Tails.

A horse will use its tail to swat away flies, and birds use their tails to help steer themselves whilst flying. Animals which have evolved with tails use them for important things such as Lemurs will use their tails when climbing. So why do humans develop to not have tails?

1. Humans do not need tails. Because we stand on two legs we are perfectly balanced due to gravity, animals need tails to help stabilise them for the weight of their heads.
2. We also don't need a tail to grip onto things such as tree branches.
When a human is in the womb for 30 days it will have a tail like structure, although most people re-absorb the structure as we develop, some people have been born with tails. This is known as atavism, a trait of distant ancestors that reappears  in modern day. Usually these tails are only a few centimetres long and are usually removed shortly after birth.

Human vestigiality

Charles Darwin listed a number of putative human vestigial features, which he termed rudimentary, in The Descent of Man (1890). These included the muscles of the ear, wisdom teeth, the appendix, the tail bone, body hair, and the semilunar fold in the corner of the eye. Darwin also commented on the sporadic nature of many vestigial features, particularly musculature. Making reference to the work of the anatomist William Turner, Darwin highlighted a number of sporadic muscles which he identified as vestigial remnants of the panniculus carnosus, particularly the sternalis muscle.^[1][2]

In 1893, Robert Wiedersheim published The Structure of Man, a book on human anatomy and its relevance to man's evolutionary history. This book contained a list of 86 human organs that he considered vestigial, or as Wiedersheim himself explained: "Organs having become wholly or in part functionless, some appearing in the Embryo alone, others present during Life constantly or inconstantly. For the greater part Organs which may be rightly termed Vestigial."^[3] His list of supposedly vestigial organs included many of the examples on this page as well as others then mistakenly believed to be purely vestigial, such as the pineal gland, the thymus gland, and the pituitary gland. Some of these organs that had lost their obvious, original functions later turned out to have retained functions that had gone unrecognized before the discovery of hormones or many of the functions and tissues of the immune system.^[4][5] Examples included:

• the role of the pineal in the regulation of the circadian rhythm (neither the function nor even the existence of melatonin was yet known);
• discovery of the role of the thymus in the immune system lay many decades in the future; it remained a mystery organ until after the mid-20th century;
• the pituitary and hypothalamus with their many and varied hormones were far from understood, let alone the complexity of their interrelationships.

Historically, there was a trend not only to dismiss the vermiform appendix as being uselessly vestigial, but an anatomical hazard, a liability to dangerous inflammation. As late as the mid-20th century, many reputable authorities conceded it no beneficial function.^[6] This was a view supported, or perhaps inspired, by Darwin himself in the 1874 edition of his book The Descent of Man, and Selection in Relation to Sex. The organ's patent liability to appendicitis and its poorly understood role left the appendix open to blame for a number of possibly unrelated conditions. For example, in 1916, a surgeon claimed that removal of the appendix had cured several cases of trifacial neuralgiaand other nerve pain about the head and face, even though he stated that the evidence for appendicitis in those patients was inconclusive.^[7] The discovery of hormones and hormonal principles, notably by Bayliss and Starling, argued against these views, but in the early twentieth century, there remained a great deal of fundamental research to be done on the functions of large parts of the digestive tract. In 1916, an author found it necessary to argue against the idea that the colon had no important function and that "...the ultimate disappearance of the appendix is a coordinate action and not necessarily associated with such frequent inflammations as we are witnessing in the human..."

There had been a long history of doubt about such dismissive views. Around 1920, the prominent surgeon Kenelm Hutchinson Digbydocumented previous observations, going back more than thirty years, that suggested lymphatic tissues, such as the tonsils and appendix, may have substantial immunological functions.

Werewolves.

1. The Shapeshifter Wolf

Fans of the Twilight series will recognize this type of "werewolf". Like the character Jacob Black and certain other members of the Quileute tribe, the shapeshifter wolf has the ability to change form at any time.  This is believed to have been the original power of the first werewolf before it was taken away.  The shapeshifter wolf can transform from human form to wolf form at will, though aggressive energy or anger may increase the likelihood of causing an unintentional transformation.  The shapeshifter wolves considered "werewolves" can only change from human to wolf form, though "pure" shapeshifters can transform from human form to any other animal form, including a wolf. It is believed that all shapeshifters are born into this ability, and one cannot be transformed into a shapeshifter by the bite from the creature. The exception to this is the Navajo Skinwalker, which is not a true shapeshifter, but a witch using an animal hide to transform.

2. The Wolfman

Many "werewolf" stories, including sightings of the legendary Bray Road Beast, describe a creature that is physically a combination of a wolf and a man.  This mutant wolf-man typically has a mostly human-shaped body, stands on two legs, but is covered in wolf hair and has claws and fangs. The Wolfman is often called a "werewolf" because in many legends this creature is believed to share many of the traits of the werewolf "curse". Depending on the legend, some wolfmen are humans by day and wolf-men by night while others are in their duel human/wolf form at all times.  I believe the generally accepted theory is that one begins by transforming from human to wolfman on full moons only, then over time it increases to every night, and eventually the body settles into a pure wolfman form at all times. The degree to which a wolfman can control his mind and emotions also degrades as these transformations become more permanent.

3. The True Werewolf

A true "werewolf", according to most legends, is a human being that uncontrollably transforms into a wolf during a full moon.  The original werewolf curse transformed a Shapeshifter Wolf into a Werewolf, effectively taking away the ability to control the shift but also taking away the ability to think as a human while in wolf form. Werewolves, when in wolf form, have uncontrollable rage and hunger.  They are driven to kill everyone and everything they encounter, regardless of their relationship as humans. The curse causes these wolves to lose all control of their minds, and when they wake up in human form in the morning, they don't remember anything (though they may revisit certain memories in dreams). It is this form of werewolf that can transfer their condition through a bite, assuming of course that the human being bitten survives the attack.

Animals that change colour with the seasons.

Ptarmigan
Ptarmigans are a mottled brown throughout the Summer to blend in with their surroundings like this white-tailed ptarmigan. As the days become shorter during the Fall, the ptarmigan begins to molt its brown Summer feathers and grow thick, white plumage. The white feathers of the willow ptarmigan allow the bird to creep across the snow unnoticed by its predators.



Arctic Fox.
During the Summer, the arctic fox boasts a gray-black coat that allows it to stalk its prey unseen in the dense arctic underbrush. The arctic fox turns white in Winter to camouflage the carnivore from both prey and predator: the fox is a tasty meal for polar bears, wolverines, golden eagles, and snowy owls. It can use its bushier Winter tail to cover its face and shield it from icy arctic winds. 


Stoat.
This weasel-like creature has a sleek brown coat in the Summer accented by a white chest and belly. In Winter, the stoat sheds its brown fur in favor of a warm white coat.

Snowshoe Hare.
While it gets its name from its large hind feet, the snowshoe hare is perhaps most distinguishable by the colorful transformation it undergoes from season to season. In the Fall, the brown fur that blends so well with its forested surroundings begins to turn white. By Winter, the only telltale signs of this bunny are the black tips of its ears and its dark eyes.


Roe Deer.
In Summer, the roe deer's coat is a vibrant golden-red. Though it doesn't turn white in Winter, the roe deer sheds its red Summer coat in favour of a dark brown one, which is much thicker to trap body heat.