Short answers, pulled from the story.
The world's oldest preserved linen shirt is a highly sophisticated garment from a First Dynasty Egyptian tomb at Tarkan, discovered by archaeologist Flinders Petrie. This piece dates to the 3rd millennium BCE and features finely pleated shoulders and sleeves designed for both form-fitting trimness and movement.
The shirt remained a hidden undergarment worn only by men until the twentieth century. By the seventeenth century, men's shirts were allowed to show, and a visible shirt with nothing over it was considered improper even as late as 1879.
Hannah Montague, a housewife in upstate New York, invented the detachable collar in 1827. She solved the problem of washing entire shirts by cutting off collars and attaching them to the neckband after washing.
In the eighteenth century, men relied on the long tails of their shirts to serve the function of drawers. Costume historian Joseph Strutt believed that men who did not wear shirts to bed were indecent.
Collar stays became popular in the 1930s, although early accessories resembled tie clips more than modern stiffeners. They connected the collar points to the necktie to keep them in place.