HOMO AESTIMARIS: A Dualistic Model of Human Evolution

Reference & EducationCollege & University

  • Author Robert Depaolo
  • Published May 17, 2024
  • Word count 3,441

by Robert DePaolo


This article presents a speculative model of human evolution based on a sequence of events and conditions that caused mutations and various developmental features, leading to the unique anatomical, linguistic and cognitive traits that define humanity. While the theory of natural selection refers to random mutations as a prime determinant the idea is offered that mutations guiding human evolution might have been caused in large part by sunlight and radiation exposure, as bipedal hominids became more migratory. Rather than using the term Homo sapiens to describe the "final product" the crossroads leading from earlier hominids to modern humans is presumed to have been an enhancement of aiming skills that in turn enhanced hunting, perceptual and cognitive faculties and reached a high point due to the collating capacities of the human frontal cortex. In line with that model the name Homo Sapiens is changed (here) to Homo Aestimaris.

The Seeds of Humanity...

Arguably, momentum for human development began in the trees. We are the descendants of arboreals who had a unique brain/body synthesis. Negotiating among branches requires superb sensory integration capacities. The arboreal constantly engages in visual comparisons and in a sense, mathematical assessments regarding variables such as the stability of branches, the distance between them, and a kind of self-evaluation as to one's position in relation to what limb alternations and coordinates are needed to swing safely among the branches. Since monkeys use their arms and legs interchangeably, neural circuits governing motor actions have to be flexible and capable to weighing more than one thing at a time in execution of those actions. This was a fortunate template for the eventual emergence of the human brain/body system. Another beneficial factor was involved - momentum toward encephalization (brain growth).

Since tree dwellers (especially highly social tree dwellers) have the largest brains relative to body size in the phylum so there was likely a drift toward brain expansion from the beginning. Enhanced brain volume creates greater sensory discrimination capacities. Components of the natural world are more easily identified and distinguished from one another. Therefore, in the arboreal domain there arose what might be called an era of specificity, featuring not only increased perceptual identification of objects but also enhanced capacity to identify members of the group, and general social awareness to usher in interactive phenomena such as attachment, hierarchies, alliances and rivalries.

It is important to begin with the arboreal mind as a template of human evolution because it is conceivable (though not a scientifically mainstream idea) that evolution is not random, instead operates by a probabilistic and fairly straight forward momentum.

For example, with passing generations lions might evolve in the direction of larger or smaller teeth, or perhaps a slight color change in the mane of a male, but they will not develop gills. The probability of a zebra mutating a different configuration or number of stripes is greater than the likelihood of their evolving opposable thumbs. In other words, there is a somewhat orderly template (governed by the mathematics of AGCT alignment - i.e. Cytosine, Guanine, Adenine and Thymine, the four biochemicals comprising the DNA molecule) that guides mutations and evolution per se. In that context, a large brain devoted to the complexities of arboreal life might tend to evolve further in the direction of brain expansion.

Such was the case with the hominid line. While the leopard, jaguar and lion are of similar genetic lines there is no substantial difference in the brain volume among them (Yamaguchi et al. 2009) Conversely, the succession of hominids did feature significant size increases, from Australopithecus to Homo Habilis to Homo Erectus, and eventually to Neanderthal and Homo Sapiens, featuring more than a doubling of brain volume along the way (Pestana et.al 2023) The Yamaguchi study showed that there was a difference in brain volume between big cats in the wild and those in captivity but while over time hunting prowess would depend on having the best and biggest brains such would not be the case in animals living within the same time frame- especially since both would have a high protein diet of meat.

A second consideration in human evolution was the advent of upright walking. While this is commonly accepted as a developmental prelude there is another somewhat hidden factor, seldom discussed, that has its roots in the behavior of our closest genetic cousins, the chimps.

Chimps do two interesting things, albeit only occasionally. They walk upright and when threatened or in states of agitation they toss objects at trees and predators (Sloat 2016). Their bipedal gait is awkward, and the aim of the toss is rough and inaccurate. Nonetheless, both actions can be seen as prototypes of more sophisticated human behaviors and to have served as prototypes, not just for human hunting and avoidant actions but for many of the cognitive, memory and perceptual capacities that came to define the human species. If one were looking for a "functional missing link" for human evolution it might well be found in the biped/throwing couplet because those two behaviors could have provided the clay from which modern humans were sculpted. The question is why (once again extending the argument beyond the simple random mutation paradigm).

One possible cause - or perhaps 'antecedent' might be more accurate - is that one benefit of bipedalism is heat resistance. The upright posture exposes a small percentage of the body to the sun's heat. Also, being higher above the ground the biped can avoid some of the heat generated from below as well. Due to heat tolerance traveling long distances became more possible for hominids and then humans.

Prior to their increasingly migratory habits their primate predecessors' endocrine glands and other regulatory systems had adapted to life in the trees or on the forest floor with ample shade and minimal exposure to sunlight. Greatly increased levels of exposure to sunlight and radiation changed all that and there was possibly a dramatic shift in those systems. A study by Little et.al. (2024) indicates that is quite possible. One byproduct of that, which was pointed out in studies by Faienza et. al (2022) and Moss (2007) might have been accelerated mutations including accelerated brain growth and early onset of pubescent traits among females, making them appear sexually mature prior to actual maturation. Males would have taken notice and eventually mated with these younger females until a youngish generation with similar juvenile traits came into being.

