Warning: Spoilers ahead.
From writer and director Alex Garland (Ex-Machina, 28 Days Later), this film stars Natalie Portman, Jennifer Jason Leigh, Gina Rodriguez, Tessa Thompson, Tuva Novotny and Oscar Isaac. This is almost like an all-female version of Predator, with a team going into the forest, with guns, to take down an alien for the likes of which they are wholly unprepared.
The rapid spread of tumors is shown early in the movie. If a cancer attempts to take over the world, what would that look like? It appears as the "shimmer." We later learn that the shimmer scrambles not only lightwaves and radio waves, but also the DNA of all living beings within its territory.
OK, if you're still reading this, I will assume you've seen the movie.
We later learn that the soldier who returned to his wife was an imposter, some kind of simulacrum, an alien clone. The shimmer is a contrast of darkness and light, beauty and grotesque, creation and destruction.
In the Octavia E. Butler novel Dawn, an alien race perceives cancer as a gift from humanity that allows the aliens to regenerate their body parts. Similarly in this movie, a cancer can be a benefit for an alien attacking a planet. We are asked whether the shimmer is judged as evil simply because it is bad for humanity. In some way, is there beauty in destruction? Evolution is a godsend for the evolved. It's only the enemy of those who weren't naturally selected.
Kane asks Lena if she if Lena. Is Lena indeed still Lena, or a double like her husband? We see her beat her clone and walk away, but that is only her telling of the story. She may be an unreliable narrator, slipping by her interrogators. Her eyes are similar to Kane's. She never answers Kane's question.