Physical Labour Vs. Mental Labour

Why does the World today value Mental Labour much over Physical Labour ? Is it because Mental faculties are the only distinguishing factor we have compared to animals and the reckless promotion of this differentiating factor is justified by the trend the human race has put into place of overvaluing mental labour and constantly degrading the dignity of physical labour? The following questions arise - Would you not do any of your own house cleanliness work for days together and let the dirt pile up if your domestic help weren't available for unavoidable reasons? What would you do if you are a businessman of a manufacturing unit and all your physical labourers refused to come to work because they suddenly found it below their dignity to do any such work? Would physical workers then not become the most scarce resource in the market? Would you then not pay them more than your managers? What would each of us do if suddenly due to 'dignity of physical labour' problems, no one agreed to drive public buses, no one ever cleaned our roads, no one ever cleaned the offices we work in, no one agreed to work on any construction site as labourers, if mothers refuse to cook as they now do not want to get an inch close to house work, there were no gardeners etc etc etc. ?

All this and we still value the so called mental labour much much more than physical labour. In fact even the jobs in organizations requiring continuous computer work from morning to night are now looked at as more physical work than mental and is hence probably underpaid, and the cadre above this is said to be the 'thinkers' , those who generate ideas which are then implemented by someone else, and the 'thinkers' are heavily paid for each idea they generate. But, can you not see, that as one rises up the hierarchy, the work changes to more Physical? You say that a manager has to do no physical work because he is not carrying stones on his back, but does not he have to walk in his Woodland shoes up and down his departments floor space all day long, does not he have to keep on talking and talking and talking- answering calls, answering his subordinates, answering his seniors, developing PR with his peers, typing out emails all day long, bending in front of the computer screen all day long, arranging and rearranging filed papers (all the more worse for the females, they have to do the same in heeled shoes!)... The point therefore remains, why do we as a so called developed race set trends which are soon going to backfire on us and bring us back to base one with the worth of the so-called physical labour shoots up a million times higher than the mental work, a term which would soon be as a satire describing the laziest of the lot!