A period of intensified neoteny likely occurred. Neoteny is a process in which youthful traits are retained during mating and passed on to subsequent generations so that juvenile features are retained and passed on. Often time this is a result of early pubescence.

Neoteny is generally acknowledged as a feature of human evolution (Faienza 2022) though scientists differ on how much impact this had as well as the causes of it. It does appear all primates tend toward juvenilization, as typified by increasingly flatter faces. For example, it was noted in the Faienza study that the infant skulls of early hominids like Australopithecus are similar to the infant skulls of larger hominids like Erectus and even modern humans.

The question is why. Some have opined that the juvenile facial features of females through neoteny would give been deemed more sexually attractive to males (Jones et. al. 1995). This is an interesting conclusion because it presumes a youthful (less mature) facial look would have been more attractive to males. However, since more than facial recognition is involved in mate selection it is also conceivable it lowered sexual interest in males for youngish females.

One possibility, as suggested by the results of the Jones study is that it wasn't a juvenile face per se that proved attractive but a more equal proportion around the skull with frontal lobe brain expansion. It would have caste a more symmetrical look and studies have shown symmetry is one feature that appeals to all creatures because it signifies a healthy constitution (Rhodes et. al 2012).

One must also consider how neoteny fits into a broader human evolutionary pattern. It seems not just neoteny but developmental timing as governed by genetics was involved. Certainly. human infants have delayed development and extended play periods beyond the timelines of other primates. But it is also true that the development of human females became skewed, not in a neotenous pattern but toward having the appearance of being in perpetual estrus. The breasts and pelvises (signs of estrus in most primates) are not seasonal with humans but are obviously a constant anatomical feature. Yet equally obvious is that human females are not in estrus all the time. In other words, nature created something of a feminine mystique requiring considerable negotiations between males and females as well as provocative actions by both genders to resolve this dilemma.

Females who are not in heat do not typically show interest in mating. Certainly, sexual activity has a bonding effect, and sex beyond reproduction would have solidified bonds between parents. That in turn would have increased the likelihood that both parents would be available to care for a child. Still, sexual confusion would have arisen between males and females prior to the establishment of a pair bond within the early human species. Some sort of signal system would have to be developed to override the ambiguity created by pseudo-permanent estrus. That could have provided a boost to language development (Worden, 2022). Words or sounds signifying "no" to ward off awkward advances and other types of communications would have been necessary. As a result, some part of the motivational dynamic in which females communicate subtle signals with males would have begun, especially if the hominid line retained the mating habits of other primates which are based largely on alpha male mating dominance rather than pair bonding. Her communicative task would have included language devoted to restraint by the male and conversely to keeping the male around to help raise a helpless infant...a no/yes strategy.

In addition to pseudo-permanent estrus, the timing factor in brain growth changed with expansion of the forebrain in humans and expansion of the cranium per se (Vanderhaghen, et al. 2023) The timing-glitch element is seen in virtually all aspects of human development We are considerably taller than our closest genetic cousins the chimps. Moreover, the timing of growth in head circumference in human infants goes beyond a normal biological scenario - as seen in the fact that the human skull cannot fully accommodate the brain, thus the splits in the skull case known as the fontanels.

In effect, the human brain had a shift in its primate developmental time frame and kept growing. That goes beyond neoteny as a causative factor. There would have been both bio-adaptive and socio-psychological effects from this.

It is conceivable mutations in the genetics that govern developmental timing might have been the result of a substantially increased exposure to sunlight (Lei et al. (2021), (Gailani et al. 1996), (Adewoye (2015) and to radiation which in turn resulted from the capacity to walk upright, tolerate heat and light and thus become more susceptible to the evolutionary influence of the sun.

Bipedalism also facilitated more effective use of the hands and tool making became the calling card of hominids likes Homo habilis but that in itself might have been a byproduct of something more fundamental in human evolution.

Encephalization created a new twist in cognition for the human line. The frontal cortex expanded in the human line without providing a specific sensory or motor function. That suggests growth in that area occurred relatively quickly by evolutionary standards. The frontal and prefrontal cortex did not support sensory, motor, or emotional/motivational functions but featured something of a freelance orchestration of neurons - much of which were inhibitory (meaning they served as a pause function in neural transmission and experience) and provided a new twist on cognition. Somehow the frontal lobes became a kind of clearing house of neural activity by innervating virtually all other networks in the brain. In other words, most roads of mind passed through and were to an extent governed by this nonspecific circuit, which expanded rapidly enough to become the largest area of the human brain (Catani 2019).

