Here are some research findings:
The most common 100 words cover 60% of the content of a conversation
The most common 4,000 words cover 98% of the content of a conversation
An average adult’s vocabulary contains about 60,000 words. As only 4,000 are used, constantly, we can ask ourselves what is the purpose of the other 56,000? What good is teaching them? (up to 18 years old, children learn 18-20 words a day, according to Geoffrey Miller’s calculations)
The remaining 56,000 are good for sex. Here’s how: there is an 80% correlation between general intelligence and vocabulary size (see A. Jensen, 1998, The g factor, London: Praeger). Identical twins raised separately correlate 75% to vocabulary size (environmental effects therefore have a modest contribution) As such, a sufficiently rich vocabulary is a good indicator of intelligence and functions, in specialized language, as an indicator for matching.
A woman looks at a man and has no way of knowing how smart she is. People can’t go to intelligence tests for practical reasons. There’s no need. Our brains automatically infer levels of intelligence by processing the sentences of our interlocutors. A good idea to seduce a woman is to speak to her using more than 4,000 words, not at all emphatic but eloquent and casual.
It is possible that sexual selection has decisively influenced the evolution of language and to explain the dimensions in relation to the practical needs of everyday life. Anyone can survive with just 1,000 words.
Kanzi, the famous bonobo monkey, now 31 years old, failed to learn more than 200 visual symbols (and this monkey is unusually intelligent). Primates generally use between 5 and 20 signals. Only we, humans, can afford much broader communication.
If you don’t have much sex, get a dictionary of neologisms or, even better, read good quality literature. The size of the vocabulary is a kind of disguised advertisement for fitness.