Someone asked this question on Reddit. Below, I quote their post and provide answers.

Could human intelligence be consider[ed] the "best" or "ultimate" adaptation?

We have seen many different adaptations from organisms as they try to survive their environment. A very basic example is thick fur is good for keeping you warm in cold environments. Or some snakes [sic] ability to produce venom. These adaptations we[re] evolved by these organisms because they made them more successful in the face of natural selection.

Just to be clear, because the way the last sentence is phrased might confuse some: organisms don’t evolve anything in the sense that they ‘decide’ to grow into something else. Nor are organisms the unit of selection. It’s the genes that evolve, and changes to the organism are downstream of that evolution. And the word “because” might mislead some as it could suggest that evolution is purpose-driven – it is not. You point this out below yourself, I just want to be clear.

Humans evolved the greatest intelligence of any other animal.

You’re fudging two different concepts here. I like to differentiate between smarts and intelligence. Smarts are a matter of degree and describe the sophistication of existing knowledge; intelligence, on the other hand, is the ability to create new knowledge. Intelligence is a binary matter: an organism either has it or it doesn’t. A synonym for ‘intelligence’ in this sense is creativity.

Humans are smarter in almost all domains than all other animals (there are some minor exceptions such as dogs having more sophisticated noses, say), so in that sense what you say is correct: humans are the smartest animal. But they are also the only intelligent animal as defined above.

With the help of our hands, we built society from the ground up and achieved things no species on Earth ever has. Our intelligence let[s] us make all kinds of things. We can make glasses for people born with poor eyesight, accommodate those who are disabled, and can literally grow ourselves food.

It’s intelligence, not smarts, that enables us to do these things. It’s conceivable that some animals grow food because their genes instruct them to, and they cannot help but execute those instructions mindlessly. For animals, purely zoological explanations apply. But human genes don’t contain any such instructions. Humans create that knowledge for themselves. That makes them special.

While humans continue [to] evolve since evolution does not have any end or goal, could you consider intelligence to be the ultimate adaptation?

The biological evolution of humans will continue, at least until we figure out how to upload our minds to non-biological hardware. But yes: in a sense, intelligence is the ultimate adaptation. It makes us what physicist David Deutsch calls universal explainers and universal constructors: we can explain anything that is explicable and perform any physical transformation that can be performed, respectively.

Another reason intelligence is a big deal is that it allows humans to make up for many genetic shortcomings. For instance, several animals are born with the ability to walk, as were our non-intelligent ancestors, presumably. A mutation which compromises or even removes an animal’s ability to walk almost certainly means death: such a mutation is deleterious. But for humans, it isn’t necessarily because they can learn to walk. If their genetic instructions for walking are buggy, they can disregard them and create the requisite knowledge for themselves. If they are born with a physical handicap, they can make a cane or something, similar to glasses helping with poor eyesight. (To be sure, some animals have ‘learning’ algorithms but they’re different from how humans learn and extremely limited in comparison.)

So humans can create the knowledge that their genes fail to give them. No other animal can do that. Once intelligence evolved – and I have some thoughts on how that might have happened – selection pressures must have favored it at roughly the rate at which disadvantageous mutations occur, as I’ve written elsewhere. Since such mutations are more common than favorable ones, intelligence must have spread through the population rapidly. In this sense, intelligence is certainly the ultimate tool for survival.

Or at least it can be – there are no guarantees. As you write yourself, “humans might be capable” (emphasis mine) of surviving the explosion of the sun. Humans are certainly the only animals that could possibly ensure their own survival indefinitely – that is, if they play their cards right, continuously correct errors, and never give up.

This thought came to me when thinking about how the Sun will continue to expand and eventually render Earth inhospitable and even destroy it far in the future. There's no way for any organism to survive that. Something like Tardigrades could "survive" but would eventually die off in the vaccum [sic] of space. However, humans might be capable. Not because we've adapted to extremely hot temperatures or are durable enough to survive the destruction of a plan[e]t, but because our intelligence allows us to build space crafts [sic] that can escape the looming demise the Sun brings. It's only a coincidence that our intelligence could let us survive such an event because when we evolved it those millions of years ago, the demise of the planet was NOT the environmental pressure that lead [sic] to its development.

What you describe here isn’t a coincidence but a phenomenon Deutsch calls reach: in biology, it’s the ability of some adaptations to solve problems they weren’t ‘meant’ to solve. By the way, intelligence might not be millions of years old. According to Wikipedia, homo sapiens evolved about 300,000 years ago, and intelligence is arguably the defining attribute of homo sapiens since it means “thinking man”.

But, the fact remains that our intelligence will let us survive practically anything that isn't the end of the universe. So, does this not make intelligence the best adaptation? An adaptation which allowed a species to not just survive in their environment, but conquer it and any other threat towards it. If the only thing Life wants is for organisms to survive and reproduce forever, than [sic] humanity and our intelligence is as close to forever as any other species will ever get.

What you say reminds me of what Deutsch writes in his book The Beginning of Infinity (last paragraph of the main text in chapter 6):

[O]f all the different forms of universality, the most significant physically is the characteristic universality of people, namely that they are universal explainers, which makes them universal constructors as well. The effects of that universality are, as I have explained, explicable only by means of the full gamut of fundamental explanations. It is also the only kind of universality capable of transcending its parochial origins: universal computers cannot really be universal unless there are people present to provide energy and maintenance – indefinitely. And the same is true of all those other technologies. Even life on Earth will eventually be extinguished, unless people decide otherwise. Only people can rely on themselves into the unbounded future.

Overall, I agree that intelligence is the best adaptation, and it makes man the best animal – more than just an animal. And while intelligence can be used nefariously, I don’t share the cynicism of some of the other replies calling intelligence potentially “maladaptive”. Their view undercuts reason, and this undercutting (ironically) hurts our ability to survive.