Who sits on the lowest branches in our family tree? This question has been nagging scientists for decades. Now, a small skull found in Kenya may solve this riddle and put a face on humanity’s oldest relative.
Another (very) tiny piece of the puzzle of human history falls into place
One late afternoon in February 2014, excavation assistant John Ekusi walked away from his colleagues at a dig site in western Kenya. From habit, Ekusi looked around, scanning the ground, and he saw an odd object. A small, yellowish ball was sticking out of the brown sand and angled pebbles at the plain. The excavation had been going on for years, and the team, headed by anthropologist Isaiah Nengo from De Anza College in California, had almost given up finding more fossils. Ekusi therefore thought that he had found an animal bone. In any case, the excavation team decided to take a closer look at the bone.
Once the scientists had brushed away the sand, a small ape skull emerged. The size and shape revealed that the ape belonged to a species that had become extinct ages ago. Analyses of the sand showed that the ape lived some 13 m years ago. At this important time in history, man took his first steps away from the other apes, but so far, researchers have only found few fossils from this period. So Ekusi’s little ball may be a very important piece of the puzzle.
FOSSIL LINE HAS GAPING HOLES
All living humans and apes derive from a common ancestor. Our branch of primates,
the man-apes, came into being some 20 m years ago, and man then branched out from the other man-apes 7 m years ago.
From fossils, scientists know about early humans’ appearance and way of life, but they know almost nothing about the time immediately before. From the geological age, the middle Miocene epoch, which stretches from 16 to 11.6 m years ago, scientists have only found one intact cranium. Other finds have been few and limited to jaws, parts of the face or a part of the frontal bone. The lack of fossils is mainly due to the fact that apes of the time lived in the rainforest where bones easily perish.
The gap in the family tree is frustrating to scientists, as this period is decisive for man’s history. At that time, several new ape species emerged, and also, men and apes also branched away from each other. Many of the new species died out due to climate change, but one of the survivors is the ancestor to all presentday apes and humans.
TEETH SIMILAR TO HUMAN’S
The newly found skull is very well preserved, and at first sight, its shape bore similarities to contemporary gibbons. Yet, the team of scientists could not immediately place their find in the family tree.
“Several primates – living and extinct – have skulls similar to the gibbons, with a small head and short snouts,” explains anthropologist Christopher Gilbert from The City University of New York, one of the scientists, who has helped analyze the rare find.
The skull did not have any other traits that could reveal the ape’s place in the family three. So the scientists examined the interior of the fossil using advanced X-ray equipment and 3D technique. The images showed that the ape still had the roots from its first teeth, while the permanent teeth had not yet erupted, but lay in a straight line in the jaw.
The appearance of the teeth showed that the ape lived of mainly fruit and belonged to a group of species called Nyanzapithecus by researchers, but as the molars were significantly larger than in the other members of the group, the infant ape has been categorized as a new species. They named it Alesi, which means ancestor in the local language.
The molars suggest that Alesi is close to humans in the evolution. The scientists came to the same conclusion when examining the ape’s inner ear. Unlike the gibbon, whose ear canals are large, Alesi’s are small and semi-circular. The canals control balance, and the large canals enable the gibbon to swing from tree to tree safely. With its narrow ear canals, Alesi would probably have been moving at a slower pace.
The find also confirms the prevailing theory that man’s segregation from the other apes took place in Africa. According to the theory, our line separated from the other apes 7 m years ago, and humans remained at the continent for 5 m years before spreading to the rest of the world. So all living humans originate from Africa.
“The discovery of Alesi shows that its lineage was close to the origin of modern-day apes and humans,” says head of the excavation Isaiah Nengo. “This knowledge is important, as it allows us to reconstruct the environment and climate, and thus explain how and why the apes developed at all.”
SCIENTISTS RECREATE THE FACE
By combining the sensitive X-ray equipment and 3D rendering, scientists have been able to examine minute details of the fossil.
The scientists have, for example, examined the enamel rings of the teeth. They show the age of the ape in the same way as growth rings tell the age of a tree. Based on this, the team of scientists found that Alesi was 481 days old at the time of death – around 16 months. How the infant ape died, the scientists do not know, but as the skull was covered by a layer of volcanic ash, the scientists imagine that the infant ape died during an eruption from a nearby volcano.
Based on the size of the skull and the teeth, the scientists also estimate that, as an adult, Alesi would have weighed some 11 kg – which is rather more than an adult gibbon. Alesi’s gender, on the other hand, cannot be established, as the ape died before the characteristics in the skull, which show the gender, were developed.
The next step for the scientists will be to examine the inside of the skull, which has imprints of the infant ape’s brain. This will show the developmental stage of Alesi’s brain and help place the ape more precisely in the family tree. The scientists will also examine bones from fingers, back and forearm, which were found in 2015 close to the place where John Ekusi discovered Alesi. The fossils are of the same age as Alesi and may belong to it. Last, but definitely not least, the team plans to make a 3D model of Alesi, so that we can finally stand face to face with one of our very first ancestors.
ISAIAH NENGO HEAD OF EXCAVATION TEAM With this new knowledge, we will be able to explain why the apes evolved into humans.
The excavation team removes sand and loose pebbles using brushes.