This ant and plant have co-evolved - and evolutionary opportunities like this aren't always predictable.
This ant and plant have co-evolved - and evolutionary opportunities like this aren't always predictable. Max0rz/Flickr
Ideas sometimes click into place, as we all experience. I recently realized that some unknown range of evolution must be taking place beyond the familiar mechanisms thought of in evolutionary biology. Ideas clicking into place are a natural growth process. In posts for NPR, there has been a requirement for some repetition of the formative steps that led to the "click". I hope you will therefore forgive some repetition of those steps in this post.
First, what are the "standard" drivers of evolution? For Darwin, there was heritable variation and natural selection - we are all familiar with these. Less well known to the general public, a famous Japanese geneticist, Moto Kimura, in the 1970s, proposed that most genetic mutations were selectively "neutral". Imagine a gene that can mutate to make eye colors of a wide diversity, but that eye color is of no selective advantage or disadvantage at all. Then population geneticists worked hard to understand the ever changing "genetic drift" among neutrally different versions, or "alleles" of the eye color gene, in an evolving population. This aspect of evolution is called, "genetic drift". Starting with a famous book by D'Arcy Wentworth Thompson, "On Growth and Form", in 1917, and followed by many, including myself in my first book, "Origins of Order: Self Organization and Selection in Evolution", the theme of "self organization" and its potential roles in evolution has become rather broadly accepted.
The relative roles of the three aspects of evolution above, and how they intermingle, is a very important topic. Yet there may be a further, virtually unseen, aspect of the evolution of the biosphere beyond the above three "drivers". To lay it out, I must repeat material from past posts.
Recall Darwinian preadaptations. The function of your heart is to pump blood, that is its biological "function" because that is what it was selected for, and why hearts exist in the universe when most complex things will never exist. But your heart makes heart sounds and jiggles water in your pericardial sac. These causal effects are not the biological function of your heart. Presumably they are of no selective value in the current environment.
Darwin realized that a causal property of some part of an organism of no selective significance in this environment, might become of selective significance in some other environment, so come to exist and even be modified. These are now called Darwinian preadaptations, with no implication of foresight in evolution, or called "exaptations". Typically a new function comes to exist.
I always use the example of the evolution of the swim bladder in some fish. These are sacs partly filled with air and partly filled with water, and their ratio adjusts neutral buoyancy in the water column. Paleontologists believe swim bladders evolved from lung fish. Water got into some lung(s) and now there was a sac with air and water in it, "poised" to evolve into swim bladders.
Let's assume the paleontologists are right.
Now when I have written about this in the past years, my major points have been: 1) A new function, neutral buoyancy, came into existence in the biosphere. 2) The swim bladder altered the future evolution of the biosphere - new species with swim bladders, new proteins, and the point I want to focus on today, below, new niches. 3) I then go on to talk about whether we can prestate preadaptations and other issues I've posted before and will not repeat now.
I want to raise a new issue. It concerns the fact that when the swim bladder arose, it constituted a New Adjacent Possible Empty Niche. Why? Well, a bacterium might evolve able only to live in swim bladders. A similar bacterium is only able to live in the lungs of sheep. Then the new existence in the biosphere of swim bladders is a real new niche, initially unoccupied by a creature. So it is a Real Adjacent Possible Empty Niche. But the very existence of this adjacent possible empty niche does or may, in fact, change how the biosphere evolves. Why? Because a bacterium or other parasite might evolve by, say natural selection, that can only live in swim bladders, occupying the "new empty niche" and filling the new adaptive opportunity. The occupancy by the bacterium of the swim bladder as a new adjacent possible empty niche, does truly change the future evolution of the biosphere.
But here is the central point: The evolution of the swim bladder itself as a preadaptation may have taken natural selection. However, The coming into existence of the new adjacent possible empty niche itself was not itself selected for! The new adjacent possible empty niche just "came into existence" with no selection to "create" that niche as a niche, when the swim bladder was selected.
But this is the point! The biosphere is, as I've remarked before, evolving the very empty adjacent possible niches that it may/will become! And those niches appear without themselves in any way being "selected for". Then, beyond Darwin, heritable variation, natural selection, drift, and self organization, the biopshere is, without any of the above familiar drivers of evolution, building the very possibilities, the empty adjacent possibilities, it will become. Beyond Darwin, the biosphere is building its own Adjacent Possible and then evolving into that Adjacent Possible and building a yet further new Adjacent Possible empty niches.
Finally, if each new feature, whether preadaptation or not, on average creates more that 1.0 new empty niches, the Adjacent Possible of the biopshere is "exploding", to create the expanding set of empty niches that come to be occupied! The biosphere, beyond Darwin and natural selection, is building how it it builds itself.