A Tale Of Monkey Tails, And Why Curious George Is Not A Monkey.

“George was a good little monkey and always very curious.”

This line opens nearly every one of the adventures that Curious George has set upon since he was first brought to life by HA Rey in the 1939 children’s book “Cecily G. and the Nine Monkeys.” These stories, which have sold over 25 million copies over the last 75 years, and are beloved by child and parent the world over, begin with a lie – a big fat lie because, in fact, Curious George is NOT a monkey.

We at THE ‘SCOPE thought it would be a good idea – in this Year of the Monkey – to clarify some things about our beloved primate pal, George. So what is a monkey, and why is George not one? Generally speaking, monkeys are haplorhine primates with external tails. Another way of saying this is that they have dry, furry noses (not wet ones like lemurs or dogs or cats) with more than just the vestigial tailbone that apes have, including humans. All monkeys have tails,* although some are longer than others. And because Curious George does not have a tail (along with other reasons explained elsewhere), he is not a monkey but an ape.

Frankly, and we’re just gonna throw this out there… Curious George would be way cooler if he were a monkey, precisely because he would have a tail. And monkey tails are fascinating structures because they come in so many varieties: long, short, skinny, fat, hairy, partially bare, prehensile, nonprehensile… wait, what does that mean?

We’ll tell ya!

Prehensile tails are ones that are capable of suspending the entire body weight of the animal. So, an animal with a prehensile tail can hang from its tail, which frees up its hands and feet for other activities like picking fruit or leaves to eat. Based on observations of living and fossil species, it is generally thought that prehensile tails evolved at least 14 times independently among 40 different genera of extant mammals. And this doesn’t include all the other living vertebrates with prehensile tails, like some snakes, lizards, salamanders, and seahorses, to name a few.

Not all monkeys have prehensile tails, which is a shame for those that don’t because prehensile tails are much more interesting than nonprehensile ones. In fact, the only monkeys that have prehensile tails are in Central and South America (platyrrhines or New World monkeys), but not even all those have prehensile tails. Prehensile tails likely evolved twice in the New World monkeys that have them: once in the ateline monkeys, which include spider monkeys, woolly monkeys, howling monkeys, and muriquis, and then a second time in the capuchin monkeys.

Left: Capuchin monkey (Cebus apella); Right: Spider monkey (Ateles geoffroyi)

In most respects, both instances of prehensile tail evolution in monkeys resulted in similar anatomical structures. Monkey prehensile tails are comprised of vertebrae that are structured to resist higher bending and torsional forces. This seems intuitive because animals that hang from their tail put more stress on the bones in their tail. So having bones that can resist higher forces would safeguard against accidental fracture. The ends of these tail vertebrae are more convexly rounded at the point where they articulate with one another, which allows for a greater range of motion than in nonprehensile tails. Also fascinating is that some of the muscles in prehensile tails are structured to produce higher contraction forces than those of nonprehensile tails, while other muscles have developed shorter extrinsic tendons that cross fewer joints along the tail, enabling the animal to have tighter control of the tail to wrap around substrates.


But the parallel evolution of prehensile tails in New World monkeys has also led to some pretty interesting anatomical differences that reflect functional differences in the way the tail is used. In addition to hanging from the tail during feeding bouts, ateline monkeys use their prehensile tails during locomotion to assist with moving through the forest canopy – much like a fifth limb. This is fundamentally different from the way that capuchin monkeys use their tails because capuchins tend to brace themselves with their feet and tail (like a tripod) for stability while feeding on fruits at the ends of thin tree branches, but they do not use their tails while moving. And this basic distinction in the way the tail is used can be seen in specific anatomical differences between ateline and capuchin prehensile tails.





Friction pad on tail of mantled howling
monkey (Alouatta palliata) at Hacienda La Pacifica,
Guanacaste, Costa Rica, 2004.

Capuchin monkeys, like most other primates, have tails that are completely covered in hair. The skin underlying the hair is replete with slow-adapting pressure and touch receptors (Ruffini endings) that allow the animal to detect the position of the tree branch substrates during postural behaviors like sitting or lying down. The ateline monkeys, however, uniquely possess a hairless friction pad on the ventral (anterior) and distal (tip) of the tail. This friction pad senses touch and pressure with slow-adapting sensors like the skin of the capuchin tail, but it is also full of rapid-adapting sensors (Meissner’s and Pacinian corpuscles) that are useful for detecting the substrate during locomotion. Additionally, the ateline tail friction pad contains dermatoglyphics, or “finger” prints, similar to those found on fingers and toes. This pad, with its dermal ridges, provides the source of friction so that the tail does not slip during suspension and locomotion.


