Are mermaids real? Let me start by saying that humans are very different than all other terrestrial (living on land) mammals. Aside from our sentience and sapience and our amazing intelligence, our spines are much straighter and more flexible in comparison to other terrestrial mammals; our fingers are partially webbed. We can control our breathing like no other mammal on Earth. Did you know that human babies can hold their breath instinctively? Any other terrestrial mammal's offspring would drown. We have a thick layer of insulating fat thats purpose is to keep us warm in water . The only other type of mammal with a fat layer similar to ours is marine mammals. We are also the only land mammals that sweat, an adaptation more suited for marine life. What I'm trying to conjecture here is that maybe, somewhere in our evolutionary lineage, we were borne of the sea. Before discarding this thought, think about it: earlier in Earth's history , food was much more plentiful in the oceans than it was on land. It was advantageous and probable that our ancestors adapted in some way, over millions of years, to accommodate this. Look at modern polar bears. Hundreds of thousands of years ago, a group of brown bears that lived in frigid regions split from the normal line of evolution to take advantage of the plentiful supply of food in the ocean . They grew to hold their breath longer, and grew a tolerance for colder weather and freezing waters. These bears are what we know today as polar bears. We're actually witnessing a species adapting to its environment over time right now! If polar bears are changing into marine mammals now, why, somewhere down the line, couldn't this have happened to humans?
In recent years, there have been recurring spottings of an unknown genus of dolphin, or a completely unknown species of marine mammal. All of these spottings have only been in partiality; only parts of these species have been recovered. What has been recovered suggests that, due to the discovery of a hinged ribcage, finger-like bones in the tail fin, a large spleen (common in marine mammals), and the remains of leg and hip bones with an iliac crest (a bone formation designed to support weight), these creatures are very, very similar to us. If you didn't already know, a vestigial structure in an organism is a part that serves no purpose, but still appears in said organism, like how many species of whales still have hip bones. Vestigial structures were most likely used in past variants of a species. The iliac crests found have to mean that these unknown, humanoid creatures once walked on land. And there's only one type of creature that walks completely upright on two legs with iliac crests like the ones found in this creature... You and me.
I believe mermaids exist, just not in the idea that many believe it in. They are a remnant of an early evolution that branched off of us because most of the early world was water. Some of our ancestors may have gotten stranded on an island and turned to the water instead of staying on land like we did. They were forced to go to the water and evolutionized into what I believe are Mermaids.