Complex sentence: Thomas Jefferson was a firm supporter of the Great Chain of Being and an opponent of extinction, famously denying the extinction of the wooly mammoth on the grounds that nature never allows a race of animals to become extinct.
Split into simpler sentences: Thomas Jefferson was a firm supporter of the Great chain of being and an opponent of extinction. He famously denied the extinction of the wooly mammoth on the grounds that nature never allows a race of animals to become extinct.