Gaia on the Move: the Rise of the Savanna Monkeys

This text had already been published as an appendix to a longer post on the evolution of forests. It is republished here as a stand-alone post on the role of humans in the evolution of the world's forests (link to the image above)

Primates are arboreal creatures that evolved in the warm environment of the Eocene forests. They used tree branches as a refuge, and they could adapt to various kinds of food. Modern primates do not shy from hunting other species, maybe even ancient primates did the same. From the viewpoint of these ancient primates, the shrinking of the area occupied by tropical forests that started with the "Grande Coupure," some 30 million years ago, was a disaster. They were not equipped to live in savannas: they were slow on the ground: an easy lunch for the powerful predators of the time. Primates also never colonized the northern taiga. Most likely, it was not because they couldn't live in cold environments (some modern monkeys can do that), but because they couldn't cross the "mammoth steppe" that separated the Tropical forests from the Northern forests. If some of them tried, the local carnivores made sure that they didn't succeed. So, "boreal monkeys" do not exist (actually, there is one, shown in the picture, but it is not exactly a monkey!).  

Eventually, monkeys were forced to move into the savanna. During the Pleistocene, about 4 million years ago, the Australopithecines appeared in Africa, (image source). We may call them the first "savanna monkeys." In parallel, perhaps a little later, another kind of savanna monkey, the baboon, also evolved in Africa. In the beginning, australopithecines and baboons were probably practicing similar living techniques, but in time they developed into very different species. The baboons still exist today as a rugged and adaptable species that, however, never developed the special characteristics of australopithecines that turned them into humans. The first creatures that we classify as belonging to the genus Homo, the homo habilis, appeared some 2.8 million years ago. They were also savanna dwellers. 

This branch of savanna monkeys won the game of survival by means of a series of evolutionary innovations. They increased their body size for better defense, they developed an erect stance to have a longer field of view, they super-charged their metabolism by getting rid of their body hair and using profuse sweating for cooling, they developed complex languages to create social groups for defense against predators, and they learned how to make stone tools adaptable to different situations. Finally, they developed a tool that no animal on Earth had mastered before: fire. Over a few hundred thousand years, they spread all over the world from their initial base in a small area of Central Africa. The savanna monkeys, now called "Homo sapiens," were a stunning evolutionary success. The consequences on the ecosystem were enormous.

First, the savanna monkeys exterminated most of the megafauna. The only large mammals that survived the onslaught were those living in Africa, perhaps because they evolved together with the australopithecines and developed specific defense techniques. For instance, the large ears of the African elephant are a cooling system destined to make elephants able to cope with the incredible stamina of human hunters. But in Eurasia, North America, and Australia, the arrival of the newcomers was so fast and so unexpected that most of the large animals were wiped out. 

By eliminating the megaherbivores, the monkeys had, theoretically, given a hand to the competitors of grass, forests, which now had an easier time encroaching on grassland without seeing their saplings trampled. But the savanna monkeys had also taken the role of megaherbivores. They used fires with great efficiency to clear forests to make space for the game they hunted. Later, as they developed metallurgy, the monkeys were able to cut down entire forests to make space for the cultivation of the grass species that they had domesticated meanwhile: wheat, rice, maize, oath, and many others. 

But the savanna monkeys were not necessarily enemies of the forests. In parallel to agriculture, they also managed entire forests as food sources. The story of the chestnut forests of North America is nearly forgotten today but, about one century ago, the forests of the region were largely formed of chestnut trees planted by Native Americans as a source of food (image source). By the start of the 20th century, the chestnut forest was devastated by the "chestnut blight," a fungal disease that came from China. It is said that some 3-4 billion chestnut trees were destroyed and, now, the chestnut forest doesn't exist anymore. The American chestnut forest is not the only example of a forest managed, or even created, by humans. Even the Amazon rainforest, sometimes considered an example of a "natural" forest, shows evidence of having been managed by the Amazonian Natives in the past as a source of food and other products. 

The action of the savanna monkeys was always massive and, in most cases, it ended in disaster. Even the oceans were not safe from the monkeys: they nearly managed to exterminate the baleen whales, turning large areas of the oceans into deserts. On land, entire forests were razed to the ground. Desertification ensued, brought upon by "megadroughts" when the rain cycle was no more controlled by the forests. Even when the monkeys spared a forest, they often turned it into a monoculture, subjected to be destroyed by pests, as the case of the American chestnuts shows. Yet, in a certain sense, the monkeys were making a favor to forests. Despite the huge losses to saws and hatchets, they never succeeded in completely exterminating a tree species, although some are critically endangered nowadays. 

