#3. Human Reproductive Control [population, engineering, evolutionary psychology]

PO   EN   EP

Red, theory; black, fact

Here, I go into detail about the human population controller introduced in the previous post.

The Relevance of Engineering 

I assume that this controller is a masterful piece of engineering, like everything in the natural (i.e., evolved) world, as Leonardo Da Vinci declared.

Application of Filter Theory

The way to build an ideal feed forward controller is the inverse plant method, where the controller contains the mathematical inverse of a mathematical model of the system to be controlled.  To derive the model, you take the Laplace transform of the system's impulse response function. For populations, a suitable impulse would be the instantaneous introduction of the smallest viable breeding population into an ideal habitat.

The Impulse Response Function 

What happens then is well known, as least in microbial life forms too simple to already have a controller: unrestrained, exponential population growth as per Malthus, with no end in sight.

This exponential curve is then the impulse response function we need, and its Laplace transform is simple: 1/(S - r), where S is complex frequency and r is the Malthusian constant, that is, percent population growth per year. 

The Inverse Model

The mathematical inverse is even simpler: S - r, which is multiplied by the sensor-error Laplace transform to get the controller output. Multiplication by S followed by subtraction of the zero-time signal is equivalent to differentiation in the time domain. The effect of S-domain subtraction and multiplication by a constant remain the same when transferred to the time domain.

In humanly engineered systems, a feedforward controller typically operates in conjunction with a downstream feedback controller.

  

The Sensor Signal

The level of the noise produced so copiously by small children is probably the signal that people unconsciously use to estimate birth rate, and the wailing and long faces following a death probably serve the same purpose for estimating death rate.  My married older brother once showed me the developmental time course of child noise in the air with his hand, and it looked like an EPSP, the response of a neuron to an incoming action potential. The EPSP is the convolution kernel by which a neuron decodes a rate code. This suggests that the differentiation operation is telescoped into the sensing operation.

#2. The Iatrogenic Conflicts of the Twentieth Century [population, engineering]

PO   EN

Red, theory; black, fact

Center: a centrifugal speed governor that would have been familiar in 1914. The Steam Museum, Kingston, Ontario

Medical Advances During a Turbulent Century

In 1911, the anti-syphilis drug salvarsan, invented by Paul Ehrlich, became widely available to the public, at a time when this disease was cutting a wide swath of morbidity and mortality. Three years later, World War I broke out.

In 1937, sulfa drugs, the first effective treatment for tuberculosis, became available to the public. Two years later, World War II broke out.

In 1945, both penicillin and streptomycin became available to the public, followed in short order by the first mass vaccinations, notably against smallpox. In that decade (1945-1955), the Cold War between the United States and the Soviet Union began. That one nearly finished us in 1962, the year of the Cuba Missile Crisis, when a nuclear WW III was narrowly averted.

A Possible Mechanism 

In the human brain, there may be a wholly unconscious controller for population density with a feedback delay of some two to four years, that answers every sudden downtick in the death rate with a brutal, reflexive uptick. Recently, these downticks in the death rate have been due to advances in medicine, hence my title for this post. "Iatrogenic" means roughly "caused by doctors."

Supporting Evidence

Moreover, last year I noted that the headlines were all about ISIS, an unusually disruptive phenomenon of the Muslim world. I then checked to see what the main preoccupation of the headline-writers had been exactly four years previously. This seemed to be the Arab Spring, when many old governments in the Arab world were being thrown off. I concluded that these regimes had somehow been suppressing population growth.

An Engineering Model

If this controller is real, it should be just as analyzable as Watt's steam-engine governor, using standard engineering approaches. If it has a significant feedback delay, then a perturbation sufficiently rich in high-frequency harmonics (i.e., sufficiently sudden) should drive it briefly into a damped oscillation.

Evidence for the Engineering Model

In support of these conclusions, here are the US Census Bureau statistics on the percent growth rate of the human population for the 20th century, international yearly figures, aggregated to "World," and extended back to 1900 with decade-wise World data from the historical estimates table. At roughly the end of WW II, there is a huge jump in the growth rate followed by a sharp drop bottoming at 1960, followed by another sharp peak at 1962, followed by a leveling off superimposed on a gradual decline, the latter possibly due to increasing absolute numbers. This time series could be construed as showing a damped oscillation. See below.

The historical global population growth rate scaled to population.

The surmise that the post-1964 decline in the plot would disappear if corrected for changing absolute numbers is confirmed by calculation based on US Census Bureau data. See below. Furthermore, the plot shown below appears to level off at 78 million new people per year, which is probably the upper trigger level for the controller. There is probably no formal lower trigger level, making this controller asymmetric. Oscillation begins well before this level is reached, however, indicating the possible presence of a differential control term. 

Other Features of the Data

The sharp upstroke in growth rate that occurs at 1980 may be due to the eradication of smallpox over the decade 1967-1977. The downturn after 1988 was probably due to the AIDS pandemic. The data are coarse-grained before 1950 and do not show the upstrokes in 1911-1914 and 1937-1939 that I would have predicted from the two world wars.

World population growth rates in persons per year with no scaling. Note the reaction in 1960.

Mechanism of the Putative Damped Oscillation

A scan of historical events for the period 1954-1960 turned up nothing notable except in 1957, the year the down-dip anomaly began. That year saw a flurry of atmospheric nuclear bomb testing, rocket development, and regime changes. Racial integration began in the USA. The dominant sentiment driving all these changes may have been: “We gotta protect the kids.” Of which there were quite a few. Perhaps the downturn in population growth lasted until parental concerns about security were allayed. In general, how does one provide security, universally desired but universally elusive? The matter may be complex and demand a formal science of security.

Had the issues simmering below the surface been different, the dominant sentiment may have been different, but the population growth curve reversal would have looked the same, being due to a child-driven loss of tolerance for problems previously tolerated.

#1. The Origin of the Eukaryotes [evolution]

EV

Red, theory; black, fact

A fossil (oncoid or stromatolite) of a colony of prokaryotes. Photographed in situ.

The eukaryotic cell may have arisen from a clonal array of prokaryotes that selectively lost some of its internal partition walls while following the colony path to complexity. The remaining partitions gave rise to the internal membrane systems of present-day eukaryotes. Those prokaryote colonists specializing in chemiosmotic processes such as oxidative phosphorylation and photosynthesis could not lose any of their delimiting walls because of the need to maintain concentration gradients, so they remain bacterium-like in morphology to this day. This is an alternative to the phagocytotic theory of the origin of mitochondria and chloroplasts. Modern blue-green algae genetically resemble the DNA in chloroplasts, and modern aerobic bacteria have genetic resemblances to the DNA in mitochondria, but this is not necessarily differential support for the phagocytosis theory. The resemblances can be accounted for by convergent evolution or by the existence of an ancestor common to the modern organisms and the ancient colony formers I suppose here.

These prokaryote colonies would have originally reproduced by sporulation, not mitosis, which would have come later. The "spores" would be actively-metabolizing prokaryotes and before growing into further colonies, would be subject to natural selection. In the spore phase, the rapid evolvability of typical prokaryotes would have been recovered, allowing the formation of large, slow-growing colonies without sacrifice of the high evolvability of the original solitary prokaryotes. Modern-day eukaryotes often secrete tiny bodies called exosomes containing all the macromolecules of life. Exosomes may be the evolutionary vestige of the sporulation phase of the original eukaryotes.