Why do we need bones anyway? The octopus does just fine without a skeleton. In fact a skeleton would cramp its style. You don’t start with a bony skeleton. While you were floating in your mom’s womb you had a soft skeleton of cartilage, just like the fish from which we evolved. So what happened? The salt water fish started to exploit a new environment – fresh water. They swam up the rivers since fish gotta’ swim, as the old saw says, and there they encountered a problem. There was not enough calcium in the water, and whether you are a fish or a frog or a person you need calcium to live. Without it you can’t do nerve impulse transmission or muscle contraction or blood clotting. Long story short without calcium you would be dead before you hit the floor. Seawater has plenty of calcium. In the ocean you easily absorb it through the food and even from breathing through the gills so it’s never a problem. Certainly not for a pufferfish.

But in freshwater you can’t rely on a constant source. If you want to make it as a freshwater fish you’ve got to have some reliable way to store calcium for times when you can’t get any – a calcium bank as it were. So some fish adapted by storing calcium in their skeleton. They also came up with calcitonin and parathyroid hormone which keep the blood calcium levels balanced by making calcium deposits or withdrawals from the bone calcium bank. To this day, purely salt water fish like sharks have a cartilage skeleton, and freshwater fish like salmon and trout have a bony skeleton like us.

For more on this picture see “The most beautiful science book ever.” 

Another quality of a bony skeleton is rigidity. You can resist gravity. One fine day a fish hauled itself on land, and that gave rise to the amphibians, then the reptiles, then the mammals. It is ironic that in fixing a problem so they could survive in fresh water, the fish came up with a solution that allowed them to leave the water completely. In a way, we are all fish out of water. But that’s the way evolution works. There is a challenge. You find a solution or you die out. Often that solution opens up whole new possibilities that take life in a completely different direction. Dinosaurs invented feathers for insulation, and we still use feathers for that today. But feathers also allowed for flight, which gave its owners the edge they needed to survive the great extinction that knocked the other dinosaurs out. The only living dinosaurs you see today are in the sky.

There is a disadvantage to bones reinforced with stones. Calcium is heavy and it costs a lot of energy to move that bony skeleton around. If the bones were solid mineral they would be a lot stronger, and three times heavier than they are. Imagine dragging that across the planet’s surface every day. Therefore the body wants the skeleton to be strong, but only as strong as you need it to be. There are teams of osteoblasts (which increase the bone matrix) and osteoclasts (which break down the bone matrix) constantly altering the structure of bones to make them only as strong (and heavy) as is absolutely necessary. How do they know what is strong enough? Electrical fields. The bones are piezoelectric, meaning when a force it applied to them (like supporting your body) they generate electrical fields. That stimulates the osteoblasts and osteoclasts to strengthen or lighten the bones to match the forces they are generally exposed to and trim away excess mass. In the following pictures you can see the lines of force that run through a bone by the lines of reinforcement in the matrix. Those little beams of bone (called trabeculae) are not laid down randomly, they are built to resist that force. In this picture of the interior of the head of a femur I’ve drawn in lines tracing where the main force is directed. The weight comes off the pelvis and is directed to the shaft of the femur much like the weight of a cathedral roof is distributed to the walls. The bones even use little gothic arches, visable in the shaft toward the bottom of the picture. The patella, on the lower right shows no such organization becasue forces on the patella are evenly spread around.

Xrays reveal the same internal structure for the femur as it takes the weight off the pelvis.

In this picture of the calcaneus (heel bone), the lower left is almost solid bone material because that is where the heel strikes the ground. The shock is then transmitted up and to the right, indicated by the arrows. Another arrow traces lines of force from the lower right where the calcaneus attaches to the plantar fascia, supporting the arches of the foot. This line sweeps up in a big curve much like the cables on a suspension bridge. The arches are suspended by tension in the bones and fascia. The right central part of the bone is almost hollow as there is no need for strenght in an area that gets little force.

If you work out you put more force on the bones and muscles and they get heavier and stronger. Less force, less strength. On the space station there is almost no gravity and the bones suffer from severe osteoporosis.

By the time the astronauts come down they have almost no bones left and they have to be carried off the capsule. Once under the pull of gravity the bones rebuild (mostly.) Your whole skeleton – every cell, every fiber, every grain of mineral – is replaced over the course of about two years.

Bones will adapt to whatever you are doing. If you exercise they get stronger, if not they weaken. An added bonus to regular exercise is that when osteoblasts are stimulated they release hormones that create proteins that aid the hippocampus – the main engine of memory. This may be why exercise has long been linked to improving memory.

Jogging jogs your memory.