The most important action of the monkeys was their habit of burning sedimented carbon species that had been removed from the ecosphere long before. The monkeys call these carbon species "fossil fuels" and they have been going on an incredible burning bonanza using the energy stored in this ancient carbon without the need of going through the need of the slow and laborious photosynthesis process. In so doing, they raised the concentration of CO2 in the atmosphere to levels that had not been seen for tens of millions of years before. That was welcome food for the trees, which are now rebounding from their former distressful situation during the Pleistocene, reconquering some of the lands they had lost to grass. In the North of Eurasia, the Taiga is expanding and gradually eliminating the old mammoth steppe. Areas that today are deserts are likely to become green. We are already seeing the trend in the Sahara desert. 

What the savanna monkeys could do was probably a surprise for Gaia herself, who must be now scratching her head and wondering what has happened to her beloved Earth. And what's going to happen, now?  There are several possibilities, including a cataclysmic extinction of most vertebrates, or perhaps all of them. Or, perhaps, a new burst of evolution could replace them with completely new life forms. What we can say is that evolution is turbo-charged in this phase of the existence of planet Earth. Changes will be many and very rapid. Not necessarily pleasant for the existing species but, as always, Gaia knows best. 

Feathered Dinosaurs -- The Many Faces of Gaia

 

A feathered T-Rex? Why not? (Image from Safari Ltd.)

A recent paper by Olsen et al. appeared on "Science Advances". It discussed the fauna and the climate of the Earth of Late Triassic, just before and during one more of the great mass extinctions of its long history.

The authors claim that "The Late Triassic and earliest Jurassic are characterized as one of the very few times in Earth history in which there is no evidence of polar glacial ice sheets," which I am not so sure about. Anyway, this Late Triassic Iceless age is interesting for us because it is where we may end as the result of the current burst of fossil carbon combustion, deforestation, and marine desertification. It is another example of ice-free earth, probably similar to the Eocene epoch, some 30-50 million years ago.

It seems that the Late Triassic was not so hot, despite the high CO2 concentrations (maybe 1000-6000 ppm). In the high latitude regions, the temperature was cold enough that ice would form in winter, likely not perennial. Dinosaurs lived in the Northern and Southern areas of the Pangea, and they already had "filamentous integumentary cover" -- beautiful term! -- that is protofeathers, clearly used for thermal insulation. In the equatorial regions, instead, the heat made life easier for cold-blooded animals, the pseudosuchia -- which indicates crocodile-like creatures. Apparently, it was too hot for dinosaurs there.

Does this have some relevance to the current climate? Everything is correlated, although it must be said that the conditions of the earth some 200 million years ago were quite different. The fact that there was ice at the poles, despite a very high CO2 concentration, is no proof that CO2 is not the greenhouse gas we know it is. Among many other things, the solar insulation at that time probably around 2% lower than it is today.

Today, if we were to go back to those CO2 concentrations, crocodiles may still have a good time, but they will probably invade a much larger share of latitude. On this point, this is a paleontological study, so they don't mention modeling the climate of those times. They tend to attribute the low temperature to volcanic ashes. They seem to say that the mass extinction was caused by cooling, unlike the later K-Pg event. That despite the fact that the CO2 concentration was so high. Their main conclusion is that dinosaurs were adapted to cold temperatures, and they were mostly feathered. Which means that the creatures seen in "Jurassic Park" are all wrong!

They also report this interesting graph with the CO2 concentrations over 300 million years. It is stuffed with acronyms, apparently well known by paleontologists, but not so much by us, mortals. Anyway, "EPE" stands for "End Permian Extinction" (the huge one)   "ETE" stands for "End Triassic Extinction" (less well-known, but it was not a joke). "T-OAE" stands for "Torcian Oceanic Anoxic Event" (quite an event, it must have been). The "K-Pg-E" is an acronym of acronyms, but you know what it stands for: it is the end of the dinosaur age -- the big asteroid falling on Earth (maybe) or/and the Deccan giant igneous province (more likely). Finally, the PETM is the "Paleocene-Eocene Thermal Maximum", quite a maximum in temperatures, but it didn't do as much damage as one would have expected.