Apes don't swim
Hominins who foraged in the intertidal zone often thrived, but sometimes they died en masse when a high tide swept across mudflats. For hundreds of thousands of years there was an equilibrium between increasing local populations and drownings among those foraging on the mudflats. The hominins gradually evolved an ability to quickly learn to dog paddle when they were swept off their feet—swimming in the manner of dogs and many other animals.
Infants clinging to their mothers’ backs were most vulnerable to drowning. In the course of hundreds of thousands of years, infants evolved a suite of reflexive behaviors that often prevented them from being drowned. When an infant’s face became submerged in water, the child would immediately stop breathing, and its metabolism would slow. (In modern humans this is known as the diving reflex.)
A child who had been clinging to its mother’s back would release its grip and begin to swim when its head went into the water. Its face would still be submerged in water, but the child’s mother would retrieve her child. Mothers no doubt learned how to bring a child to safety by floating the child on its back and then pulling the child along in the water.
If the water was deep, a mother could allow her child to grasp the hair on the top of her head, which was always out of the water, and then pull the child along. She could do this even if she lost her footing or if she was swept off her feet by an incoming tide.
Infants evolved a physical characteristic that helped them to survive in a semi-aquatic environment. They were born with a layer of fat under their skin, making it easier for them to float on their backs. In addition, the hominins began to grow longer hair on the tops of their heads. This, of course, helped mothers to tow their infants and children through deep water.
The layer of fat under the skin of infants also protected them from loss of body heat in cold water. Even adults evolved to have a layer of fat under their skin, because the hair on their bodies, unlike the furs of many semi-aquatic animals, did not have the water-shedding and air-trapping qualities of those other semi-aquatic animals, and did not conserve body heat when it was wet.
Youngsters were not able to wade into deep water, where they could escape from terrestrial predators. However, as the hominins became increasingly semi-aquatic mothers and older siblings began to teach youngsters to swim. Those who could swim could often escape from terrestrial predators by swimming into deep water.
However, not all youngsters learned how to swim. Consequently, they often needed to be carried or towed into deep water, and a mother might not be able to rescue all of her children when a terrestrial predator appeared on the scene. Consequently, the mother's mate would likely participate in the task of evacuating youngsters from the shoreline when a dangerous predator came onto the scene.
Our ancestors of this time most likely were dimorphic to about the same degree as chimpanzees, who do not form harems but instead formed male coalitions to control females. This would quickly change when our ancestors were forced to become terrestrial:
Groups of terrestrial hominins, slow on their feet and often having to cross open country where there were few trees and no water, would then be extremely vulnerable to predation, and intragroup cooperation became extremely important to them. Moreover, groups of wandering terrestrial hominins avoided each other so as to maximize their chances of finding unbroken bones that had been left by large herbivores, and bone marrow was the best food available to terrestrial hominins. This meant that the groups became extremely inbred, and it mattered little who was the father of which child.
Teaching and learning behaviors
Infants’ possession of the diving reflex allowed mothers to blithely dunk their charges whenever it was convenient. Perhaps dunking their infants even became an element of play. Older siblings of an infant would naturally imitate their mother in this behavior.
Of course, such behavior led to constant dunking that extended well beyond the period when the diving reflex would normally have been extinguished. The constant dunking caused the diving reflex to become a conditioned reflex.
The playful dunking behavior was selected for because it ultimately led to the ability of even adults to duck their heads into the water without starting to drown. This, of course, helped all of the hominins to forage in the surf, where food was often found in deep water.
The playful dunkings often forced youngsters to swim, momentarily. The dunking and forced swimming then evolved into teaching and learning behaviors. Behaviors that are not naturally part of apes’ behavioral repertoire.
When apes imitate the behaviors of others, they do so because they perceive the benefits of the behaviors. But there were no obvious benefits to the young hominins in swimming or in ducking their heads into the water. The young hominins did these things, in response to teaching, because the behaviors were viewed as normative. As was teaching. These behaviors, teaching and learning, are quintessentially human.
The learners assumed that if their mothers or their elders wanted them to learn to duck their heads into the water and to swim, then it was “proper” that they should learn to do it, regardless of whether they could perceive any benefit to themselves. Likewise, the teachers took it upon themselves to teach the swimming skill to youngsters. They thought the youngsters “should” be able to swim and dive. Swimming and diving were part of their culture, as was the teaching of these skills. The teachers, for their part, thought that teaching youngsters to swim and dive was “proper” behavior for themselves.
