Yes, sort of. All crops are /have been improved and selected by humans, and yes, you can still find wild/unimproved corn.

yes.

no...what makes you think that

It's been altered by selective breeding so much that you'd never look at the "wild" ancestor of corn and suspect that it was related. So I'd say yes.

It's a little outdated but this old Walt Disney's cartoon will answer your question.

"The Grain That Built A Hemisphere"

https://vimeo.com/152130398

No, but it has been naturally genetically modified (yes, grafting and other techniques ARE genetically modifying plants, but naturally and over a period of time) over thousands of years. Seriously, a "big" cob of corn 7 thousand years ago would have been about the size of what we call "baby corn".

If, by "corn", you mean maize, the American grain, it was developed from teosinte, a wild grass. Teosinte is a branching grass but some plants carry a gene tb1 (teosinte branched 1) which suppresses the lateral branches and shortens the others. Selecting teosinte plants with this mutation and breeding from them led to the development of maize as we know it today. Maize was probably domesticated between 5000 and 6000 BCE.

"Corn" is commonly used for maize in the Americas and has spread to other countries but in the UK, "corn" refers to any cereal crop such as wheat, oats, barley etc, which is why it is better to use "maize" to avoid confusion.

No. Wild corn was first domesticated by "indigenous" peoples in southern Mexico about 10,000 years ago.