I can't believe they discussed plurals in English and missed the most interesting piece!
The -s endings came after Norsemen conquered England, and the introduction of it was from their language, connected to old French. This also is why in English, you have words like "ox/cows" and "beef": the Norsemen who were nobles essentially influenced the English to use their words for the animals since they were served as food to them (beef), while the English people who slaved in the fields raising the actual animals (cow) continued to use their ancestors' words for the live animals. This is why we have different words for the meat of the animals (beef, poultry, mutton) vs. the actual animals (cows, chicken, sheep).
The -s endings came after Norsemen conquered England, and the introduction of it was from their language, connected to old French. This also is why in English, you have words like "ox/cows" and "beef": the Norsemen who were nobles essentially influenced the English to use their words for the animals since they were served as food to them (beef), while the English people who slaved in the fields raising the actual animals (cow) continued to use their ancestors' words for the live animals. This is why we have different words for the meat of the animals (beef, poultry, mutton) vs. the actual animals (cows, chicken, sheep).