Evidence that the Neanderthals were the first seafarers?

they find human-made tools (which they can assign dates to) on islands distant from shore.

Their only explanation that they are hypothesizing is that humans traveled there across water. Do you have a better idea? They're not saying they found boats, they're saying there is clear evidence of human travel.

Focus on the evidence there is, not evidence you would like to see. What do you hypothesize that fits the evidence?

"Sail" can mean any travel over water by ship. It's one of those weird words that can be really confusing even when used correctly but out of the context where that portion of its meaning is customarily used.

It suggests some sort of navigable floaty thing. They saw an island offshore, thought, let's go there, and figured out a way to do it.

This was an artifact from a long-running debate about how we should organize the taxonomy of genus Homo. On one hand, people made good arguments that archaic hominins like Neanderthals were distinct enough to consider them separate species. On the other, there were reasonable arguments that they were closely related enough that archaic and modern hominins were a single species with a number of distinct subspecies. Modern humans would be called H. sapiens sapiens in the latter scheme.

This debate was mostly ended in favor of the separate species perspective by the early 2000s, but not everyone was reconciled and archaeogenetics forced us to rewrite the human taxonomy anyway. People will understand what you mean if you continue using H. sapiens sapiens, it's when you use "H. sapiens" to include Neanderthals and Denisovans that people will be confused. Sometimes that terminology is also also used it to exclude transitional subspecies like idaltu, which I think is why wiki uses it.

imo the correct answer is this stuff is incredibly complicated and in incredible flux due to revolutionary advances in genetic research on our prehistoric ancestors and present day people. There's a lot of different perspectives but anyone with some humility would admit a new finding could be announced tomorrow that would upend quite a lot of what we think we know. Already e.g. Naledi, Denisovans, Floresiensis, Longi, Oase, etc are pretty mind-blowing to the consensus views 20 years ago. I would pay less attention to the labels used and more on the broader research.

The "Human taxonomy" page on Wikipedia still adds the second sapiens to Homo sapiens sapiens: https://en.wikipedia.org/wiki/Human_taxonomy

This may be because Homo sapiens sapiens is the Homo sapiens type species, but I'm not sure.

Might also just be talking about specific geographical range. There is still a lot of debate on the time line and nature of the diaspora of modern homo sapiens.

What's so hard to believe is humans once roamed the Earth.

Yep, that's definitely the rub. And to be sure, you're right that that verb doesn't necessarily imply a sail is involved. However, in fairness, the original article talks about how neanderthals "went sailing", which isn't typically what people say when they go rafting or rowing. At any rate, it's a pretty ambiguous word to use when there are less suggestive ones out there!

It is laughable to think that the first supported travel over water was done in “boats“ or by “sailing“. Children instinctively climb onto floating objects. It seems very likely to be that some unwary homo-something crossed an unswimmable span of water quite by accident and survived. Perhaps some other individual observed their fate and followed, perhaps from the same species or perhaps not. Perhaps alone, or perhaps with others.

The evidence is merely that there are early tools on islands.

Given our recent performance in extinction level interspecies violence and our considerable capability of intraspecies violence I find your characterization of violence as only one of many competing theories surprisingly ... endearing. But you are not wrong, given the low populations involved on both sides it's not impossible at all that violence wasn't the decisive factor.

I thought there was some decent evidence including butcher marks on bones and widespread genetic immunity to human specific prions