"The man has a bear."
Translation:Mannen har en björn.
There's no good reason for them. It's just a historical thing, our language family has had genders historically, two or three of them. Further back in history we had three, but they merged into the present day two. They used to have gender in English too, but lost it. German still has three, and so on.
"Ett" is neutral, as in stuff that is genderless. "En" is the common gender as in male or female. Bears can be male or female, therefore it has to be "en". A table does not have gender, therefore "ett bord". There may be some exceptions from this rule, but it generally works like this
I disagree with this explanation. The allocation of gender to nouns appears to be completely random, regardless of whether the thing in question is genderless or not. A sandwich cannot be male or female. A meal does not have a gender. A newspaper does not have a gender. A cup does not have a gender. A ticket does not have a gender. A child CAN be male or female, so according to your explanation it has to be "en barn".
"Some exceptions" you say... Just off the top of my head I've listed several above and there are hundreds more, which indicates that there is no such "rule".
Clearly, whether something is "en" or "ett" has nothing whatsoever to do with the thing itself actually having a real gender or not. The WORDS have been allocated one or the other, but that has nothing to do with the actual thing the word refers to.