Savannah Apes from Rainforest Apes

. . . e v o l u t i o n e m . . .

taking a fresh look at evolution

From Rainforest Apes to Savannah Apes

This article covers an important stage in the origins of mankind and examines many of the factors which determined our characteristic form. It outlines the early transition stage from Rainforest Ape to creatures which I have named Savannah Apes, taking their name from the habitat they adapted to initially.

I will continue the discussion of the evolution of these intermediate forms into modern humans in a subsequent article.

Most, if not all, of our evolution was of the type which involved incremental improvement, by selection, of traits advantageous to survival in a given environment. This environment was the African Savannah/scrub-land.

In the article Mechanisms of Evolution I described how a change of habitat of a species of animal can eventually bring about a profound change in that type of animal. The change from a Rainforest (semi-arboreal) to a more open Savannah is an example of a profound change of habitat.

It was the Savannah scrub-land of East Africa which provided the constraints which determined, to a great extent, our ‘format’ or characteristics as humans. But these characteristics are basically adaptations - making the best of a configuration (that of apes) which was most suited to arboreal life in the African Rainforest.

It is assumed that some seven million years ago, that a group of rainforest apes, living at the edge of the Central African Rainforest, decided to move into the adjacent more open scrub-land. There are many reasons why they should want to do this - the most obvious one associated with the stress of overpopulation.

It is difficult to speculate where this exact location could have been in Africa - but let us say it was somewhere in what is now the western border of Tanzania. The Google map of Central Africa below indicates the rainforest area in dark green and the Acacia scrub-land and savannah in lighter green.

Another reason why I choose this area is because there are several volcanoes and two large lakes - Lake Victoria and Lake Tanganyika. These water resources may have played a part in attracting the first apes out of the rainforests. I have coloured these lakes on the map in turquoise.

Once one departs from the thick canopy cover of the rainforest, the harshness of the equatorial sun is soon evident. Dehydration problems could have been mitigated by regularly drinking water from these resources.

Each new habitat makes its own set of demands on a pioneering species. The scrub-lands are dominated by various Acacia species, many of which are endowed with sharp thorns. The only climbable species are perhaps Acacia tortilis (umbrella tree) and these tend to be spaced apart. Huge baobab trees (Adamsonia) are often represented but these generally present difficulties for climbing.

Assuming these pioneering apes still took refuge and nested in trees, to get from one tree to another would necessitate a lot of time on the ground and they would have been vulnerable to attack by predators such as lions and leopards - not to mention large sabre toothed cats existing at the time. Gorillas are noted for wandering from area to area, never nesting in the same tree twice, so it is likely these pioneer apes would have moved around in a similar fashion.

I denote these pioneering apes as rainforest apes originally - as a general label for what could have been chimpanzees or gorillas. Similarly, as these pioneer apes get established in the new habitat I will name them savannah apes, a general term that covers many intermediate stages between rainforest apes and humans and avoids the pedantics of arbitrary hominid classification.

I would speculate that they were likely to have been more like gorillas than chimpanzee because gorillas are so much bigger, more aggressive and therefore more capable than chimpanzees of defending themselves from predators. Gorillas do spend less time in trees than chimpanzees and therefore must be more accustomed to challenge from ground based predators. Predators seem to assess prey vulnerability by their height. Lions tend to target the neck for attack in order to asphyxiate their prey with the grip of their powerful jaws. The taller the animal - the more difficult this may appear to them. If you look at the nearby photo of the male gorilla you will see that his height is increased by the hump on the top of his head. A large male gorilla standing upright, mouth open to display large canines and defiantly staring back - might be enough to intimidate or bluff away the fiercest of predators.

It is recognised now that we are, as humans, genetically closer to chimpanzees than gorillas and so it follows from this that the pioneering savannah ape must have been a chimpanzee rather than a gorilla. However, the process of reversion (described elsewhere) can confuse direct genome comparisons. In actual fact, the gorilla could have been the original savannah pioneer. This is because gorillas are likely to be derived from chimpanzees anyway (having evolved for mountain dwelling - where it is much cooler and where the forests are less dense). Many of the derived characteristics of gorilla genetics, however, could have been abandoned in a process of reversion - with the result that many gene sequences could return to a pattern more in common with chimpanzees. This could have occurred at a much later stage of the savannah ape’s evolution, when they were defending themselves with crude weapons - and great size and brute strength were no longer necessary attributes - a more gracile form being sufficient.

