Humans Are Causing Mammals to Shrink!

Guest commentary by David Middleton

From the No Schist Sherlock files…

PUBLIC RELEASE: 19-APR-2018

Humans have been driving a global reduction in mammal size for thousands of years

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE

The dispersal of humans out of Africa coincided with a dramatic global reduction in the size of mammals, a new study reveals. This “downsizing” trend may continue, suggest the authors, to the extent that, in just a couple hundred years, the largest terrestrial mammal left may be the domestic cow, weighing in at 900 kilograms (kg). Felisa A. Smith et al. sought to understand how the size of mammals has changed over time. They updated and created two datasets that capture the global distribution and body size of terrestrial mammals that lived between 66 million years ago through the present. The authors found a substantial bias in mammal extinction during the periods when humans were dispersing around the globe, whereby species that went extinct tended to be two to three times bigger than mammals that survived, a trend that was evident globally. Notably, prior to humans’ migration out of Africa 125,000 years ago, Africa was home to mammals of smaller size (with a mean body mass roughly half that of mammals found in Eurasia), which the authors suggest is reflective of the hominin-mammal interactions that had already been at play. Perhaps most striking is the reduction of mammals in the New World during the late Pleistocene, which coincided with humans’ adoption of long-range weapons. The authors report a greater than 10-fold drop in both mean and maximum body mass of mammals during this time; for example, mean mass of terrestrial mammals in North America fell from 98.0 to 7.6 kg. If current trends continue, the mean body mass of mammals in North America will drop from 7.7 to 4.9 kg in a few hundred years, the authors say. As mammals play a critical role in shaping ecosystems, the downsizing trend will have a cascading impact on other organisms.

Eureka Alert

The paper is pay-walled.  Here are a few highlights from the abstract:

  1. Today, it is well known that human activities put larger animals at greater risk of extinction. 
  2. If the current trend continues, terrestrial mammal body sizes will become smaller than they have been over the past 45 million years.
  3. Since the late Pleistocene, large-bodied mammals have been extirpated from much of Earth. 
  4. This decline is coincident with the global expansion of hominins over the late Quaternary. 
  5.  Moreover, the degree of selectivity was unprecedented in 65 million years of mammalian evolution.
  6. The distinctive selectivity signature implicates hominin activity as a primary driver of taxonomic losses and ecosystem homogenization.

And my comments on the highlights:

  1. They were in the way, some of them hunted us and most of them tasted good.
  2. Where do you think Chihuahuas, Pomeranians and Corgis came from?  Besides, when was the last time a large mammal species became extinct?  What percentage of megafauna bought the farm in the Early Holocene vs the fictitious “Anthropocene”?
  3. I’m sure we didn’t intend to extirpate most of them.  My guess is that most of them were long gone before the word “extirpate” was invented.  It’s highly likely that our ancestors used the word “eaten” in the early days of language.
  4. Are you saying we should have stayed in Olduvai Gorge?  Or that we should have extirpated ourselves?
  5. Blame the dinosaurs.  If they didn’t get extirpated. none of this would be happening.
  6. So what?

Is “the bleeding obvious” really a scientific discipline?  Humans played a big role in wiping out 169 out of 244 genera of mammalian megafauna from the Late Pleistocene through the Early Holocene.  This isn’t a eureka-worthy new discovery:

ElephantEvolution

Mammoths, Stegodons and Mastodons loved the Plio-Pleistocene but never got acquainted with the Holocene. I wonder why?

Here’s another gem from the Eureka Alert article:

Perhaps most striking is the reduction of mammals in the New World during the late Pleistocene, which coincided with humans’ adoption of long-range weapons.

What’s even more striking than most striking is that it was also coincident with human domestication of wolves.  Dogs may have played an integral role in enabling humans to out-compete Neanderthals.   Humans began the process of shrinking wolves between 20,000 and 40,000 years ago.

New data from ancient dogs indicates that dogs became distinct from wolves between 20,000 and 40,000 years ago, researchers report July 18 in Nature Communications.Dogs then formed genetically distinct eastern and western groups 17,000 to 24,000 years ago, the researchers calculate. That timing and other genetic data point to dogs being domesticated just once.

