Talkin’ bout Regeneration: Why can’t humans regrow limbs?

The life of a seastar (read: starfish) is a pretty enviable thing. Aside from the artistically inspired body plan, seastars get to spend their days relaxing in the ocean, enjoying the ebb and flow of the tides. They watch all manner of interesting marine life pass by overhead without ever having to worry about jobs, bills, or crooked mechanics. However, if I had to pick one thing from a seastar’s life to really get jealous about it would have to be the ability to regrow limbs.

If, during their care-free oceanic existence, something comes along that wants to make a meal out of them seastars don’t have a lot of options. They are hardly built for speed and camouflage isn’t exactly in their wheelhouse. However, if something does get a hold of them, they have the ability to detach one of their limbs and hopefully escape with the other four. Over a period of a few months or up to a year or so they can regenerate the lost limb. Not only that, the limb they left behind (if it somehow managed to escape becoming octopus food) can regrow the rest of it’s body and form a second, genetically identical seastar.

Seastars are hardly alone in this ability. Earthworms, salamanders, snail firs, some fish, and even the occasional mouse have been known to regrow complete or partial limbs. Seastars often go one step further, though by voluntarily detaching their own limbs to reproduce asexually when lady seastars are not being especially receptive to their advances.

So what’s the deal? Why do all these other animals have this clearly convenient ability while us humans are left twiddling our phantom thumbs? Well, first off, we aren’t totally outside the club of regenerative species. Many children have lost the tips of fingers or toes only to turn up at the doctor’s office a few months later with everything back in place (minus fingerprints). The interesting thing in each case where this happens is that when the fingertip was cut off some of the nail bed was left intact; and it is this fact that gives some insight into how regeneration works.

It seems that to regrow body parts, the bits that are left behind in the wake of a serious injury need to know how to communicate. If you’ve ever tried to explain to someone how to build something specific out of Lego without actually doing the work yourself, you can begin to understand how challenging communication can get in the world of construction. At the cellular level, communication falls on the shoulders of stem cells left at the site of an injury. Scientists have discovered two kinds of stem cells that do this work: somatic stem cells and pluripotent stem cells. Unfortunately, in the world of limb regeneration, not all stem cells are created equal.

Somatic stem cells can close a wound, regrow some skin, and fill in the gaps with scar tissue but not a whole lot else. Pluripotent stem cells are the real professionals. They send signals known as Wnt communications throughout the body, getting bones and even nerves involved in the healing process. These are the cells that allow structures to reform. The bad news for humans and most other mammals is that, outside of the time we spend in our mothers’ wombs, we don’t get too many pluripotent stem cells. In fact, most of the ones we are left with by the time we are born are in our hair follicles and our fingernails... It’s all starting to come together now.

Scientists aren’t exactly sure why mammals seem so deficient in what are obviously handy (no pun intended) bodily resources. Some believe that our fast metabolisms that require constant food preclude us from hiding in a dark cave for a year while our limbs regrow. Instead we have to stop the bleeding and get back to hunting as soon as possible. Others believe that the complex body plans of mammals are too complicated to be regenerated in the same way that seastars' body parts can be.

A few optimistic souls say this might just be a temporary state of affairs. Sometime in the next few decades we may unlock the chemical communication secrets of pluripotent stem cells and set to work regrowing our own body parts. However, until that day comes, I wouldn’t get too close to any wood-chippers.

Sketchy Fact #50: Visiting the Neighbours

If you wanted to travel to the closest star to Earth (other than the sun) on the fastest space vehicle humans have ever built (240,000 km/h on Helios 2) the trip would take you 19,000 years. All the road-bingo in the galaxy wouldn’t make that trip bearable.

Olfactory Fun: The Seriously Underrated Science of Your Schnoz

When you sit down, as everyone does at some point in their life, to rank the importance of the holes in your head you are likely to get caught up on deciding which is more important, the mouth or the ears. Human beings are among the most communicative animals to ever evolve of this ball of rock and water, so it makes sense that we would consider the tools that let us talk to one another to be of the utmost importance. But to think of these organs as the sensory dream team is to overlook a potential MVP in the world of things that help us perceive the world. The true star of the show might already be front and centre.

Your nose is surprisingly important in your experience of the world. Humans are by no means powerful smellers in a world that includes heavyweights like blood hounds, sharks, and grizzly bears but that hunk of bone and cartilage in the middle of your face serves a very important purpose, possibly even more important than we can currently appreciate.

First off, without a serious leg-up from your nose, your mouth would be significantly impaired in one of it’s most enjoyable functions: taste. Our senses of taste and smell are so intertwined that some scientists believe it would be more accurate to just combine them and call the whole experience flavour. You see, when you take a bite of pizza, or cake, or seven-layer lasagna your mouth and nose initiate a sensory alley-oop, bouncing the chemical components of your meal back and forth and interpreting them in different ways.

