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Richard Dawkins wrote The Blind Watchmaker in 1986.
(Picture from here.)
His intention was to refute the idea that the complexity of living systems made a Creator self-evident. The analogy was of finding a watch implied a watchmaker, a metaphor created by William Paley. I am not a fan of Dawkins in that I think his idea of evolution—especially human evolution—to be far too narrow. But TBW was a good starter book on evolution.
Current life origin hypotheses put the start at about 3.7 billion years ago. This is the evidence of life that survived on the early Earth. Earth is about 4.5 billion years old and the conditions amenable to life are supposed to have been present at 4.3 billion years ago. So, there’s a six hundred-million-year gap where life could have started, failed, and restarted. Or, life could have started and left nothing that could be traced until that 3.7-billion-year mark.
The current hypothesis of Moon formation is that it was struck from the Earth by a collision from a Mars-like body early on. This would have left the surface of the Earth in a molten state. Unless you want to imagine lava-breathing ichthyosaurs, that pretty much lets out life until things cooled down.
The base for what we call complex life—Eukaryotes—seem to show up about 1.6 billion years ago. That means we have something like bacterial life on the planet for 2.1 billion years or so. If they breed like bacteria—say, a division on the order of 1/hour—that’s 50.4 billion generations before we get to Eukaryotes. Maybe more generations since some bacteria divide every twenty minutes. I’d say that should be plenty of time to evolve pretty much anything.
We have no idea if pre-Eukaryotes were like bacteria. We have no idea of “Eukaryotes” actually had all the components that we identify with Eukaryotic cells. That would things like a nucleus, mitochondria, etc. We think it’s likely but it is speculative at best.
Animals, whose evolution I am most familiar with, arose about 650-700 million years ago. So, roughly a billion years. Cell division in Eukaryotes is considerably more complex and, understandably, it takes longer—approximately 16-24 hours.
The Ediacaran period happens just before the Cambrian. In the Ediacaran, early animals developed. These were defined into modern phyla in the Cambria. The Ediacaran began roughly 635 million years ago—barely fifteen million years after Eukaryotes were first identified. We can use sponges as an example. The sponge reproductive cycle can be budding—where a chunk breaks off and ends up somewhere, takes root, and grows—or sexual. In either case, there has to be a minimum time between a larva and the first offspring. If we go by sexual periods, this breaks down to once or twice per year.
We’ve gone now from an hour for generation time, to approximately a day, now to a year. We know of many animal species—us, for example—where the generation time is measured in years. Evolution is the selection of variations within offspring. The irreducible atom of evolution is the generation. While animals can adapt within a generation, the only means by which these changes are realized is in the next generation. Looking at this, we might expect animal evolution to slow down.
Instead, it speeds up. The Cambrian isn’t called the Explosion for nothing.
This is the point that if we would invoke a Creator if we were so inclined.
We are not.
But something happened.
That something is embryonic development.
The embryo is a well of potential. It has to go from a zygote to a larval form (at minimum) containing only the information it starts with. Most zygotes in the animal kingdom are cast into the wild. A few (I’m looking at you, placental mammals) develop within the mother organism. Even there, the mother is walled off from the developing embryo so that there is little interference.
Here’s where we get muddy about the language. We talk about how the “design” of the zygote results in the new organism. Or how the process of embryonic development is like a symphony, each part played and leading to the beautiful.
None of this is true. There is no design. If you boil down what’s in the nucleus for a human you won’t see a gene for blue eyes or red hair. You might see a melanin deficiency that manifests at a particular point in development such that the iris of the eyes is without pigment. You might see a keratin gene get over expressed in the creation of hair follicles. But there is no one gene for the shape of your nose, angle of your neck, or your height. Repeat: there is no design. (See here.)
Imagine two dancers on a floor. One dancer moves their arm. The other responds by waving a hand. The first then turns. The other turns the opposite. Both of them are following their own understand of their actions—Dancer 1 knows to move the arm. The other knows to respond with a hand wave. But Dancer 1 does not know that Dancer 2 is going to wave a hand. Dancer 1 does know to respond to Dancer 2’s turn with another turn. To the audience in the balcony, this appears to be a wonderful dance. But neither dancer knows the ultimate goal. Neither dancer even knows there is a dance.
The egg of an animal is packed with energy and data—not a design, remember. The first few divisions are self-contained with regard to energy. The yolk of the egg or the material of the placental environment is not immediately consumed. Oxygen is, of course. But for those first crucial divisions, the cells consume material inside. Later, they will take in nutrients from the inside.
As they divide, different cells get different material from the original egg. This is the initial specialization. Even sponge development results in cell specialization.
About thirty years ago, scientists began to realize that there was some kind of developmental module. Not a design as such, but a pre-program that enforces a path in those first few divisions and later, with each division, triggers responses that result in an actual organism.
There is no design in the genes. But there is a design in how the gene interactions play out.
This is where evolutionary-developmental (Evo-Devo) biology comes in.
The idea is that there are genes responsible for the development across multiple phyla. These determine body plan. For example, the gene responsible for the development of eyes exists across multiple phyla: arthropods, vertebrates, cephalopods. Where, when, and how they get expressed determines if you get a beetle, possum, or octopus eye.
Is this design? I don’t think so. The gene triggering the eye development does not contain any internal representation of an eye. It triggers a cascade of responses that result in an eye. That’s been useful and is therefore retained.
There are beginning body plan genes—prepared for operation by the egg. These genes determine segmentation, organs, vascularization, and the like. They tend to be lined up in roughly the expression order required by the organism. Changing the order can result in different organs or blood vessels originating in different segments.
Developmental genes of this sort have been found in animals, plants, and fungi. They were a critical step in the origin of complex organisms. But they do not exist in isolation. Each gene responds to and is responded to within the context of its environment. There are past events that prepare the operation of the gene and future events to which it is contributing. We call the some of these bits of DNA “body plan genes” or “regulatory genes” because they are central to the process. But in the absence of their important context, they are just sequences of nucleic acids—like any other bit of DNA.
It's a subtle point—we would like there to be a design in place because that would be more understandable to us. Humans design things. Why shouldn’t nature? Why shouldn’t we have a design or a program?
I’m going to quote Alessandro Minelli quoting Keller on this one: “More explicit is Keller (2000), who suggests that to speak in terms of genetic programme is to commit a basic error in categorisation: genetic is equated to programme at the same time as epigenetic is equated to data. But development depends not only on genetic memory, but also on the machinery of the cellular structures, which in turn are set in place by cellular memory rather than by genetic information.”
I think that just before the Ediacaran Period, this fundamental body plan embryology began to be emplaced. Possibly, cells that cooperated and produced a consistent offspring did better than others. An organism had a few cells that cooperated to produce sex cells. That cooperation became the basis for a coordinated embryologic process. Then, at the beginning of the Ediacaran, these now somewhat complex organisms themselves competed.
Something happened at the end of the Ediacaran. Some have suggested the introduction of predation, changing the world into predator and prey and vastly increasing the natural selection process. There was enough variation in the body plan genes that new forms came into existence. Those that were successful propagated their new forms further.
What happened at that point was a system built to evolve was in place.
The rest, as they say, is our history.
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