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Big Brains Require An Explanation, Part II: Sexual Selection, and What Does “Paleolithic” Mean, Anyway?

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.

Oldowan choppers

They don't look like much—but they were much better than fingernails or teeth at scraping meat off of bones.

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!

Geological timeline of the Earth, from The Economist

Click the image for a larger and more legible version, and an interesting article from The Economist.

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.

The Pleistocene began exactly 2.588 MYA and ended 11,700 BP. These dates are defined by our best estimates of the age of two specific pieces of rock (or ice) somewhere on the Earth.

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 first known art: carved red ocher

Click the image for more information about Blombos Cave.

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
“The Hadza”
Michael Finkel

“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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Permalink: Big Brains Require An Explanation, Part II: Sexual Selection, and What Does “Paleolithic” Mean, Anyway?
  • Asclepius

    In the course of evolution a good ‘invention’ is quickly spread and can arise independently several times. I’ve read that the pre-Cambrian explosion may well have been driven by the ‘development’ of the eye, prior to which the main senses were smell, vibration, and touch.

    An eye allows you to plan well ahead – you get much more information from an image than via other senses (eg. not only the size of a predator/prey but also vector information – is it coming towards me? Is it a threat? And we are all aware how much of communication is non-verbal).

    I’m suspecting that your theory for an increase in brain size is moving towards the notion of ‘fugitive calories’ and an environment dominated by physically superior predators that we learned to outwit.

    An ‘eye’ might let you see ahead over the next rendezvous with a predator/prey, but a brain lets you plan ahead over days, weeks and years. With ingenuity you can outwit the biggest, strongest and fastest animals and you can also get around chemical defense (fermenting and cooking are examples of this).

    I’m still sold on the importance of sexual selection, but am looking forwards to the next installment to be convinced otherwise!

    It is interesting to note that the human brain still has a reptillian brain at it core. Through the sieve of evolution we just added on to it.

  • anand srivastava

    What about the gatherer? Aren’t they supposed to collect tubers and fruits wherever available. Those IMO would be in most places in Africa even during cold times. What about Turkana basin which is supposed to have been warm for at least the last 4 million years, and is supposed to be the cradle of humanity, and gave us our lack of fur and high sweat glands?

    According to Wrangham, cooking must have divided us into hunters and gatherers. Also the fact is that hunting is hard, and is not successful all the time. There would need to be an alternate food for the times it fails. Humans couldn’t be just starving like carnivores, when our body can digest carbs, and there is plentiful carbs around as tubers.

    The other issue is that during low vegetation periods, animals become very lean, and not really useful for eating, unless supported by tubers. Its not like every tribe was able to do things done by the native americans.

    Could it be that we are seeing only one side of the story?

  • Andrea Reina

    I don’t think J means to discount tubers and other starchy plant foods as fuel sources during the paleolithic, just that in the context of mate selection there’s a much bigger difference between a good hunter and a bad hunter, and a good gatherer and a bad gatherer. If I knew what to look for I would do a decent job of collecting tubers, fruits, edible leaves, etc. Give me a spear and point me at a herd of, well, anything, and I’d probably be lucky to escape without a self-inflicted wound. And J does include tubers and other non-seed glucose sources in “Eat Like A Predator”.

  • Beth

    Off the wall question: If a person were to meet J IRL & then describe this person to others, would the pronoun be “he” or “she”? That is, is JS of the male or female persuasion?

    It’s not important, but I am curious. I hear the words coming from JS in a female voice, but I see that others refer to J as “he”.


  • Grace (Dr.BG)

    Very nice!!!!! I’m glad you conceded to include sexual selection’s mark on the evolution of the brain. I concur with Asclepius’ comments (and past ones)!

    So… My question. *haaaa aahh* If we outwit, outplay and outseduce our predators and partners, then are our big brains the bigger gonads?!???

  • Grace (Dr.BG)

    I like the reasoning here btw…

    Out hunt/Out forage = Out feed = Out breed

    AAAaaahhhhh ha (unfortunately this applies also to modern refined high energy food sources and the legion of bottom feeders created who fail to fully utilize their big phat brains)

  • Asclepius:

    General-purpose intelligence has arisen many times in the animal kingdom.  Even sufficient abstraction and dexterity to make and use tools has been demonstrated by birds as well as primates.  The question we must always ask is “to what survival advantage?”

    And yes, the human brain is absolutely a big layer cake, with the forebrain being a thin layer of rationality grafted onto hundreds of millions of years of 'instinct'.


    Exactly.  Whether we ate a food isn't the same as claiming that it exerted significant selection pressure.  For example, humans eat fruit, but so do bats, monkeys, and almost everything that can get to them…it's difficult to argue that frugivory requires big brains.


