"The Vacant Interstellar Spaces"

Poul Anderson's Brain Wave is noteworthy for its galactic connection and its change to human nature. (See posts earlier this month.) What it did not need was the interstellar travel that became a major feature of Anderson's later science fiction. Human beings express their freedom and maintain their dynamism simply by traversing interstellar distances.

In Brain Wave, the reasoning is:

the premise of the novel is a sudden significant increase in global intelligence levels;
it follows that many people will learn about science for the first time and that many already working in the sciences will make new theoretical and technological discoveries very quickly;
these will include the very rapid building and launching of a fleet of faster than light spacecraft (powered by a psi field, which ties in with the increase in mental abilities).

People of enhanced intelligence fly these starships through atmosphere and galaxy and land them anywhere on the ground more readily than you or I drive and park a car. In a matter of months, they have observed fourteen inhabited extra-solar planets, discovering, e.g., tailed barbarians, centaurs with local interplanetary flight and three species of hydrogen breathers on a single giant planet, and even measuring their intelligence levels. Before long, all the enhanced human beings bequeath Earth to former morons and imbeciles, whose intelligence has now risen to the former norm, and go off to become a guiding presence for lesser intelligences throughout the universe, while now linguistically able dogs and chimpanzees cooperate with the former morons on Earth. An improbable scenario, especially since a more important topic for a novel would have been the intellectual control of instinct that, we are told, results from the increase in intelligence. (One character makes a good critique of the cultural specificity of IQ tests.)

The later Anderson would have acknowledged that, even if intelligence were increased, the laws of physics might not grant us the freedom of the universe as easily as that. And I would expect the enhanced intelligences to retain different interests and purposes, some of them remaining on or near Earth.

In Anderson's later novels, Orbit Unlimited, The Boat Of A Million Years and Harvest Of Stars, groups that are thwarted or stifled at home assert their freedom by departing at sub-light speeds to colonise extrasolar planets. If, in our future, such voyages become both possible and necessary, then they are to be encouraged but, meanwhile, freedom is to be found on Earth and in the Solar System. I do agree that, for long term racial survival, we need to get off Earth:

first, an asteroid defence system;
then, solar-powered, self-sustaining habitats;
next, exploration of the outer planets and the Oort Cloud.

To survive there, we will need to take our environment with us and therefore will not be dependent on finding any (improbable) uninhabited but habitable planets further away.