I read an interesting article at Wired about the 10 worst evolutionary designs in animals, and decided that I would briefly comment on a few evolutionary challenges that we, as humans, often find ourselves grappling with. As with most things in life, nothing is black and white, and what may seem like a bad design is actually found to contribute something advantageous. I know what you’re thinking already… but the haunting beauty versus evolutionary utility of the “unibrow”, as most conspicuously worn by Frieda Kahlo, will be explored at a later time.
#1. The Appendix – if you were asked to think of a useless part of the human body, chances are the appendix would get the most attention. It is a small pouch that branches off the main intestinal tract and can be responsible for appendicitis, a potentially fatal condition if not treated. Appendicitis occurs in 7% of people. It is commonly thought that the appendix is a vestigial organ, existing as an evolutionary remnant with little useful purpose. More recent studies and speculation have looked at whether the appendix might help with immune function, especially in children, or in restoring good bacterial gut flora after diarrheal illness. Surgeons used to remove the appendix routinely in any abdominal surgery, but now many do not. The appendix seems to have arrived in our evolutionary ancestors for digestive purposes, but has perhaps found a new use in bolstering immunity.
Scorecard: Appendix, originally an evolutionary loser, making a comeback lately
#2. The human spinal column – I don’t think I’ve practiced medicine one day that someone has not asked for help with a sore back or neck. The medical literature estimates that at least 90% of people will have back pain at some point in their lifetimes… but who among us has never had back pain? By the time you are 50 years old and an X-ray of the lumbar spine is done, chances are very high that the radiologist will report degenerative changes. Standing upright often hurts. I’m not sure if dogs, horses, or other mammals have such problems – their axial loads are distributed like clothes on a line. I have never had a horse walk into my office and ask me for naproxen, so that has to tell you… something. But other research points to the fact that the human body is uniquely designed for long distance running, and that evolution strongly selected for body traits that made us better runners, including a vertical bipedal stance. For example, the unusually prominent ridge of bone at the back of our skulls is an attachment point for muscles that stabilize the head while we run. Our prominent gluteus muscles and springy Achilles tendons are particularly well suited for distance running instead of walking. It has been noted that (well-trained) humans can outrun many other animals over long distances, which gave us an advantage as predators by widening our range. Now running five miles is an accomplishment.
Scorecard: Spinal column and bipedal stance, good for shorter lifespans and long distances, losing out to the wear and tear of aging and cubicle life
#3. The balance of neurotransmitters – serotonin, epinephrine, dopamine… it is estimated that around 12% of patients seen in a primary care office have major depression, while the lifetime incidence of all psychiatric disorders including mood disorders, anxiety disorders, eating disorders, schizophrenia and other non-affective psychoses, and substance use disorders in the general population was found to be 41%. Conversely, the right balance of chemicals can set the table for incredible accomplishment and human productivity, as well as contribute to an enjoyment of life that borders on euphoria at times.
Scorecard: Our brains do a remarkable job of paving over the nasty existential dilemmas that come with self awareness, but should we really be as sad as we often are? What does the psychological burden of our humanity contribute to our reproductive fitness?
# 4. Metabolism and blood sugar regulation – diabetes is endemic to the developed world, with the total diabetes prevalence anticipated to be 11.5% of the US population (25.4 million) in 2011, 13.5% (32.6 million) in 2021, and 14.5% (37.7 million) in 2031. This is a result of human culture outpacing our bodies’ ability to adapt to refined carbohydrates, high fructose corn syrup, increases in total caloric intake, and a very sedentary lifestyle. But in times of scarcity, and in our history as hunter-gatherers, a thrifty metabolism helped us stay alive.
Scorecard: human metabolism clearly losing for many people, except for nomads in the desolate steppes of Siberia subsisting on permafrost
# 5. Other candidates for discussion might include the more serious aesthetic controversy over whether chest hair on men is attractive and confers a reproductive advantage (see Travolta, Selleck, et al), or whether it has become an evolutionary relic in today’s pantheon of bizarrely hairless celebrities, and any other characteristics you as the reader might expertly contribute.
