Combine Individual Items From Separate Arrays Into a Third Array

I have two arrays, one with a list of first names and a second with a list of last names. What I would like to do is combine the first name and the last name that reside at the same index position in their respective arrays into a third array. Each pair of arrays will always have the same number of items, but that number may change - i.e., in some instances there may be 5 first names and 5 last names, but at other times there may be 15 first names and 15 last names.

So, for example:

Array $firstName contains:

$firstName[0] = Jon

$firstName[1] = Bob

$firstName[2] = Tom

Array $lastName contains:

$lastName[0] = Smith

$lastName[1] = Jones

$lastName[2] = White

And I want to create array $fullName like this...

$fullName[0] = Jon Smith

$fullName[1] = Bob Jones

$fullName[2] = Tom White

Thanks for the help.