[singular]

Well, not surprising that was down-voted, but seriously - if somebody contends that we're 'not designed for X', yet we have actually evolved to be able to do X, I think it's reasonable to point that out, even if the fact is that we do too much sitting down.

[shpxnvz]

While it may in fact be true that we evolved to able to sit, the sentence you quoted is in no way evidence of it. A link to supporting evidence, or even a well reasoned argument, would go along way towards backing up your claim.

[singular]

It was indeed an (uncited) quote from a wikipedia article which is hardly the same as concrete evidence :-)

Regardless, it is certainly the case that we have evolved to be able to sit comfortably and take weight off our legs - that, I think, is indisputable.

I would argue that the buttocks provide a structural base for the weight of the body which would otherwise be transmitted through the upper parts of the legs more so than they are in reality. That is something of a guess, however.