Homo erectus

13-4 Homo erectus

After Homo habilis, the next human ancestors in the fossils record, Homo ergaster and Homo erectus (Figure 13-12), appeared approximately 2 Ma and survived until 500 ka years ago. Homo erectus brains became much larger (900-1100 cc) than previous Homo species and they had human-like body proportions. As with all Homo species, Homo erectus was an omnivore. In order to sustain their large bodies and large brains, anthropologists think that they must have consumed a substantial amount of protein (meat). Other sources of food may have been tubers and honey. It is controversial whether they mastered fire and cooking prior to 400 ka. Fire might have enabled them to cook food, which along with higher quality food sources might have led to increased energy consumption and the ability to sustain a larger brain. The teeth of Homo erectus are similar to human teeth (no large canines), which might be an indication that they cooked their food.

The first Acheulean tools were at Turkana in Africa where they shifted from Olduwan to Achuelean tools. The fossil record of Acheulean tools is extensive in the Middle Pleistocene (Figure 13-15), which was the period of the transition from Homo erectus to Homo heidelbergensis to Homo sapiens. Homo erectus ranged throughout Africa and Southwestern Europe and England, and through South Asia. The fossil record of Indonesia indicates that Homo erectus constructed boats (a tool) in order to migrate across the seas of Indonesia between 1 and 0.8 Ma.

The Homo erectus anatomy was like that of modern humans. They probably walked like humans. The shoulder structure indicates an ability to throw spears to kill animals. The fossil record indicates that there was little difference in the sizes of male and female Homo erectus. They were generally in the range of 5 to 6 feet tall. Genetic evidence indicates that Homo erectus lost hair and had a dark skin by 1.2 Ma. This might be one reason that they did not enter colder northern climates. A fossil infant from 1.8 Ma (Mojokerto child) with a large brain indicates that early Homo erectus children were born with greater brain maturity than modern humans. If children were born with a relatively large brain, then they probably did not require as much maternal care as Homo sapiens infants. 

As with Homo sapiens, Homo erectus ate whatever food was available. In addition to various types of plant foods, the large game animals of the Pleistocene were an essential part of the Homo erectus diet. The body size of Homo erectus indicates that they required approximately 2,000 calories per day. Fossils at their campsites indicate that much of their caloric intake came from the consumption of large game animals. Hunting of large animals might have led to larger groups since this may have been advantageous in hunting. It is difficult to determine the size of groups from the fossil record of Homo erectus, but some evidence indicates that they traveled in groups of a few dozen individuals. 

Although a larger and more intelligent brain can be advantageous, brains consume a high amount of energy and are thus expensive to maintain. The human brain requires 25% of the body’s rest energy while constituting only 2% of body mass. The high cost of maintaining a large brain is why so few species have large brains. If there is no advantage to greater intelligence, then a large brain is only an expense. For example, a mollusk that filter feeds has no need for a high caliber brain. Nonprimate animals only expend about 4% of resting energy on the brain. Primates other than humans expend about 8% of their energy on the brain.

According to those who promote the cooking hypothesis,[1] cooking enabled consumption of higher quality foods such as nuts, tubers, and animals, which had greater caloric density and might have required less time to consume. In addition, cooking also broke down foods and made them easier to digest. Those who oppose this theory argue that there is no demonstrable correlation in the fossil record between cooking and a large brain.[2]  The fossil record is not very helpful in this question. Estimates of the time that Homo erectus learned to control fire range from 1.8 Ma to 500 ka (500,000 years ago). Some estimates are based on the fact that Homo erectus had relatively small teeth, which would indicate that food was cooked. On the other hand, they had stronger jaws, which indicates they could apply more pressure when chewing. The estimates of a more recent development of fire for cooking are based on direct evidence of cooking and fires in the fossil record and on dispersal of Homo erectus into colder climates such as northern China (0.7 Ma).

Human foraging is complex and requires training in childhood. A trained forager obtains extra food in adulthood. One proposed cause of larger brains is the social brain hypothesis, which is that a larger brain enables social interaction. This aided in foraging because they could communicate information about sources and acquisition of food, train children, and cooperate in food acquisition. Those who propose the social brain hypothesis think that large brains, extended childhood, and longer lifespan probably coevolved in a complex foraging niche.  

The large human brain causes problems with birth. With upright walking, female humans have a limited birth canal diameter, and a large head causes exertion and strain. Thus, humans are born with an immature brain. At birth, the human brain is 12% of body mass, which is approximately the same as other primates. Most of human brain growth takes place after birth. Thus, unlike other placental mammals, humans are helpless at birth.  In fact, monkeys are smarter than human babies at the same age. An advantage of late brain development is that the development of intelligence during childhood enables us to process information and develop skills. Human brains have high plasticity, which means that thought processes can be implanted by parents, and everything is not just by instinct. Early childhood could be called the brain phase of human development. Half of human newborn resting energy is consumed by the brain and it reaches 66% in toddlers. Human babies are fat in order to have a reserve of calories for the brain.

Humans have approximately the same resting metabolic rate as other primates. The kidney, heart, and liver are still high energy users because their size cannot be decreased in humans. If the other organs remain the same, then the only way to compensate for the larger brain is to consume more calories or to decrease the size of the gut. Cooking and consuming meat decreased the energy needed in the gut (intestines), which freed up energy for the human brain.

There was a gradual progression (Figure 6-16) in the development of the brain size in Homo erectus. For example, one early subspecies was Homo erectus georgicus, which lived in Georgia approximately 1.8 Ma. Its small brain (600 cc) was similar to that of Homo habilis, which is why some paleontologists classified Homo habilis as an early Homo erectus. Homo erectus pekinensis (Peking Man) lived 0.7 Ma in China and had a 1,000-cc brain size (Figure 6-12). Possibly, Homo erectus controlled fire by this time since this was a cold region. Most if not all Homo erectus were replaced by more evolved Homo species by 500 ka.

Homo erectus were fully mature within 12 years of birth and skipped the teenage years; however, adolescence made its first appearance in Homo heidelbergensis. This was an important step in human evolution because the delay in maturation and the addition of adolescence allowed for an extended training period prior to adulthood. [3]

Although other Homo species appeared beginning 800,000 years ago, Homo erectus survived in Java until 108,000 years ago, and they continued to make technology advancements as time went on. The oldest confirmed shelter and campfire in the fossil record were 0.7 Ma in Czechoslovakia. There is possible evidence in the form of markings on shells of a form of art (0.5 Ma). They were also the first Homo species to collect red ochre pigments (0.4 Ma). Fire also became an important part of life with evidence of fire and daily cooking in the fossil record.

References

[1] Wrangham, Richard. "Control of fire in the Paleolithic: evaluating the cooking hypothesis." Current Anthropology 58, no. S16 (2017): S303-S313.

[2] Cornélio, Alianda M., Ruben E. de Bittencourt-Navarrete, Ricardo de Bittencourt Brum, Claudio M. Queiroz, and Marcos R. Costa. "Human brain expansion during evolution is independent of fire control and cooking." Frontiers in neuroscience 10 (2016): 167.

[3] Ania Lichtarowicz  Prehistoric man 'was never a teenager'. BBC News. Wednesday, 5 December, 2001. http://news.bbc.co.uk/2/hi/science/nature/1694591.stm

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Homo erectus pekinensis. Credit: Cicero Moraes. Used here per CC BY-SA 4.0.