Food Resources

New pioneers to savannah/scrub-land would perhaps have the following food resources. I have selected these - bearing in mind the eating habits of gorilla and chimpanzees and their capabilities of procurement. These animals are considered to be omnivorous but their diet majors on leaves, flowers, fruit and seed. They do eat a variety of insects and occasionally kill monkeys (mainly colobus) and infrequently kill and eat their own kind.

Leaves and seed pods of Acacia species and the gums they exude from branches would probably provide the staple of pioneering apes.

Insects such as termites are widely available and as many a five million insects can be found in one termite mound. Mounds can be easily broken away by hand, stone or stick and it is possible that this nest damage was not beyond the capabilities of these apes. Constant digging into termite mounds with crude implements would increase motor skills and technical know-how in ‘tool’ choice. Improved techniques would be copied by younger generations and other groups.

Locusts are often present in vast numbers and could provide some nutrition There are many other types of insects too, including beetles, crickets and bugs of many different types.

Turn over any stone in this part of Africa and you will find a host of other creatures too - including scorpions, worms, and spiders. There are also some reptiles which are easy to catch including lizards, chameleons, tortoises - and near lakes or rivers - small crocodiles.

Bird’s eggs like those from the many large species which nest near the African Lakes would also provide the occasional treat.

Coloration and Skin Covering

If we consider the pioneering species of the savannah was a mountain gorilla - one of the biggest problems in a new environs would be associated with the thickness of their coat - ideal for cool nights on the mountain slopes - but inappropriate for the harsh sun-soaked savannah. The black coloration not only absorbs heat radiation but would make them conspicuous in the new landscape.

There would be natural selection for a sparser hair covering throughout the body - except for the head region where it would serve as protection against ultraviolet light damaging the brain. Thick hair on the head would act like a tropical pith helmet protecting both the brain and brain stem. Those individuals with thin hair on their heads would no doubt suffer the deleterious effects of sunstroke.

I believe this is how we arrived at our own head hair characteristics with regards to density and growth pattern. It is likely the hair would have been without any crinkle as I believe the African type crinkling is a modern derivation - for reasons I will discuss in another section.

There would be natural selection for cryptic coloration - that is colour which would make them blend more effectively into the savannah land back-drop. Those that were paler or more cryptic would be more successful in concealing themselves from predators. In many parts of East Africa, river beds and erosion gullies, termite mounds and ‘pathways’ are often of a red earth colour. The river beds are areas where early savannah apes would have needed to collect water and would have been most vulnerable to predator attack. Other areas of East Africa, commonly, have the grey soil type known as ‘black cotton’. So coloration could have been either reddish brown or grey in relation to the two soil types. Another possibility could have been cryptic coloration in relation to the savannah vegetation itself and this could have been the flecked gold and grey of the schemes adopted by vervet monkeys, baboons and mandrills.

The single tone grey was perhaps the most likely colour scheme to be adopted by early savannah apes as it is the one commonly used by several other creatures which frequent the same areas. These are the wart hogs, elephants, rhinoceroses and hippopotamuses. Perhaps it is no coincidence that all these animals, too, have sparse hair coverings on their bodies.

Locomotion and dedicated bipedal-ism

The original rainforest apes were already well on their way to being bipedal. Like all primates they sit upright with their heads placed at right angles to their spinal column (not in line - as in most other animals). Gorillas often walk biped-ally, supporting themselves with their long arms.

Having to move considerable distances across open ground to the safety of another tree would necessitate improvements in the ability to walk on two feet.

Savannah grass, which can be a metre high or more, would perhaps demand that the ape frequently stand up for a better look round.

An improved ability in bipedal locomotion would see the hallux (big toe) aligning with other toes. The opposing hallux configuration needed for gripping branches would be abandoned in lieu of a more compact and robust supportive arrangement.

