Eight-Legged Envy

This morning, on my way to my car, I walked through a gargantuan spiderweb. A diligent arachnid had been hard at work, industriously spinning his beautiful web, only to have some bumbling human destroy it in one fell swoop.

Of course I had my hands full, since these incidents never occur when one is unencumbered. I tried swiping the web from my face, only to realize its owner had conveniently hopped aboard my person. I suddenly became aware of a chunky spider the size of a malt ball taking a leisurely stroll down my arm.

Despite the burden of my computer, a coffee mug, and my purse, I managed to flail my limbs with enough vigor to dislodge him. He gracefully sailed down his web, landing gently at my feet and then scampering off into the undergrowth. After giving myself a thorough rubdown to ensure I wasn’t toting a giant egg sack on my back, I gathered my belongings and went on my way.

I’m not particularly afraid of spiders. I hold them in the same regard I hold snakes: cautious respect and deep admiration for the way they ambulate. Image what humans would be like with eight legs instead of two? It would probably render automobiles obsolete.

My eight-legged encounter got me thinking about our own mode of locomotion. In the animal kingdom, walking on two legs (bipedalism) is pretty unique. Only two other bipeds readily come to mind – penguins and kangaroos, both of which have devised their own strategies for getting around. Penguins have sacrificed efficient walking for swimming, and kangaroos took to hopping, which sure beats walking across the Australian bush.

So why did humans evolve such an unusual gait? Perhaps we should first ask, "when?"

Ancient fossils are hard to come by. The older they are, the less chance they have of being preserved intact. But there are clues to bipedalism among the fragmented remains of our earliest ancestors, and some of the best evidence has nothing to do with legs.

The hole in the base of the skull where our spine enters is called the foramen magnum. And it’s the position of this hole that provides a clue to upright walking. When it’s oriented at the base of the skull, it shows that the creature stood upright. If the hole is located toward the back of the skull, it indicates a quadruped (think about your dog or cat).

And it turns out our bipedal gait evolved much earlier than once believed. It was once thought that walking on two legs evolved in concert with our large brains. But what we find in the fossil record is that bipedalism was in place millions of years before our big brains arrived on scene. Even the seven million-year-old Sahelanthropus tchadensis, unearthed by a group of French paleoanthropologists in 2001, is believed to have been bipedal, based on his foramen magnum. Although scientists are still quibbling…

But the bigger question is why? Why did humans switch from four to two legs?

Theories of bipedalism go all the way back to Darwin, who believed the freeing of our arms allowed us to concentrate on the production of tools and weapons. This makes sense until you take into account that stone tools don’t show up until many millions of years after we started scooting around on two legs.

Others believe climate change had a hand in it. Perhaps humans took to walking as their forests were reduced and food became harder to come by, prompting males and females to partner up for provisioning. Males could gather food (in their arms, of course), and provide for their female and offspring, which would cement their bond and benefit both parties.

Or perhaps the reduction in forests required our ancestors to traverse longer distances. Walking upright, or better yet, running, has been shown to be more energy efficient than the knuckle-walking of our primate cousins, and there’s a whole new line of research examining the role running may have played in the evolution of humans.

Whatever the reason, we humans wouldn’t be human without our unusual gait. Sure, spiders have it made, what with their eight legs and their ability to walk on water. But it’s hard to imagine how humans could have accomplished all we accomplished if we were still ambling about on all fours. Stone tools, pottery, weapons, and art would have been quite a challenge without free hands, as would carrying, whether it be food, firewood, or children.

So you can keep your eight legs, Mr. Spider, and I’ll stick with my two. Your arachnid abilities may grace you with unusual gifts, but it only takes one of my two feet to squash you like a pancake.

Post Script - I would never dream of stepping on a spider...

In case you didn't get enough.

My Father's Daughter

Here’s a thought: if the sperm that created you had come in second in the race to the egg, you would be an entirely different person. Think about it. Among the million or so sperm vying for that egg, the one that contained the recipe for you won, and if any other tadpole had gained entry, you would not be who you are. Quite a gamble, procreation.

As Father’s Day approaches, we naturally think of our dads. Which got me thinking about the process of conception and the traits a father passes on to his children. Man, was I lucky.

First and foremost, there’s the brain. I was fortunate to have a very intelligent father, and he exploited his intelligence to achieve great things. He was born and raised in Mississippi, the son of a prominent architect. But when he was still a boy, his father left to start a new family, leaving him and his mother behind. So he dropped out of school and went to work.

