a plea for our sister species

Our species, Homo sapiens sapiens, emerged in East Africa in between 100,000-200,000 years ago¹.  At that time we shared the world with several different hominid species throughout Africa and Eurasia^2,3.  It did not take long for us to explore most of our home continent, and eventually the rest of the world.  In only 50,000 (~70,000-20,000 B.P.) years we managed to colonize almost every landmass except for Antarctica^3,4.  However as we explored ancient and balanced ecosystems crumbled in our wake.  Every continent our species touched soon experienced mass mega faunal extinctions^5,6.  Literally hundreds of mega fauna species were casualties of our emergence as a global species: the giant short-faced kangaroo (Procoptodon goliah) in Australia⁷, the Gorgon-eyed river horse (Hippopotamus gorgops) in Eurasia⁸, the stag-moose (Cervalces scotti) in North America⁸, and the saber-toothed cat (Smilodon) in South America⁹ are but a handful of examples⁵.  Despite this, the eco-systems eventually re-balanced and some mega fauna species survived by adapting to our presence⁵, and extinction rates dropped back to their ‘natural’ pre-human migration levels.

However, the industrial revolution marked what many geologists believe is a new epoch in earth history, the Anthropocene¹⁰.  Over the past 250 years, we have completely transformed the face of the planet, and now possess the ability to wipe out entire ecosystems in weeks, if not days.  The damage we reap on ecosystems globally is unparalleled, not just in human history, but in natural history.  The rate of extinction has risen to levels 100-1000 times the ‘background’ or natural extinction rate¹¹.  If this continues, humanity may cause the sixth, and potentially most catastrophic, mass extinction event in the history of life¹¹.

Our sister species, the chimpanzee (Pan troglodytes), like many other non-humans, are struggling to survive the Anthropocene.  When Dr. Jane Goodall began her research in Tanzania, there were thought to be more than 1 million chimpanzees on the planet.  Today, generous estimates of the total population of chimpanzees on the planet barely eclipse 200,000¹².  Within the past forty years, some populations of chimpanzee have declined by over 90%¹³.  While we continue to grow (our population should reach 7 billion within the year¹⁴) our kin species are disappearing.  Zoologically speaking the chimpanzee, the bonobo (Pan paniscus) and humans are the only remaining members of the hominin tribe.  As a result of habitat destruction, disease transmission, and hunting, our sister species may not live to see the 22^nd century.

How did this happen?  How did one member of the hominin tribe become so powerful, so pervasive, and so destructive, while the other members of the hominin tribe appear to be on the edge of demographic collapse and extinction?

THE SPLIT

Approximately 6 million years ago, somewhere in the jungles of Africa (probably Equatorial East Africa) the hominin line diverged¹⁵.  Whoever the common ancestor of chimpanzees, bonobos and humans were (there are several contenders) they were certainly forest dwellers well adapted to arboreal life in Africa.  They were also probably quadrupeds, with limited bipedal abilities, making simple tools, living in small groups and subsisting on fruits and vegetation¹⁶.  Although it will almost certainly never be known what happened to cause the split, the hominin line underwent a speciation event.  Perhaps some cataclysmic disaster separated the species, or perhaps one group of the population bravely ventured into a different environment where other populations did not bother to follow.  Whatever happened, we do know that one population gave rise to the Pan genus and one population gave rise to the Homo genus.  Over the course of the next few million years different species of the hominin tribe led very different existences.

While the populations giving rise to Pan remained in the jungles of Africa, very little is known about how the lineage changed and evolved over the past 6 million years.  The line that eventually gave rise to Homo gradually moved into the woodlands and savannahs of East Africa and began adapting to an increasingly terrestrial existence¹⁷.  They began walking upright, utilizing their hands for carrying tools, food and infants across long distances¹⁸; this also had an added benefit of increasing heat loss and reducing water requirements¹⁹.  They entered a competitive environment dominated by carnivorous mega fauna²⁰.  At this time, they were more than likely scavengers, while still subsisting primarily on fruits, vegetables and tubers²⁰.  They started to experiment with their opposable thumbs and eventually developed the most advanced tool complexes the planet had ever known²¹.  They also began to evolve the largest brain to body size ratio the planet had ever known and their group sizes increased exponentially²².  Whereas previous hominins had lived in groups of less than 50, these terrestrial savannah dwellers lived in bands of up to 250 individuals²³.  However they were still vulnerable and on many occasions perilously close to extinction.  Yet after a few million years, several hominids emerged from the early hominin savannah experiment.  They were adventurous, and eventually became a multi-continental family of organisms.  Homo habilis, H. erectus, H. ergaster, H. georgicus, H. rudolfensis, H. heidelbergensis, H. floresiensis and H. neanderthalensis among others, occupied a variety of environments from the tip of South Africa to the oceanic islands of Southeast Asia to the most northerly climes of Eurasia²⁴.  Homo sapiens sapiens evolved approximately 1.9 million years after the first members of the Homo genus¹, and the rest is history.  After anatomically modern humans emerged from East Africa, we replaced all other hominids³.  We could not share the planet.  H. floresiensis endured the longest, but was finally driven to extinction only 13,000 years ago²⁵.  All through this Homo evolution, our sister species remained safe in the forests; the Pan lineage had continued evolving in the jungles of Africa.

