Comes word that another one of the pillars of Darwin's theory is being quietly buried by investigators convinced that the evidence is against it. I say "another one" because it was only recently that a conference was held to essentially eulogize the demise of natural selection as a major player in evolutionary change. Now it turns out the whole idea of a progression of development from simple forms to more complex, a progression Darwin illustrated by a "tree of life," is being called into question.
It's beginning to appear that the relationships between living things have the appearance more of a web than of a tree. If this is so, what are the implications for evolutionary theory? Perhaps one is that the concept of distinct species is becoming even more difficult to define than it was previously. Here's an excerpt from the link:
Some researchers are also convinced that hybridisation has been a major driving force in animal evolution and that the process is ongoing. "It is really common," says James Mallet, an evolutionary biologist at University College London. "Ten per cent of all animals regularly hybridise with other species." This is especially true in rapidly evolving lineages with lots of recently diverged species - including our own. There is evidence that early modern humans hybridised with our extinct relatives, such as Homo erectus and the Neanderthals.
If early man could interbreed with H. erectus and Neanderthals then what is the basis for treating these as separate species from H. sapiens? A species just is a population of organisms which can interbreed and produce fertile offspring. H. erectus and Neanderthals may have looked different than H. sapiens, but that doesn't make them different species. The dozens of breeds of dogs all look very different from each other, but they're all the same species.
[I]t is clear that the Darwinian tree is no longer an adequate description of how evolution in general works. "If you don't have a tree of life, what does it mean for evolutionary biology?" asks Bapteste. "At first it's very scary... but in the past couple of years people have begun to free their minds." Both he and Doolittle are at pains to stress that downgrading the tree of life doesn't mean that the theory of evolution is wrong - just that evolution is not as tidy as we would like to believe. Some evolutionary relationships are tree-like; many others are not. "We should relax a bit on this," says Doolittle. "We understand evolution pretty well - it's just that it is more complex than Darwin imagined. The tree isn't the only pattern."
In fact, it's not even the main pattern which means that the grand story of Darwinism - molecules to man progression - a story that had been supported by molecular studies that once showed similarities and thus relationships between the proteins of certain organisms, is now obsolete. More recent studies reveal a more chaotic interplay of genetic relationships. Thus:
Others, however, don't think it is time to relax. Instead, they see the uprooting of the tree of life as the start of something bigger. "It's part of a revolutionary change in biology," says Dupr�. "Our standard model of evolution is under enormous pressure. We're clearly going to see evolution as much more about mergers and collaboration than change within isolated lineages."
Rose goes even further. "The tree of life is being politely buried, we all know that," he says. "What's less accepted is that our whole fundamental view of biology needs to change." Biology is vastly more complex than we thought, he says, and facing up to this complexity will be as scary as the conceptual upheavals physicists had to take on board in the early 20th century.
If he is right, the tree concept could become biology's equivalent of Newtonian mechanics: revolutionary and hugely successful in its time, but ultimately too simplistic to deal with the messy real world. "The tree of life was useful," says Bapteste. "It helped us to understand that evolution was real. But now we know more about evolution, it's time to move on."
This is certainly ironic. Most of the arguments people like Darwin and others made to persuade us that macroevolution (molecules to man evolution)occured are being discarded, replaced by other arguments which may eventually suffer the same fate. Yet the truth of macroevolution is not to be questioned:
Syvanen recently compared 2000 genes that are common to humans, frogs, sea squirts, sea urchins, fruit flies and nematodes. In theory, he should have been able to use the gene sequences to construct an evolutionary tree showing the relationships between the six animals.
He failed. The problem was that different genes told contradictory evolutionary stories. This was especially true of sea-squirt genes.
Conventionally, sea squirts - also known as tunicates - are lumped together with frogs, humans and other vertebrates in the phylum Chordata, but the genes were sending mixed signals. Some genes did indeed cluster within the chordates, but others indicated that tunicates should be placed with sea urchins, which aren't chordates. "Roughly 50 per cent of its genes have one evolutionary history and 50 per cent another," Syvanen says.
In other words, all those studies which showed close relationships between different taxa based on genetic similarities and differences are rendered useless by these findings. The famous comparison of humans to chimps based on so much shared genetic material really means little in terms of actual evolutionary relationships.
If the idea of a tree of life is obsolete then the idea of descent through modification will have to be reassessed as will the idea that some organisms are more "primitive," both in time and in structure, than others. This is why the scientists quoted above talk in terms of a "revolution" in biology. Much that was thought to be true is being turned inside out, and it will almost be as if biologists will have to start all over again to piece together their story of how life got to where it is today.RLC