This was only a minor modification from a skeletal point of view - as the the foot of a gorilla is identical with that of a human. It is mainly the separated toe that creates the difference in the outward appearance of the foot. From time to time humans are born with a significantly deflected big toe and the condition is known as Hallux varus.

Sweat glands and the Cooling Effect of Evaporation

We have sweat glands on the entire surface of our bodies. Perspiration serves two purposes. One is to create a cooling effect from evaporation of moisture from our body surfaces. The other purpose is to release a disinfecting brine to kill pathogens such as bacteria and viruses colonising the skin layers and surfaces.

This quite elaborate function of sweat glands are likely to be modified sebaceous glands which normally secrete oils for conditioning and often waterproofing fur or feathers.

Birds are understood to have heat exchange areas under their wings which deploy the effects of evaporative cooling. If birds are indeed on the pathway of pre-mammalian ancestry (we look at the evidence in another section) - then this may explain why we perspire so much under our arms.

Perspiration, although essential for cooling in an equatorial climate, is expensive on water and sodium chloride resources held by the body and in these high ambient temperatures considerable water intake would be essential. Their common dietary intake would provide very little moisture replacement. For this reason, these apes would need to maintain a proximity to water resources such as rivers, springs or lakes in order to secure an intake of a least two litres per day. There are vast areas of East and Southern Africa without constant water supplies where pioneering apes would find survival difficult and this may strengthen the notion that the vicinities of the great lakes were perhaps the first areas of habitation.

Losing a great percentage of the hair covering to provide a more effective surface for evaporation, however, would have its disadvantages. The ‘naked’ ape skin would become more vulnerable to damage from thorns and sharp rocks etc. To counter this, an increase in skin sensitivity will have been selected for so that these animals would automatically recoil to avoid damaging their integument where possible.

Secure Nesting

Pioneering savannah apes, like their rainforest ancestors, will have built crude nests in trees each night to rest safe from predators. These could have been the lower branches of suitable Acacia species or perhaps younger baobab trees. In many areas of East Africa there are thickets of thorn bushes and it is common to find natural ‘dens’ amongst these bushes. It is possible that these apes could have exploited these enclosed areas and once inside them - sealed the entrance area with additional thorn branches. Once a discovery like this is made, the procedure would be repeated and the concept copied by other groups. In time, the concept could have been developed, and it is easy to imagine how a purpose built kraal (thorn enclosure) could have originated. Kraals are still built by nomadic tribes in Africa and parts of India, today - although they are now much larger to include livestock.

Again, motor skills would be practiced in building more and more elaborate nest enclosures. General knowledge would also accumulate regarding optimum branch length and crude intertwining techniques etc.

Slightly more intelligent apes would build better and safer enclosures than the others and so their chances of survival were greater. In this way genes for intelligence would survive to be passed onto future generations.

Digging Sticks

Digging sticks may have been the first real tools. A hard straight stick would have been a valuable accompaniment for an early savannah ape as it could be used for:

1. Digging for termites, other insects and worms.

2. Self defence against predators or threatening rivals.

3. As a club for killing smaller animals like snakes, lizards, and small crocodiles.

4. As a crude spear for throwing at a group of say gazelle (a wide target area) drinking at a water hole. I will discuss the elaboration of weapons in a different section.

Development of the Protruding Nose

Wind blown dust particles can be a serious problem in East Africa, in contrast with the moist rainforest which, apart from some pollen, is relatively particle free.

It can be assumed that the protruding nose evolved as an increased capacity for filtering particles through nasal hairs and mucus glands.

Rainforest apes have flattened noses. It is likely that the bridge of savannah ape noses will have arched up over many thousands of generations of selection - to provide a more effective dust filter system culminating with the basic shape we humans now exhibit.

A Summary of Early stage Adaptation to Savannah scrub-land.

So the main adaptations of pioneering apes in the new habitat during the early phase (0-1 million years) could have been mainly associated with the harsh equatorial climate of the open savannah. The expedients of this ‘uncomfortable stage’ of habitat pioneering would be adaptations such as less body hair, and an effective body cooling mechanism (from the cooling effect of evaporating perspiration).

