No, it has not. But some “scientist” in Pakistan either said it, or was reported (by an idiot journalist) to have said it.
I have some professional interest in this topic and wrote about secular trends in height here
I would regard this claim (that average height has dropped 4 inches in Pakistan) as complete bullshit for now. Official figures for different countries (as much as is known) are given in this link
A quick search of the medical literature turns up no such trend. I did find a publication for India which indicates that Indian average height has increased, though slowly. I would guess the same for Pakistan but will try to find better data.
I am calling bullshit on this report for the following reasons:
1. No scientific data has been cited.
2. Such a decrease is practically unheard of in the modern world. If it has not happened anywhere, I find it hard to believe it would happen in relatively better fed Pakistan (better compared to the Indian and African average, and better compared to our own past).
3. Last but not the least, the tendency of Pakistani officials (including scientific ones) to pull shit out of their behind without any fear of being contradicted, and the tendency of our journalists to convert hearsay into established fact.
This means that while the average IQ of officials and journalists may indeed have dropped 40 points, average height has not. Nazria e Pakistan can have the first effect, but has no direct effect on physical height. (if the nation crashes and burns and sinks to Somalia level, then yes, average height may eventually decline).
btw, to see an example of how the ideology of Pakistan impacts IQ, see page 258 onwards of this report to see what a supreme court judge regards as undisputed historical fact (including the fake Macaulay speech and tons of BS about…oh well, see for yourself).
In fact, forget about height, read that Supreme court judgment and have a pleasant afternoon contemplating the horrors to come (I know Justice Katju has been writing his own version of pop history recently and people have criticized some of his information, but compared to these guys he is a subtle, deep and erudite genius). Justice Ijaz even managed to quote Shahabnama (the autobiography of former senior civil servant Qudratullah Shahab, where he reveals that he went on a secret mission to Israel that involved not falling asleep for ten days straight, since in his sleep he might have revealed his real name…I kid you not).
Keep in mind that the Pakistani supreme court regularly copies portions (or wholes) of judgements from India, so some of the history may have come from India..(as always, we find a way to blame India).