A transaction on a stock exchange must be made between two members of the exchange—an ordinary person may not walk into the New York Stock Exchange (for example), and ask to trade stock.
If I understand correctly, even when I issue a buy/sell order via a computer, it is ultimately delivered to a person that does the actual transaction or places the order.
Am I right? Why is there a middleman here - is it just legacy from before we had computers? Why aren't all trades done directly software-to-software, mediated by the central computer of the exchange? Why the need to human middlemen?