looking for indications of fundamental change

It had been about two years since I had seen a friend’s daughter. She was about thirteen and much taller than the last time I had seen her. He made complaints about having to buy new clothes and her appetite, but such is growth in kids. Consulting a children’s growth chart it is easy to see she was probably at the end of her growth spurt so future clothing purchases will be driven by other needs.

 

It is more interesting to look at growth velocity - the rate at which a child grows. Babies grow at a much higher rate than older kids with girls and boys having similar rates. Around the age of ten girls have a second much smaller growth spurt and boys follow a bit more than a year later with a longer spurt. The changes mean something interested in taking place. Quite a bit is known about the secondary adolescent spurts, but the slowing of a baby’s growth is really fascinating. Why doesn't growth take palce at the more constant rates seen in many other mammals?  Why is the period between this change and the next spurt as long as it is?  And many other 'whys' ...  it must be an amazing playground for the people who study it.

 

The end of the infant growth spurt marks a process deeply fundamental to humans. The brain undergoes considerable development during childhood and the energy required has to come from somewhere.  Around six months glucose is diverted to the brain slowing rapid body growth.  This process accelerates slamming the brakes on the rate of physical growth.  Development in the brain turns it into an energy hog - a five year old's brain uses more energy than an adult's.  After peaking around first grade the energy balance begins to shift back towards the body and puberty marks a point where the focus moves more towards the body's growth.  Our big brains and their development are very expensive.  This is limiting in some ways and is probably responsible for some of our social structure to offer protected care throughout childhood.

 

Other bumps in curves are just as fascinating withthe  development of steam engine offering an example.  Steam engines had been around in the form of toys and novelties of the wealthy since the time of Hero.  But increasing development of industry in England had offered a challenging problem - how to pump water from mines.

 

A few very early steam engines appeared but all suffered from low efficiency and the inability to pump water vertically more than thirty feet.   Thomas Neucomen cracked the verticle lift problem with an inefficient, but almost practical steam engine around 1712 and a nearly 300 year journey to efficiencies exceeding 40% was underway.  Plotting the efficiencies of important steam engines gives roughly fifty years between efficiency doubling - with an important exception.

 

James Watt invented a radically new type of steam engine - one with about five times the efficiency of the Neucomen.  Engines of ten and twenty horsepower were built and that steam engines became practical for many industrial niches. Industry finally had power that wasn't dependent on wind or moving water.  A revolution had begun and it was powered by coal.

 

Coal had been used for centuries, but it was particularly easy to mine in England , was cheaper than and  produced more heat per pound than wood.  Coal is a form of long dead plant life that has been compressed and heated for a long time - usually millions of years  - changing its chemical structure a bit in the process.  Around the time of the American Civil War the mining and processing of petroleum became practical and a second hydrocarbon based 'fossil fuel' was made available.  In the next fifty years it was on its way to becoming the ideal fuel for the automobile.  Natural gas was the third of the major fossil fueld largely being used for heating.

 

Fossil fuels have great energy densities, are relatively easy to mine, inexpensive and easy to handle.  Sunlight is converted to stored energy in the form carbon bonds by photosynthesis.  Some of the plants and animal life that feed on them die and escape normal decomposition and become sequestered in the Earth.  In some regions rich sediments form - coal, natural gas and petroleum depending on the initial material and the process.  The process is enormously inefficient - it varies, but generally is less than a ten thousandth of a percent efficient.  We only have a significant supply as the process has been going on for a few hundred million years. has been going on for a few hundred million years.  We could easily exhaust almost all of it in a thousand, but that is infinite time as far as we're concerned.

 

Burning fossil fuels is problematic.  Not only are dangerous compounded created from most the combustion processes, but carbon dioxide is released and is driving the acceleration of global warming.  There is some talk about natural gas as being a 'bridge' fuel between coal and petroleum to 'greener' sources of energy - for the same energy coal produces about 1.7 times as much carbon dioxide as natural gas and petroleum about 1.3 to 1.4 times as much.²   Problems can be mitigated somewhat by increasing efficiency, but going futher is requires a much deeper exploration so it is time to return to the central point.

 

The dramatic departures in the normal shape of a curve mark serious change - perhaps these are the markers of innovation.  The larger systems that these changes are embedded in respond.  Important elements become unimportant, often suddenly, and new elements arise out seemingly out of nowhere.  In hindsight we label some of these shifts as good and some as bad - much of this is difficult or impossible to predict ahead of time.  

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¹ 
This has been known for some time, but has been difficult to quantify until recently. A fascinating paper appears in PNAS.

Metabolic costs and evolutionary implications of human brain development

Christopher W. Kuzawa^a,b,1, Harry T. Chuganic,^d,e, Lawrence I. Grossman^f, Leonard Lipovich^e,f, Otto Muzikd, Patrick R. Hofg, Derek E. Wildman^f,h,i, Chet C. Sherwood^j, William R. Leonarda, and Nicholas Lange^k,l

^aDepartment of Anthropology, ^bInstitute for Policy Research, Northwestern University, Evanston, IL 60208; ^cPositron Emission Tomography Center, Children’s Hospital of Michigan, Detroit, MI 48201; ^dDepartment of Pediatrics, ^eDepartment of Neurology, and ^fCenter for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201; ^gFishberg Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029; ^hInstitute of Genomic Biology, ⁱDepartment of Molecular and Integrative Physiology, University of Illinois, Urbana, IL 61801; ^jDepartment of Anthropology, The George Washington University, Washington, DC 20052; and ^kDepartment of Psychiatry and ^lDepartment of Biostatistics, Harvard University and McLean Hospital, Cambridge, MA 02138

