Upon writing Part I of this article, it expanded to two parts…and now it’s expanded to three parts! So if an issue you were hoping to learn about hasn’t yet been covered, rest assured I’ll get to it.
(Or, go back to Part I.)
Let’s Get Oriented In Time: What Does “Paleolithic” Mean?
Since we’ve talking about the "paleo diet" for years, and this series explores the increased brain size and behavioral complexity that took place during the Paleolithic, I think it’s important to understand exactly what the term “Paleolithic” means. Yes, everyone knows that it happened a long time ago—but how long? And how is the Paleolithic different from the Pleistocene? What do all these terms mean, anyway?
First, Some Common Archaeology Terms And Abbreviations
BP = years Before Present. “The artifact was dated to 6200 BP.”
KYA (or ka) = thousands of years Before Present. “The bones were dated to 70 KYA.”
MYA (or ma) = millions of years Before Present. “The Permo-Triassic extinction occurred 250 MYA.”
industry = a technique that produced distinct and consistent tools throughout a span of archaeological time. Examples: the Acheulean industry, the Mousterian industry.
The word itself is a straightforward derivation from Greek. “Paleo-” means “ancient”, and “-lithic” means “of or relating to stone”, so “Paleolithic” is just a sophisticated way to say “old rocks”. Its beginning is defined by the first stone tools known to be made by hominids, dated to approximately 2.6 MYA—the Oldowan industry—and it ends between 20,000 and 5,000 BP, with technology generally agreed to be transitional towards agriculture (the “Mesolithic” industries).
The Paleolithic age is further divided:
- Lower Paleolithic: 2.6 MYA – 300 KYA. Defined by the Oldowan and Acheulean industries.
- Middle Paleolithic: 300 KYA – 30 KYA. Defined primarily by the Mousterian and Aterian industries.
- Upper Paleolithic: 50 KYA – between 20 and 5 KYA. Defined by a host of complex industries.
(Click here for more information, including links to all the above terms.)
The reason for the imprecise ending of the Upper Paleolithic (and the overlap between Paleolithic stages) is not because there is doubt about the dates of such recent artifacts…it is because the Paleolithic is a technological boundary, not a temporal boundary, and is defined by the suite of tools in use. So for the first cultures to transition towards agriculture, the Paleolithic ended approximately 20 KYA (and was succeeded by the Mesolithic), whereas other cultures used Paleolithic technology until perhaps 5000 BP.
It’s also important to keep in mind that there are continuing definitional squabbles, particularly with the Mesolithic and Neolithic. What constitutes a Mesolithic culture vs. an Epipaleolithic culture? If a culture never takes up farming, is it still Neolithic if it uses similar tools and technology?
I don’t like to spend too much time in this morass, because it’s not an interesting argument—it’s just a failure to agree on definitions. However, it is always true that Paleolithic cultures were hunter-gatherers. Furthermore, it is almost always true that Neolithic cultures were farmers. (There are a few cases where nomadic cultures adopted Neolithic technology, such as pottery.)
So when we are speaking of a “Paleolithic diet”, we are speaking of a diet nutritionally analogous to the diet we ate during the Paleolithic age—the age during which selection pressure caused our ancestors to evolve from 3’6″, 65# australopithecines with 400cc brains into tall, gracile, big-brained, anatomically modern humans with 1400cc brains. (A figure which has decreased by roughly 10% during the last 5000 years.)
No, we can’t just ‘eat like a caveman’: the animals are mostly extinct and the plants have been bred into different forms. I discuss the issue at length in this article: The Paleo Identity Crisis: What Is The Paleo Diet, Anyway?
Now Let’s Orient Ourselves In Geological Time
In contrast to archaeological ages, the Pleistocene is a geological term (an “epoch”), defined precisely in time as beginning 2.588 MYA and ending 11,700 BP. It’s preceded by the Pliocene epoch (5.332 to 2.588 MYA) and followed by the Holocene epoch (11,700 BP – present).
You’ll see a lot of sources that claim the Pleistocene began 1.6 or 1.8 MYA. This is because the definition was changed in 2009 to its present date of 2.588 MYA, so as to include all of the glaciations to which I referred in Part I.
(More specifically, geological time divisions are defined by a “type section”, which is a specific place in a specific rock formation, and which is dated as precisely as possible given available technology.)
Remember, these are all just names…changing the name doesn’t alter the events of the past.
To give some idea of the time scales involved, our last common ancestor with chimps and bonobos lived perhaps 6.5 MYA, the dinosaurs died out 65.5 MYA, and Pangaea broke up 200 MYA.
