Naturally, there was stiff resistance. Physicians were quite comfortable with the venerable, “no fault” concept of homeostasis whereby local, error- correcting mechanisms are thought to impose constancy without the brain, except for emergencies. All medical education centered on this idea, and it still does. But it turns out that most parameters are not constant— only a few are rigorously fixed. And, although (Page 12)
local, error- correcting mechanisms belong to the overall equation, the brain is definitely in charge. (Page 13)
The key goal of physiological regulation is not rigid constancy; rather, it is flexible variation that anticipates the organism’s needs and promptly meets them. The model clarified why the brain should be in charge: it is simply more efficient to predict a need and satisfy it rather than to wait for an error and correct it. For this model of “predictive regula tion” to challenge homeostasis it would need a name. Therefore, advised by a professor of ancient Greek, we called it allostasis— meaning “stability through change.” (Page 13)
Allostasis has been criticized as a just a fancy name for nothing new.5 But it offers something quite specific, not to be found in any textbook of medicine: principled definitions of health and disease. Whereas homeosta sis tends to define “health” as a list of “appropriate” lab values and “dis ease” as “inappropriate” values, allostasis defines health as the capacity for adaptive variation and disease as a shrinkage or compression of that capacity (Page 13)
Global warming is generally viewed as a political problem, and the addictions are seen as medi cal problems. However, in a broader view they all share a common cause, unbounded consumption driven by a shrinking diversity of small reward (Page 29)
A comprehensive model of human design must recognize the core epochs and their relationships: how key features of our cell biology cooperate to form our organism. Then how and why our metabolism and physiology respond to our daily experience and our character. The model must recognize that the human life cycle is normally navigated with considerable difficulty and explain why that is so. It must explain why humans require sacred practices— to which they respond with relief and tears. For that matter, the model should explain relief and tears! (Page 29)
homo_sapiens espiritualidad ritual emociones modelos
To be useful, a model must be constrained. That is, it must emerge from some set of principles and be governed by them. Current medicine lacks any overarching principle. We teach principles from physics and chemistry: Bernoulli’s principle for fluids, Fick’s law for diffusion, and the Michaelis Menten equation for enzyme kinetics. Each constrains some particular part (Page 29)
One route to success is to shrink the niche. For example, the fruit fly Dro sophila carcinophila develops as a larva in the nephric grooves beneath the flaps of the third maxilliped of the land crab Gecarcinus ruricola on certain Caribbean islands.13 A narrower niche harbors fewer unpleasant surprises, thereby allowing a narrower physiological and behavioral repertoire. The more faithfully an individual fly hews to what its niche offers and requires, the better its chances to survive and reproduce. This narrow- niche strategy fosters physical and behavioral uniformity: study one D. carcinophila and you’ve pretty much studied them all.14 Homo sapiens took the opposite route, evolving the ability to occupy any niche and every niche— land, sea, and air. Far from avoiding surprise, H. sapiens seeks surprise and cannot tolerate uniformity for very long.15 Of course, a quasi- infinite niche presents innumerable surprises to which the species must adapt, but H. sapiens’ low birth rate and long generation time disallow a fly- like rapid genetic adaption. So H. sapiens developed a quasi- infinite capacity to adapt its behavior, and this capacity involves an extreme degree of within- species diversity. In contrast to D. carcinophila, no two H. sapiens look alike or behave alike— not even “identical” (monozygotic) twins.16 Consequently, whatever the surprise, some member of the community can usually handle it. Naturally, H. sapiens’ extreme complexity and extreme individuality cre ate difficulties for maintaining individual cohesion and group cohesion, both of which are essential to sustain the species. So human design includes mechanisms to overcome the various dissipative tendencies that drive mar iners from their course. These tendencies include neural circuits devoted to music, art, sex, play, comedy, laughter, and tears. Of course, each culture expresses these features differently. But, just as all members of our species … of our mechanism, but none constrain our overall, integrated design. For such a constraint we must turn to Darwin, who, in articulating the deepest principle in biology, identified the key: resource availability. … harbor neural circuits for language but speak differently, we all harbor cir cuits for music but sing differently and beat a different drum. (Page 30)
The main resource for which H. sapiens competed was fuel for its metabolic engine. An adult human burns about 2,000 calories per day, a quantity equivalent to about 3 kilowatt- hours or a quarter liter of gasoline. (Page 31)
El cerebro consume el equivalente a 250 ml de bencina al día.
Walter Cannon later used this idea to frame his own physiological studies, naming it “homeostasis”— stability achieved through constancy.19 Now a century has passed without serious challenge to Cannon’s slogan, with few scientists even noticing that the slogan lacks a theoretical foundation (Page 32)
Human design goes well beyond a simple aggregate of self- correcting mechanisms. No animal could function like a free-market economy— every cell for itself. Free competition would defeat the primary advantage of multicellularity, which is efficiency through cooperation. Efficient design, as will be explained, must anticipate needs— deliver supplies before they are needed and make adjustments before errors can occur. Predictive control requires top-down, feed-forward signaling and, thus, a brain that speaks to every cell. (Page 32)
alostasis predicción cooperación metacelular
This type of regulation, combining prediction with cooperation, arose with the advent of the first brains— because it was actually the reason to have a brain— and it has been named allostasis. (Page 33)