I think 100 years from now people will wonder why we couldn’t have evolved web feet and hands so that we could better swim to work… Hey, maybe the appendix could be used as a tethered buoy to keep us afloat!?
Permafrost could be climate’s ticking time bomb
http://www.reuters.com/article/environmentNews/idUSTRE56S53E20090729
I liked your post. I’d also like to submit the sinuses as a structure poorly designed by evolution – always filling up and becoming infected. Who’s idea was that?
Along the bipedal lines . . . the pelvis is good for running, bad for pushing out babies with big brains in caves. Along the cave lines. . . hypercoagulability in pregnancy was good when we were bleeding in caves, bad that we are now fat, sedentary, and post-op from c-sections and prone to deep vein thrombosis and pulmonary embolism. On the plus side of evolution, those babies with big brains invented antibiotics, blood transfusions, and c-sections.
About the balance of NTs and moods, I would like to submit for consideration that perhaps mood disorders were less prevalent when man roamed the African savannas (still debated as are of origin) and have only increased in frequency when we as a species have reduced the selective pressure medical conditions with an inherited component place on groups of individuals who inherit that trait. Medications and therapeutic interventions allow people with NT imbalances and possible structural defects of the brain to lead lives that are rewarding, independent, sustainable and often reproductive. It stands to reason that from an evolutionary perspective, however, 5,000 years ago if a group of individuals inherited a predilection for mental illnesses such as depression or severe and persistent mental illnesses such as bipolar disorder or schizophrenia, they would be at a significant disadvantage and experience decreased fitness. Of course I need to acknowledge this only affects the components of mood disorders are heritable and have high penetrance.
Horses certainly can have spinal problems, though that’s arguably from overwork (“swaybacked”).
Both the depression and diabetes issues likely represent responses to our modern environment, which we’ve pushed way out of the range that we evolved for. A lot of other health issues we have, represent tradeoffs — as you note, our spine represents a drastic adaptation for vertical stance and running, as does our narrow pelvis, which as Micha points out is a problem for childbirth.
Could we please talk about the human knee, and the myriad ways it goes wrong versus the one way it can go right? Between that and the capacity of differentiation to go terribly wrong, I have a variety of bones (as it were) to pick with the Great Designer.
Just for the record, all 7% of those people with appys were in my ER last week.
And I can vouch for chest being a reproductive advantage. In a major way. Back hair? Not so much.
Great post …how about adding Belly buttons!! Neither use nor ornament from the day we are born to the day we die…can’t they just heal up and save health care services money treating fungal infections, foreign bodies ( http://maxenurse.wordpress.com/fbs/ ) and of course umbilical hernias.
Mind you they do give you somewhere to put a pen when filling in the crossword at bed time!!!
Max: I think that belly buttons are very useful. Many years ago I had an omniscient professor of Philosophy who one day said to me, “I’m only human.” My response was “OK, show me your belly button.” He refused. To this day, I am convinced that he is actually a god. Now I am a nurse and I have seen variations in human anatomy (including missing parts) that would cross your eyes and make your head spin. But I have yet to see a missing belly button.
I nominate the disaster that is the gluteal cleft for pilonidal cysts, the pancreas for its fickleness and propensity for creative adjustment of insulin levels, the coccyx, and plasma transport of cholesterol – why export it from the liver? It doesn’t do so well in the arteries and every cell can make its own anyway. Also I seem to be missing an ink bladder; how did my ancestors ever escape from predators?
Of honorable mention: most organs. Sure they do their job, but there is always some species with one that does it better. Take the lungs for instance, why is it that we have such trouble with scaling tall mountains yet many birds have no problems with those altitudes? Their environmental stressors resulted in a far better organ than ours.
see -> http://www.erj.ersjournals.com/cgi/content/abstract/29/1/11