Doug's excerpts are to the point. The section quoted is from the article 'The part played by labour in the transition from ape to man.' The section quoted is a reflective check upon the overall thesis that man alone has mastery over nature, through labour, and that is his differentia specifica from the animal kingdom. The specific egs that Engels is cites of falling back are all from the ancient world: Asia Minor, Mesopotamia, Greece. Needless to say the greater part of the article runs in quite the opposite tendency from the section isolated. So Engels continues:
'Thus at every step we are reminded that we by no means rule over nature like a conqueror over a foreign people - but that we, with flesh, blood and brain, belong to nature, and exist in its midst, and that all of our mastery of it consists in the fact that we have the advantage over all the creatures of being able to learn its laws and apply them correctly.
And, in fact, with every day [Engels continues more optimistically] that passes we are acquiring a better understanding of these laws and getting to perceive both the more immediate andthe more remote consequences of our interference with the traditional course of nature. In particular after the mighty advances of the natural sciences is the present [ie 19th] century, we are more than ever in a position to relaise and hence to control even the most remote consequences of at least our natural day-to-day production activities.'
Of course, there's no need to take Engels word for it.
Take this small example from the State of the World 1999:
In 1900 an American farmer fed seven other people. Today his great grandson feeds 96. Turn your back on the increased grain yields and mechanisation that made that possible if you want, but don't complain if you are one of the 89 in every 96 people who are surplus to requirements. -- Jim heartfield