Edited* by Peter T. Ellison, Harvard University, Cambridge, MA, and approved July 25, 2014 (received for review December 28, 2013)

The high energetic costs of human brain development have been hypothesized to explain distinctive human traits, including exceptionally slow and protracted preadult growth. Although widely assumed to constrain life-history evolution, the metabolic requirements of the growing human brain are unknown. We combined previously collected PET and MRI data to calculate the human brain’s glucose use from birth to adulthood, which we compare with body growth rate. We evaluate the strength of brain–body metabolic trade-offs using the ratios of brain glucose uptake to the body’s resting metabolic rate (RMR) and daily energy requirements (DER) expressed in glucose-gram equivalents (glucosermr% and glucoseder%). We find that glucosermr% and glucoseder% do not peak at birth (52.5% and 59.8% of RMR, or 35.4% and 38.7% of DER, for males and females, respectively), when relative brain size is largest, but rather in childhood (66.3% and 65.0% of RMR and 43.3% and 43.8% of DER). Body-weight growth (dw/dt) and both glucosermr% and glucoseder% are strongly, inversely related: soon after birth, increases in brain glucose demand are accompanied by proportionate decreases in dw/dt. Ages of peak brain glucose demand and lowest dw/dt co-occur and subsequent developmental declines in brain metabolism are matched by proportionate increases in dw/dt until puberty. The finding that human brain glucose demands peak during childhood, and evidence that brain metabolism and body growth rate covary inversely across development, support the hypothesis that the high costs of human brain development require compensatory slowing of body growth rate.

Significance

The metabolic costs of brain development are thought to ex- plain the evolution of humans’ exceptionally slow and protracted childhood growth; however, the costs of the human brain during development are unknown. We used existing PET and MRI data to calculate brain glucose use from birth to adulthood. We find that the brain’s metabolic requirements peak in childhood, when it uses glucose at a rate equivalent to 66% of the body’s resting metabolism and 43% of the body’s daily energy requirement, and that brain glucose demand relates inversely to body growth from infancy to puberty. Our findings support the hypothesis that the unusually high costs of human brain development require a compensatory slowing of childhood body growth.

 

² A bit of chemistry to understand if a reaction requires or produces energy.  

 

Natural gas is mostly methane - four hydrogen atoms bonded to a single carbon to form a molecule.  Energy is stored in the carbon-hydrogen bonds.  Combustion requires two molecules of oxygen with some energy required to break bonds. Carbon dioxide and water are products along with a release of energy from the new bonds forming.  

a few bond energies (kJ/mole)
H-H	432	C=O	799
O=O	494	C-C	347
O-H	460	C=C	611
C-H	410	C-O	360

consulting the table and working out the energy of each molecule

CH₄   ( C-H)       4 * 410 kJ = 1640 kJ

O₂       (O=O)      2 * 494 kJ = 988 kJ

CO₂     (C=O)      2 * 799 kJ = 1598 kJ

H₂O    (O-H)       4 * 460 kJ = 1840 kJ

the change in energy is then

(1640 + 988) - (1598 + 1840) = -810 kJ

In other words 810 kJ of energy is released  for every mole (16 grams) of methane that is burned.

You can do similar math for the other fuels, coal is reduced to the point where it can be though of a multiple C-H bonds.  It's energy density varies as it is contaminated with water and minerals.  "hard" coals have as much as twice the energy density of "soft" coals.  Petroleum is more difficult as it is a mixture of large hydrocarbons. In the end it is important to consider the ratio of hydrogen to carbon.  Methane is 4:1, petroleum about 2:1 and coal 1:1.  Higher H:C ratios imply a higher energy content.

Carbon dioxide production per unit of energy released increases with unsaturation (a saturated hydrocarbon has all of the carbon bonds filled).  Methane is more saturated than petroleum which is more saturated than coal.   

Coal isn't clean, natural gas is somewhat better and petroleum is somewhere in the middle.  The subject is way to complex for a footnote.

 

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Recipe Corner

 

This is something I've been throwing together for years.  It only works when you have perfect tomatoes.  Extremely easy to make and one of the best meals you'll have.  I'll forgo my normal formatting and just add the note I sent to one of you a few years ago.

 

Tomatoes and Pasta

Two really amazingly blimpishly ripe tomatoes that are going to have great
flavor. I would go with an heirloom tomato as the new ones have so much
goodness bred out of them. My guess is I had maybe about one and a half
pounds of tomato. Chop these into half inch pieces and scape them into a
big enough bowl (how is that for precision?) be sure and get some of the
juice that is sitting on the cutting board.

Pour a bunch of a good olive oil on them. Maybe two glugs (another quality
measurement). Put a good amount of of a good Malden salt and ground pepper
on them and stir to mix. Let them sit.

Start some water boiling for the pasta and throw some salt in. Cheap salt
of course

Now chop a strong red onion or some scallions into slivers. Maybe about a
quarter cup

Chop a handful of good arugula

Cook about a half pound of pasta and try to stay away from the marinating
tomatoes

put the onions on top of the tomatoes spreading them out, then make a layer
of arugula choppings

Now dump the pasta on top of the layered mixture in the bowl and leave it
for a two or three minutes. To deal with the frustration grate some good
cheese for a topping and top it. The heat from the pasta is slightly
cooking the stuff underneath, but just barely.

Now mix it all up and serve.

 

Comments

[Jean]

There are many measurements where sufficiency trumps precision. :) Love your little notes on it though.

[steve]

Of course Jean - it is always about having a confidence level and being able to rationalize a prediction or action against it. If my plane goes into a spin and I see most of the right wing has come off, I have enough information to have a high enough confidence level that tells me to leave use a parachute:-)