Ive always felt like things from mythology such as Unicorns, Ogres, gnomes, griffins, basalisk, ect ect ect ad nauseum, are signs of evolution.
Its not hard to think that someone who sees a mutated animal, or something with anomalous traits was misunderstood, and in turn, interpreted in different ways.
Back in those early days, knowledge was shared predominantly via word of mouth. And if anyone has ever played the game of purple monkey dishwasher, it is easy to see how the story of someone who didnt understand what they were looking at, could easily get distorted into something infinitely more grandiose.
Now, again knowledge is shared word of mouth, so when one person at the end of the purple monkey dishwasher line of the original instance, years later, hears of another aberration that sounds vaugely similar, they recall the original one and claim it must have been what was seen before... when these things happen repeatedly it does not take long for them to become fabled, and the longer it is perpetuated, the closer it becomes to lore.
I could see things like ogres easily being misinterpreted for the 7 foot guy, who felt misunderstood by the folks in his home village, leaving to find a place to fit in, then another village villifying him because he is different, and assuming hes not even human. Similarly with vastly smaller people, to a different end.
So to say these things could have existed under differing circumstances is a no brainer. Genetics is a somewhat schizo thing. Look at the potential for other worlds, Do you really think you would see animals and sentient life on other planets that mirror life here on earth? Infinite possibility in infinite combination.