New findings about the great white shark highlights this. Australian great whites and the Mediterranean type have genes that point to common ancestry. It is believed that a few related female sharks split up. Some going north to the Mediterranean from the larger gene pool in the south, or they peeled off from the main group in the Atlantic some going north the others going south. Narrow channels in the Mediterranean stopped this group from rejoining the Australian gene pool.
This happened 450,000 years ago. Mutations since that time make the timeline clear. It is believed that swordfish and tuna the main food of the great white also split off from the their main groups. Great white sharks followed the food supply.