Can you explain why that would be certain? The reason there is a mutation rate is that replication is never 100% perfect. LMEs in particular have much higher mutation rates compared to things like bacteria.
I would say that is less of a claim and more of a logical necessity.
I don’t know what you’re asking me to explain exactly. Historically, there’s a lot that is different between different people groups. Patriarchal drive refers to how older men produce offspring with more mutations, so if a particular subgroup had a lot of older men reproducing, that could explain higher levels of mutations. Also a history of being much more geographically isolated with a smaller effective population size, etc. There are many reasons why the mutation load would not be perfectly homogenous across isolated groups. It’s certainly not because selection is removing all of it.
Logically, there would have to be, since evolution happens in time, which is a string of moments. So either no species ever come into being, or they do and there is a moment when it happens.
You seem to be conflating the existence of an event with our ability to pinpoint that event ourselves. You’re also dancing around the problem that there really is no solid and universal definition of “species” to begin with, so of course we cannot say when one begins because we don’t even know what we’re talking about when we say it.