In your mouth, receptors that cover your taste buds respond to chemicals called tastants to provide the experience of the five principle tastes: sweet, sour, bitter, salty, and umami/savoury. Contrary to popular belief, different regions of your tongue do not specialize in any of these tastes, you can experience any of the big five on any part of your tongue. Your taste buds also lead the charge in your experience of spicy foods. That is because each oral nub is generously packed with pain receptors that are triggered by capsaicin, the key chemical in foods that make you sweat.

You may also be fortunate enough to be what scientists call a “super-taster” if you were born with an unusually dense network of taste buds. It is estimated that one in four people fall into this camp (most are women), and their experience of food is the gustatory equivalent of front row seats for a cage match between the Loch Ness Monster and the Kraken.

However, beyond the five key tastes and your experience of spice, your tongue plays a surprisingly small role in the overall flavour of food. As you chew you force air to circulate into you nasal cavity, carrying with it odorants that trigger the hair-like receptor cells in your nose (cilia) to set off a neuronal fireworks show. Each type of odorant has its own pattern of activation but all the input gets shot directly into the brain’s olfactory bulb and is then distributed throughout the brain to form your overall impression of flavour. In fact, no other sense gets such direct access to the brain. The axons coming from the neurons in the olfactory bulb actual end in the cilia. Effectively, your brain’s root system is hanging from the ceiling of your nose.

As you probably already know, smell is also very closely tied to memory. If I showed you a picture of your grandmother’s kitchen, you would pretty quickly be able to put yourself into a nice memory possibly involving some delicious chocolate chip cookies. However, if instead of the picture I gave you a whiff of the cookies, you would be a sticky fingered 6-year old again before you even knew what hit you. The response is automatic and lightning fast, but it might be even more complicated a relationship than you can imagine.

Research has shown that your sense of smell might actually be able to predict if you will develop neurological disorders like Parkinson’s Disease or Alzheimer’s later in life. In one study, researchers evaluated the ability to smell in a group of people and sorted the best and the worst among them into two groups. They followed up with their participants many years later and all of the people who developed Parkinson’s Disease came from the bottom 10% of smellers. Scientists don’t completely understand the link between smell and memory quite yet, but it is theorized that brain degeneration could be caused by environmental factors, and those environmental factors might be coming in through the nose.

Clearly your nose contains mysteries far beyond what we currently know. Who know’s what scientific treasures could be hidden beneath you next dried-up booger?

Sketchy Fact #49: Small-Pox Won't Cause Pandamonium in Animals

Smallpox only infects humans and is not carried by any wild animals. It is the only natural biosafety level IV infectious disease (maximally dangerous) not to have an animal host.

Prosopagnosia: Facing the Facts About Face-Blindness

In 1976 NASA had their eyes on Mars. The Viking program was well underway and humans were at the cusp of getting up close and personal with the red planet. The plan was for the spacecraft Viking 1 to circle Mars and photograph possible landing sites for its sister ship Viking 2. After narrowing down possible landing sites, Viking 2 would be sent to the surface and the super-nerds in Houston could pop some bubbly. While doing its reconnaissance work however, Viking 1 snapped a picture that shocked not only the scientists at NASA, but the entire planet. The picture was of a human face staring up from the surface of Mars.

Conspiracy theorists and alien enthusiasts quickly began postulating the existence of subterranean Martian civilizations, touting the face as proof that humans are just transplanted people from our celestial neighbor. It wasn’t until 2001 when the Mars Global Surveyor spacecraft re-photographed the same geologic feature that the face controversy was put to bed. It was just a pretty distinct hill with some convenient shadows. In hindsight we should have known right away that it wasn’t actually a face, it isn’t entirely our faults though. It turns out our brains are wired to find faces everywhere they look.

If you’ve ever read a news story about a piece of toast that looks like Jesus or a bagel that looks like Elvis, you know what I’m talking about. One of the easiest things in the world is imagining a face where one doesn’t exist. We even have a specific chunk of our brains with the designated job of finding faces. It’s called the fusiform gyrus, but its function is so specific that most scientists just call it the fusiform face area. Under an fMRI scan if you show someone an apple the fusiform gyrus will stay as silent as a mouse, but show the same person a face and it will light up like the Fourth of July.

It makes a lot of sense when you think about it. We humans are some of nature’s most social creatures. We have large families, even larger circles of friends, and most of us live together in clusters with populations in the thousands or even millions. If your brain wasn’t insanely well-equipped to quickly sort out friends, enemies, and former employers from the crowd your life would be a lot tougher.

