This notion derives from the traditional rendering of Genesis 2:7 in the King James Version (“and the man became a living soul”). The Hebrew word translated “soul” is nephesh. According to the Bible, animals also possess the nephesh. For example, in Genesis 1:20, when we read that God made swarms of “living creatures,” the Hebrew text underlying “creatures” is nephesh. Genesis 1:30 tells us the “living nephesh” is in animals.
