Yes is the same word as yea which is the same in germanic. It's a very old word. Being one of the most used words in the English language, yea probably was said as yep and yup in many colloquial settings, workshops, pubs many times before it was recorded in writing. yup is a fairly low energy way of say the word, which is probably easier to pronounce than yea, so laborers saying yea would have ... More @Wikipedia
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