Science News

As early as 10,000 years ago dogs in the Americas were so valued as companions and fellow hunters that at least three of them were given proper burials rather than being eaten:

WASHINGTON — A trio of dogs buried at two ancient human sites in Illinois lived around 10,000 years ago, making them the oldest known domesticated canines in the Americas.

[…]

Ancient dogs at the Midwestern locations also represent the oldest known burials of individual dogs in the world, said Perri, of Durham University in England. A dog buried at Germany’s Bonn-Oberkassel site around 14,000 years ago was included in a two-person grave. Placement of the Americas dogs in their own graves indicates that these animals were held in high regard by ancient people.

An absence of stone tool incisions on the three ancient dogs’ skeletons indicates that they were not killed by people, but died of natural causes before being buried, Perri said.

[…]

Science News

So… Yes, “humans have been driving a global reduction in mammal size for thousands of years” and it had nothing to do with fossil fuels, CO2 or Gorebal Warming… Nor would renewable energy sources or a Tesla in every garage have prevented it.

Some of the big mammals wound up here:

And some wound up here:

The moral of the story: Big animals that chose to help us hunt fared better than those that didn’t.

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99 thoughts on “Humans Are Causing Mammals to Shrink!

  1. Ye, this is called “evolution”, you creationist morons.
    Nature is a cruel mother, and stand by the “Vea Victis” motto (aka “eat or get eaten”). And Humans are the victor, and all other animals AND vegetal unfortunate enough to compete against humans (that is, pretty much anything weighting more than ~5kg) are the loser.
    Obviously they wont survive unless humans turn him into some sort of pet or slave.
    But don’t worry. Humans are themselves out-competed by their own creation, those artificial beings we call states and corporations, and themselves won’t survive long.
    Have fun

    • Not that I am a ‘creationist’ but creation, or the origin of life, and evolution, i.e. what happened to life along the way, have nothing to do with each other.

    • While you are pondering the moment a man was created by God (another individual), I was wondering how it was possible for a self-replicating molecule in a dilute soup to assemble itself in a survivable form. Your miracle, my miracle.

    • On the other hand, the common cold viruses, various flu viruses, and various bacterial disease have proliferated by feeding on US!

  2. News Flash: For the last 100 years humans have been causing electronic devices to shrink. Film at 11.

  3. I accidentally ran over a rat, this morning. On my way home from a nightshift.
    I did look in my rear view mirror, and it definitely looked smaller. Or at least, flatter.
    Then again, rear view mirrors do make objects look smaller.
    And then we must take account of the effects of perspective as I drove away from the crime scene.
    This is not really very scientific, but I will take solace in the fact that it all looks like an exacting experiment compared to an attempt to reconstruct the global average temperature at one point in time – from the behaviour of just one tree.

  4. Progressives might have to make a decision: at what stage of human development did we become evil, and who are the people today who are supposedly less evil? Is any use of tools bad? I like the story that the more they look at the Amazon, the more they think that at the time of European contact, the forest was not truly wild; to some extent it was farmed or managed. That’s what the big brains are for.

  5. The three heifers I raised last summer didn’t shrink: I bought them at ~800 lbs each last spring and by the end of last year they produced 2,140 lbs of prime beef, all cut and wrapped.
    I know at least a dozen human animals, all customers of that beef, who also aren’t shrinking!

  6. There are proposals to try to recreate mammoths and the like. It is probable some of my ancestors found them yummy.

  7. Damn Straight Skippy. Humans didnt spend millions of years evolving into the apex predator on planet Earth to eat tofu.

    • LOL. That’s more the result of the emaciation of brain matter that results from “low-fat diets” and other such junk science-based “fads.”

  8. This “study” didn’t do its homework. The smaller the animal, the lower the liklihood that we, today, will find any remants to study. The effect is proportionate to size. We have many more records of larger animals than smaller, so of course it will appear that larger animals disappeared faster. Did humans have an effect? Most likely yes. The bigger the animal, the bigger the payoff for a successful hunt. Also, there isn’t much macho in collecting a ton of rats, and they have a much poorer carcass yield(% of edible compared to overall weight). Cows average about 65%, depending on age and weight, chickens are more uniform at about 75% and produce 1 lb of meat for every 2.5lb. of feed. Cows require about 7lb of feed per pound of meat. When you get down to really small mammals such as rats the yield is much less and requires an immense amount of work.
    Capybara, the world’s largetst rodent at around 80kg has been hunted nearly to extinction. It would be a good candidate for a meat animal but for the fact that it’s preferred habitat is shallow swamps.

