Some whales and dolphins have been discovered to have a set rear flippers. They are labeled as atavisms, based on the presupposition that whales and dolphins are descended from land animals that had hind limbs. However, from a creationist and design perspective there are two other possibilities.
It needs to be noted that these flippers do not have any bones. The rear bones in both whales and dolphins serve reproductive purposes. They serve as anchor points for reproductive structures and are different in males and females. However, it needs to be pointed out that these are flippers, not lags. They cannot be considered evidence that whales and dolphins descended from four-legged land animals.
The first possible explanation for these hind flippers is that they are indeed structures that were once common in whales and dolphins but have since deteriorated and are no longer used. While this does have an evolutionary twist to it, it is also consistent with the creationist idea of degenerative change. Furthermore, when they do reappear there is no new genetic information it is the reactivation of existing information.
The second possibility is that these hind fins are an example of the built-in potential variation within the created kinds. The potential of producing these fins could have always existed but simply are not being used in general. In that case while these are new structures, they do not represent new information, but they were programmed from the beginning. They are simply appearing now even if in a non-functional form.
Even if these rear flippers do represent a reemergence of ancestral traits, they do not qualify as evidence for universal common descent, or evidence that whales and dolphins descended from four-legged land animals. These structures regardless of any other factors are simply fins. The most they show is that whales and dolphins once had rear fins that they usually no longer produce.
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https://creation.com/index.php?option=com_content&view=article&id=4748