    Gathering is absolutely an important source of calories…but see my reply to Andrea above.  Like I said, I'll get to Wrangham soon.  (Next week, unless another intermediate topic expands greatly.)


    I try to keep the focus on the science, not on myself…thus the lack of self-portraits or biography.

    Dr. BG:

    As I said in the article, I find sexual selection both important and fascinating!  In this particular case, the evidence is that sexual selection was providing the same pressures as natural selection — so we don't need to invoke it separately in order to explain the existence of big brains.  However, I believe it's probably the most parsimonious explanation for some of the things we've done with those big brains since we got them!

    Big brains are gonads for memes.  That's a meme, btw.

    And your final point is excellent.  Natural selection doesn't care if you're healthy or happy: it's a statement of fact about which genes are surviving and propagating to subsequent generations.


    Thanks again for the perceptive comments, everyone!  I appreciate your patience with these stage-setting articles…we'll be enjoying some conclusions soon.


  • vizeet

    I think it is important that blog mentions the difference between human and our primates in terms of evolution of brain.
    This will help me better understand evolution.
    I assume since homoerectus were doing more scavanging and hunting then its primates he required certain physical features:
    1. Running away fast
    2. Seeing predators from distance
    3. Need to have better co-ordination
    Just like spotted hyena.
    High fat from bone marrow and brain helped simplify gut so he could stand straight. Also humans are taller then our primates which might also have helped in seeing predators early.
    Also Homo Erectus also moved out of Africa just like human ancestors. There should be a strong reason why this happened.

  • vizeet:

    The consensus narrative has undergone several revisions as we discover more fossil hominids from the Pliocene.  I'll make sure to summarize it next week.

    Interestingly, spotted hyenas are most likely descended from scavenger ancestors, but developed into strong hunters as they speciated (while keeping their bone-crushing abilities and ability to eat rotten meat).  Brown and striped hyenas are still nearly 100% scavengers.

    You raise a great point, which I plan on discussing: the Homo Erectus migration out of Africa demands an explanation.  What adaptations allowed Homo erectus to travel and survive outside of Africa?  And why were they supplanted by the later migration of Homo sapiens?


  • Scotlyn

    Since it’s been mentioned several times, here are a couple of things I remember from “Catching Fire” by R. Wrangham, which I found absolutely fascinating.
    1) the differences between chimp hunting and human hunting.
    a. chimps spend, at most, around 20 minutes on any individual hunt, this being the longest they can manage to free up enough time and energy from the endless round of chewing their food (5-7 hours per day) that is necessary for them. If they don’t catch their prey within this timeframe they give up. Humans go on lengthy hunts, sometimes lasting many hours to days, and on their return need to have a meal ready for them that can be quickly consumed (cooked food meets this need), often in the dark (the fire that cooked the food, also provides enough light to see what you’re eating).
    b. chimp males hunt, chimp females not so much. The males seldom share, although sometimes they may reward a persistent female or juvenile “beggar,” meaning females and juveniles eat much less meat than males. In humans, the meat hunted is shared, sometimes with extreme attention to providing equal shares, with everyone within the band, family or locality. There is little discernible difference between female and male or adult and juvenile meat consumption.

    2) This food sharing between the different sexes, and all ages, is the singular human “fact” that Wrangham stresses as making humans different, and argues that it is difficult to conceive of in a context with no cooking, as raw food is time-consuming to eat, and frees up little time for other activities, especially human style extended hunting activities. Hunting AND gathering, as a way of life, implies some specialisation in the methods of obtaining foods, as well as a common base to which all foods are brought for sharing so that everyone benefits from the same diet combining the different specialised activities. Human hunters, in Wrangham’s view, may or may not require gatherers (eg Inuit and other almost exclusively meat-eating cultures), but definitely do require cooks. Likewise cooks, require protection for their kitchen stores and fires from food thieves. Wrangham gets to the beginning of a very interesting line of thought about human gender relations with this argument.

    There is more, but this is a taste of a book that leaves the reader with a great deal to think about for long after.

  • Scotlyn:

    I’ll get to Wrangham next week, but in the meantime: be very careful to read him critically.  His writing is a mix of real science, entertaining speculation, selective citation, and interpretations completely at odds with the rest of the scientific community (and, often, the evidence) stated as incontrovertible fact.

    In other words, he tells a great story…but it’s not necessarily true.

