Learn English – “Wise man” vs. “wise guy”

Two very similar expressions yet quite opposite connotations. Wise man is an older phrase but wise guy is a newer one.

I found two possible connections to wise man. There is the surname Wiseman which is a long-established surname of Anglo-Saxon origin, and derives from the Olde English pre 7th Century "wys", meaning "wise", and "mann", a man, and was originally given as a nickname to a wise and learned man, perhaps one who was regularly consulted by other village inhabitants on matters pertaining to law or business transactions.¹

Wise men is also mentioned as another name for biblical magi who were, in the Gospel of Matthew and Christian tradition, a group of distinguished foreigners who visited Jesus after his birth, bearing gifts of gold, frankincense and myrrh.²

Opposite connotations of the words from thefreedictionary:

wise man: a sage / a wise and trusted guide and advisor

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wise guy: a smart aleck / a person who is given to making conceited, sardonic, or insolent comments

Etymonline says:

Wise man was in Old English. Wise guy is attested from 1896, American English…

• How do these two phrases happen to have different connotations (one positive, other negative)?
• Is it possible to find an explanation regarding to their origins?

_{1 http://www.surnamedb.com/Surname/Wiseman
2 http://en.wikipedia.org/wiki/Biblical_Magi}