How have ochestras developed?

Answer 1

Orchestras began to exist in the late renaissance/early baroque period. At first the orchestra was made up of the instruments you happened to have available in your town, and scores for the orchestra was not written for specific instruments. Instead the composers at that time wrote different parts and then handed them out to suitable instruments "on the spot".

In the 18th century notable improvements were made to the woodwind instruments so they could play more notes, but it was not until the 19th century that they were more or less made the way they are today.

The brass instruments had a very limited number of tones they could play up until the 19th century when inventors came up with the idea of valves, letting them play all tones. It was not until the end of the 19th century that musicians and composers accepted this however since they believed the sound of the "natural" brass instruments were superior.

The string instruments were improved (some instruments such as the viola da gamba was used but later abandoned in the orchestra) and "perfected" around the 17th century. The way today's orchestras have their string sections was standardized around the late 18th century, but it took until about the end of the 19th century before you could say there was a standard number of string musicians in every orchestra.

During the 19th century the orchestra was constantly growing and instrument makers made instruments to play both higher and lower tones. This was partly because composers like Hector Berlioz and Richard Wagner demanded bigger orchestras and wider ranges in their music, but also because instrument makers were creative and frequently came up with new inventions.