Unfortunately for some of us, this actually is the case. Recent research as begun to reveal that as many as one in every 50 people might suffer from at least mild face-blindness, known as prosopagnosia on more formal occasions. The term face-blindness likely gives you the wrong idea about the disorder. Someone with prosopagnosia doesn’t see a blank skin mask when they look at the front part of a person’s head. They can see eyes and noses and mouths and ears just like the rest of us. The problem is, that is all they see. The pieces don’t come together to form a single coherent picture that allows them to recognize the people they interact with. Imagine if I showed you a line up of noses, just noses, and asked you to identify one of them. Odds are you would have a tough time even if one of them belonged to your mother.

Prosopagnosia comes in a full spectrum of intensities. On the milder end, you might have a hard time recognizing when someone you saw in one movie appears in another. On the severe side, you might not be able to recognize yourself in a photograph. Famed psychiatrist and author Oliver Sacks didn’t realize that he was face-blind until he was well into middle-age, despite having a particularly severe case. Sacks has apparently failed to recognize his own therapist in encounters at the grocery store, missed his assistant of 6 years in a hotel lobby he went to specifically to meet up with her, and has over and over again “apologized for almost bumping into a large bearded man, only to realize that the large bearded man was myself in a mirror.”

Funny stories aside, prosopagnosia can be a source of immense frustration for the people it afflicts and the people they fail to recognize. Imagine if you had to convince your spouse that you were you every time to met them at the movies or the mall. The quirks would get old fast. That is why face-blind people often come up with other ways to recognize their close contacts. Someone who always wears pink shoes or has an affinity for large hats, for example, would make a great best friend for a prosopagnosia patient.

Face-blindness can either be lifelong or the result of brain trauma from an accident or a stroke. Regardless of how it is picked up or how severe it is, prosopagnosia makes a great get-out-of-jail free card for that guy at the office whose name you can never remember.

Sketchy Fact #48: It's not moon, it's me.

The moon is drifting away from the Earth by about 1 cm each year. It’s like the longest, most dramatic break-up in the solar system.

Sugar-Loaded Surprises: Why We Need to Stop Ganging Up on High Fructose Corn Syrup

Here at Sketchy Science we publish a lot of articles about living a healthy lifestyle. In particular we like to help people wade through the fact and fiction that goes along with eating a nutritious diet. There is a lot of misinformation floating around in the ether of western civilization and we like to think that it helps to hear the truth about what we are putting in our bodies. With that in mind, we decided to write about high fructose corn syrup (HFSC) for this week’s post.

 If you pay attention to the news at all, you have probably heard about how evil HFSC is. It is making us fat, diabetic, and hopelessly addicted to soda. No matter where you look, from articles written by doctors, to the Huffington Post, to one of my personal favourite websites HowStuffWorks.com the message is clear: “High fructose corn syrup will kill you.” That is the apparent consensus and it is fully the message of the article that I expected to write. I even thought I might throw in some jabs at the Corn Refiners Association for ridiculous brainwashy ads like this one. However, when I hit up the scientific literature, what I actually read shocked me.

The actual science on HFCS is a lot less doom and gloom than you would expect. First off, HFCS is a processed form of corn syrup where some of the glucose is turned into another sugar called fructose. Average, run-of-the-mill table sugar (sucrose) contains both glucose and fructose at about a 50/50 ratio. HFCS has slightly more fructose. Since fructose is sweeter than glucose, HFCS is friggin’ delicious. It makes anything you put it into crazily sweet. Pretty much to the point where you really don’t want to stop eating it.

Therein lies the problem with HFCS. Its tastiness, combined with the fact that food manufacturers understandably put it in everything (their goal, after all, is to sell a lot of Oreos), makes HFCS dangerous. The poison is in the dose, as the old saying goes; and we are happily dosing ourselves at off-the-charts levels. An American study recently found that a full one-third of the calories consumed by middle school students was in the form of added sugars.

However, just because gorging ourselves on something is bad for us doesn’t make it fair to point the finger in one direction if the thing we are pointing at isn’t especially harmful. When you look at research comparing HFCS to sucrose (table sugar) you end up reading the same thing over and over again: HFCS isn’t really any worse. If you don’t believe me (and I completely understand being surprised by this) read some of the studies I’ve linked to at the bottom of this post. Over and over again, the effects of HFCS and sucrose are the same. While scientists agree that pure fructose has terrible consequences for your body, there is actually little evidence to support the idea that the combination of fructose and glucose in HFCS is any worse than classic sugar.

I did manage to find one study about how HFCS led to greater weight gain over the long-term in mice, but researchers only compared mice eating HFCS to controls who weren’t getting any extra sugar. When you stack the deck against something like that, you are not conducting good science. Admittedly the same study also found differences in short-term weight gain with HFCS causing more flub than sucrose, but I haven’t found any other research to support that.

