Cov kab mob ntawm tus kab mob liab tau txuas ntxiv mus thoob ntiaj teb. Raws li World Health Organization (WHO),tsawg kawg yog 27 lub teb chaws, feem ntau hauv Tebchaws Europe thiab North America, tau lees paub cov neeg mob. Lwm cov ntawv tshaj tawm tau pom cov mob uas tau lees paubhauv ntau dua 30.

Qhov xwm txheej tsis tas yuav musevolve mus rau hauv kev sib kis, tab sis muaj qee qhov kev txhawj xeeb. Tej zaum lub ntsiab lus tseem ceeb ntawm kev txhawj xeeb yog tias tsis yog txhua qhov xwm txheej tshwm sim muaj feem cuam tshuam, thiab qee qhov xwm txheej sib cais tsis muaj kev sib raug zoo rau tus kab mob uas twb muaj lawm. Qhov no taw qhia rau qhov teeb meem taug qab, thiab qhia tias ntau qhov sib txuas sib txuas yuav tsis raug kuaj pom.