Realizing the grim future in store for a Mississippi kid with a ninth grade education, he enlisted in the Navy when he was just sixteen. And once he left the south, he never looked back.

That young, uneducated sailor went on to travel every corner of the globe, complete a master’s in theology from Northwestern University, and achieve the rank of Captain. All of it through sheer force of will.

He is the reason I pushed on for a PhD. In fact, he’s the reason for much of what I’ve done in my life, for he represented the pinnacle of success, the example of what hard work and hard-headed determination can achieve.

But conception is like life; we must take the bad with the good.

Aside from determination, he also passed on some less-than-desirable traits. For instance, that same hard-headedness, which can border on stubborn; a deep and abiding love of gin; and above all else, a temper.

My father’s temper could go from zero to sixty in a matter of seconds; a trait which in my case has fortunately mellowed with time. Although my father was a chaplain and a man of God, he could swear like any seaworthy sailor. Politics, the economy, or criminal activity would set him off and he would launch into a tirade, cursing all of civilization, damning human weakness.

But he was also one of the funniest individuals I’ve ever known. He loved to laugh and my fondest memories are of sipping martinis and listening, enthralled, as his stories unwound. Like when his ship was torpedoed, plunging him and his crew into the dark depths of the Pacific. And how his commander had silenced him with, “SHUT UP SAILOR, WE’LL GET TO YOU!”

Dad was also a philosopher. His world view was an intriguing blend of religion, philosophy, and the hard life lessons of his youth. He had several famous sayings, such as, “If it’s worth doing, it’s worth overdoing,” a creed he employed whenever he ordered Chinese takeout. Or his other motto, “Why do today what you can put off until tomorrow?” which is ironic, considering all he achieved in his lifetime.

He spent forty-two years in the Navy and survived two wars – a feat no man can endure without being forever altered. But his cynicism was balanced by a love of laughter, a warmth of spirit, and a clever mind that never failed to see the humorous side of life.

My father is gone now. A slow-growing tumor bloomed deep within his frontal lobe, dimming and eventually snuffing out that most vibrant of personalities. I still see him in the mirror. I share his eyes, the shape of his face, and his strong, white teeth. But his most important traits reside within me, for he graced me with a curious mind, steely determination, and a will that has sustained me through every crisis in life – one of the hardest being his death. 

To all the fathers out there, I wish you a warm and wonderful Father's Day.

I See Dead People...

It happens as it always does, whenever I pass through that particular intersection. As I cross the lanes of traffic, I think about the dead girl.

I’m in Orlando for the weekend, visiting family and friends, returning to all the places I love in the city where I’ve spent so much of my life. I moved here when I was twelve, left when I was thirty-six, and spent thirteen of those twenty-four years as a firefighter/paramedic before moving on for a PhD. And I find when I come home, the city is haunted with the ghosts of my past.

As I navigate the city’s streets, scenes from my life as a medic flash before me in vivid detail. For instance, that intersection I mentioned.

I was a new medic, working grueling hours on the ambulance, when a young pedestrian tried to cross the many lanes of traffic, only to be taken down by a semi. Her body was defleshed from the waist down, a condition known as “degloving,” and I can still remember the heat radiating off the pavement, the stench of the truck’s smoldering brakes, and the roar of nearby traffic as we wrapped her shredded limbs.

There’s the schoolyard where my partner and I performed CPR beneath the gawking gaze of schoolchildren. The sidewalk where I tried in vain to staunch the flow from a suicidal gunshot wound to the head. The strip mall, where the young man set himself on fire. And the trauma center to which I delivered countless patients, victims of the city’s unrelenting violence. My brain is a virtual card catalog of tragedy.

I know why this happens. These memories are part of my past, forever etched into my psyche. The bigger question is how it happens. How does the brain pull forth memories buried deep within the subconscious?

It turns out neuropsychologists have been hard at work studying the processes involved in memory retrieval.

It all starts with retrieval cues: clues or prompts that trigger the brain to recall information. But it’s the type of retrieval cue that determines just how the brain pulls forth long-buried events.

Recall involves the straightforward retrieval of information, such as answering a simple question. There’s little work involved and the information simply pops up when prompted. Recollection requires a bit more effort. Your brain reconstructs the memory by pulling together bits of information, such as clues or partial memories, reassembling them into a greater whole.

Recognition retrieval occurs when your brain latches on to something familiar, like selecting your favorite dish from a menu. And finally, relearning is just as it sounds – retrieving information you have learned on some previous occasion, which often results in stronger memories that are easier to recall.

