LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
Ringer, Tank’s replacement, arrives two days later. Nugget gets excited—he hears about Ringer and thinks immediately that it’s Cassie, although no one has seen Ringer yet. It turns out Ringer is a girl of about 15 or 16 who has dark hair and pale skin—the same girl Zombie saw earlier while training. Ringer proves to have excellent aim with a rifle.
The novel shows how both for better and for worse, guns can make people equally dangerous, erasing divides between ages or genders.