Similar leaf types evolved independently in three species of plants found in cloud forests of Oaxaca, Mexico and three species of plants in similar environment in Chiapas, Mexico. This example of parallel evolution is one of several found by Yale-led scientists and suggests that evolution may be predictable.
The problem is that the environment, which is the underlying driver of evolution, is itself subject to unpredictable changes and the operation of chaos, where a small change here or there can have a large effect some way down the line - the proverbial butterfly effect where a butterfly flapping its wings on a Pacific island can result in a hurricane in the Himalayas. Small, randon fluctuations in weather patterns or ocean currents can have widespread effects on the distribution of different species in food chains, for example.
This piece of research, although interesting in that it shows the effect of the environment as a driver of evolution, doesn't really answer that question because it shows what can happen when the environment is a constant. This is, of course, the prerequisite for convergent evolution, where, not surprisingly, from a similar starting point, in a given environment, evolutions tends to home in on the same phenotypic solutions, albeit by different genetic routes.
As explained in a Yale News article by Bill Hathaway:
Evolution has long been viewed as a rather random process, with the traits of species shaped by chance mutations and environmental events — and therefore largely unpredictable.Incidentally, note the readiness of Professor Donoghue to admit he was wrong in the 1970s and the willingness to change his mind in the light of new information. This is one of the things that gives science it great power to move ever closer to the truth, in contrast to religions, where discoveries that contradict 'faith' have to be ignored or dismissed, and preferably not even looked for in the first place.
But an international team of scientists led by researchers from Yale University and Columbia University has found that a particular plant lineage independently evolved three similar leaf types over and over again in mountainous regions scattered throughout the neotropics.
The findings provided the first examples in plants of a phenomenon known as “replicated radiation,” in which similar forms evolve repeatedly within different regions, suggesting that evolution is not always such a random process but can be predicted.
The study is published July 18 in the journal Nature Ecology & Evolution.
For the study, the research team studied the genetics and morphology of the plant lineage Viburnum, a genus of flowering plants that began to spread south from Mexico into Central and South America some 10 million years ago. Donoghue studied this same plant group for his Ph.D. dissertation at Harvard 40 years ago. At the time, he argued in favor of an alternative theory in which large, hair-covered leaves and small smooth leaves evolved early in the evolution of the group and then both forms migrated separately, being dispersed by birds, through the various mountain ranges.The findings demonstrate how predictable evolution can actually be, with organismal development and natural selection combining to produce the same forms again and again under certain circumstances
Maybe evolutionary biology can become much more of a predictive science than we ever imagined in the past.
I came to the wrong conclusion because I lacked the relevant genomic data back in the 1970s.
Professor Michael Donoghue, lead author and co-corresponding author
Sterling Professor Emeritus of Ecology & Evolutionary Biology.
Department of Ecology and Evolutionary Biology
Yale University, New Haven, CT, USA
The new genetic analyses reported in the paper, however, show that the two different leaf types evolved independently, in parallel, in each of a number of mountain regions.
These plants arrived in Bolivia less than a million years ago, so we predict that the large, hairy leaf form will eventually evolve in Bolivia as well.
The team found that a very similar set of leaf types evolved in nine of 11 regions studied. However, the full array of leaf types may have yet to evolve in places where Viburnum has only more recently migrated. For instance, the mountains of Bolivia lack the large hairy leaf types found in other wetter areas with little sunshine in the cloud forest in Mexico, Central America, and northern South America.This collaborative work, spanning decades, has revealed a wonderful new system to study evolutionary adaptation. Now that we have established the pattern, our next challenges are to better understand the functional significance of these leaf types and the underlying genetic architecture that enables their repeated emergence.
Professor Ericka Edwards, co-corresponding author
Professor of ecology and evolutionary biology
Department of Ecology and Evolutionary Biology
Yale University, New Haven, CT, USA
Several examples of replicated radiation have been found in animals, such as Anolis lizards in the Caribbean. In that case, the same set of body forms, or “ectomorphs,” evolved independently on several different islands. With a plant example now in hand, evolutionary biologists will try to discover the general circumstances under which solid predictions can be made about evolutionary trajectories.
Sadly the paper in Nature, Ecology & Evolution is behind a paywall, but the abstract is available here.
What the research illustrates is how evolution, far from being a random process, is directed by the environment, so organisms come to look superficially as though they were designed to live in that environment. It also shows, that, with long periods a environmental stability, there is nothing to cause evolutionary change, so evolution progresses at different rates depending on how and when the environment changes.
The problem the planet is facing at the moment is that global warming is a profound environmental change occurring across all environments, that is happening at a rate many times faster than the slow, accumulative process of evolution can keep up with, so very few species will be able to evolve quickly enough to adapt to it.
Earth is not fine-tuned for life; life is fine-tuned for Earth.
Evolution is what keeps it in tune.
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Evolution is what keeps it in tune.
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