I don't know if English started out with 300 words, but I like Mark Twain's take on it. Steve.
“Ours is a mongrel language which started with a child's vocabulary of three hundred words, and now consists of two hundred and twenty-five thousand; the whole lot, with the exception of the original and legitimate three hundred, borrowed, stolen, smouched from every unwatched language under the sun, the spelling of each individual word of the lot locating the source of the theft and preserving the memory of the revered crime.”
— Mark Twain
Test Your Vocabulary - The Nitty-Gritty Details: "