Why is it so easy to eat and so hard to work out? People invariably need no coaxing to eat. They look forward to it, consume mass quantities with gusto, and even look back on the meal with a certain fondness. One out of five people force themselves to exercise, and the other four out of five people don’t work out at all except in front of the fridge. It’s open and bend and reach and up and close and open and bend and reach and up and close, repeat. There are whole professions dedicated to help people work out. Not so with eating. You don’t find eatotonics classes where we all get together around a big table with a horribly enthusiastic cheerleader egging us on. Hard to imagine a personal eating trainer at dinner. ”O.K. O.K. That was good. Lift that fork again! C’mon! You can do it! Three more reps and we’re done.”

There are exceptions. Some people don’t eat enough and some people do work out too much, but the overwhelming tide of humanity goes the other way. When given the chance of working out or watching other people work out (sports on TV), most people will do the latter, and eat while they are doing it. Since everybody knows you are supposed to exercise and not overeat, why does the average person do just the opposite?

We are the victims of our own success. In the beginning, when the world was young it was also hungry. Humankind grew up in the East African rift valley over the last million years or so. Estimates are, to get enough food those early hunter gatherer societies would walk six or seven miles a day.

You didn’t need a coach, you had a built-in coach called hunger. Hunger is an excellent coach. Exercise was provided by the lifestyle and nobody liked it then either, so we invented ways to avoid it ultimately inventing the car. We have gotten so good at it that by now you have to schedule exercise.

People in cities that were built up after the invention of the car (cities like LA, Dallas, Phoenix) get no exercise unless they seek it out, and the general population is not in good shape. You can’t even walk around because cars require big roads and big parking lots so everything is spread out.  LA has sidewalks, but I don’t know why. My first time out there I went for a walk.  I was the only pedestrian for miles. Eventually a police cruiser started to follow me, I suppose because I was involved in the suspicious act of walking. Without a car, you can’t exist in these places. People in cities that were built up before the invention of the car (Chicago, San Francisco, and all the big eastern cities) get more exercise and the populations fare a bit better. Without cars, the cities are more dense and you can walk from place to place. Many people don’t have cars. The cities solved the problem of getting around with subways and busses, which you still have to get to. Most New Yorkers climb many flights of stairs every day just to get to work. Even so, they are hardly clocking seven miles.

Since we used to walk all over, why no urge to do it now? Simple, then as now, the internal urge was to conserve energy. Food was hard to come by and what you could depend on was sometimes it would be really hard to come by – famine. Famine was always around, and for much of the world it still is. The survival strategy then would be to get as many calories as you can whenever you can and expending as few calories as possible to do so. The ultimate expression of this universal desire is driving to the Olive Garden.

If they could figure out a conveyor belt to take you from your car to a booth they would do it. There are drive through deli’s in California where attendants put anything in your car you like. Not only do we want to eat as much as possible, we want to eat as much food with as many calories as possible. Carbohydrates (sugar, high fructose corn syrup, bread, cereal, crackers, cake, pasta, potatoes) are a great source of calories and fats (butter, cheese, oil) are even better. Too improve a carb, just add fat. Bread is improved with butter. Bread is really improved by deep frying it and rolling it in granulated sugar – churros! Pasta is improved with a cream sauce. Potatoes are improved with sour cream and butter (even better, deep fry the potatoes in oil to make fries and smother them in melted cheese!) Heck, you can even fix vegetables with fat. Salad dressings (ranch, blue cheese, creamy Italian) are more than half fat. What does asparagus need? Hollandaise sauce which is fat squared! What can we do for this broccoli? I know, lets pour some melted cheese on it. Hungry yet?

This particular desire for fats is driven by a neurotransmitter called cholecystokinin, a mouthful of a word that causes you to eat many more mouthfuls. Cholecystokinin is THE BEAST WITHIN YOU.

Plants generally don’t have fats. Animals have fats, and they want keep them. If you want a fat now you need do no more than walk into a convenience store. If you wanted a fat in the old days it would be attached to some animal who was running away from you. You’d have to sharpen a stick, make a strategy, walk even more miles then try to kill it and if it was big it just might kill you. What a pain. You can almost see Thag looking out of his cave on a winter morning at some wooly mammoth who is looking right back at him as if to say, “Just try it.” Thag turns to Mrs. Thag and says, “Can we just have pasta tonight?”

We used to need a strong incentive to hunt down those fats. Cholecystokinin is a neurotransmitter that can control your mood. The stomach releases it when you eat food with fats and that makes you feel good. Everybody has their own comfort food, and every one of those foods is laced with fat. Nobody looks at rice cakes as a comfort food. Wrap them in bacon and you are getting closer.

Not only do we have a sweet tooth, we have a fat tooth. We still have the cave man drives that we used to need to get calories, and especially fat calories, but now we can get them easily, and we do. We’ll take things that already have plenty of fat and add more fat to it. “I’ll have the double bacon cheeseburger with fries. Supersize me.” Dominos sold a lot more pizza when they doubled the cheese on it. Now they even have cheese inside the perimeter crust.