    “chimps spend, at most, around 20 minutes on any individual hunt”

    This is because monkeys are small and the energy cost of chasing monkeys up trees is very high — and it is therefore energetically counterproductive to spend too much time chasing them.  (See the extensive calculations in Boesch 1994.)  In contrast, human hunters prey on much larger animals, for which a much longer chase is still energetically profitable, and we do so in a much less energy-intensive way (walking or running on open ground).

    I find it bizarre that Wrangham would bypass this basic fact (in a paper by a fellow chimpanzee researcher with whom he cannot fail to be familiar) in favor of the needlessly complicated hypothesis he proposes.

    “Human hunters, in Wrangham’s view, may or may not require gatherers (eg Inuit and other almost exclusively meat-eating cultures), but definitely do require cooks.”

    Another false statement.  Humans have no trouble digesting raw meat.  (You can ask Lex Rooker or Peggy the Primal Parent about that…both have lived for extended periods entirely on raw meat.)  It’s certainly quicker to chew cooked meat…but when we’re talking about something with the energy density of meat and fat, it’s not a limiting factor.

    What this is telling me is that I need to write an entire article just on that book!  It won’t be part of this series, though, because many of these points aren’t directly germane to the topic at hand.


  • aaron blaisdell

    Let’s not forget that gathering included not only plants but many animals, too, both invertebrate (snails, grubs, shell fish) and vertabrate (lizards, turtles, etc.) alike.

  • Aaron:

    Absolutely true!  Furthermore, much of the animal protein that was gathered is in forms we don't eat in the Western world (e.g. insects, grubs).

    If I recall correctly, this dietary shift has been a source of confusion in the past when arguing about hunter-gather dietary composition.  From the modern viewpoint, calories from “gathering activities” would have to be exclusively carbohydrate from plants…but that's clearly not the case.

    I'm doing my best to stick to the narrative…but the implications of all these facts could easily support an entire book.  At least I'm in no danger of running out of topics to write about!


  • Asclepius

    “This is because monkeys are small and the energy cost of chasing monkeys up trees is very high — and it is therefore energetically counterproductive to spend too much time chasing them. (See the extensive calculations in Boesch 1994.) In contrast, human hunters prey on much larger animals, for which a much longer chase is still energetically profitable, and we do so in a much less energy-intensive way (walking or running on open ground).”

    A great point. Furthermore humans are ingenious enough to set traps. One of man’s most sedate activities is a form of hunting; fishing! I recall seening Africans hunting monkeys simply by putting treats in holes deep in rocks. The monkeys – ever curious – reach in to grab the treat, but their fist traps them. They will not release the treat to get their hand out even though the hunter walks towards them to kill them. There are sites in the UK where we see evidence of mammoth being scared by hunters to run over cliffs (we assume fire was used to do this). The base of the cliffs show much evidence of butchery. Also we have long range weapons.

  • eddie watts

    something that interests me a great deal is whether humans are the only animal which has ever changed it’s dietary source, this assuming we did come from small ape-like creatures which largely ate plants.

    looking forward to the rest of the series!

  • Aaron Blaisdell

    @Eddie Watts. Well, think about it this way. If every extant (currently living) species on earth is the descendant of a long lineage of ancestors traced all the way back to the first prokaryote (simple, single-celled organism) circa 3.5 bya (J hasn't defined this acronym, but it means “billion years ago”), then EVERY extinct and extant species that ever lived on the planet has changed its dietary source. This must be the case if you accept that all life on Earth is monophyletic in its origins.

    @J, yes, the hraf (human relations area file, which is a database of ethnographies with searchable keywords–a fascinating place in which to lose yourself!) generally classifies the collection of bugs, worms, snails, etc. as gathering, not hunting. Thus, estimates of the ratio of plant (obviously gathered) to animal (hunted AND gathered) sources of contemporary or recent hunter gatherer diets is biased towards the plant side if gathering is interpreted to only mean plant materials. This is the problem with using terms like “hunting” and “gathering” as proxies for animal and plant consumption, respectively.

    JS, next time your in LA, I'll take you to the Santa Monica airport at which there is a nice restaurant called Typhoon. They have an invertebrate section on their menu that includes scorpions (quite crunchy!, served on toast, but you can ditch the toast), fried crickets, Vietnamese waterbugs, etc.

    Btw, when I first met JS at AHS11, my first thought was “he sure looks like a gnoll!”. By the way, male and female hyenas can be difficult to tell apart due to the androphication (is that a word?) of the females, including some of their, ahem, crotch anatomy.

  • Asclepius

    @Aaron Blaisdell – “when I first met JS at AHS11, my first thought was “he sure looks like a gnoll!”.” That made me smile.

