Not impressed with the extended evolutionary synthesis
This Guardian article, “Do we need a new theory of evolution? has its moments, but I hated the title and didn’t care at all about the opening. It’s true, scientists don’t know everything, but we know more than the author thinks.
Strange as it may seem, scientists still don’t know the answers to some of the most fundamental questions about the evolution of life on Earth. Take the eyes, for example. Where do they come from, exactly? The usual explanation of how we got these stupendously complex organs relies on the theory of natural selection.
You might remember the gist of biology lessons in school. If a creature with poor eyesight produces offspring with slightly better eyesight, through random mutations, then that tiny bit more vision gives them a better chance of surviving. The longer they survive, the more likely they are to reproduce and pass on the genes that endowed them with slightly better eyesight. Some of their offspring might, in turn, have better eyesight than their parents, making it more likely that they too will reproduce. Etc. Generation after generation, over incredibly long periods of time, tiny benefits add up. Eventually, after a few hundred million years, you have creatures that can see as well as humans, cats, or owls.
It’s the fundamental story of evolution, as told in countless textbooks and best-selling pop science books. The problem, according to a growing number of scientists, is that it is absurdly crude and misleading.
For one thing, it starts in the middle of the story, taking for granted the existence of light-sensitive cells, lenses, and irises, without explaining where they came from in the first place. Nor does it adequately explain how these delicate and easily disturbed components came together to form a single organ. And it’s not just the eyes that mainstream theory struggles with. “The first eye, the first wing, the first placenta. How they emerge. Explaining them is the fundamental motivation of evolutionary biology,” says Armin Moczek, a biologist at Indiana University. “And yet, we still don’t have a good answer. This classic idea of gradual change, one happy accident at a time, has so far fallen flat.
But we don’t take the existence of light-sensitive cells for granted at all! It’s biochemistry. There are organic molecules that can absorb the energy of a photon and undergo a conformational change; there are single-celled organisms capable of recognizing the impact of light and modifying their behavior or biochemistry. We don’t need to explain any gradual change in the properties of biological materials, because that’s just organic physics or chemistry. Is evolutionary biology incomplete if it does not support that physics has evolved? Do we have the right to understand that chemistry existed long before life?
The article spends a lot of time on extended evolutionary synthesis, giving it more credence than it deserves, and plays the drama of the theory of evolution changing, as if it’s not a normal scientific response to new evidence and ideas. Stuff like that doesn’t help.
Then came a devastating series of new findings that challenged the foundations of the theory. These discoveries, which began in the late 1960s, came from molecular biologists. While modern synthesists looked at life as though through a telescope, studying the development of huge populations over huge slices of time, molecular biologists looked through a microscope, focusing on individual molecules. And when they looked, they discovered that natural selection was not the all-powerful force that many had assumed it was.
They discovered that the molecules in our cells – and therefore the gene sequences that underlie them – mutate at a very high rate. This was unexpected, but not necessarily a threat to mainstream evolutionary theory. According to the modern synthesis, even if mutations were to be common, natural selection would, over time, remain the primary cause of change, preserving useful mutations and discarding unnecessary ones. But that’s not what was happening. Genes changed – that is, evolved – but natural selection played no role. Some genetic modifications have been preserved for no reason other than pure chance. Natural selection seemed asleep at the wheel.
Evolutionary biologists were stunned.
“Devastating.” “Dizzy.” No. There is an ongoing debate about the relative importance of various processes, but no one has been emotionally upset by the discovery that evolution is complicated. There are conservative scientists who refuse to budge or even acknowledge the existence of stuff like the neutral theory, but they’re not particularly interesting. On the other side are wacky extremists with their hair on fire screaming that the existence of developmental plasticity means we have to throw it all away. Most scientists see new phenomena and say, “Cool. Now, how does that fit in with that? »
The article refers to a Nature article, “Does the Theory of Evolution Need a Rethink?”, and it takes an odd angle. It only mentions the EES side, but the Nature article had two sides, one answering the question with “YES, URGENTLY”, the other saying “NO, ALL IS WELL”. So the EES side sets everything up just as deeply in opposition to the Standard Evolutionary Theory (SET) side.