That created, quite naturally, perhaps even accidentally - a regulatory function and a focal point of experience, through which passed prior memories, motor planning skills, vocal expression, vision and audition. That focus of human experience created a capacity to gather disparate inputs from around the brain, compare and contrast inputs, govern emotions through language, plan actions, anticipate, and summon the necessary anxiety to provide impetus for preventative actions before dangers actually occurred. It was possible this was a crossroads leading from Neanderthal (whose brain volume was greater than Sapiens but more posterior) to modern humans.

Thus was born an anticipatory, predictive, futuristic, highly focused artistic and superbly attentive neo-primate. .

Another factor came into play. Located in the parietal cortex are motor centers that are aligned functionally in order of their relation to one another. Control of the mouth, hands, fingers etc. is facilitated in this area and gives the human brain a capacity to articulate sounds with great specificity. It is likely this circuit enabled early humans to use basic labels and concise social signals to issue warnings, provide cooperative cues to one another, interact with potential mates and use self-guiding phonetics while sculpting tools. However, it wasn't until frontal expansion occurred that modern humans could use sophisticated language, for example abstractions and figures of speech to conjure up associations among objects such as plants, animal groupings, weather patterns and so on. The reason why is that only with the connective breadth of the frontal lobe with virtually other brain sites could language circuits extend beyond the parietal cortex into various sensory, memory, emotional inputs emanating from other brain sites. In effect, frontal expansion connected the entire brain. It evolved as an experiential bridge.

Interestingly, while in the past language centers in the human brain were said to be located in Broca's and Wernicke's area in the parietal cortex, language is now believed to extend to the frontal lobes and to be governed in a number of locations around the brain (Barbas et. al. 2013) (Pet rides 2015).

A possible tipping point in human evolution occurred with a fusion between cortical and frontal cortical networks because that fusion enabled the brain to sustain sensory and memory focus. This transition might have taken place during the Pleistocene Ice Age, which William Calvin suggested was an epoch in which Homo Sapiens separated from the pack by developing superior aiming skills. Calvin referred not just to throwing objects to take down prey but also to the capacity to "aim" in the broadest, perceptual and cognitive sense. (1990) Focus improved, feedback from all around the brain to the frontal and prefrontal cortex created a vortex of learning and experience. The world opened up. Enhanced labeling improved the taxonomic zeitgeist. Plants, animals, the geography became more specific, but more than that, blended into art, myth and symbolism. A new species emerged, but while this species could capture its social and natural worlds with enhanced focus its actual experience was perhaps based on a very basic template- one that began with the toss of the chimpanzee and the traveling hominid.

Just as the frontal lobes gathered inputs into a vortex of experience so too did the cognitive vista of these new primates unfold according to that same mechanism. It was simply a question of the aiming primate extending a rather simple skill into the creation of complex experience - a process Darwin referred to as a conversion.

The idea that the frontal lobe's "gravitational pull" on other brain sites originated from basic aiming behavior to eventually create the focus and synthesis seen in human cognition might seem a bit ethereal. However, it is consistent with certain aspects of nature that transcend human development yet do exist in not only organic evolution but all energy systems in nature. The Constructal Law proposed by Andrew Bejan and Peder Zane in their book Design in Nature (2012) offers numerous examples in the natural world of how energy systems tend to flow in the direction of the least resistance and in one direction. If the frontal lobe had a tabula rasa quality unbound by specific functions it would be an ideal endpoint for the flow of neural energy- like the branches of a tree feeding into a trunk. In that sense the rise of Homo Aestimaris would have been caused not just by mutations resulting from the life-giving, life altering entity known as the sun but from a central rule of nature.

Homo Aestimaris.

All the above speculations might seem abstract for a theoretical structure - at least until one examines closely how Homo Aestimaris conceptualizes his or her world. One could ask if most, if not all human ideas and expressions could be considered a form of aiming. Consider the following common expressions.

I'd like to conclude by...

We solved the problem by finally putting our heads together...

In the final analysis....

My goal is ultimately to get from point A to point B...

The central tenet of Christianity is...

The common factor that ties those disparate ideas together is...

The United States of America...

E Paribus UNM...

Unified Field Theory...

What love hath brought together let no man tear asunder...

A nation divided cannot stand...

Central to our belief system is the idea of arriving at the final resting place...

The distance to the moon is 238,858 miles...

The whole is greater than the sum of its parts...

I am the Lord thy God, Thou shalt have no other Gods before me...

The core family unit...

Scientists are focusing on the genetic causes of cancer...

All roads lead to Rome...

The General Assembly...

Central planning...

The heart of the Matter...

Sums, multiplication products, division quotients...

We have a lot in common...

All the world's a stage...

What it boils down to....

Linguist Benjamin Whorf proposed that humans think the way we talk. While that might not apply in all instances it does seem possible that the evolutionary journey from the trees to the age of technology might have been surprisingly straightforward. and ultimately of dual causation: including upright walking and all its influences, sunlight exposure and the aiming response and how it might have provided a mental template for the subsequent artistic, scientific and cultural accomplishments of our species.


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Robert DePaolo author of seven books and many articles on science. religion, politics, psychology. and child development. MS Clinical Psychology. Retired Clinical Practitioner, former Adjunct Professor of Psychology NH University System. Producer, Writer of Film; Morality; A Historical Perspective.

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