I don't quite get how you can first acknowledge the point quoted and then follow it up with a "but...", in context of the subject, but whatever.
usually when something simple evolves in something complex, the simple trait is kept
"usually", so not always. Without even going in on the very very vague point you make here in order to have some clarity what exactly you mean... the use of the word "usually" implies "not always".
So after 3.8 billion years of evolution, it would be kind of strange that it would be "always"' instead.
For example complex eyes evolved from simple eyes, but we still have simple eyes.
Certainly "simple" in comparision with the complex.
But in any case, eyes, even simple eyes, are relatively complex as well.
And first life certainly didn't have eyes. To have eyes, even the simplest proto-eye you can think of, is ALREADY a rather major increase in complexity as compared to life's simple beginnings.
It's also rather disenginious of you to compare the selection pressure of a single
trait with the selection pressure of a
complete organism.
Life that is stuck for example in total darkness for some reason and continues to be so, will not have any change in selection pressures concerning the ability to see light.
But that doesn't mean that there aren't any other changes in that environment..... there's LOADS of factors here. Finding one thing that might remain the same for prolonged periods of time, doesn't say anything about the countless other variables.
It is hard to belive that simple cells where never selected by natural selection nor genetic drift given the fact that presummibly there wher trillions and trilios of simple cells in all sorts of environments.
Environments as they existed 4 billion years ago.
The earth has changed quite a lot since then, in case you weren't aware of that.
There is no place on the surface of the planet that still has the same environment as back then.
And the same pretty much goes for the oceans. I'm sure you can find some isolated volcanic vents on the ocean floor that are poor in free oxygen and which are
similar to early earth conditions, but the
exact same? Forget it!
It is simply unreasonable, not to say completely absurd, to assume that there is a place on this planet where a population lives which has been subject to
identical and unchanged selection pressures for 3.8 billion years and where natural selection favoured the ultimate status quo and where evolution simply has NOT occured during all that time.
One would have to be quite ignorant to even suggest such an absurd idea.
So should we call this a rere exception where the simple stuff was completely 100% overwhelmed by the complex stuff?
This also gives a false idea of what really happens.
The way you phrase that, you make it look as if there is one "simple" species and then another "complex" species which overwhelms the first species.
That's what "overwhelming" means in such evolutionary context. Like homo sapiens moving into neanderthal territory "overwhelming" the already existing population of neanderthals, causing the latter's extinction.
But this is not always what happens. A species disappearing doesn't necessarily mean that the species went extinct. It can also mean that the
lineage simply evolved and speciated further.
So, it's not necessarily the case that populations of "first life" were overwhelmed by populations of "further evolved life", causing the extinction of the first.
Instead, the population of the "further evolved life", is simply the evolved offspring of the population of "first life".
Consider the "americans come from europe, but there are still europeans".
What if ALL europeans moved to america?