Note that the middle timeline of the illustration below zooms in on the end of the top timeline, and the bottom timeline zooms in on the end of the middle timeline. Also note that the time period we’re exploring takes up one tiny box in the lower right, so small that the word “Pleistocene” doesn’t even fit inside it!
For a slightly deeper look into the significance of each geological period, I highly recommend you click here for a graphical, interactive timeline. And here’s a long explanation of the terminology: ages, epochs, eons, and so on.
Summary: Paleolithic or Pleistocene?
The Paleolithic began approximately 2.6 MYA, with the first known stone tools, and ended between 20 KYA and 5 KYA, depending on when the local culture adopted a Mesolithic or Neolithic industry. Since it’s defined by our knowledge of hominid tool use, these dates could change in the future.
So though the two terms are measuring nearly identical spans of time, they’re defined by two completely different phenomena…and since we’re speaking of human development, it is appropriate to use the term defined by human artifacts—the Paleolithic age.
Did Sexual Selection Drive The Australopithecus -> Homo Transition?
Evolutionary psychology is great fun to read about…but the problem with extrapolating it back into the Lower and Middle Paleolithic is that it’s pure speculation. The entire fossil record of this era of hominids can be itemized on one Wikipedia page, and I think it’s extremely risky to draw behavioral conclusions so far beyond the physical evidence.
More importantly, though, it’s unnecessary to invoke sexual selection in order to explain the growth in human brain size.
“Even if the survivalist theory could take us from the world of natural history to our capacities for invention, commerce, and knowledge, it cannot account for the more ornamental and enjoyable aspects of human culture: art, music, sports, drama, comedy, and political ideals.”
-Geoffrey Miller, “The Mating Mind”
While this may very well be true, the first known archaeological evidence of art (blocks of ocher engraved with abstract designs) is dated to just 75,000 years ago, at Blombos Cave in South Africa—long after our ancestors first became anatomically modern c. 200,000 years ago. (Venus figurines are much more recent: the earliest is dated to 35 KYA.)
The term “anatomically modern humans” refers to ancestral humans whose remains fall within the range of variations exhibited by humans today. We refer to such humans as the subspecies Homo sapiens sapiens.
Note that as with all fossil classifications, “anatomically modern” is a judgment call. There was no instant transition: a beetle-browed, heavy-limbed, archaic Homo sapien did not suddenly gave birth to Salma Hayek, and there are indeed many transitional fossils with a mix of archaic and modern features, usually known as “Early Modern Humans”.
Furthermore, the behavior of the few remaining African hunter-gatherer tribes, such as the Hadza and the Ju/wasi, supports the interpretation that sexual selection simply reinforced the same selection pressures as natural selection:
Human Nature 15:364-375.
Mate Preferences Among Hadza Hunter-Gatherers
Frank W. Marlowe
“Women placed more value on men being good foragers (85% of those women said “good hunter”) than on any other trait.”
National Geographic, December 2009
“Onwas joked to me that a Hadza man cannot marry until he has killed five baboons. [...] Ngaola is quiet and introspective and a really poor hunter. He’s about 30 years old and still unmarried; bedeviled, perhaps, by the five-baboon rule.”
The Old Way: A Story Of The First People
Elizabeth Marshall Thomas
“A young man may not marry until he has killed a big game animal (preferably a large antelope, although a duiker or a steenbok will also suffice) and proved himself a hunter.”
“His [/Gunda's] victim had been only a duiker, but a duiker is plenty big enough to qualify a boy for marriage.”
“He [≠Toma] had few living relatives and no close ones, and thus could offer her no in-laws who could help her if the need arose, but he was an excellent hunter. This would appeal to any girl. So !U nagged her parents until they consented to the marriage.”
In conclusion: the evidence is that sexual selection, if it was an important force, was providing the same selection pressure as natural selection—and that the behaviors most attributed to sexual selection postdate our evolutionary transformation into anatomically modern humans. Furthermore, it seems prudent not to invoke a factor for which our evidence is entirely speculative when there are other factors sufficient to explain our ancestors’ transformation.
Therefore, while sexual selection is a fascinating subject worthy of discussion, I don’t see a need to invoke it as a separate force to explain the increase in hominid brain size and behavioral complexity from the beginning of the Paleolithic (2.6 MYA) to the time of anatomically modern humans (200-100 KYA).
Live in freedom, live in beauty.
Continue to Part III, in which we explain Optimal Foraging Theory and begin the story of our ancestors.
(Or, go back to Part I.)
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