    • ” The smaller the animal, the lower the liklihood that we, today, will find any remants to study”
      Nope. Microfaunal sites and remains are usually more common than megafauna.

  9. Just ain’t buying it, never have. First why didn’t humans drive megafauna in Africa to extinction prior to out migrating. Had an anthropology professor who was selling this hypothesis back in the 1960s about the Americas. Her understanding was a bit bizarre. She somehow had concluded that humans were extremely abundant at the time they arrived in the America like some flood and then they went around willy-nilly slaughtering megafauna in some blood feast. Even then she believed that male human were the personification of evil and responsible for all the problems in the world, if women were in charge none of the megafauna extinctions would have happened. Even though she accepted the ice/ land bridge hypothesis as to how humans arrived in the Americas she really believed that the climate was stable after humans arrived in the Americas so it couldn’t have possibly been a change in climate that caused megafauna extinction.

    • There actually was a number of extinctions in Africa about 100,000 years ago. But remember that Homo sapiens evolved in Africa so the fauna had time to adapt. In the rest of the world Homo sapiens arrived suddenly and encountered a fauna that had either only experience of less efficient hunting hominids (Eurasia) or non at all (America, Australia).
      And as for the “change in climate” hypothesis. Isn’t it rather odd that the changes happened at different times in different places, but always just after the first humans arrived?

      • tty, What mass extinctions in Africa? Do you hunt? Have you ever hunted megafauna? Have your ever hunted with a stabbing spear, throwing spear, atlatl, wooden bow, all with stone points, etc? Species go extinct and the vast majority of the time it has absolutely nothing to do with humans hunting for food which was the excuse my professor and others have made for mass extinctions. And why hunt megafauna in the first place? Extremely dangerous since one has to get up pretty close and personal with a “primitive weapon.” The whole hypothesis is flatly just another progressive fantasy blaming all humans from the beginning of time for all problems. Funny, those promoting such hypotheses never see themselves as the evil ones, just everyone else.

        • Eating isn’t evil. And, oddly enough, the extinction that took out the megafauna isn’t classified as a mass extinction.

  10. Wasn’t there a rise in temperature during that period? With a big jump some 12Kyr ago?

  11. “when was the last time a large mammal species became extinct?”
    About 2002, Chinese River Dolphin Lophotis vexillifer.

    • Not exactly large…
      https://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Baiji_size.svg/220px-Baiji_size.svg.png
      And not exactly extinct…

      China’s ‘extinct’ dolphin may have returned to Yangtze river, say conservationists
      Chinese conservationists believe they may have caught a rare glimpse of a freshwater dolphin that was declared functionally extinct a decade ago having graced the Yangtze river for 20 million years.
      Scientists and environmentalists had appeared to abandon hope that China’s baiji, or white dolphin, could survive as a species after they failed to find a single animal during a fruitless six-week hunt along the 6,300-km (3,915-mile) waterway in 2006.
      […]

      https://www.theguardian.com/world/2016/oct/11/china-extinct-dolphin-returned-yangtze-river-baiji

      • By the way would you accept the Caribbean Monk Seal Neomonachus tropicalis as “large” (8 foot, 500 pounds) and extinct (last seen in 1952)?

        • Borderline large. Placed on the endangered species list 15 years after it supposedly went extinct…

          Surprisingly little was done towards attempting to save the Caribbean monk seal; by the time it was placed on the endangered species list in 1967 it was likely already extinct.[20]
          Unconfirmed sightings of Caribbean monk seals by local fishermen and divers are relatively common in Haiti and Jamaica, but two recent scientific expeditions failed to find any sign of this animal. It is possible the mammal still exists, but some biologists strongly believe the sightings are of wandering hooded seals, which have been positively identified on archipelagos such as Puerto Rico and the Virgin Islands. On April 22, 2009, The History Channel aired an episode of Monster Quest, which hypothesized an unidentified sea creature videotaped in the Intracoastal Waterway of Florida’s southeastern coast could possibly be the extinct Caribbean monk seal. No conclusive evidence has yet emerged in support of this contention, and opposing hypotheses asserted the creature was simply a misidentified West Indian manatee, common to the area.

          https://en.wikipedia.org/wiki/Caribbean_monk_seal
          Do Monk seals really rate two genera and three species (2 extant and 1 currently extinct)?
          If the Monk seals had all snuffed it in the Late Pleistocene, would their fossils be recognized as two genera and three species? It strikes be in the same way that dog breeds have been declared extinct.

