William Howard Calvin

The 1,000-fold differences between countries in bringing the 2020 pandemic under control show the consequences of failures to stockpile, a century-old anti-science, anti-expertise streak in American culture, and of tolerating incompetent leadership. The extreme weather in the last twenty years has featured surges in severe windstorms (now 7x as common as before 2008), inland floods, mega heatwaves, hot-dry-windy “fire weather,” and stalled hurricanes. They threaten a human population crash via famine and genocides. Here I adapt the physician’s mental check list to show what a “climate doctor” would consider. First, sensible precautions: beefing up infra­structure to resist floods, burying power lines and creating city-wide battery backup, and relocating people out of flood plains and coastlines. Stockpile. We need economic modeling for emergency measures, what we should have done before the pandemic’s recession. Protect the patient from the usual causes of terminal downhill slides. This is commonly called “stabilizing the patient.” The Civilian Conservation Corps in the 1930s likely prevented civil disorder. Recognize what’s wrong. For climate, the working diagnosis since 1965 is a global-scale overheating caused by the accumulation of CO2, contributed by the annual emissions of fossil fuels. Attacking the root cause may not be fast enough. To evaluate urgency, guess where things are likely headed (prognosis). Climate models are good for estimating slow climate change, but they are only beginning to address the dynamic aspects that can create climate flips and extreme weather. Rule out other problems. Repeatedly search for secondary climate problems, analogous to shock and internal bleeding, that could provoke a fast track to disaster. Formulate a plan of action and explain it to get consent. The annual bump-up in CO2 from emissions is now 50% greater than before 2000. We must now focus on a quick cleanup of the existing CO2 accumulation, as in using a kidney dialysis machine to quickly clean up an aspirin overdose. Gradual overheating is no longer the correct focus for under­standing the risk we now face. We are in the territory where fast tracks to disaster must be forestalled. Something, perhaps the passive drama mindset for the surreal, is preventing effective climate action, even by the knowledge­able.

Hominin procedures for fire-starting, sharpening rocks, and softening roots by pounding or chopping require sustained attention for hours; shade is sought in the brush fringe bordering a grassland. Clustering these more versatile adults, while others are away hunting and gathering, provides a setup for assortative mating. This can lengthen attention span, enhance versatility and, with it, brain size. The rate of enlargement is accelerated by a boom-and-bust cycle in their meat supply, predicting the observed initiation of enlargement at −2.3 myr in the Rift Valley once boom-prone grazers evolved from the mixed feeders. Several months after lightning created a burn scar back in the brush, the new grassland enables a population boom for those grazers that discover it. Several decades later as brush regrows, they are pushed back. Their hominin followers, wicked in from the grassland’s shady fringe, boom together with the burn-scar grazers. They then follow their meat supply back to the main population. This creates an amplifying feedback loop, shifting Homo gene frequencies centrally. Brush fires are so frequent that the cosmic ray mutation rate becomes enlargement’s rate-limiter, consistent with 460 cm ³ /myr remaining constant during many climate shifts. The apparent tripling of enlargement rate in the last 0.2 myr vanished when the non-ancestors were omitted. Asian Homo erectus enlargement lags the ancestral trend line by 0.5 myr. Neanderthals lag somewhat less but have a late size spurt after the −70 kyr Homo sapiens Out of Africa, suggesting enlargement genes were acquired via interbreeding.

The rapid three-fold enlargement of the hominin brain ^1,2 began about 2.3 million years ago (myr) as Africa dried and grass replaced brush, creating great savannas ³ . Seeking an amplifying feedback loop, I analyzed the lightning-brush-fire ecology for grazing animals in a grassy burn scar ⁴ . Discovering the new grass by exploring brush byways could promote a population boom–but only after grass-specialized herbivores evolved from mixed feeders ⁵ at 2.4 myr. When the brush returned several decades later, the grazer boom would turn to bust, squeezing numerous descendants back into the core grasslands. Meat-eating Homo species would boom and bust when grazers did, enriching the core in whatever alleles were earlier concentrated in the brush fringe catchment zone for that boom. This return migration for Homo is what creates the amplifying feedback loop that speeds brain enlargement rate, likely up to the mutation rate limit. It also promotes trait hitchhiking: any brush-relevant allele, not just those for hunting, can experience amplifying feedback merely by hanging out in the catchment zone ⁴ . The shade offered by brush would have been the default location for cooperative nurseries, time-consuming food preparation, and toolmaking. Increased behavioral versatility correlates with larger brain size and the more versatile brains of a current generation need only spend more-than-average time in the boom’s catchment zone for this recursive evolutionary process to keep average brain size increasing via assortative mating. This helps account for the time when enlargement began, why it was linear, when it ended, and why it slowed in Neanderthals and in Asian Homo erectus . Without utilizing Darwin’s selective survival, the feedback loop makes advance room for “free” future functionality in the cerebral cortex, likely relevant to the evolutionary emergence of our structured intellectual functions ⁶ such as syntax, contingent planning, games, and logic.

Here I analyze the brush-fire cycle behind the brushy frontier of a grassland, seeking evolutionary feedback loops for large grazing animals and their hominin predators. Several months after a lightning strike, the burn scar grows enough new grass to expand the carrying capacity for grass-specialized herbivores,which evolved from mixed feeders in Africa during the early Pleistocene. The frontier subpopulation of grazers that discovers the auxiliary grassland quickly multiplies,creating a secondary boom for its hominin predators as well. Following this boom, a bust occurs several decades later when the brush returns; it squeezes both prey and predator populations back into the core grassland. This creates a feedback loop that can repeatedly shift the core’s gene frequencies toward those of the frontier subpopulation until fixation occurs. Any brush-relevant allele could benefit from this amplifying feedback loop, so long as its phenotypes concentrate near where fresh resources can suddenly open up, back in the brush. Thus, traits concentrated in the frontier fringe can hitchhike; improved survival is not needed. This is natural selection but utilizin selective reproductive opportunity instead of the usual selective survival. Cooperative nurseries in the brush’s shade should concentrate the alleles favoring eusociality, repeatedly increasing their proportion via trait hitchhiking in the feedback loop.

Long before signs of staged toolmaking appeared, Homo erectus made symmetrical tools. The handaxe is a flattened tear-drop shape, but often with edges sharpened all around. Before we assign their obsession with symmetry to an aesthetic judgment, we must consider whether it is possible that the symmetry is simply very pragmatic for one particular use in the many suggested.