I believe that there are Martians living on Earth. Many many people have reported seeing them. Since they are geniuses, and thousands of years ahead of us in technology, they have managed to easily avoid detection. And, they have adroitly managed to make sure that they never leave a scrap of physical evidence behind, including any bones or body tissue when they die.
And although we have explored the habitat in which they live, by the thousands of close-up photos we taken of Mars, and the probes we have landed on Mars, they are so smart and adept that they can hide from these machines, just like they hide from the tens of thousands of game cameras and security cameras we have across the country.
So, my belief that Martians walk among us, is founded on the exact same arguments that are made for the existence of Bigfoot.
But the Bigfoots may even be smarter! Despite the fact that our earliest African ancestors in Africa, more than a million years ago (Lucy and her lineage, Austrailopithicus), were a very very small population of pre-humans, we have nonetheless managed to recover at least three skeletons of them, which are currently on display.
Those Bigfoot, which if they exist have been around for thousands and thousands of years, and which allegedly walk around today, are so brilliant that they have left absolutely no skeleton remains whatsoever in the current or historical fossil record! I guess they must grind up the bones of their dead and mix them with chocolate milk.
Mannyrock