LiveScience is continuing with their series on nature’s “Greatest Mysteries”. Today it’s “What drives evolution?“.
In the second paragraph, we find this intriguing question:
Natural selection is accepted by scientists as the main engine driving the array of organisms and their complex features. But is evolution via natural selection the only explanation for complex organisms?
No, it isn’t. Genetic drift also plays a major role. However, as Dawkins points out repeatedly, natural selection is the only known mechanism capable of resulting in complex adaptations. The legitimate debate is therefore about how much phenotypic (or genetic) change is adaptive and how much is a product of chance. I wouldn’t consider it a “great mystery” but a debate about the relative contributions of fairly well understood mechanisms. Dawkins sees adaptations as the only interesting things to explain. Lynch (2007) provides an equivalently extreme argument from the drift side of the aisle. But this can’t be what the author has in mind, as it is all very standard.
“I think one of the greatest mysteries in biology at the moment is whether natural selection is the only process capable of generating organismal complexity,” said Massimo Pigliucci of the Department of Ecology and Evolution at Stony Brook University in New York “or whether there are other properties of matter that also come into play. I suspect the latter will turn out to be true.”
So we see that, indeed, the discussion is not about whether processes besides selection can generate complexity (they can, though it may not be adaptive complexity). It’s about whether totally different processes are at play. Reading Pigliucci’s statement immediately brings to mind thoughts about self-organizing complexity as emphasized by Stuart Kaufman and others about 15 years ago. Interesting ideas, but they didn’t really lead anywhere. But this is not what is discussed, and it’s here that the story takes a turn for the bizarre.
“Over the past decade or two, scientists have begun to suspect that there are other properties of complex systems (such as living organisms) that may help, together with natural selection, explain how things such as eyes, bacterial flagella, wings and turtle shells evolve,” Pigliucci told LiveScience.
One idea is that organisms are equipped with the flexibility to change their physical or other features during development to accommodate environmental changes, a phenomenon called phenotypic plasticity.
Phenotypic plasticity is a “property of matter”?
The change typically doesn’t show up in the genes. For instance, in social bees, both the workers and guards have the same genomes but different genes get activated to give them distinct behaviors and appearances. Environmental factors, such as temperature and embryonic diet, prompt genetic activity that ends up casting one bee a worker and the other a guard.
The cells in my fingers typing these words are very different from the cells in my brain thinking them, but they contain the same genome. The exact details of gene regulation and cell differentiation are still being studied, but this hardly constitutes either a “great mystery” of evolution or a challenge to Darwinian mechanisms. Same goes for castes within a bee hive, which has been described as being like a superorganism.
And just to prove that this is all very standard:
If beneficial, this flexibility could be passed on to offspring and so can lead to the evolution of new features in a species. “This plasticity is heritable, and natural selection can favor different kinds of plasticity, depending on the range of environmental conditions the organism encounters,” Pigliucci said.
So, phenotypic plasticity is not a property of matter but a standard biological process, and it can be shaped by natural selection like other heritable characteristics. Nothing new here.
But then we do finally get back to evolutionary changes resulting from “properties of matter” such that the mechanisms are non-Darwinian.
Self-organization is another evolutionary force that some experts say whips up complex features or behaviors spontaneously in living and non-living matter, and these traits are passed on to offspring through the generations.
That a Lamarckian process of inheritance of acquired characters played an important role would be surprising indeed. Perhaps it is not so silly as that. Maybe the author is thinking of epigenetic changes that can be passed on. But that would still be only a minor variant of the standard Darwinian process — natural selection was conceived long before any specific rules about hereditary systems were identified. Genetic or epigenetic, if it is inherited and has effects on fitness, it can be subject to natural selection.
“A classic example outside of biology are hurricanes: These are not random air movements at all, but highly organized atmospheric structures that arise spontaneously given the appropriate environmental conditions,” Pigliucci said. “There is increasing evidence that living organisms generate some of their complexity during development in an analogous manner.”
A biological illustration of self-organization is protein-folding. A lengthy necklace of amino acids bends, twists and folds into a three-dimensional protein, whose shape determines the protein’s function. A protein made up of just 100 amino acids could take on an endless number (billions upon billions) of shapes. While this shape-shifting takes on the order of seconds to minutes in nature, the fastest computers don’t have the muscle yet to pull off the feat.
The mechanism that triggers the final form could be a chemical signal, for instance.
So are we relying purely on chance every single time a protein folds? Or is three dimensional structure consistent given a particular string of amino acids? If the latter (which it is, or we’d be dead), then this would imply that self-organizing that could go any which way is not the explanation. Rather, the string of amino acids and the conditions in which it folds (e.g., the chemistry of the cell) are heritable and have fitness consequences. Where might that “chemical signal” comes from, pray tell?
After this, there is more about phenotypic plasticity. There’s an example of butterflies with different colour patterns depending on season (so again, a question of how the environment affects gene expression during development — interesting and important to consider in evolutionary biology, but not a challenge to natural selection because the switch in colouration is adaptive).
The last example is of shorebirds called red knots which “can morph their phenotypes depending on their migration routes.”
When brought into captivity and placed in colder temperature environments, the shorebirds’ flight muscles and organs shrink to reduce heat loss. The birds pass on to offspring the capacity to make these changes.
Maybe this is an innocuous statement, like claiming “If people work out, they will get big muscles, and they pass on the capacity to get big muscles by working out to their offspring”. One could even say that some individuals’ offspring (say, Arnold Schwarzenegger’s) have a higher capacity to become muscular under conditions of heavy exercise than others’. But then, this wouldn’t be nearly as interesting as implying that soft inheritance is taking place.
Overall, this piece was really quite confused, mixing very different issues in a strange sequence, which is a shame in light of the good article they posted last week.
I still wonder what can be done to improve the accuracy of science reporting; “nothing” seems less and less like an acceptable answer.
