Archaeological and Palaeontological evidence suggests it is an inherited trait. 

Bipedalism is ancient in our family. It arises before our own genus; Ardipithecus already shows anatomical adaptations to bipedalism. http://science.sciencemag.org/content/326/5949/71

Australopithecines walked fully upright over extended distances. http://rsif.royalsocietypublishing.org/content/9/69/707.short

Hand morphology changes through human evolution, because its role in locomotion diminishes. Although some adaptations to arboreal locomotion are retained in Australopithecine hands, they appear not to function as obligately in a locomotory capacity as ape hands. http://science.sciencemag.org/content/333/6048/1411.full

Moreover, the use of tools and the transport of bone materials and stone materials over several kilometers by the lower Pleistocene suggests that humans habitually carried things over long distances and did not use their hands/arms for locomotion. http://www.sciencedirect.com/science/article/pii/S0305440308000502

Finally, the inner ear of hominins has been extensively remodelled as an adaptation to balancing in a bipedal posture. http://www.nature.com/nature/journal/v369/n6482/abs/369645a0.html

All these anatomical changes have genetic bases and to my mind could not be explained simply by conditioning.

Thank you Sir for such an elegant explanation. My doubt is, as naive as it is, is how characters acquired during the lifetime of our ape ancestors became inherent to our species?After all, I assume bipedal posture evolved out of a need to migrate over longer distances, or perhaps the relative advantage of carrying food, but anyhow it must have been an acquired adaptation. Going by Darwinism, is there a scope for accounting for this fact?

I think your doubt stems in part from viewing quadrupedal locomotion as the ancestral situation. It isn't. Chimpanzee and Gorilla knuckle-walking are at least as much an evolutionary novelty as bipedalism. It has even been proposed that bipedalism can quite naturally develop from bipedalism, while the transition to quadrupedal locomotion is much larger. http://science.sciencemag.org/content/316/5829/1328.full

A second misunderstanding is the inheritance of acquired characteristics. This does not happen, as muscle/bone/etc. characteristics acquired throughout an individuals' life cannot be coded in the genetic material in the germ line.

The development of bipedalism likely took place from a non-quadrupedal starting point around 7 million years ago (the common ancestor we share with chimps and bonobos) and took a long time to evolve. Postcranially, only with the appearance of Homo erectus does our style of bipedalism fully develop. Although earlier forms were bipedal for much of the time, anatomically, they retained some arboreal features. Only with the well-preserved skeleton of Nariokotome Boy does the development of human bipedalism seem completed (Walker, A. & Leakey, R. The Nariokotome Homo erectus Skeleton (Springer, Berlin, 1993)).

This gives a duration of over 5 million years for the various adaptations to accrete.

Thank you Sir. Is it suggestive then that bipedalism happened to be a chance mutation that got naturally selected under the prominent environmental circumstances?

Or whether it would be more precise to say that bipedalism evolved out of a series of chance mutations in the anatomy of early hominins?

I guess it is germane to recognise that there is not one single "bipedalism". Bipedalism is apparently a solution that developed in different ways in different species. It may also have developed in apes not directly ancestral to ourselves living long before our common ancestor with chimpanzees. http://www.pnas.org/content/96/15/8795.full

In our own clade this is demonstrated by different organisation of locomotion in different australopithecines (see e.g. http://science.sciencemag.org/content/340/6129/1232999.full) and the newly discovered species Homo naledi suggests diverse locomotion anatomy in our own genus https://elifesciences.org/content/4/e09560

This means that not one single mutation suffices for bipedality identical for our own to arise. There is not even one single series of consecutive mutations that leads to bipedalism. Rather I imagine there are manifold mutations leading to manifold bipedal or bipedal-like outcomes that occurred in a large variety of species. In hindsight, one of these "series" led to our own anatomical organisation.

(Also possibly in ape families not ancestral to our own)

Thank you so much for your interaction Sir. I am really keen to work on human evolution, probably through a genetic perspective, and would highly value your advise and opinions upon it.

Rajit you have raised an interesting debate. Gerrit has very nicely explained too. certainly bipedalism not an exclusive human trait but much more ancient trait. even quadrupedal monkeys do at time express erect posture. among great apes bonobo carries bipedalism more than chimp. our common ancestors were must have been versatile in different locomotory repertoirs. it was bipedalism which provided selective advantage in hominin lineage for various activities in which carrying and fast running excellerated this behavior. Even aquaboreal life style enhanced bipedalism. Certainly it is a polygenic inheritance which is true for most bodily adaptations.

Thank you SIr. The debate is indeed an interesting one. I believe that the more we try to figure out our own history as a species, the more it makes us wonder at the elegance of the way evolution has taken place. There's indeed a lot more to explore. I think that's the beauty of science.

Still, the question of Uner Tan Syndrome sustains. How can we account for it? Is it 'reverse evolution', as is being commonly depicted in popular media?