to be related to the development of leafy plants. Given that leaves don’t exist in these algae, she thinks YABBY must have played another role early in green eukaryotic evolution.
- Make like a leaf: The April 15 entry by David Dilcher in the Origins blog took another angle. Many of the plant fossils thought to have living counterparts may actually be extinct species. Improved microscopic techniques are leading some paleontologists to discount the similarity of fossil plants to extant species, even though the macroscopic similarities are striking. It’s not clear how this helps the story of angiosperm evolution, but Dilcher repeated the Darwin-Hooker story to set the stage. Darwin’s oft-quoted “abominable mystery” phrase “represents Darwin’s frustration with the paleobotanical record of his time.” How are things now?
“With the study of detailed leaf venation and leaf epidermal cell characters, it is clear that many of the earliest flowering plants represent extinct species, extinct genera, extinct families, and perhaps even extinct orders,” he said, referring to a paper of his from 1974. “This paradigm change has caused a revolution in the study of fossil flowering plants which only in the past 40 years has begun to present a realistic record of extinct flowering plants.” Realism is always nice to have in science. Presumably it went missing till the 1970s. But does the new wave of realism shed light on the abominable mystery of flowering plants? Dilcher offered a paradigm shift that might give Darwin something to smile about (for a change):
The success of early paleobotanists depended upon making such matches. It has taken a philosophical shift in angiosperm paleobotany in order for researchers today to strive to understand relationships between fossil and living plants, based upon detailed characters, rather than feeling the need to find a living genus to which they can name a fossil. Using character analyses, we now have an emerging new fossil record of flowering plants with many extinct taxa that would have delighted Darwin. This new record is one he could have understood because it demonstrates the evolution of flowering plants, a major group of organisms on Earth. We do not yet know all the details, but there is no longer any “abominable mystery” to the origin of flowering plants.
Let’s attempt to restate this argument. Look-alike plants from the past may have gone extinct. Now we have new look-alike plants. All of them, old and new, have the whole angiosperm package and appear virtually indistinguishable to the untrained eye. Dilcher didn’t mention any ancestors, or any transitional forms. It seems Darwin’s delight at this suggestion would be short-lived.
Let’s back up to an earlier epoch and see if evolution does better there. The first land plants are thought to have colonized land in the mid-Ordovician, but trilete spores, characteristic of vascular plants, appear in the late Silurian. In today’s issue of Science,2 Steemans et al announced their discovery of trilete spores from the late Ordovician. This “suggests that vascular plants originated and diversified earlier than previously hypothesized, in Gondwana, before migrating elsewhere and secondarily diversifying.” Placing complex structures earlier in the fossil record does little to help evolutionary theory, because it compresses the time for innovation. Notably, they did not discuss how their find helps evolutionary theory. They hardly discussed evolutionary theory at all. (Compare a similar story with fossil fish from 03/26/2009.)
1. Elisabeth Pennisi, “On the Origin of Flowering Plants,” Science, 3 April 2009: Vol. 324. no. 5923, pp. 28-31, DOI: 10.1126/science.324.5923.28.
2. Steemans et al, “Origin and Radiation of the Earliest Vascular Land Plants,” Science, 17 April 2009: Vol. 324. no. 5925, p. 353, DOI: 10.1126/science.1169659.
Not every reader will want all this tedious detail, but it’s important for showing how the Darwinist tricksters ply their propaganda. Lack of data has been shielded behind hope: hope in hopeful monsters, like gymnosperm seeds that sprout flowers, and bryophyte spores that sprout vascular systems. The story is full of miracles (“innovation piled on top of another innovation”) ad infinitum, as if by magic. They rub their Darwin genie and wish for ancestors and transitional forms that never appear. They curse the abominable mysteries under their breath, smiling to the media they are really close to solving them. The only abominable mystery is evolutionary faith. The only hope-full monsters are the Darwinians.