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It was not until relatively recent times that scientists came to understand the relationships between the structural elements of materials and their properties.
The earliest humans had access to only a very limited number of materials, those that occur naturally: stone, wood, clay, skins, and so on. ( ① ) With time, they discovered techniques for producing materials that had properties superior to those of the natural ones; these new materials included pottery and various metals. ( ② ) Furthermore, it was discovered that the properties of a material could be altered by heat treatments and by the addition of other substances. ( ③ ) At this point, materials utilization was totally a selection process that involved deciding from a given, rather limited set of materials, the one best suited for an application based on its characteristics. ( ④ ) This knowledge, acquired over approximately the past 100 years, has empowered them to fashion, to a large degree, the characteristics of materials. ( ⑤ ) Thus, tens of thousands of different materials have evolved with rather specialized characteristics that meet the needs of our modern and complex society, including metals, plastics, glasses, and fibers.