ID Each Duplicate In A Column

I have a spreadsheet with a large number of records. Each row contains info about people and there are multiple rows for each person. The database is sorted by the last name column so you can see each row of data for that person. We have been manually highlighting the name by each group, alternating so you can easliy see when the name changes. (hightlight Adams, don't hightlight Brown, higlight Carter, etc) But the file is long and this will take forever. I would like to highlight each group of names without manually scrolling thru the large spreadsheet. It would even be fine to just hightlight the first occurance of each name so that you can easily find the first record for that name. Conditional Formatting doesn't seem to work since I need it to hightlight when the last name changes - not find duplicates.