Without string, or as some call it, cordage, we would be a lot colder today, and wouldn't be able to build many of the great structures and machines that make up modern life.
When Otzi the iceman was found in the Italian Alps, he had clothing and equipment which used lots of different types of cord from multiple different materials. One of the earliest cords was simple sinue taken from dead animals. This is an interesting material to sew with, but it's strong and quite durable.
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