Our sweet tooth is sharpened by the bacteria in our gut. If we eat a lot of carbs, the bacteria in our gut that breaks down carbs is getting more nutrition, so it is fruitful and multiplies. Since more is better it will secrete its own hormones and neurotransmitters that make you crave even more carbs, thereby ensuring its own food supply. It’s not so much that you think with your gut as your gut often thinks for you.

If you are having a hard time accepting the idea that gut bacteria – the micribiome – are influencing your behavior this sort of thing goes on all the time. We have a dynamic and shifting relationship with the civilizations we carry within us. Various species within the intestinal biota can be “good guys” one day and “bad guys” the next, so such labels are not so useful. Think of it more like the UN. Everybody has their own agenda and sometimes these agendas coincide and sometimes they do not. If you are curious about this topic, I recommend I Contain Multitudes by Ed Yong, a fascinating walk through the various relationships within ourselves.

The body is well designed for the hardscrabble existence it evolved in. It is not good for the land of milk and honey. When you go “on a diet” you are going against the grain. One thing is certain. All extreme diets fail. Unless you want to suffer and gain weight don’t go there. They all advertise about how much weight people lose but everybody on them gains it back within a year. A workable diet is what you do eat, not what you don’t eat, and cutting out your favorite stuff will only make you want it more. Also, your body interprets extreme rationing as famine and decreases its calorie use which makes you tired and crabby. So eat what you want, just not as much as you want to. (That said, junk food is not a good idea.) Decreasing eating by a little bit is way more effective because it has to be something you can sustain forever. If you link that with moderate exercise the weight will come off. Exercise is at least as important as diet, probably more so. This is easier said than done. Behavior modification seems to be about the hardest thing in the world. Ask anyone who smokes.

My next post will address why we don’t have an exercise tooth to go with the sweet tooth and the fat tooth.

“Parochiality and narrowmindedness are, alas, as much a part of normal human response as generosity and expansiveness. People wall themselves within the comforts of their own profession and hurl derisive formulae at folk in other fields. Academicians brand athletes as dull lumps of brawn, succeeding only by lucky gifts of inherited muscle; athletes, in turn, dismiss academicians as effete and inept in all but their artificial world. In fact, excellence is both precious and similar in mental construction across all fields. True, both gifts of birth and a little luck never hurt, but the only common denominator is obsessive focus, mental discipline, hard work.”

So Stephen Jay Gould opens the elegant introduction to “Fossils”, by Niles Eldredge, photography by Murray Alcosser. Since science involves a close examination of nature, it helps if the nature attracts the eye.  This is the most beautiful collection of photographed fossils that I have ever seen.  Virtually every page is a stunner. But this is far more than a gorgeous coffee table book.  It is also an exposition of the evolutionary theory of punctuated equilibrium.

Charles Darwin visualized evolutionary change as a stately, gradual process whereby variation of offspring would occasionally confer an advantage over other creatures. These new and improved creatures would be fruitful and multiply, edging out their neighbors. Variation is obvious. We see it in our children, otherwise they would be exactly like us. Most variation is of no advantage so the offspring will be no more likely to succeed than any other so you get the status quo.  Useful variations will guide evolution. That’s how a fish eventually becomes a racehorse.  Q.E.D.

Not quite. Evolution turns out to be as lazy as we are. Things don’t evolve unless they must. The humble horseshoe crab hasn’t seen the need to evolve much for three hundred million years.  That’s a long time hanging out at the beach.  They go back before the dinosaurs, and they are still here.

Bacteria on the other hand are evolving so fast that we may be in trouble. Why the difference? If the environment changes creatures must adapt or go extinct. We are driving the adaptation of bacteria by creating a hostile environment.

Stephen Jay Gould and Niles Eldredge pointed out that the fossil record shows periods of stability in whole ecosystems that can run for many millions of years, punctuated by periods of great change where many lines go extinct and others change quickly, say in one hundred thousand years.  It is often the dominant species, comfortably settled in the center of their ecosystems that die out when change comes. They are so well adapted to one environment that when it changes abruptly, they can’t make it. It is the life forms living a hardscrabble existence on the edges of an ecosystem that are more nimble and can adapt faster that survive. The dinosaurs are a large example. They dominated the earth for several hundred million years and were mostly wiped out by a planetary cataclysm. A comet crashed into the Yucatan peninsula plunging the earth into darkness and freezing temperatures that would have lasted for years. Eighty percent of the species around perished. Mammals that up to then were no more impressive then rats filled the void. Were it not for that comet, the dinosaurs would most likely still be around and we never would have gotten our moment in the sun. Mammals are dominant – for now.

“Fossils” is one of those great works that both educates and delights. Trilobites almost jump out of the pages at you. Compliment it with “The Age of Wonder.” 

The only thing it is missing is galaxies. My opening picture in this essay compares a shell to a spiral galaxy. That is not in the book. I included it here because the Golden Ratio that governs the curvature of shells also governs the curvature of spiral galaxies like the Milky Way. When nature finds a solution that serves, she uses it over and over again. Scale is not a limitation.