So, as you can see, if Curious George was actually a monkey, there is no question that he would be infinitely more interesting** because monkey tails are interesting. And if he were a New World monkey with a prehensile tail, I have no doubt his curiosity would get him into so many more pickles because he would have the ability to hang from his tail and manipulate things with his hands and feet. Unfortunately, for over 75 years George has been given credit for being a monkey, when all signs point to him being an ape – the biggest clue being that he does not have a tail.

*Ok… so almost all monkeys have tails. There is an interesting case of near taillessness in Macaca sylvanus, also called the Barbary macaque. These monkeys, who live in Gibraltar and constitute Europe’s only wild population of monkeys, have a vestigial, stumpy, soft tail – a bulbous nubbin. And although they have tail vertebrae like every other monkey, these vertebrae do not actually extend into the external tail at all, so they are more like the tailbone (coccyx) that apes have than those of a typical monkey tail. For this reason, Barbary macaques are mistakenly called Barbary apes. But they are not apes. They are monkeys – unlike Curious George.

**Tamping down the hyperbole for a moment, the truly most interesting aspect of George, given that he is not a monkey, is the history of how he came to be so beloved by so many. You can read this fascinating history here.

Contributed by: Jason Organ, Ph.D.
Tail Jason on Twitter.




Organ JM, Teaford MF, & Taylor AB (2009). Functional correlates of fiber architecture of the lateral caudal musculature in prehensile and nonprehensile tails of the platyrrhini (primates) and procyonidae (carnivora). Anatomical record (Hoboken, N.J. : 2007), 292 (6), 827-41 PMID: 19402068

Organ JM (2010). Structure and function of platyrrhine caudal vertebrae. Anatomical record (Hoboken, N.J. : 2007), 293 (4), 730-45 PMID: 20235328

Organ JM, Muchlinski MN, & Deane AS (2011). Mechanoreceptivity of prehensile tail skin varies between ateline and cebine primates. Anatomical record (Hoboken, N.J. : 2007), 294 (12), 2064-72 PMID: 22042733

Deane AS, Russo GA, Muchlinski MN, & Organ JM (2014). Caudal vertebral body articular surface morphology correlates with functional tail use in anthropoid primates. Journal of morphology, 275 (11), 1300-11 PMID: 24916635

Russo GA (2015). Postsacral vertebral morphology in relation to tail length among primates and other mammals. Anatomical record (Hoboken, N.J. : 2007), 298 (2), 354-75 PMID: 25132483

Where Do “New” Viruses Come From?

Every year there seems to be a new virus that just popped up out of nowhere to cause us a great deal of pain and suffering. Is it the work of a mad scientist vying for global domination? Are these viruses coming back to life after being frozen for millennia? Are they hitching a ride to Earth via meteorites?

The truth is many of these viruses are not so new – but we are creating new opportunities for them to infect us. Many viruses jump from other animals into people – a process known as “zoonotic transmission” – and some of our actions roll out the red carpet for the virus. Let’s take a closer look at where some of these “new” viruses may have originated and how they spiral out of control.

Zika

Microcephaly is a term used to describe babies born with much smaller head size than normal, which is indicative of incomplete brain development. In Brazil, this birth defect occurs about 150 times per year. However, in the past 4 months, nearly 4,000 babies have been born with microcephaly - a dramatic spike that has set off alarm bells.

Photo of a child born with microcephaly, which has been linked to the Zika virus.

While evidence is still circumstantial, the primary culprit is a previously obscure virus called Zika, named after the forest in Uganda where it was first identified in a rhesus monkey back in 1947. Zika is transmitted through mosquitoes, which basically operate like flying dirty syringes. If they fed on an infected person, they can transmit the virus to the next person they bite.

Global warming and increased travel have conspired to create excellent opportunities for viruses like Zika to spread. It only takes one infected person to attend a major spectacle (for example, the 2014 FIFA World Cup in Brazil) to start a chain reaction of viral transmission. Viruses need no passports and can jet set around the world in unprecedented time. Global warming is an issue because it has allowed the species of mosquito that carries these viruses to thrive in areas that used to be too cold. Even El Niño has been catching some of the blame for helping to spread Zika.

Ebola

While Zika jumped to humans from other primates, the African filovirus Ebola is thought to have originated in fruit bats. Bats can transmit a number of other deadly viruses, including rabies. Bats happen to be a source of food in several of the areas where Ebola outbreaks have occurred, consistent with the idea that bats are the culprits. Once Ebola infects a human, it can spread quite easily to other people through bodily fluids.

Bats like this one are now considered to be a major carrier capable of spreading the Ebola virus to people.

Ebola first appeared in humans in 1976 in the Sudan and the Democratic Republic of Congo. The initial outbreak killed an estimated 600 people, but the latest outbreak that began in 2014 in West Africa has been the worst in history, killing over 11,000 people. This wasn’t due to an enormous fruit bat invasion, but rather human-to-human transmission. Genetic studies indicated that the entire epidemic likely stemmed from just a single infected child in Guinea, the so-called “Patient Zero”. A catastrophic mix of poor health facilities and unsanitary practices ignited to spread the virus like wildfire.




