Immigration increases native wages because when lower or differently skilled immigrants enter their country, natives are incentivised to specialise in jobs in which they are more productive. Then they can subcontract their other jobs to the migrants.

A man with a tool is more productive than a man without. What is another man’s labour if not a type of tool available to the worker? Even if the native is better at every conceivable task, the law of comparative advantage reveals that trade between him and the native is still mutually beneficial. Immigration is the free trade of labour where trade is a means of each entity specialising and trading their product for what they need. With trade, a country’s miners can turn iron ore into computers. While low-skilled migrants farmland, clean houses, and cook food, natives can write code, teach physics, and run hospital wards. 

High-skilled migrants’ benefits speak for themselves, but the low-skilled migrants also irrefutably increase productivity.