    – ——
    One thing that stikes me about modern HG commentary is that it often fails to note that many of the HGs that have been studied are surviving in arguably marginal conditions – either pushed out by agriculture and colonialism to remote land (which is impoverished as the most fertile land was taken for farming), and, is existing in a post-megafauna age.

    The geographic distribution of HG would have varied massively over the past 2my. Where HG have thrived/prefer to exist and where they are now found are not necessarily the same thing. Also, we might see HG hunting birds in the Savannah – but if they could hunt something much bigger and juicier, I am sure they would do! We should not confuse 'optimal/preferred behaviour' with 'survival bahviour'.

  • Vizeet

    I think that Homo-Erectus lived in small groups and there were frequent clashes between these groups. I read somewhere that cannibalism was wide-spread in early paleolithic and it did existed until recently (though insignificant). In such condition surviving will need following traits:
    1. Intelligence (Strength is less important because others are almost as strong)
    2. Communication (Which might have caused development of verbal ability)
    3. Learning
    4. Co-ordination
    So humans ancestors were competing with each other for survival.

  • Asclepius:

    The article, and the paper it's based on, seem to spend a lot of time dancing around and failing to understand one very simple concept: Prey animals can only adapt in evolutionary time, whereas humans can adapt in cultural time. 

    Unfortunately, succinct summations don't get you published.  If you're lucky, they get you quoted (and already being famous helps).

    Moving on: trapping is an excellent example of using toolmaking and brainpower to catch prey in an energetically efficient way.  I don't know when the first archaeological evidence of trapping occurs, but I know fishing dates to at least 40 KYA — and 140 KYA is likely, given the indirect but relatively persuasive evidence at Blombos Cave.


    Aaron has ably answered the general case, but there are plenty of specific examples.  For example, the aardwolf has become completely insectivorous — it eats only termites, unlike its carnivorous hyaenid relatives — and the panda bear, though a true bear of the order Carnivora, subsists entirely on bamboo.  (Though pandas will eat meat and eggs if given to them.)


    Hot buttered scorpions…sounds delicious!  I'll take you up on that offer someday, though I won't be as suave about it as this man.

    I'd love to have access to the HRAF…maybe someday I'll sign up for the free trial.

    Is there still any debate about the monophyletic origin of eukaryotes?  I thought that was a long-settled question…


    I've seen articles which purport to debunk that assertion, but they're based on metrics like rainfall and biomass…so rainforests end up balancing out the desert.  The problem is that the rainforest is a relatively poor environment for biomass edible to humans

    There's a reason the American Indians regularly burned off the forest understory and kept the trees thinned…savanna and grassland support lots of tasty grazing animals.  They might have less absolute productivity, but the amount edible to humans is much greater.


    “Widespread” is probably an exaggeration, but there is evidence for it in several Paleolithic sites, the earliest dating to 780 KYA.  However, the evidence is not unequivocal until much more recently (AFAIK).

    Intra-species competition is a feature of every animal, especially territorial animals (which includes most animals that aren't strict herbivores, for which foliage/grass is nearly everywhere).  The rarer the food source, the more likely intraspecific competition is to exert selection pressure.  Though the direct evidence is thin and speculative, I plan on discussing this.  Thanks for bringing it up!


  • “…savanna and grassland support lots of tasty grazing animals….”


    Not sure if you’ve read Simon Fairlie’s “Meat, A Benign Extravagance” but he makes this point (drawing on the work of Frans Vera) – arguing against the static model of climax vegetation (forest).  One example he gives is when a tree falls in a forest the clearing allows light in that favour grasses and bushes – which encourage herbivores to come in to the clearing and graze.  This grazing and trampling or roots expands the clearing and so you get this ripple-on-a-pond effect where the clearing expands outwards.  Eventually trees recolonise the centre of the clearing, and they themselves expand their territory outwards.


    Forgive me (yet another) shameless link back to my blog where you can find further detail.  It seems that savanna and grassland are intrinsic to supporting megafauna whereas the ‘modern green agenda’ seems to favour a ‘forests as optimal’ policy.  What is 'optimal' is a pulsate, ever-adapting, cyclical model.  There is NO climax to steady state.


    One other thing that ties this back to your point above, I've read a few books where it is suggested that agriculture is recognisable in some form, long before 10kya.  Slash and burn is one example of how such an agriculture may well manifest.  Rather than being settled agriculture, it has been suggested that humans practiced a kind of stewardship approach to the landscape and the animals upon it. 


    Not sure if you’ve read Fairlie’s book but I’d highly recommend it and would be interested in your thoughts.

  • Asclepius:

    You're always welcome to link to relevant posts on your own site.

