> 'Closeness' (whatever you mean by that) doesn't really imply ancestry without some hefty presuppositions
Of course it does. It doesn't prove ancestry. But genetic similarity implies proximate shared ancestry.
We can take microbes (or fruit flies), subject them to stress, let the survivors reproduce, and watch the genotypes branch into a diverse population. We can then take the observed path of genetic variation and compare it to the relative closeness of the population at the end of the experiment. That's one way we validate the statistical techniques used to relate genetic similarity to probable ancestry.
...And science isn't really about proof, it's about predictive models that are falsifiable but which have resisted falsification. While it hopes to reach or approximate truth, ultimately it's about pragmatic utility.
You're making a whole lot of unfounded and unproven assumptions here!
For example: what if the current genetic diversity on Earth is the result of genetic engineering by ancient aliums?
That's a facile example, but there are serious deeper issues here. The mechanisms of gene transfer are too complex for us to explain presently, including things like viruses, horizontal transfer, etc.
You're assuming a simplistic darwinist model that we already know isn't true.
> You're making a whole lot of unfounded and unproven assumptions here!
The grandparent post makes no unfounded assumptions. It makes unproven ones for a strict definition of “proven”, but that's trivially true since no statements about physical reality can actually be proven, only statements about the relation of abstract concepts can be proven, and then only within a given system of axioms.
> For example: what if the current genetic diversity on Earth is the result of genetic engineering by ancient aliums?
That is indeed an example of an assumption that is not merely unproven but actually unfounded, but it's not an example of one made in the grandparent post so I don't know how it is relevant.
> The mechanisms of gene transfer are too complex for us to explain presently, including things like viruses, horizontal transfer, etc.
There are aspects that lack complete explanation, but that doesn't diminish the power of what we do understand (also, viruses and horizontal gene transfer aren't two things we can't explain, viruses are one of the main mechanisms of horizontal gene transfer.)
> You're assuming a simplistic darwinist model that we already know isn't true.
I see no evidence that that is the case; modern models are not simplistic Darwinism models of the type that involve only transfer by descent.
> what if the current genetic diversity on Earth is the result of genetic engineering by ancient aliums? [sic]
For purposes of explaining the last 4 million years of human evolution, it’s irrelevant whether conscious or unguided phenomena created forms even as recent as mammals.
> You're assuming a simplistic darwinist model that we already know isn't true
No, nobody is.
Retroviral horizontal transfer is fascinating, but it’s one of many mutation vectors. At the scale of speciation, the specific way a mutation arises can be largely ignored. (Creationism aside.)
> what if the current genetic diversity on Earth is the result of genetic engineering by ancient aliums?
What if? Obviously they must have engineered it such that current evolution theories have the best predictive value for their achievement. A clever bunch, no doubt, but unfortunately outside of the realm of science because it can't be falsified.
