Why do people say "Ummm" or "Like" a lot when nervous?

To give them time while they think of the words they want to say.

I think "ummm" is a kind of universal sound people make when thinking. Also "like" could be a shortening of "it's kind of like..." I was always taught just to pause in speaking if I couldn't collect my thoughts because it sounded more intelligent.

im not sure. its a good question - i have a college english teacher that says um more than any other word in our class - you should see my notes just a bunch of umms!!!!

because it has been passed down from generations of years past.

maybe in english accent, but we indians have different words but I think it all depends on your habitual words.

because they dont know how to speak.. i always hear 'big shots'

'college educated' people.. sayin in their speechs.. uhhhh uhhhh... mmmm..mmm ... oh ya ... uhhhh... you would think all the education they have, they would have proper english....