But where do these memories reside?

The brain stores memories in one of two ways. Short-term memories are processed in the prefrontal lobe, that clump of brain located just behind your forehead. The short-terms are translated into long-term memories in the hippocampus, a small horseshoe-shaped structure within the limbic system that rounds up memories from various sensory regions in the brain and binds them into a single memory episode. Over time, the neuronal connections associated with that memory become fixed and can be replayed at will.

The hippocampus also helps solidify the connections that form our memories and each memory serves as an index for our recorded thoughts and sensations. Through functional MRI, scientists have been able to observe the brain as it reconstructs memories. And as each memory is recalled, different regions of the brain light up as various sensations and thoughts are replayed.

So when I return to Orlando, memories of my patients reemerge, triggered by the sights, sounds, and smells of the city. I recall their faces, their injuries, and their pain, and once again I experience the intense emotions they evoke whenever they resurface in my mind.

These memories are relics from a previous life, carved into my subconscious, and forever part of who I am. 

"Memories are bullets. Some whiz by and only spook you. Others tear you open and leave you in pieces."

                        - Richard Kadrey, Kill the Dead

Body Double

Imagine, for a moment, what it would be like to be attached to another human being. Think about it… every day, every night, every moment spent linked to another person. I’ve always been fascinated by conjoined twins. I remember seeing pictures of them when I was a child, marveling not only at the day-to-day logistics of such a setup, but that nature could actually produce something so spectacular. So let’s take a look at this most unique phenomenon.

Conjoined twins are rare. They occur about once in every two hundred thousand live births and around half are born dead. Of those who are born alive, about a third survive for just one day. It’s a small minority who live on.

Girls have a better chance of surviving than boys. Doctors are not sure why. Although the chance of twinning is higher among males, females are about three times more likely to survive than boys. Thus, females make up about seventy percent percent of all living conjoined twins.

So how does it happen? How are conjoined twins made?

Conjoining occurs when a single fertilized egg fails to divide completely during the first week of conception. The process that would normally produce two identical twins is halted for some reason, and the partially separated egg continues on its developmental pathway. The result? Two bodies, fused as one.

And the fusion can occur anywhere on the body, resulting in an array of amalgamated individuals.

The most common are joined at the chest. "Thoracopagus" twins make up about forty percent of the conjoined and usually share a heart, which can make surgical separation tricky. Another common form is those connected from the waist to the breastbone. "Omphalopagus" twins are similar in design to thoracopagus and account for about a third of all twins. The number of shared organs can vary, depending on the degree of conjoining, but it’s not unusual for them to share livers, digestive tracts, and genitourinary systems.

"Parapagus" twins share a body and sport two heads; a condition most intriguing when you think what it must be like to share a single body. And then there are the "craniopagus" twins. These individuals are joined at the head and this range from superficial attachment (bone and tissue) to the sharing of a single brain. They make up a very small percentage of conjoined twins, but arouse the most fascinating contemplation. What would it be like to share a brain?

Take Krista and Tatiana Hogan, two eight-year-old brunettes who are joined at the head. As craniopagus twins, they are unique. Only a fraction of this type survive, yet not only are they remarkable as twins, they are also remarkable for the manner in which their heads are attached.

The conjoining of their brains has produced an unusual condition: the girls share a thalamus. The thalamus is a lobed organ within the brain that processes the bulk of the sensory signals received by the brain. It plays a role in controlling the motor systems responsible for voluntary movement and coordination, but it is also an essential aspect of consciousness. And this is where things get truly interesting when we’re dealing with craniopagus twins.

Doctors who have studied Krista and Tatiana believe their unusual neurological arrangement enables them to share sensory input through what the docs have termed a “thalamic bridge.” And what this allows the girls to do is share sensations.

For instance, if one of the girls takes a sip, the other is compelled to swallow. If one is pricked in the finger, the other grimaces in pain. A pacifier in one mouth has a soothing effect for both. The list goes on and on…

Throughout history, conjoined twins have evoked curiosity, fear, and even scorn. The 16^th century French surgeon, Ambroise Paré, believed conjoined twins were the result of God’s anger and the Devil’s influence. But his notions were cloaked in the ignorance of his time.

For me, conjoined twins reflect the remarkable range of human expression, the amazing variability of embryological development, and the beautiful complexities of nature.

Here's a great video on parapagus twins, Abigail and Brittany Hensel, and how they cope with the day-to-day challenges of being conjoined.


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