I see there are new fossil finds in Morocco which have been reported on the BBC. Here is the Nature Letter that reports the new find. What were modern humans up to prior to the flowering of human civilisation that left no mark prior to, lets say, ten thousand years ago? Why the large brains? Why the capacity for complex communication? Why the gap of over a quarter of a million years before the burst into human civilisation?
103 thoughts on “Human Evolution: the evidence evolves!”
Leave a Reply
You must be logged in to post a comment.
“Human Evolution: the evidence evolves!”
As is evolution itself…
https://www.youtube.com/watch?v=FdghRwWfaOQ
There are a couple of reasons for this, I think. The main reason why apes didn’t undergo significant cognitive evolution is that foraging for leaves, grubs, termites, and berries in a forest environment is less cognitively taxing than foraging for nuts, berries, roots, eggs, and small game in a woodland or savanna. We know from the palynology associated with Ardipithecus that it lived in a forested woodland, with more distance between food caches than apes would find in a forest. That probably drove the evolution of bipedalism, which is more energetically efficient than knuckle-walking over long distances.
But there doesn’t seem to be much cognitive evolution in the hominid line between when hominids branched off from the other apes around 5-6 mya and the evolution of Homo around 2.5 mya. My guess is that the real bottleneck to cognitive evolution was calorie extraction, since brains are metabolically expensive. Evolving more efficient intestines would have helped (chimps enjoy eating meat when they can get it, but in fact their intestines are not good at digesting it). But it probably took the discovery of fire to really drive the transition to Homo ergaster/Homo erectus. That coincided with significant drying out of sub-Saharan Africa, with woodlands being replaced by savanna. We know from the Nariokotome skeleton, dated around 1.6 mya, that Homo erectus had a growth pattern intermediate between that of extant apes and modern humans. That would have to include prolonged dependence, more human-like patterns of childrearing and pair-bonding, and probably reduced sexual dimorphism as females evolved larger bodies for the gestation of larger and larger-brained infants.
As long as an adaptation pays for itself in the long run, no matter how sub-optimal, that’s all that matters. Life is all about avoiding extinction one generation at a time.
That said, hunter-gatherer life is cognitively quite demanding, both of terms of the physical environments that must be navigated and the complexities of the social environments. Clothes and weapons need to be made, alliances forged and broken, children to be raised and taught, etc.
I don’t think there’s been much significant cognitive evolution over the past 300,000 years of Homo sapiens. There’s been a lot of cultural and technological evolution, sure. But at the cognitive level? I’d need to see some evidence for that. The skulls found in the Moroccan cave deviate from the modern human norm in terms of overall shape but not (from what I understand) cranial capacity.
I’m looking forward to Against the Grain in a few months. But I will admit that I’m not well-read in the literature on the origins of agriculture.
I wonder why they didn’t go back to becoming small game.
This veers pretty close to just-so-storyism. Indeed, it could easily be the reverse – that the fortuitous appearance of larger brains, due to accident and drift, enabled a more effective variety of hunting strategies.
Your story sounds uncomfortably like “giraffes evolved long necks so that they could eat leaves higher up in trees.”
Sure, but then there’s also the fact that baboons–not great at cognition–do quite well in environments thought to be much like the kind in which our lineage arose. So I don’t think it fits the evidence we have in any case.
Of course there could be effects that would be different for hominins, like they’re not as good at defense as baboons (australopithecus certainly seems not to be). So there could be issues of banding together, and perhaps needing to make weapons, in order to be safe from lions and hyenas. But who knows? And anyway, that’s a different matter.
Glen Davidson
Ask the designer. Oh,right, no can do.
newton:
To paraphrase Michael Shermer, asking is easy. The tough part is getting an answer.
Oh absolutely, LOL!
Alan,
The metabolic expense alone is powerful evidence for the usefulness of large human brains. Brains account for about 2 percent of our mass but around 20 percent of our energy expenditures. For natural selection to tolerate an expense of that magnitude, there has to be a payoff.
Sure. What was that usefulness?
Alan,
You asked for evidence, so I provided it.
keiths,
You suggest that large brains must be useful because they are costly. I totally agree. My question is what is the evidence for suggestions as to what that usefulness might involve.
Such suggestions: social living, shared and coordinated activity such as large animal hunting, control of fire, cooking, tool manufacture and use – especially flint-knapping… all very plausible.
