I mean, all of non-viral life is descended from a single organism, right? I find that even more remarkable.
If you look at bacteria even, there's a lot of genetic transfer beyond just strict parent/child relationships either just directly or via viruses or other things I'm sure I've never heard of.
The earliest life was probably more like some kind of soup of self-replicating things, closer to a chemical reaction than biological, and then it would have been kind of a sliding scale over a long period of time before we get to anything that really looks that much like "<this> organism begat <that> organism".
The entire concept of organisms themselves are an abstraction over the truth, that kind of works for today's world, but probably less worked when things were new and interesting and messy.
There's probably nothing special about life and it's everywhere where water is warm.
First it starts to stink, then it gets fuzzy, then it starts to stink worse as the irregular fuzziness in the surface is replaced by geometric patterns spitting light and clouds of smoke. Eventually the surface is suddenly awash in fire and burnt black.
I just mean: at some point there was a pool (or ocean, or ocean with hotspots, or a beach with chemical goo, or etc.) of stuff doing weird chemical or physical things that we would not call biology, and over a period it moved way more towards something that we _would_ call bioloy. But it was not a hard and fast cut off, where <here> is the first living thing, one cell and then it grew and replicated. It was likely a stew of goo all intermixed at various concentrations and states that what we'd call life messily transitioned out of over such a period that there _was_ really no first living thing that you could realistically point to, because life is not well defined enough for that to make sense.
convergent evolution is a thing, even pretty common (e.g. see crap like animals)
and while very rare and unlikely different species can "merge" especially if we speak about relatively simple live form through the more complex the more problematic and limited it gets
through that isn't the relevant point I want to make
The point I want to make is that the linear tree few of evolution often presented in documentations is wrong, species diverged but also reconverged all the time. E.g. neanderthal might have died out but to some degree also mixed into what later became homo sapiens sapiens.
This might seem irrelevant for anyone not studying this topics, but it isn't as the tree one survives the other dies out view is often one of the building blocks of white supremacist race theory (which theoretically also doesn't make sense even if evolution is a clean tree as they extend concepts from inter-species relation ships to ethnic groups which average difference in DNA is too small to call them different races, but it's not like such people care about since).
With same reasoning, it's not hard to think we are not alone in this universe, given the sheer scale of cosmos.