A couple things have nagged me about Bigfoot more than others: How does he fit in evolutionary-wise when he is overly developed physically yet seems to be less evolved mentally, and why does he insist on being so shy?
Typing up a report for my work (hospital medical transcription) something dawned on me - cortisol, hormones, the pituitary gland and the endocrine system.
Adrenal glands in the human body sit atop the kidneys. They produce and release cortisol hormone in times of stress to help with fight-or-flight. They also control the proportions of salt and water in the body, as well as the growth of the mammal. Interestingly, these hormones that help regulate growth also can give one extra fullness around the neck and upper back and excessive hair growth with male characteristics. The adrenal glands release cortisol hormone that helps with energy necessary to deal with stress. The adrenal glands are driven by the pituitary gland in the brain. In the case of those with acromegaly (who grow to enormous heights), a disruption in the pituitary gland, such as a tumor, has caused it to keep sending out signals for release of growth hormones. It also releases the male hormones that give muscles and hair growth - typically male characteristics.
Imagine a being who has enlarged adrenal glands by adaptation or a robustly overactive pituitary gland; this would be a hairier, taller, and possibly more fight-or-flight driven being with stress hormones that make it inherently shy. If this being had been originally evolving in a northern climate, he would have needed hairiness, power, height, and fight-or-flight senses to survive harsh conditions, not to mention mastodons and other threats. The endocrine system would have been the most important aspect to develop to have immunity, power, warmth, and acute senses. What this would have evolved into would be a shy and nervous, on the alert, hairy giant by evolutionary adaptation means and not the more magical nephilim (angels who mated with human women creating a giant race) explanation.
Let's talk for a moment about a potential race of people who could have originated this adaptation - Neanderthal. This branch of the human family was believed to be in Europe from 600,000 to 350,000 years ago and believed to have stopped existing around 32,000 to 33,000 years ago. Paleo-Indians were believed to launch into the Americas around 15,000 to 17,000 years ago. Perhaps beside them were another group of humans seeking more resources.
Although many artist renditions of early modern man show Neanderthal in various stages of cave-man appearance, they also show him often fairly hairless. The truth is, given the lifestyle of hunter gatherers, it would likely have been that every follicle produced a coarse hair for protection from elements. Such changes as more fine sparse hairs that we have today are the result of living in agricultural situations and protected from the elements. Now, imagine this Neanderthal below with hair -
So, even those these artist renditions might be fanciful of what Neanderthal was like, he might be the more likely to be the ancestor who adapted. Neanderthal perhaps did not die, but in Northern European climates, adapted larger adrenal glands, a more robust pituitary gland, surviving the climate and mastodons and other dangers, to eventually move into the Americas and settle in to become what is now known as the shy hairy giants.
Of course, this is just another one of my theories I'm knocking around, but I do like how it neatly explains a tall hairy shy nature in a way that makes sense by evolutionary means.
Frame of reference: World's tallest recorded man, 8 feet 11 inches - a common height reported for Bigfoot -