Prior to the steam engine, the oxen/bullock/horse/donkey/elephant was the dominat non-human power-source.
Humans can work at about 125-250W continuously (1/8 to 1/4 of a kilowatt, or 1/6 to 1/3 Horsepower). Elite athletes can produce 500W or more for short periods.
All biological systems have a short and medium term "duty-cycle" - our muscles get tired, non-linearly, and need short-term recovery and longer-term rest and recuperation. Sleep and recreation are about the nervous system/mind/brain.
From chapters of Taylor's book Scientific Management here's proof you get more out of people by making them rest! He improved average output from 12 tons/day to 47 tons/day through careful (psychological) selection and enforcing rest periods. Counter-intuitive, but well-researched.
For example, when pig iron is being handled (each pig weighing 92 pounds), a first-class workman can only be under load 43 per cent of the day.
He must be entirely free from load during 57 per cent of the day.
And as the load becomes lighter, the percentage of the day under which the man can remain under load increases.
So that, if the workman is handling a half-pig, weighing 46 pounds, he can then be under load 58 per cent of the day, and only has to rest during 42 per cent.
As the weight grows lighter the man can remain under load during a larger and larger percentage of the day, until finally a load is reached which he can carry in his hands all day long without being tired out.
For an 8-hour day at 125W, a total of 1KwHr (kilowatt hour) useful work is done, ignoring rest breaks.
Animals are heat engines as well. We 'burn' fuel with oxygen, releasing Carbon Dioxide and some useful work. For that 8-hour day, the energy input is probably 10,000KJ (kilo joules) [or 2500 (kilo)'calories']
Electricity sells for ~20c/KwHr in the western world. The minimum wage in Australia is ~$100/day now.
The raw "Physical Amplification" on a cost basis is ~500:1
A 500 HP bulldozer is controlled by one operator. There's a 3000:1 amplification. But machines are under 50% effective at converting their output to 'work done' compared to people.
On a cost-basis, the bulldozer might costs $150/hour to operate (40-50L of fuel, Wages, Maintenance, Depreciation).
Or 10c/hour/person-equivalent. Probably 400:1 ratio based on the operator wages.
The same comparison calculations as with Physical Tools and Machines can be done for humans and computers.
The human brain runs at ~50 watts - with around a 4MJ total energy input (1000 'calories') per day.
Like muscles, it has a "duty cycle' and requires rest and recuperation, as well as sleep and longer-term "recreation" and holidays. There appear to be no studies of "Human Response to Cognitive Workload". [Looking for the wrong thing?]
Directly comparing the human brain's I/O bandwidth, processing and storage capacity with electronic computers is difficult because they are organised so differently and probably complementary. The are best at different tasks.
45 years of "Aritifical Intelligence" research tells us that we don't understand in fine detail our brain processes and capabilities or the fully appreciate the complexity of "ordinary tasks". To recognise, not understand, human speech takes around a 1.5Ghz CPU and 256Mb of RAM - plus a very large, complex training dataset. Recognising speech, without understanding it is the equivalent of talking gibberish.
For repetitive cognitive processes that humans do poorly - computers with their methodical exactness, excel.
A $5,000 computer system that costs $10,000 over a 5-year life (excluding software) can run an accounting systems that processes 25,000 transactions/hour and is able to store, summarise and report on perhaps a decades' worth of data.
The equivalent human processing using mechanical 'tabulators', themselve 5-10 times faster than pen-and-journal, would take 250 operators just for data-entry. Consolidating and reporting the accounts requires another largish group (25?).
The yearly wages bill for the operators would be ~$4M. On-costs, leave, recruitment and training - say $25M for 5 years.
A 2500:1 amplification on a cost basis.
I.T. Systems benefits are "cheaper, better, faster, more, all-the-same".
I.T. systems embed the business processes used and their interfaces, performance and reliability define the productivity possible across the whole organisation.