The 2014 Ebola outbreak started with a toddler who fell sick in Meliandou village in Guinea. Source.
Credit: Live Science

MERS

MERS, Middle East Respiratory Syndrome, first made headlines in 2012. This life-threatening respiratory virus reared its ugly head in Saudi Arabia first, but has since been reported in 25 other countries, including those not in the Middle East (due to unwitting travelers carrying more than their luggage). MERS is caused by a coronavirus, so the causative agent is typically referred to as MERS-CoV. Like many other respiratory viruses, coughing in close proximity can spread MERS-CoV between people.

But how did MERS-CoV get into people in the first place? According to the World Health Organization:  “It is believed that humans can be infected through direct or indirect contact with infected dromedary camels in the Middle East. Strains of MERS-CoV have been identified in camels in several countries, including Egypt, Oman, Qatar and Saudi Arabia.”

It is easy to understand the respect and admiration one can have for a noble creature like the camel. But getting a little too intimate with a camel may literally leave you breathless.

So stay away from coughing camels! In some areas, camels are butchered for food and their milk and urine (yes, urine) is consumed. These practices provide additional avenues for possible transmission of MERS-CoV to humans.


UPDATE (3/1/16): A new study suggests that we have bats to thank once again for spreading MERS-CoV to camels.

HIV

Human Immunodeficiency Virus (HIV), which causes AIDS, wasn’t on anyone’s radar until an unusually large number of people starting suffering from rare diseases with strange names like Kaposi’s sarcoma, toxoplasmosis, and pneumocystis. These diseases are hardly ever seen in people with normal, healthy immune systems. Turns out they were secondary infections – the primary infection was HIV, which was destroying the very immune cells that are needed to keep those other illnesses at bay.

Historical records have placed the earliest cases of HIV infection to the 1950s, which suggests it has been moving through humans slowly through the decades prior to its explosion in the early 1980s. An increase in international travel, unsafe sexual practices, and intravenous drug use are all factors that have contributed to accelerating the epidemic.

HIV (yellow particles) is a cunning foe that destroys the immune cells (blue) designed to protect us from foreign invaders.

We still don’t know how HIV leapt into the fabric of human DNA, but the evidence is very strong that it came from other primates. SIV, or simian immunodeficiency virus, has been found in African primates and is highly similar to HIV; it is easy to imagine that blood from infected primates, some of which are butchered for food or kept as pets, found its way into a person's open wound. Once in humans SIV evolved into HIV, transmissible to others through bodily fluids. HIV likely spread around Africa in its early days through the use of shared needles in impoverished hospitals.

It’s a virus world after all

As you can see from these examples, many “new” viruses were actually pre-existing in other animals and just made a “species jump” into humans. But how did these viruses get into the other animals in the first place? That question is a lot harder to answer.

Viruses are little more than a fragment of DNA or RNA, perhaps rogue genes that escaped a cell and became independent, infecting other cells in order to replicate and spread. Richard Dawkins coined the term, “the selfish gene”, and that is a very accurate description of viral DNA/RNA. What we do know is that viruses have been around a long, long time, perhaps before the dawn of life itself. There are even viruses that infect bacteria.

Once inside host cells, viruses replicate quickly, which means they are very adaptable. Their ability to evolve quickly is likely to be a key factor explaining why these selfish genes can make a reproductive factory out of a wide variety of different hosts…and why “new” viruses can appear to spring out of nowhere.

While viruses are a nuisance to us now, they may have been important drivers of evolutionary change in the past. It has been proposed that RNA viruses may have led to the formation of DNA and DNA replication mechanisms, without which we would not even be here to complain about them!

Contributed by:  Bill Sullivan, Ph.D.

Follow Bill on Twitter.

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Koonin EV, Senkevich TG, & Dolja VV (2006). The ancient Virus World and evolution of cells. Biology direct, 1 PMID: 16984643


Baize, S., Pannetier, D., Oestereich, L., Rieger, T., Koivogui, L., Magassouba, N., Soropogui, B., Sow, M., Keïta, S., De Clerck, H., Tiffany, A., Dominguez, G., Loua, M., Traoré, A., Kolié, M., Malano, E., Heleze, E., Bocquin, A., Mély, S., Raoul, H., Caro, V., Cadar, D., Gabriel, M., Pahlmann, M., Tappe, D., Schmidt-Chanasit, J., Impouma, B., Diallo, A., Formenty, P., Van Herp, M., & Günther, S. (2014). Emergence of Zaire Ebola Virus Disease in Guinea New England Journal of Medicine, 371 (15), 1418-1425 DOI: 10.1056/NEJMoa1404505