The Thinning by Inga Simpson

Kris grew up by an observatory, learning about telescopes and planets, inspired by the passions of her mother and father, then leaders in their fields of astrophotography and astronomy. Those days are long over. Now Kris, her mother Dianella, and a band of outliers live deep off the grid, always on amber alert and always ready to run. In the outside world, things are not good: extinctions and a loss of diversity threaten what's left of the environment. With a new disaster looming, Kris finds herself thrust into an unlikely partnership with a stranger who has appeared in their camp. Terry is one of a new breed of evolved humans, the Incompletes, who are widely distrusted. But the pair will need to work together during a dangerous journey if they are to play their part in a plan to help restore the natural world - and humankind.