At the start of this chapter, we asked an important question: How did we humans come to be the way we are today? This question is important not only because we all have a personal stake in the answer but also because it would have us seek answers to a fascinating mystery - one that might well be solved, at least in part, by better understanding physical activity, play, and other topics related to our own professional interests.
One version of the mystery story goes like this. As the evolutionary theorist Stephen Jay Gould observes, species can enter periods of equilibrium or stasis. During such periods, very little new adaptation occurs in generation after generation, but the species continue to survive, if not flourish, in some kind of environmental niche. Then, for some reason - and here is where the mystery comes in - this same species enters a period of rapid change. Why this change? Why now? Why so quickly? What is the stressor that, so to speak, upsets the previously stable applecart? These questions have been asked about some of the patterns shown in the chronology of life provided earlier, which ended (at least for now) with us.
Emerging Bipedalism and Related Advances
The first "great leap" identified by scholars of human evolution involves the move made by our hominid ancestors five to eight million years ago from the densely forested areas of Africa to the relatively open spaces of the savannah. These original bipedal hominids - they walked fully upright on two feet - entered a highly competitive savannah environment with what, at first glance, appeared to be few of the physical attributes necessary to compete for survival. Scholars who have studied the extraordinary ecosystems of the African savannahs have postulated that, over millennia, these environments produced an "arms race" between predators and prey that developed fast and strong species among both the hunters and the hunted. This context casts an intriguing light on the motto of the current Olympic games - citius, altius, fortius - which is a Latin (not Greek!) phrase that can be translated as "swifter, higher, stronger." It underscores our penchant for celebrating the power of our bodies in contests of speed, strength, and explosiveness.
Unfortunately, our ancestors on the African savannahs seemed ill equipped for this intense struggle for survival. They were neither swifter nor stronger nor able to jump higher than any of their competitors or even most of the prey they hunted. The speed kings and queens of this world - lions, leopards, cheetahs, and their kin - were far stronger and swifter than humans. The consummate pack hunters, such as African wild dogs, could also easily outrun hominids. Similarly, the favored prey in this ecosystem - a variety of fleet antelope species, zebra, and water buffalo - were much too fast for humans to catch. Meanwhile, large herbivores, such as elephants and giraffes, were far stronger than individual hominids. Some species inhabited niches where they scrounged the carcasses of prey brought down by swifter and stronger hunters, but hominids did not even have the speed or strength to compete directly with these hyenas, vultures, or other highly evolved scavengers. At first glance, our ancestors seemed to possess few capacities to compete in the "arms race" that shaped this world.
In this competitive environment, however, our ancestors eventually became the dominant predatory species through a combination of physical, mental, and social traits that allowed them to become, as physiologist Bernd Heinrich dubbed them, "super-endurance predators." The physical foundation for the emergence of these predators was provided by an interrelated set of attributes that began to develop roughly six million years ago, when our ancestors diverged from other apelike species. Hominids never evolved to outrun or outmuscle either competing predators or the prey that they sought over short distances - the typical pattern in deadly encounters on the savannah. Nor did they develop the capacity to outrun or outmuscle scavengers who survived on the kills of predators. Instead, hominids developed an enormous capacity for endurance. They could run - or walk, jog, amble, march, trot, or hike - over long distances, traveling for hours and even days in pursuit of prey. They could make these treks in all sorts of weather and at any time, including the heat of midday, when the competing predator species, such as the great cats and dog packs, hid from the intense African sun. Even hyenas and vultures fled from the sun in the hottest periods of the day, thus giving hominids, who could stand the heat, an important advantage in getting to carcasses.
One key attribute in this process was the development of bipedal locomotion, a trait that distinguished human ancestors from other species that evolved into modern apes. Bipedal locomotion provided an efficient gait for covering long distances. It also freed hominid hands to carry their young offspring, their captured prey, and their tools and weapons. In addition, their upright posture raised them above ground level on the savannah and helped them to see over longer distances. As compared with quadrupeds, bipeds also exposed far less surface area on their bodies to the sun, thereby increasing their capacity to work even in the heat of midday. Furthermore, the relative lack of fur or hair on their skin allowed these bipedal hominids to sweat in order to regulate heat, which gave them an advantage over competing thick-pelted predators that needed to rest in the shade during the hottest periods of the day.
Bipedalism provided hominids with advantages not only over other predators but also over their prey. Chasing antelope and other quarry in the heat of the day allowed hominids to use the evolutionary strengths of their targets against them. Antelope, for example, relied on massive bursts of speed to escape predators. They did not generally need to run for long periods - just for a bit longer than the cheetahs, leopards, and lions that pursued them. If these chases did not end quickly, the great cats lost interest and looked for easier game. In contrast, with the capacity to engage in long chases, the hominid hunters could repeatedly evoke the flight responses of their prey, using the high midday temperatures to make their quarry run over and over again until they were exhausted and became easy victims.
In summary, bipedalism made hominids the best thermoregulators on the savannah, and the interlinked physical attributes eventually made hominids the most successful predators in that environment. These physical attributes were also linked to a series of developments that increased hominids’ intellectual and social capacities. For instance, bipedalism and upright postures widened the hips and allowed females to give birth to infants with larger cranial capacity. Bipedalism also freed the hands to carry infants, who were born at earlier stages of development than most other species and thus required more care but also had greater capacity for cranial growth after birth. Hands were also free to manipulate the environment and to carry and throw objects.
Success in the hunt provided regular sources of the protein necessary for physical and mental development. Crucially, the hominids were not solo hunters; rather, like other primates, as well as many other species, they lived in social groups and hunted together in common endeavors. Of course, team hunts required communication, a trait not unique to hominids but common to other species of social hunters, including the dog packs and baboon troops that inhabited the savannah alongside the hominids. The necessity of communication for survival led hominids to develop increasingly complex languages that privileged more complex and larger brains. In addition, the reality that hominid infants, like the newborn of later human groups, required long periods of intensive nurturing made food sharing a key social trait in hominid bands. All of these interrelated factors produced powerful forces that contributed to the growing intellectual and social development of our hominid ancestors.
Finally, and crucially, according to Heinrich - a leading scholar on human evolution and the complex interactions between our bodies, our brains, and our social worlds - our hominid ancestors developed "vision," the trait that transformed them into the super-endurance predators who eventually spread to every ecosystem and niche on the globe. By vision, Heinrich did not literally mean the mechanics of sight but rather the ability to picture things in the mind not immediately seen in the same temporal moment. This sort of vision allowed hominids to envision the end of the hunt, even if running an antelope to the ground in order to easily dispatch it might take days of persistent chasing. The capacity to set long-term goals and work to achieve them distinguished the hominids from most other species they encountered, both predators and prey.
Thus our evolutionary history as humans gave us bodies designed for consistent and regular locomotion over long distances. It made us into social beings who function as members of groups, and it made these groups essential to our survival. It provided us with powerful brains that can envision the future and hold distant goals in mind as achievable realities. In fact, some studies have shown that humans and certain other primate species possess far more brainpower than necessary to merely earn a living from their environments. Some scholars have built on these studies to speculate that our powerful minds developed in order to help us navigate the social worlds that we inhabit. In other words, more than anything else, we need big brains in order to deal with other members of our species. In this view, we need the challenges and stimulations of the hunt, or other suitable endeavors, in order to engage not only our bodies but also our minds and our social inclinations.