    • Rather like the Ivorybilled woodpecker in “revived” every decade or so, but unfortunately always without any proof…

      • Once an animal is declared extinct, there is no longer any need for the EPA to protect it’s habitat.
        That can’t be allowed.

    • “If the Monk seals had all snuffed it in the Late Pleistocene, would their fossils be recognized as two genera and three species?”
      They would certainly be recognized as separate species since they are osteologically distinct. Whether they would be regarded as two genera is more uncertain. This is based on DNA studies that show that while Caribbean and Hawaian Monk Seals have been isolated since the Panama gateway closed about 3-4 million years ago the separation from the Mediterranean species dates back to the Miocene 6-7 million years ago. That means that the Hawaian/Caribbean and Mediterranean Monk Seals are about as different genetically as humans and chimpanzees.

    • The Northern White Rhino is on the brink. If not over it. I’m not sure if every biologist would consider it a distinct specie.

      • The question was in response to this:

        2. If the current trend continues, terrestrial mammal body sizes will become smaller than they have been over the past 45 million years.

        And it was a multi-part question:

        2. Where do you think Chihuahuas, Pomeranians and Corgis came from? Besides, when was the last time a large mammal species became extinct? What percentage of megafauna bought the farm in the Early Holocene vs the fictitious “Anthropocene”?

        I wasn’t challenging the fact that some large mammals have gone extinct in the recent past or will go extinct in the near future.
        I was pointing out that not all of the reduction in mammal size was due to extirpation and that most of the mammalian megafauna extirpation occurred well-before the fictitious geologic time period known as the “Anthropocene.”
        Regarding the White Rhino… color is not a species.

      • It is actually thought to be an Anglicization of the Dutch “wijd”, meaning wide. White rhinos have wide square mouths while black rhinos have a pointed upper lip. The former are grazers and the latter are browsers.
        Northern white rhinos are considered a subspecies. There is some argument as to whether it is its own species, but that is probably true of most species.
        Scientists were going to attempt to harvest ova from the northern females last month, the ultimate goal is IVF with banked sperm from now deceased males. The embryo would be placed in a southern white female who is living with the northern white females. The idea is for the calf to be behaviorally and socially influenced by the northern females. We will see what happens…

  12. Where’s the mention of Climate Change? Stripped of the “models predict”, “as climate continues to change” and “worse than we thought”, etc. etc., these scientific articles are beginning to get back to a recitation of observations. Which is what they should be.
    But it also makes them look rather diaphanous (thin, flimsy, of little substance, easy to see through). I do like that word. I’m going to start using it in technical reports where I need to portray publications containing opposing hypotheses in a negative way.

  13. Most of the really large land animals come from Africa, the place where humans also come from and presumably the place where the two groups have interacted the most and for the longest period of time.
    This is the big weakness that sinks this particular theory.

    • Not at all, most of the surviving really large animals are in Africa.
      Not so long ago for example there were elephants in all continents except Australia and lions in all continents except Australia and South America (and there was a “Marsupial Lion” in Australia).

      • All you have done is repeat my point. The surviving ones are in the area that is the most impacted by humans.

      • Actually Africa is the continent least impacted by humans though inhabited for the longest time. Until very recently it was very sparsely inhabited and much less affected by agriculture than the other continents.

      • Once again, that’s my point.
        Also, all continents were sparsely populated by humans until relatively recently.

      • They seem to have largely hunted young mastodons and mammoths so it’s not very surprising that they are extinct.
        In Eurasia they became very rare already in the Middle Pleistocene but they apparently survived in small numbers until c. 40,000 years ago. In other words they went extinct at about the same time as the Neanderthalers.

      • The Short-faced Bear and the Cave Bear were different species in different genera on different continents.

  14. There is really no doubt that human selection by hunting (and fishing) has a strong effect on animal size. There is however a climatic effect at work as well. Most animals “shrink” during interglacials compared to glacials, and this is noticeable during previous interglacials as well, when no Homo sapiens were present.

