mean "hello."]]> started writing about 5,000 years ago.]]> people to communicate.]]> Soon, they will learn to speak.]]> came later.]]> borrow words.]]> phones."]]> understand language.]]> ability.]]> devices "cellular phones."]]> hear use sign language.]]> led humans to live in groups.]]> blur together.]]> connect with one another.]]> speak when they are born.]]>