MEETING AGAIN

It has hard to pinpoint an exact moment in time when humans and chimpanzees ‘re-discovered’ each other.  In reality, it is probably most accurate to say that humans and chimpanzees have been ‘re-discovering’ each other for millennia.  Chimpanzees inhabit vast territories in Equatorial Africa, as far west as Senegal and as far east as Tanzania¹².  Considering that humans have been living in East Africa for as long as there have been humans, it is likely that the two sister species have known about each other for over 100,000 years.  Nevertheless, from what we do know about historical societies, our fellow hominin tribe members have always excited and intrigued us.  Individuals in early medieval African kingdoms and states kept chimpanzees as pets and the name chimpanzee is derived from Tshiluba (a Congolese language), and translates roughly as ‘mockman’²⁶.  Throughout the European colonial era the Portuguese, Spanish, Dutch, French, English and Germans all saw the same striking similarities to humans that Africans had seen in chimpanzees for millennia²⁷.  Chimpanzees were taken back to Europe, and eventually the Americas4 as curiosities.  They were kept as pets, put in zoos, exploited in freak show acts, and eventually, studied by scientists²⁷.

The historical record indicates that humans did not have to sequence the chimpanzee genome to know that we shared many similarities.  However, decades of scientific primatological research has confirmed that chimpanzees and humans share a remarkable number of morphological and genetic traits, as well as almost every behavioural trait imaginable²⁷.  They make tools²⁸, use language²⁹, understand symbols²⁹ and build shelters³⁰.  They also develop long-term bonds³¹, live in highly social groups³²; they make jokes³³, manipulate³⁴, deceive³⁵, empathize³⁵, and show care for other members of their group³⁵, and even other species³⁵.  The behavioural differences have been relegated to artificial human-constructed continuums of complexity.  Yet humans are 7 billion strong¹⁴, and chimpanzees may not survive this century.  They are our family and we are driving them into extinction.  All of the prominent environmental pressures they face – habitat loss, disease transmission and hunting – are anthropogenic in nature³⁶.  Habitat loss is largely the result of African countries attempting to develop as rapidly as possible.  Populations are growing more rapidly in Sub-Saharan Africa than in any other region of the planet³⁷ and these societies need more infrastructure and more food.  As a result, governments and multi-national corporations are fracturing and destroying chimpanzee habitat, replacing it with large highways, cities and farmland. Disease transmission is increasingly becoming a problem.  Due to our similar genetic makeup, almost all diseases that infect humans also infect chimpanzees³⁸.  Chimpanzees easily avoided humans and their diseases throughout most of human history in Africa; however, rising population sizes, habitat encroachment and potentially even primatological work over the past few decades, means avoidance is no longer a possibility for them.  They are forced into contact with us, and the diseases we carry.  Chimpanzees have also become the target of bush meat hunters³⁶.  Similar to disease, human hunting did not threaten chimpanzee existence throughout most of human history in Africa.  In the modern world, hunters now use much more efficient and effective technology – shotguns instead of machetes.  This is coupled with the rising demand for bush meat in many of Africa’s largest cities³⁶.

It is true that humans possess the ability to wipe out entire ecosystems and we even possess the ability to destroy the entire planet.  It is, however, possible to share this planet with our sister species; or they can be added to the long list of hominins who had prospered, only to succumb eventually to our rapacious appetite.  The problems faced by dwindling chimpanzee populations are not easily resolved.  We must protect our fellow tribe members, while still allowing the developing nations of Africa to improve the standard of living for their people.  This is a major 21^st century issue that must be addressed now before there are no chimpanzees left to save.  Our sister species has survived with us throughout the epochs; their ability to continue surviving is minimized by our direct actions.  The onus is on us to make sure we treat the planet, and the ecosystems that enabled our existence, with respect.  We must share this planet with our family.

As a member of the ERuDeF team, I hope this is something we can help accomplish through our research, our projects, and the people we inspire.

- Cadell Last

REFERENCES

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