    • Makes you wonder if some of them might recover from extinction during the next glacial stage… /sarc

    • Makes me wonder if Homo are smaller now than during the last glacial? But as far as I know, people don’t follow Bergman’s Rule very well, so perhaps not.

    • There is really no doubt that human selection by hunting (and fishing) has a strong effect on animal size.

      But not until humans invented gunpowder and guns to use it in …. and monster fishing nets and harpoons deployed by men in boats.
      Excerpted from “public release” portion of above commentary, to wit:

      Perhaps most striking is the reduction of mammals in the New World during the late Pleistocene, which coincided with humans’ adoption of long-range weapons. The authors report a greater than 10-fold drop in both mean and maximum body mass of mammals during this time; for example, mean mass of terrestrial mammals in North America fell from 98.0 to 7.6 kg.

      “DUH”, an associated “coincidence” is not proof of causation.
      NOTE: the late Pleistocene includes the last interglacial–glacial cycle ending at the Holocene boundary about 11,700 years ago.
      So saidith David Middleton, to wit:

      So… Yes, “humans have been driving a global reduction in mammal size for thousands of years” and it had nothing to do with fossil fuels, CO2 or Gorebal Warming…

      Now humans might have played a minor role in the global reduction in mammal size during the past 20 thousand years, ….. but there is no factual or scientific evidence to support that conjecture.
      “HA”, native Americans had been using “long-range weapons” for thousands of years but the great herds of Bison suffered no ill effects from said “hunting pressure”.
      And David M, you didn’t specifically say so, but I assume your above claim of ….. “had nothing to do with CO2” ….. that you were actually inferring, to wit: ….. “had nothing to do with increasing atmospheric CO2”, ….. which I agree with.
      But, ….. in actuality, …… the global reduction in mammal size during the late Pleistocene (pre-Holocene or prior to 11,500 YBP) was the direct result of atmospheric CO2, ….. a DECREASE in CO2, …. not an INCREASE in CO2.
      Atmospheric CO2 ppm began steadily declining about 145 MYA when it was at 2,000 ppm. And at 66 MYA the CO2 was at around 600 ppm and the dinosaurs had mostly all perished. And by 11,500 YBP the CO2 had decreased to less than 200 ppm which caused the demise of most of the remaining large carnivores as the result the demise of large herbivores.

  15. Or maybe it’s just that the remains of larger mammals are more commonly found for periods farther back in history. The larger the mammal the more likely its skeletal remains are somewhat intact and discovered.

    • Very dubious. Microfaunal remains are normally more common than megafauna. It might be true for elephants which have very robust skeletons (particularly teeth and tusks) that are also easily noticed by laymen.

      • One would think that there is a fairly strong bias towards large vertebrate animals in fossil reconstructions for several reasons. For example, large is easier to find, probably to be preserved in the first place (teeth may be an exception), and more likely to attract the attention of a palaeontologist, at least until recent decades. In general, large animals are rarer than small ones, but tend to have broader distributions. So, I think it is quite reasonable to expect a bias towards larger vertebrates in the fossil record, at least as a proportion of the taxa known, that has made it into the literature. I suppose this hypothesis could be tested by comparing the number of known small to large fossil ‘species’ within a group to recent faunas.

  16. Not sure about 66 mya but certainly 66 thousand ya…just about every culture on the planet has a “Great Starvation” story in their oral history. Much more energy efficient to kill and eat a Giant Three toedSloth than a rabbit or squirrel. The North American Megafauna were hunted to extinction by the First People’s.

    • Wharfplank, I don’t see why first people would prefer to hunt a mastodon instead of going fishing or snaring bunnies….dangerous stuff that, and a lot of work….I think it much more likely that those first people’s dog’s fleas infected the megafauna with diseases that killed them off rather quickly.

  17. And yet, despite it all, we humans coexist with the Blue Whale (balaenoptera musculus), which is the largest animal to have ever existed on this planet as far as we know.

    • I suspect this is so because historically our habitats have not significantly overlapped until rather recently. But, when they did the cetaceans weren’t winning. Luckily, they seem to have survived the period where our technology surpassed our need for their body oils.
      Goodness, lets not head back that way again.

