Our beautiful earth is full of strange appearing beasts, so what is so difficult about believing bigfoot exists?
Some believe bigfoot has descended from the giants mentioned in the Bible.
These giants were called Nephilim.
"The Nephilim proved to be in the earth in those days, and also after that, when the sons of the [true] God continued to have relations with the daughters of men and they bore sons to them, they were the mighty ones who were of old, the men of fame." Gen. 6: 4
Gen. 6:1 shows that these "sons of the [true] God" were angels.
"And there we saw the Nephilim, the sons of Anak, who are from the Nephilim; so that we became in our own eyes like grasshoppers, and the same way we became in their eyes."
So it was when Noah's flood struck, the fathers of these human-angels went back to heaven and the offspring were killed in the flood. So none survived the flood. These Nephilim appeared as human not animal, and so were not taken along in the ark by animals (apes, gorillas) in their genes to survive to our day.