    No, I haven't read Fairlie — he's “on the list” of books I haven't yet had the time to read — but that's an excellent point.  In our (justified) zeal to save land from development, we mistake a land depleted of native grazers and covered with climax forest for the “natural” state of the land.

    Also, it's true that agriculture wasn't invented overnight.  We have evidence that people were regularly gathering and processing wild grains as early as 19 KYA, at Ohalo II…but it took another 8,000 years before anyone thought to deliberately plow and plant.  And the bone deformities associated with manually grinding sufficient quantities of grain to constitute the majority of the diet only appear after the transition to agriculture (see: Abu Hureyra).


  • Jeffrey of Troy

    re: rain forest

    The Amazon rain forest may not be entirely natural.

    Black Gold Of The Amazon

  • Jeffrey:

    Yes.  That topic is covered at length in 1491, a fascinating book about pre-Columbian civilizations.  Apparently the natives found a way to sustainably farm in the middle of the Amazonian rain forest — one which has since been lost in a reversion to slash-and-burn techniques.


  • eddie watts

    well obviously all animals have, but i meant concrete examples in more recent times that we have had a chance to study in any form.

    so the answer seems to be not many, and both examples given by J Stanton have moved from a more free dietary choice to a (more) specialised diet.
    seems that humans moved to a more freedom of choice diet.

    Jeffrey of Troy: that article is a very interesting read thanks!

  • Asclepius

    JS – Not sure if is available to you in the US but if so, it’s worth watching,

    “In this series Professor Iain Stewart tells a stunning story about our planet. He reveals how the greatest changes to the earth have been driven, above all, by plants.

    In the third episode, Iain discovers the remarkable impact of just one plant: grass. On the savannah of South Africa he sees how grass unleashed a firestorm to fight its greatest enemy, the forests. He shows how cutting your finger on a blade of grass shows us how it transformed life in the oceans. In Senegal, he meets the cleverest chimps in the world. And, in the ruins of the oldest temple on Earth, he tells the extraordinary story of how grass triggered human civilisation.”

  • eddie:

    Those are just the two examples that came immediately to mind. 

    Going the other direction, the spotted hyena's ancestors were most likely pure scavengers, like today's striped and brown hyenas — but they evolved into fierce and capable hunters without losing their ability to crush and digest bones, or their ability to digest rotten meat that would sicken or kill other predators.

    Ravens are another example.  Unfortunately, we don't know much about the ancestors of modern corvids…but since general-purpose intelligence is not a typical feature of birds, it is likely that ravens, which are highly intelligent omnivores, evolved from more specialized ancestors.


    Unfortunately it's blocked outside of the UK — as are all BBC television programs.  Serves me right for recommending “Ape Genius”, which is blocked outside of the US!


  • Grace (Dr.BG)

    Wow Asclepius… I also think of fossil fuels, benzene derivatives and all plastics

  • Scotlyn

    Ref Wrangham, you are probably right about his work being a mix of science and speculation that requires critical reading, and you are certainly correct that this mix is very entertaining to read. Nevertheless, I believe he is correct to highlight the human propensity to share our food with one another – as opposed to hunting/foraging for oneself and only sharing with any “beggars” one can’t shake off – as a dietary habit of humans that, in itself, is as important to explain as any changes in the contents of our diet.

    In our (justified) zeal to save land from development, we mistake a land depleted of native grazers and covered with climax forest for the “natural” state of the land.

    We’ve had the opportunity to observe this first hand in Ireland. EU farm policy over the past 30 years has massively incentivised the destocking of grazers on marginal lands, to the point where much of it became covered, not in climax forest, but in impenetrable scrub (gorse) that became a substantial fire risk this past summer.

  • Scotlyn:

    I think his speculations about the impact of cooking on the human social system are intriguing, and quite possibly correct — but the evidence so far is that they happened on the currently-accepted timetable for the domestication and usage of fire, not 1.7 MYA as he claims.  You have to throw away a lot of solid evidence, and posit a lot of heretofore-unearthed evidence, to push control of fire back that far.

    As I said, the topic deserves an entire article on its own.

    Gorse sounds a lot like chaparral, but thornier.  Unfortunately there's a fine line between grazing and overexploitation: you can't simply let cattle loose on a big range and have them do what native grazers did.  You have to confine them to small areas and move them around frequently, to simulate the behavior caused by the predators that aren't chasing them anymore.  Otherwise they just spread out and eat everything down to nubs at once, which isn't good either.

    In other words, a true biotic community is a dynamic equilibrium between several opposing forces.  So unless the Irish want to reintroduce wolves and spotted hyenas to Ireland, humans are going to have to engage in active management.


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