      • I think, at least in part, the Blue whales and Sequoias were spared to a large extent for the same reason. They are so damned big the limited technology of the time available to harvest and process them just made it so it didn’t make a lot of economic or practical sense as long as there were enough of smaller species that fit the need. That is not to say that both weren’t harvested for a time. But in the case of the Blue Whale it was not like they knew their migration patterns and where to find congregations of them at certain times of the year as they did the others. We still don’t. How do you deal with an animal who’s tongue weighs as much as an elephant?

  18. Chicken v. egg. They’ve taken the side that because the extinction of some large mammals occurred during the period of human expansion, that humans were responsible. Try reversing the causation. The extinction of larger mammals enabled humans to expand into new territories. There is no evidence that early humans used poisoned weapons to kill large animals the way Bushmen in South Africa do when they hunt elephants, or indigenous people in the Amazon basin with curare and poison frog envenomed blow gun darts. Maybe they did that 100,000 years ago, maybe/probably not. But trying to kill mammoths with stone spears, or defend against cave lions, short faced bears and sabertooth cats is an extremely hazardous occupation. So which makes more sense? Small numbers of people moving into new territory as climatic conditions changed and facilitated the expansion, killed off the really big animals, or….those same climatic conditions reduced the population of the really large herbivores and carnivores, allowing little humans to move in without as much threat of getting stomped into a pancake or being the guest of honor at the sabertooth picnic.

    • The climatic changes at the end of the Pleistocene were no different than the climatic changes of the half-dozen or so previous deglaciations.
      The transitions of the glacial cycles were probably challenging times for most megafauna. The influx of humans (and dogs) was probably the straw that broke the camelops’ back.

    • “The extinction of larger mammals enabled humans to expand into new territories.”
      So you suggest that it was the extinction of the giant sloths and hutias that caused the colonization of the West Indies 4,000 years ago? Or that the extinction of Hippopotami and Giant Lemurs enabled the colonization of Madagascar 2,500 years ago?
      By the way it won’t work for New Zealand which had no native mammals (except bats) and where the last Giant Moas can be found in the kitchen middens of the first maori.

  19. My take on dogs: Humans didn’t domesticate dogs, the canine was intelligent enough to see the benefits of partnering with humans, and they domesticated humans. What other animal has so captured the love of humans than dogs. We walk them, pick up their waste, provide their health care, spend billions feeding them, and make they social media stars. And we’re supposed to have bigger brains? At my house, our dog is my wife’s best friend.

  20. One can smell the models in that ‘research’ from far away.
    Another pathetic fake research where assumptions drove alleged research’s direction.
    i.e. the authors set out to prove their what they already believed.
    Assumptions filled in their preferred data.
    Large animal bones are far easier to find, measure and count.
    Medium and small animal bones are uncommon, far harder to locate, isolate measure and track. Especially animals that are consumed whole or in portions.
    Very small animal bones are easily damaged from any handling.
    Those very small, small and medium animals identified through their fossil remains are exceptions, not the rule. Accurate counts are impossible.
    These researchers automatically assume people are the reason for animal extinctions.
    Meaning, that they do not attempt to research why some large animals prospered.
    Summing animals into some quasi average size estimates masks individual animal sizes, thus hiding animals that might’ve increased in size.
    At the end of their research, “voilà!”; all correlations and associations are assumed to be cause and effect.
    Another self satisfaction tinkering with formulas and models proving beliefs through gross assumptions.

  21. The funniest part to me was when they explained that there is a greater environmental impact from small mammals because when large mammals go up a hill they zigzag whereas small mammals make a straight path, leading to greater erosion. You could not make this stuff up.

  22. Hmmm. Just checking – is it the eco-loons that want to bio-engineer humans into a smaller-bodied species?
    Didn’t they just put out a mainstream Hollywood production, acted and produced by the usual dunces?
    Back in the fifties, ‘Dr Cyclops’ was a horror film.
    Fast forward and it’s a progressive fantasy.

  23. Now let’s make a graph showing devaluation of the US dollar vs CO2.
    Carbon is shrinking the value of the dollar !
    SOLUTION: Tax carbon, in order to produce more dollars lessened in value BECAUSE of carbon in the first place. Then create a new financial instrument based on debt accumulated by those who cannot afford to pay their carbon taxes. Carbon-debt futures, maybe ? I’m no economics expert, … obviously.

  24. I note that humans are relatively small mammals, so an increase in the number of humans will shift the average mammal size towards our size.

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