These behaviors were quite different from the behaviors of their ape ancestors. Like many other smart animals, and like the great apes of today, their ancestors had been good innovators and imitators. But they could not have passed on skills that brought no obvious, immediate benefits such as swimming and diving.
The teaching and learning of these skills required an inclination to teach, and to learn from elders and siblings, regardless of any perceived benefit to the teachers or the learners. On these inclinations would be built the ability of their descendants to construct and pass on complex culture.
Bones and carcasses
The primary food resources that semi-aquatic hominins found in the surf and the intertidal zone were the shellfish and crabs that lived there. Shellfish and crabs are very nutritious, but they are almost entirely protein, and semi-aquatic hominins, who were not natural carnivores, needed to supplement their diets with other foods − if they obtained more than about half of their energy from protein, the protein waste products would build up in their bodies and poison them.
Semi-aquatic hominins therefore supplemented their diets by falling back on the foods that their ancestors had depended on. During the winter season, especially, the best of those foods was marrow that they extracted from the bones of animals that had died.
In order to find bones, hominins would simply climb trees and look down. If they saw a flash of white where none had been seen before, they would climb down and go see if the bones had been broken open; and if not, they would break open one of the bones and see if the marrow was still edible. It was usually edible, because bones seldom remained unbroken for long in places near the sea, where there were lots of hominins.
However, since semiaquatic hominins lived primarily on seafoods and other foods that were found in water, the hominins spent most of their time in and near the water, where they had to compete with other hominins for unbroken bones. Other types of food that provided them with lots of energy, but did not overload their metabolic systems with excessive amounts pf protein were fatty deposits in the bodies of animal carcasses that they found and in the bodies of medium-sized animals that they themselves killed.
Hominins as successful predators
When attacked by predators, animals often try to escape into the surf if they can, where they will be on more of an even footing with a predator who cannot move quickly in deep water. This must have inspired hominins to begin chasing animals into the surf and then drowning them. Thus, the Killer Ape had his debut.
Hominins were successful predators, not just occasional, opportunistic predators. They were successful because they were not feared by their prey, as other predators are feared by their prey. This was because hominins did not act like predators, being slow on their feet and unable to chase other animals down.
Even after hominins became highly successful as predators, their prey did not greatly fear them (at least prior to the invention of javelins and of bows and arrows) because hominins generally trapped the animals and then slaughtered the largest of the trapped animals. This culling of land animals posed no more threat to them than that posed by the culling of domesticated animals. Moreover, the only way that animals could avoid the predation was to either avoid hominins altogether or to attack the hominins who tried to drive them into the water.
Hominins versus crocodilians
As predators, hominins and crocodilians were competitors, and they both killed their victims by drowning them or otherwise disabling them. With regard to hominins, the most vulnerable aspect of crocodilians was their egg clutches, which hominins found and ate, but a two-man team could bring down and kill a large crocodilian:
A two-man team would attack a crocodilian while diving under it and grabbing its legs and thereby preventing it from rolling or gaining speed. Then, they would drown it by holding its nose under the water. Thus, hominins had the advantages of being able to hold their breath for relatively long periods, and they were superb team players.
Crocodilians, for their part, could breathe while rolling, by rapidly closing and opening their nostrils, but they could only hold their breath for short periods (while they gained speed).
The Trachilos Creature
The finding of a set of fossilized human-like footprints, about six million years old, on what had once been a peninsula on the northern shore of the Mediterranean Sea, has upset some common assumptions about hominin evolution. These prints were found on Crete, near the village of Trachilos, and I will call the creature who made them the Trachilos creature, for want of a better name for him.
The tracks, which had been made in freshly-fallen volcanic ash, were found on the wrong continent, but in retrospect it only makes sense that modern-looking feet with forward-pointing toes, should have evolved in Europe, where trees bore fruits only seasonally. Indeed, it seems unlikely that hominins could have evolved in Africa, for this very reason.
The Trachilos creature was contemporary with Orrorin tugenensis, whose fossil remains were found in central Kenya. The latter species were also bipedal, and they had hard enamel on their teeth, which also indicates that they were hominins. The latter species, in turn are linked to Graecopithecus freybergensis by their teeth.
We use cookies to analyze website traffic and optimize your website experience. By accepting our use of cookies, your data will be aggregated with all other user data.