A Tail’s Tale

Humans and great apes seem to be the only creatures deprived of a tail. Yet, our coccyx is what scientists call a “vestigial” organ. It doesn’t serve any purpose but it is there. As Darwin writes in his Origin of Species: “Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue for its derivation.” In short, the fact we don’t have a tail doesn’t exclude the possibility that one of our distant ancestors had one. So, what is a tail for?

For some, it is a built-in fly swatter – like cows in the field; for others a navigation tool like fish; for many a means to keep their balance and for others a way to communicate. When you come home, I am sure your dog greets you by jumping around with vigorous tail wagging – that is, if you are lucky enough to have one. Scientists at the University of Bari, Italy, have been studying tail wagging and its meaning for quite some time. The results of their research show that the direction of the tail indicates different emotional states in dogs. For instance, if the tail wags more to the left, emotions tend to be negative; whereas wagging to the right is a sure sign of happiness. The direction the tail goes is a by-product of the asymmetry of the brain and dogs probably do not intentionally communicate their emotional state to others. However experiments showed that when dogs watched videos of other dogs wagging their tails to the left, they exhibited signs of anxiety; they were more relaxed when watching other dogs wag their tails to the right. A domestic cat holding its tail high up can be trusted. It is a friendly and contented cat. Stay clear if the tail is bushy though, that means the cat is bristling with anger.

Now that we know a little bit more about cats and dogs, let’s talk about wild animals. Equidae, like zebras, use their tails to keep away biting insects and, much like dogs, the position and movement of the tail is a good indicator of the animal’s emotional state and condition. Side to side or up and down wagging is a sign of irritation. A threatening zebra will lower its head, pull its ears back, bare its teeth and lash its tail around. One can also read the mood of a panther by its tail. A flicked and twitched tail indicates annoyance, anticipation or anger. As for tigers, they usually keep their tails in a low position, unless they’re curious about something, then they hold it high up.

For birds, the tail is an aerodynamic tool serving pretty much the same function as the rudders of a boat. It helps them steer while flying and provides stability when they take off and land. It also helps them keep their balance when they’re perched. However, nature can be fickle and some birds have a tail so cumbersome, one can wonder what purpose it really serves. Take the male peacock for instance – why does it have such a long, colorful tail? The theory is that it conveys a clear message to females that the individual is healthy. A peacock uses its tail in an elaborate dance to court females and hope to get lucky! Peacocks are not the only ones to attract mates with their exuberant tails, the long-tailed widowbird, Cape sugarbird, quetzal, long-tailed sylph are but a few other examples.

Not all tails are equal. Prehensile tails are by far the coolest! Arboreal mammals, like kinkajous, spider monkeys, capuchin monkeys and also pangolins, anteaters and some rodents have prehensile tails. Those provide safety and come in handy when you have to find your food and evolve in an environment full of unevenly spaced branches. Skeletal structural differences can be found in mammals with and without prehensile tails. Mammals with a prehensile tail have more vertebrae. Those are more robust and allow for increased strength and flexibility of the distal end of the tail. Prehensile tails are so strong they can support the entire weight of the animal it belongs to. Both spider monkeys and capuchin monkeys have prehensile tails – but these differ in more than one way. Spider monkey tails are long, thin and bare underneath with dermatoglyphs (i.e. ridges in the skin like our own fingers). This area of their tail is highly enervated and therefore tactile. As a matter of fact, it pretty much acts as an extra limb or hand. When touching something with the bare part of their tails, spider monkeys gather information about its texture, scent and consistency. Capuchin monkey tails, in contrast, are shorter, fully covered with hair and deprived of tactile receptors. The tail of spider monkeys represent about 7% of their total body weight, slightly less for capuchins – about 5%. While spider monkeys use their tails for suspensory locomotion and for feeding, capuchin monkeys use it mostly as a weight-bearing tool when feeding in the canopy.

Black and white (or red) Ruffed lemurs, who spend their lives up in the canopy, use their tails for balance during locomotion. They can leap great distances between trees, but the use of her tail as a balance mechanism can be easily observed when they walk on all fours along branches or (suspended fire hoses when in captivity). They hold her tails low, slightly curved to the right or the left to keep moving straight along the path. As opposed to black and white ruffed lemurs, ringtail lemurs spend a lot of time foraging on the ground and hold their tails high up in the air. So do coatis. This helps them keep track of each member of the group while foraging or traveling.

So you see, there is much to tell about tails!

Should Great Apes Be Granted Similar Legal Status as Humans?

How we treat great apes (and other animals for that matter) is a question that has been gaining momentum the last few years.
Organizations like The Non-Human Rights Project argue that a legal status, other than that of "property" should be granted to great apes in particular.

I could not agree more.  Animals are not objects and should not be considered as such by the law, no matter which country they live in.
We do know that animals (from mice to apes) have feelings and experience empathy ** (see references below) - so how can we justify trading them as mere junk?

The question is even more pertinent when it comes to the ethical treatment of great apes in facilities using them for the greater good - (think medical research).  Progress has been made and it seems that we (humans) are now moving towards a consensus that medical research should move away from animal testing where other solutions apply.  However, some argue that computer simulation, in vitro testing cannot viably replace animal testing - here's an interesting article on the subject from "Speaking Of Research".

Yesterday, non human rights were debated again in the press and the battle is far from being over if some continue to think that keeping things as they are is the right thing to do.  See "Sanity In the Court: Judge Denies Claims that Chimps are Persons".  However, per the article, an Argentinean judge granted habeas corpus to an orangutan at the end of last year.  To quote the article in Scientific American: "In Argentina, at least, Sandra now has the right to life, liberty and freedom from harm." It also mentions that in New Zealand, a river was granted rights as well "Agreement Entitles Whanganui River to Legal Identity"
This means there is hope for those who think that advanced species (and natural resources*** essential to our lives) should be granted some rights - even if they cannot plead their own case in our language.


**  The Scientist "Mice Show Evidence of Empathy"
** Frans De Waal interview about The Feelings of Animals

** Frans De Waal talks about empathy

*** The idea that natural resources should have rights first was formulated in the 1970s by Professor Christopher D. Stone when the book "The Lorax" came out.  You can check out this document "Should Trees Have Standing?" for more details.