August 16, 2015
I sat beneath the cover of low-hanging vines, sharing the shade with an adult male and his mother. Fifty some years had weighed upon the ancient woman; the top of her scalp was missing most of its hair, and she had not borne a child in over fourteen years*. The elderly chimp curled on her side, legs bent slightly and tailbone scooped forward as she lay in the fetal position. Nearby, the male’s massive body sprawled lengthwise across the ground, resting flat on the earth, one arm extended backwards and tucked behind his head, one leg crossed over the other. In the supine position the barrel shape of his ribs became smooth, spreading the thick hair of his neck and chest so that the fawn of his bare skin peeked through. Together their eyes danced about their sockets, revealing the flashes of white that surrounded their dark irises, as they traced the movements of leaves and insects that shook and stirred in the wind. When their lids became heavy they closed their eyes, succumbing to sleep in the heat of the afternoon, chests rising and falling as their lungs filled with air. From time to time, their hands would slide off of their bellies and towards one another, meeting for a second or two on the fallen brush, a mother reaching out to her son, or vice versa.
So much of what we understand about what it means to be human stems from comparative knowledge, the ability to include ourselves in one group and exclude ourselves from another. Humans are vertebrates, they are mammals. They are not brachiopods, they are not amphibians. Placing our species within the broader system of animal classification allows us to speak with some confidence about our anatomical design, method of nutrition, and relation to other life forms. It gives a way to define ourselves against alternative reference points on an interconnected web of biodiversity, to be sure that our being is of something more than, say, that of a ragworm or a leech. But what happens when we are confronted with a lack of definition? When the traits that we believe to be singularly human are found in another species, unfolding in such a way that their resemblance to our own selves becomes uncanny?
Of the countless hours I have spent in the forest alongside the chimpanzees, never do I feel less defined from our closest living relatives than when we sit together on the ground, reclining under the same umbrella of vines and brambles. For most of the day, my differences with the chimpanzees are obvious. They move across the ground and under branches in a quadrupedal knuckle-walk, while I bumble behind, a dawdling biped in a fanny pack. When they pop the pods of insects off of leaves and into their mouths, I take no interest in the food resource, and think instead of things like coffee and creamer. When they climb up to the fruit-filled canopies of behemoth trees, I stand below with sheets of data stacked against my brow and squint into the sun. My path is structured around theirs, one species recording the behavior of another, respecting a minimum distance, trying to keep up. But sometimes there is a subtle shift in our dynamic. After struggling through a dry and dusty thicket behind a nimble young male, feeling certain that my target is lost, I come upon a small forest crawl space to find a chimpanzee, or two, resting on the ground. For an instance, we are in the same small sphere, under the same trailing plants, watching the same beetles buzz overhead and feeling the same crunch of dead leaves beneath our bodies. I pause, catching my breath, and stretch my legs out against the dirt. As their heads loll from one side to another under the heft of mid-day exhaustion, our eyes meet, and for an instant my presence feels more than merely tolerated. I cannot know what they are thinking, but at the very least I can recognize that we are all tired apes, caught in the same fleeting enjoyment of a moment’s rest.
Tucked beneath the vines, watching mother and son reach for one another, relishing their minute of repose, I find my own temporary respite. My body is sprawled lengthwise across the ground, resting flat on the earth, one arm extended backwards and tucked behind my head, one leg crossed over another, when I realize that there is very little to delineate myself from the creatures to my right. As my eye lids grow heavy under the heat of the afternoon, I consider the millions of years of evolution that catapulted my species across the globe and into an unmatched realm of technology and culture. But in that thicket, as I relish a break in travel and the coolness of the shade, an animal happily tucked into warm soil and leaves, it all seems somewhat minor.
*Reproductive senescence, or a decline in female fertility during the mid-life period, is not only an evolutionary puzzle, but one that is unique to humans. In our species, menopause is inevitable, though this trait is largely absent in other non-human primates and exists only in a handful of cases .
 Alberts, S. C., et al. (2013). Reproductive aging patterns in primates reveal that humans are distinct. Proceedings of the National Academy of Sciences, 110, 13440-13445.