You don’t need to explain more, what you have to do is support your claims.
Here's an article you can ignore about how hair, feathers and scales are inherited modified structures from a common ancestor.
Feathers, hair, and scales: Do they share a common ancestry? - CSMonitor.com
From your drawing if A would have had feathers, then mammals with feathers would have been possible and even expected. (agree?)
Not just mammals. Everything that branched out of A.
And yes. But that's not what we see. What we see, is that only those on branch D have feathers.
Those on branch B have hair instead.
So finding a feline with feathers tomorrow, would violate the nested hierarchy.
The feathers would place it on branch D. The mammary glands would place it on branch A. When a creature has to be placed on 2 branches, it breaks the
nested hierarchy.
How many times must it be repeated?
And why would that be problem for evolutionary theory? yes if A woudl have had feathers then b,c, and d woudl also have feathers why woudl that be a problem for evolution?
It wouldn't. But it's not what we see. What we see, is that only D has feathers.
So finding a feline with feathers tomorrow, would not fit evolution as it would break the nested hierarchy.
How many times more?
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So in summery
1 we both seem to agree that feathers could have evolved at some other point
2 we both agree that if feathers would have had evolved in “A” (from your drawing) mammals with feathers would be possible.
3 we both agree that this would be a problem for evolution all you have to do is change the tree a little bit
Aaaaand we're back to the useless tautology that says "if everything would be different, then things would be different".
Also, this is a dishonest moving of the goalposts.
Remember the original point which started this mess of a pigeon chess game?
That point was:
evolution would be in trouble if tomorrow we find a mammal with feathers.
A mammal. As in 1 (species). The point was
NOT "let's imagine a hypothetical world where ALL animals have feathers".
4 we both agree (hopefully) that we don’t always keep the genetic remains of stuff that our ancestors had (meaning that not finding mammals with residual genes for feathers would not be surprising)
No, entire sections of DNA don't just disappear without a trace.
It's been 100 million years since birds lost their teeth, yet they still have the genetic remnants thereof.
We humans also still have the GULO gene, as do all great apes. And it's broken in the same way in all great apes. And it's been that way for millions of years also.
It is entirely unreasonable to suggest that ALL branches under A (in the drawing)
except D lost the feather genetics
without any kind of trace remaining.
That, and off course the fact that hair and feathers are homologous. So the very idea of "we had feathers and lost them", makes zero sense. This is another point you consistently ignore.
So can you please tell me which are the points where we disagree?
You have been moving goalposts so much, it's hard to keep track.
I guess the biggest problem here, is your inability (or rather: unwillingness) to comprehend nested hierarchies and basic evolutionary mechanisms.
Strawman
What I said is that we don’t always keep the remains of genes from stuff that evolved millions of years ago. Agree?
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No. What you said is that it is rare.
Clearly it is not rare as thousands upon thousands of bird species retained the genetics for teeth building.
If it was "rare" for species to retain ancient inactive genetics, we would expect only a handful of birds to still have those genes. Or even none at all, since it's been 100 million years.
Instead, we find that ALL BIRDS have these genes. ALL.
So, not rare at all. Exactly the opposite, in fact.
Losing such genetics is what is rare. So rare in fact, that not a single bird species lost it.
So no, not a strawman at all. Instead, a direct refutation of your bare assertion.