In our view, this “gene-centric” focus fails to capture the full range of processes that drive evolution. The missing pieces include how physical development influences the generation of variation (developmental bias); how the environment directly shapes the traits of organisms (plasticity); how organisms modify environments (construction of niches); and how organisms pass on more than genes across generations (extra-genetic inheritance). For SET, these phenomena are only the results of evolution. For SEA, these are also causes.
Valuable insight into the causes of adaptation and the emergence of new traits comes from the field of evolutionary developmental biology (“evo-devo”). Some of his experimental results prove difficult to assimilate to SET. Particularly prickly is the observation that much variation is not random because developmental processes generate some forms more easily than others. For example, among a group of centipedes, each of the more than 1,000 species has an odd number of leg-bearing segments, due to the mechanisms of segment development.
Maybe I’m an eccentric, but nothing is in conflict there. I learned about plasticity, niche building, and epigenetics and just incorporated them into the evolutionary process, working alongside older, familiar ideas about allele frequency changes. How can we think that evo-devo is a radical competitor to the theory of evolution? There is “evolution” in the name! I’ve been following the evo-devo for forty years now, and certainly at first some were overenthusiastic, calling it revolutionary, but really it’s just part of evolution. I don’t need to chant slogans or demand wild changes to the textbooks, they’ve all been steadily adding more and more content to these crazy ideas about mechanics other than selection in the fold. Nusslein-Volhard and Wieschaus are now in freshman biology texts!
But SEA fanatics are not satisfied.
The case for SEA rests on a simple assertion: Over the past few decades, we have learned many remarkable things about the natural world – and these things should have a place in the fundamental theory of biology. One of the most fascinating areas of recent research is known as plasticity, which has shown that certain organisms have the potential to adapt faster and more drastically than previously thought. The descriptions of plasticity are startling and reminiscent of the kinds of wild transformations you might expect to find in comic books and sci-fi movies.
Yes, the plasticity exists, it’s really cool, I’ve read a lot of articles about it, and I’m a big fan of Mary Jane West-Eberhard’s work. So? What does it mean, “given space in the fundamental theory of biology”? I don’t understand. I open an evolutionary biology textbook, and it takes hundreds of pages to explain how evolution works, and that includes plasticity, punctuated equilibrium, near-neutral theory, and lots of ideas that explain a complex process. What is this “central theory”? They talk as if there is a concise and tidy kernel from which everything is derived, and they want to go into detail. That’s not how it works. That’s not how everything works. Perhaps they should take a step back and explain precisely what this “fundamental theory” is.
The Guardian article somehow redeems itself at the end by pointing out the obvious: what is this single “central theory” they want to change? There are not any !
Computational biologist Eugene Koonin thinks people should get used to theories that don’t agree. Unification is a mirage. “In my opinion, there is not – there can be – no theory of evolution,” he told me. “There can’t be one theory of everything. Even physicists don’t have a theory for everything.
It’s true. Physicists agree that quantum mechanical theory applies to very small particles and Einstein’s theory of general relativity applies to larger ones. However, the two theories seem incompatible. Towards the end of his life, Einstein hoped to find a way to unify them. He died unsuccessfully. Over the following decades, other physicists undertook the same task, but progress stalled and many came to believe it might be impossible. If you ask a physicist today if we need a unifying theory, he will probably look at you with bewilderment. What’s the point, they might ask. The ground works, the work continues.
I’m not thrilled to introduce physics into the story. Most people don’t understand the theory of evolution, so trying to compare it to another complex field that most people don’t understand (myself included) isn’t helpful at all. I agree with Koonin on the evolution part, however: there are a lot of messy moving parts in evolution, why even try to pretend that everything is unified in a simple and clear principle? Embrace diversity and complexity. You will never get anywhere trying to claim ownership of the “fundamental theory”.
Perhaps that is the real problem. In 1859, a man, Darwin, could say “It is my theory” (with a little nod to Wallace). In the middle of the 20th century, a massive crowd of scientists were able to come up with something called the neo-Darwinian synthesis, but no one could claim it. It was too big and sprawling and crossed several sub-disciplines. Now a handful of people want to be credited with a half-ass idea they call SEA…sorry folks, it’s just some tastier ingredients for the stew, it doesn’t replace anything.