6.2: Trends

Some paleoanthropologist see the icon of humanity as footprints, some left by an australopithecine some 3,500,000 years ago, which led to footprints on the moon.

Figure \(\PageIndex{1}\) - Laetoli footprints by Momotarou2012 (CC BY-SA 3.0) .

Figure \(\PageIndex{2}\) - lunar footprint NASA (public domain)

Feet are important, but another way to look at humanness, is the hand.

Figure \(\PageIndex{3}\) - Hands in Pettakere Cave by Cahyo Ramadhani (CC BY-SA)

What makes us different from any other lifeform is this ability to leave our handprint. Of course the two go together, because to make art with your hands, you first need to walk upright on two feet.

It's convenient for us to summarize the evolution of our species into a few broad trends that fit on the back of flash-cards: two feet, smaller teeth, big brains, culture, tools, language, large body size, wide geographic range... This is how evolution made us different from our closest living relatives bonobos, chimpanzees, and gorillas. But at the same time it's important to remember that evolution is not directional. Life doesn't progress towards an ultimate goal. There is no human essence that our species strives to become. This is more of that philosophical baggage we have left over from Aristotle.

Scientists do use a creation metaphor, the concept of mosaic evolution to describe how evolution creates a picture out of many different pieces.

"Mosaic evolution" is a metaphor for how the picture of a living species can be seen as the evolution of many characteristics, or pieces of colored stones that work together to form a pattern, even though each of those pieces may have evolved at a different rate, and in our case, we can see a picture of modern human beings as a composite of many trends in hominid evolution, which are listed as column headings, roughly chronological from left to right. With locomotion we are concerned with the development of bipedalism. A fancy way to talk about an increase in brain size in the evolution of a clade (branch) is encephalization. The reduction of dentition is another trend. Toolmaking behavior is the only direct evidence we have for culture in early hominids. A good example of biocultural evolution are the trends in dentition and tool use: as we developed better tools we no longer relied on our teeth to process food.

Bipedalism

We are the only primate to walk on two feet. All primates can walk bipedally if carrying something or injured, but it's not their normal mode. This is a trend that goes back to primate evolution and our arboreal adaptation. Natural selection selected for being comfortable while vertical, both for vertical clinging and leapers with their torsos aligned with the vertical trunks of trees, and brachiators, where gravity pulls us into a vertical position as we swing from tree to tree.

There are several hypotheses for why evolution selected for bipedalism in basal hominids. Using two feet instead of four is more efficient for traveling long distances. Walking on two feet freed our hands for tools and communication. Walking tall meant we could see over the tall grass of the savanna to notice food and predators, and it could have help intimidate rivals or predators, and some claim that it would have helped us wade through shallow water. Getting up off the ground could have kept us cooler in hot savanna heat, but moving our head farther away from the hot ground, and decreasing the amount of sun our bodies got when it was at its strongest. Anthropology's acceptance of multi-causal arguments means we don't have chose one, and we can evaluate the likelihood of each in different situations.

* Locomotor Energetics in Primates: Gait Mechanics and Their Relationship to the Energetics of Vertical and Horizontal Locomotion

* Human versus horse races

Kung San persistence hunting

Encephalization

cepha is Greek for head, encephalization is the head getting bigger, but we're really more concerned with the brain. Paleoanthropologists used to take skulls and fossil skull casts and pour rice into the foramen magnum until it was full, and then pour it out and you got the individual's cranial capacity. Now we use 3-D scanners instead of rice, but it's the same principle: how much brain did the individual have. It's usually measured in volume, like cubic centimeters, abbreviated as cc'. Both the absolute and the relative brain volume tends to grow as time goes on with hominid evolution, with a few exceptions. Neandertals actually had on average bigger brains than anatomically modern Homo sapiens.

Figure \(\PageIndex{4}\) - the ratio of brain to body size by Peter Aldhous, Wikimedia Commons (CC BY 4.0)

Note

Marino 2000. Article on the SRGAP2 gene associated with brain development

Culture/tools

The classic theory is that bipedalism freed the hands from locomotion and allowed them to specialize in tool use, and this was supported by the correlation between complexity in stone tools and encephalization in hominids such as Homo habilis. Recent discoveries are pushing the dates of the first stone tools back before significant encephalization had occurred, but this is consistent with our observations of living primates. If we can see primates today make tools with a 400cc brain, we can imagine our ancestors doing the same with 450cc brain.

Note

* Radio interview on the origin of the precision grip:

Exercise \(\PageIndex{1}\)

COMPARE THE TOOL SECTIONS OF THESE PAGES: OLDOWAN TO THE ACHEULIAN TO THE MOUSTERIAN TO THE UPPER PALEOLITHIC

* Article that maps brain patterns to the hands and feet of primates suggests the dexterity required for tool used evolved before bipedalism

Figure \(\PageIndex{5}\) - flake attributes by José-Manuel Benito Álvarez from Wikimedia Commons (CC BY-SA 2.5)

Language

The evolution of the human capacity for language is tied to the development of encephalization and culture. You need a brain to process language, and language enables complex cultural transmission. Unfortunately, the evidence for the evolution of human language is scanty. The study of the evolution of human language was even banned by the French linguistic society in the 1800s.

• Approaches towards the origin of language
• Article and video on an orangutan's capacity for producing human sounds

Dentition

The evolution of hominid teeth is basically reduction, with a few counter examples. Teeth are the hardest bone in the body, and so they tend to fossilize more than other bones.

Exercise \(\PageIndex{2}\)

SKIM THE EVOLUTION OF HOMINID DENTAL MORPHOLOGY

Figure \(\PageIndex{6}\) - "Puny Humans" by Abstruse Goose (CC BY-NC 3.0 US)