A requirement for protecting the brain and brain stem from ultraviolet radiation would manifest itself as dense head hair which grows down the sides and back of the head.

Both skin and hair colour would have been altered to a lighter shade - possibly grey or red-brown - not only to be effective cryptically, but also increase reflection and reduce absorption of heat rays.

Perhaps alignment of the hallux (big toe) could have taken place within this period.

Perhaps the nose had vaulted up by the end of this early stage - to provide additional filtration and particulate capture in a dust environment.

These animals may have already been able to use sticks as basic implements for digging or defence.

They may have also, by this stage, been capable of building crude thorn enclosures for safe resting.

Communication between early savannah apes may have been restricted to a limited repertoire of gestures and grunts - perhaps very little different from those used by rainforest apes.

True Savannah Apes

These apes became adapted to a local savannah scrub-land habitat, initially, but the success of subsequent generations would allow them to range a much wider area with a similar ecosystem - and this extends eastwards and southwards, virtually unchanged, to the edges of the Continent of Africa. The limiting factors to distribution would be associated with accessibility to water resources.

In the thousands of years which followed the pioneering stage, savannah apes would require improved memory capacity for the extra gigabytes of ‘general knowledge’ and ‘know-how’ they would accumulate while gathering food and making crude tools. Some of this brain capacity would be also needed for a gradual increase in the sophistication of communication skills - because general knowledge and skills would have to be shared with subsequent generations.

Much of the rest of the physiology of these creatures would have been adequate - such as musculature, skeletal structure, digestive system etc and consequently still exists today, almost unchanged, in us as ‘modern apes’.

Our sexual dimorphism originated with rainforest apes - more markedly with gorillas than chimpanzees. The male gorilla can stand at 1.8 metres in contrast to the 1.5 metres of the female adult. The male gorilla has a distinct brain-case architecture and much more powerful musculature. I imagine early savannah apes will have shown similar levels of sexual dimorphism. These differences were mainly associated with higher testosterone levels which in turn determined aggression and the physical ability to defend the group from predators.

The life-span of gorillas is approximately 35 years in the wild but they can live to 50 years in zoos.

Females come into sexual maturity at ten years of age while males mature at 13 years.

The gestation period for gorillas is 8.3 months and usually one offspring is born at a time, rarely two. It can be assumed that established savannah apes would have had a gestation period of the order of 8.5 months, would have only one offspring at a time (normally) and sexual maturity would occur at similar ages as the gorilla.

Gorillas have 32 teeth at maturity and this is the same in humans and so it is likely that savannah apes would have had a similar arrangement.

The Savanna Ape Look: Stage 1

The established savannah apes could have resembled gorillas in their basic stature. I have digitally modified the gorilla female skull shown here by vaulting up their brain-cases into a ‘bomb-head’ shape to allow for increased brain capacity. Doing this, inadvertently accentuates the brow-ridge. It also comes to resemble the skull of Australopithecus, discovered in East Africa. If you can mentally add flesh to these modified skulls together with a mop of hair - the characteristics of a savannah ape’s face may be imagined. The artist’s impression below, was actually constructed from a fusion of images of a gorilla and a human, digitally modified.

The eyes of savannah apes would likely be deeper set in the orbits than gorillas and appear smaller. This is because, creatures which live in a constant bright level of illumination, as a rule, have smaller eyes than those that live in shaded forests or are nocturnal. To reduce light glare entering their eyes, they probably scowled continually!

They would have wide cheek bones and small chins and probably have a hair line just above the brow-ridge.

By now, arm length would have been reduced to more human proportions as these creatures became more upright in their bipedal locomotion - no longer ‘knuckle walking’, gorilla fashion. If the extended arm bones of a gorilla are a derived condition then the process of reversion can very easily bring a return to the original shorter configuration. Shorter arms may be superior to longer arms in tasks such as tool making and weapon throwing - so this shortening may have occurred at a much later stage. However, any modification, which trims unnecessary tissue (in this case bone and muscle tissue) adds to the efficiency of a competitive animal - particularly in times of food stress.