naturalselection.py: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/share/doc/php-sabre-dav-1.8.12/bin/naturalselection.py - from package: php-sabre-dav

You may install the required package with command yum install {package}

Error in other languages:
naturalselection.py: bevel nie gevind nie
naturalselection.py: comandă negăsită
naturalselection.py: comando não encontrado
naturalselection.py: commande introuvable
naturalselection.py: command not found
naturalselection.py: käsku ei ole
naturalselection.py: không tìm thấy lệnh
naturalselection.py: komanda nerasta
naturalselection.py: Kommando nicht gefunden.
naturalselection.py: kommandot finns inte
naturalselection.py: komut yok
naturalselection.py: nie znaleziono polecenia
naturalselection.py: níor aimsíodh an t-ordú
naturalselection.py: no se encontró la orden
naturalselection.py: no s'ha trobat l'ordre
naturalselection.py: opdracht niet gevonden
naturalselection.py: parancs nem található
naturalselection.py: perintah tidak ditemukan
naturalselection.py: príkaz nenájdený
naturalselection.py: příkaz nenalezen
naturalselection.py: команда не найдена
naturalselection.py: командата не е открита
naturalselection.py: 命令找不到
naturalselection.py: コマンドが見つかりません