Halin muhalli, yanayi Na muhalli ya kasance yanayi shine kowane abu, abiotic ko biotic, wanda ke rinjayar rayayyun halittu . Abubuwan kwayoyin halitta sun haɗa da yanayin yanayi, adadin hasken rana, da pH na ƙasan ruwa wanda kwayoyin halitta ke rayuwa. Abubuwan da suka shafi halittu zasu haɗa da samuwar kwayoyin abinci da kasancewar ƙayyadaddun ilimin halitta, masu fafatawa, mafarauta, da ƙwayoyin cuta . Genotype na kwayoyin halitta (misali, a cikin zygote ) wanda aka fassara zuwa cikin phenotype na manya ta hanyar haɓakawa yayin tsarin halittar kwayoyin halitta, kuma yana ƙarƙashin tasirin tasirin muhalli da yawa. Sannan kuma A cikin wannan mahallin, ana iya kallon nau'in phenotype (ko yanayin phenotypic) azaman kowane siffa mai ma'ana da ma'auni na kwayoyin halitta, kamar yawan jikinsa ko launin fata . Baya ga cututtukan ƙwayoyin cuta na gaskiya na monoogenic, abubuwan muhalli na iya ƙayyade cigaban cuta a cikin waɗanda ke da ƙayyadaddun ƙayyadaddun yanayin. Damuwa, cin zarafi na jiki da tunani, abinci, fallasa zuwa gubobi, ƙwayoyin cuta, radiation da sinadarai da aka samu a kusan duka.