The lesson here is not to go out and inhale a gallon of orange soda, it is actually pretty much the opposite. Obviously there is a problem with the way companies make and sell food. They put sugar in things that have no business having sugar. Read the ingredients list on a box of crackers next time you’re at the grocery store if you have any doubts. However, the problem is not with the substance itself. It is with the people who are making and marketing the food and, ultimately, with the people who are consuming it. Clearly we can’t rely on big companies to only provide us with healthy foods, so we need to take some responsibility for our own actions.

Read labels and make smart choices. Maybe somewhere down the line enough people will get upset about the amount of sugar in food that we can pass a law limiting it, but until then companies will continue to sell sugar loaded snacks for as long as we keep buying them. HFCS is really cheap to produce and it makes you drink more juice. If I wanted to sell you a lot of lemonade, I would keep making the kind you like the most. Capitalism isn’t rocket science.

The other lesson here is not to believe everything you hear. Just because some doctor on the internet tells you something is good or bad, doesn’t mean anything. When it comes down to it, you are trusting strangers to tell you how the world works. Read different sources, make use of Google Scholar and read some published science, make up your own mind. Sometimes what seems like an issue of nutrition is really one of psychology.

References by findings:

No difference between HFCS and sucrose:

http://ajcn.nutrition.org/content/86/6/1586.short

http://www.nutritionjrnl.com/article/S0899-9007(06)00392-3/abstract

http://www.tandfonline.com/doi/abs/10.1080/10408390600846457#.U5jFePldWqk

http://ajcn.nutrition.org/content/87/5/1194.short

http://ajcn.nutrition.org/content/88/6/1733S.short

http://ajcn.nutrition.org/content/88/6/1716S.short

http://jn.nutrition.org/content/139/6/1242S.short

Maybe a difference:

http://ajpgi.physiology.org/content/295/5/G987

http://www.sciencedirect.com/science/article/pii/S0091305710000614

http://press.endocrine.org/doi/pdf/10.1210/jc.2011-1251

Pure Fructose is bad:

http://www.sciencedirect.com/science/article/pii/S0168827808001645

http://ajcn.nutrition.org/content/79/4/537.short

Sketchy Fact #47: World's Deadliest Virus

Until 2004 when an experimental treatment saved the life of Jeanna Geise, rabies had a 100% fatality rate. It remains the deadliest known virus on the planet once an infected person shows symptoms.

Bad to the Bone: Are men’s faces evolved for fist fights?

Look in the mirror. What do you see? If you’re a man, you might be looking at the consequences of thousands of years of fist fights. It might not be the most flattering thing to consider but a new theory suggests that the features of men’s faces are more strongly built than those of women so that we are better able to take a punch.

Researchers from the University of Utah have studied the differences in the facial structure of men and women going back millions of years and concluded that the differences we see may be indicative of a violent past. Biologist David Carrier is a firm believer that the ancestors of humans relied on fist fights to sort out who got to mate with who on the African plains.

These ideas fly in the face of conventional wisdom on how the face evolved. People have long assumed that the robust jaws and cheekbones of ancient apes in the genus Australopithecus were the product of tough, plant-based diets. Much like modern gorillas whose diet is made up almost entirely of vegetation that requires a lot of chewing, it was thought that the predecessors of modern humans had strong facial bones to support strong facial muscles needed to grind up leaves and the like. Not so, according to Carrier who after looking at wear patterns on the teeth of Australopithecines concluded that they were likely eating soft fruit, rather than hard nuts.

This presented something of a problem for explaining heavy facial bones. Fortunately Carrier had an idea. As it turns out, in 2012 he co-authored another paper published in the Journal of Experimental Biology explaining how the proportions of the human hand are ideal for making fists. It doesn’t take much of a leap for a fist expert to conclude that apes with thick cheek bones might have used them to better handle frequent punches to the face.

Dr. Carrier’s ideas have been met with a lot of skepticism on the part of other scientists. Just because a fist makes a good weapon doesn’t mean that a fist evolved to be a weapon. It’s a perfect case study in one of the great challenges that scientists face. At the end of the day, you may have used perfectly objective and defensible methods to collect your data; but the tool you use to interpret that data is a human brain... And human brains have biases and preconceived notions. It is one thing to say that men have more robust faces than women, but it’s another to say that you know the reason why.

The key to good science is critical thinking. Look at what is in front of you and question it. That is not to say that Dr. Carrier is wrong, it’s just important to consider alternative explanations. Maybe human faces and hands are designed to help us beat the tar out of each other; but maybe men’s faces are tougher because they got injured more often than women while hunting big game. Maybe our hands evolved to help us manipulate tools and the design just so happened to work as a fist. Or maybe using tools and punching people in the face were equally important in shaping our hands.

In truth, that last explanation is probably a bit closer to the truth. The tricky thing about evolution is that there are so many variables acting on every single trait in an animal’s body or brain at the same time that it should raise flags whenever we read that “The reason for x is y!” Things in the real world are usually in shades of grey, regardless of our ancestors’ black eyes.