Which two details refine the author's claim that the materials used for the design of shoes has evolved over time? excerpt from “Shoes: Feet First!”
from A History of Travel in 50 Vehicles
by Paula Grey & Phillip Hoose

Despite the relatively recent age of the early shoes found to date, scientists believe that humans were wearing shoes as much as 40,000 years ago. Shoes made of reeds, papyrus, or even leather decompose easily, leaving few or no traces. But people who don’t wear shoes have wider feet and bigger gaps between their big toe and the other four. In studying bones of the smaller toes of fossilized skeletons, scientists observed that the thickness of these bones decreased somewhere between 40,000 and 26,000 years ago. They believe the change was the result of wearing shoes.
The materials used to make shoes varied with the climate and region. Ancient Egyptians made sandals from papyrus and palm leaves. The Masai of Africa used rawhide; the people of India used wood; and the Chinese and Japanese used rice straw. South Americans wove sandals from the leaves the sisal plant, and the Anasazi people of Mexico and Arizona used the yucca plant. The Dutch developed wooden clogs. People living in arctic climates created snowshoes —a hardwood frame with rawhide lacings—which distribute a person’s weight over a larger area so that the foot doesn’t sink into the snow.
Today, shoe manufacturers use rubber, plastic, cloth, and other materials in addition to leather. Most soles are made from synthetic materials such as ethylene, vinyl, acetate, rubber, and polyurethane, which provide better traction, durability, and water resistance than leather soles. Special shoes are available for running, bowling, and other sports. And shoes are often considered an important fashion accessory.