ETA and the very plausible idea of a sexual selection element. This pops up in the Nature paper with a suggestion of dimorphism of brow ridges.
Alan,
No, you quoted me as follows and asked:
The disproportionate energetic cost of the large human brain is strong evidence in support of that hypothesis.
That evidence alone should be sufficient to persuade you that large brains were useful before the advent of civilization.
I was persuaded of that a while ago. Quoting myself:
I am trying to figure out which evolution story doesn’t sound like that.
That would be hard to find.
It must be galling to be losing to a theory that’s just story. Presumably your stories are even more nonsensical. I can understand why you’d prefer to stay on the attack in that case and pretend that gaping hole in the middle of your worldview does not exist.
Parasitic eye worms exist because your designer wanted to cause children pain is not a great story, but apparently it’s the one you believe.
Alan,
That merely acknowledges the energetic cost. You missed the important insight, which is that natural selection wouldn’t tolerate such a huge cost without a compensating benefit.
Had you understood that, you wouldn’t have asked for evidence in support of my claim. It was already staring you in the face.
OMagain,
Nobody is more angry at mortality than you.
I must be a poorer communicator than I thought for you to suggest that I don’t think in terms of cost/benefit with regard to adaptation. I am an adaptationist to the extent that I question the role of drift in contributing to adaptations such as increased braininess. My question still remains. What was the benefit or benefits driving the trend to increased brain capacity in early modern humans (or apparently levelled out around 300,000 years ago, if I’m interpreting the Nature finding correctly)?
What I had in mind is not Lamarckian but rather what’s known as “the Baldwin effect. The idea is that organisms that are plastic in their response to their environment can experiment with new behaviors as the environment changes. If those behaviors are sufficiently adaptive (bearing in mind that adaptations are satisficing and not necessarily optimal), then subsequent generations will be more likely to exhibit those behaviors.
As Dennett puts it:
The suggestion then is that, thanks to the Baldwin effect, there will be a ratchet effect that drives the co-evolution of culture and cognition over the course of hominid evolution.
Alan,
You didn’t do so in this instance. If you had, then you wouldn’t have asked for evidence in support of my claim. You wouldn’t have needed to, since it was already staring you in the face.
It was just a mistake, Alan. Please accept that and move on.
But you, rightly, say that big brains must have a benefit that exceeds the cost of growing and feeding it. If that’s all your claim is, it’s trivial, the essence of Darwinian evolution. I still ask, and I’m still curious, as to what were the selective factors that led to rapid(?) expansion of brain capacity that culminated in Morocco 300,000 years ago and why does that trend seem to have reached a plateau.
Kantian Naturalist,
I believe Daniel Dennett spend his weekends parked in front of a Chuck E Cheese trying to sell Mexican Jumping Beans to 8 year olds.
Not so much for the money, but more for the high he gets thinking he might be able to sucker someone else again today.
I think this is a nice question, but it’s important not to look for a single bullet. Hominid cognitive evolution could have been driven by multiple factors, or different factors at different times. Increased manipulation of the physical environment (tool-use, fire) could have been a driving factor for the habilines and erectines, with very minimal gestural/vocal communication. (Derek Bickerton, in More Than Nature Needs, suggests that displaced reference would have aided scavenging over long distances long before syntax evolved).
The oldest solid evidence we have of hunting of large game is associated with Homo heidelbergensis, with stone-tipped spears dated to 500,000 years ago.
With H. heidelbergensis, we see the inner ear and the hyoid much more similar to later hominids, which suggests that they were evolving vocal language. In H. erectus, based on the Nariokotome skeleton, there’s a slight expansion of the vertebral foramen throughout the thoraic vertebrae, which suggests increased nervous system control over breathing. But this could have been an adaptation for long-distance running, for fine control over the lungs in vocal communication, or both.
There are several features in H. erectus that are associated with distance running that aren’t found in australopithecines. My guess is that H. erectus was the first hominid that engage in persistence hunting. In fact I’m strongly inclined towards the endurance running hypothesis as an explanation for a good deal of Homo post-cranial anatomy. Endurance running, persistence hunting, fire and cooking, displaced reference, pair-bonding — there’s no single magical thing that explains all of human evolution, but rather we need to think about the whole mosaic of cultural and cognitive evolution.
Being smart was inevitably accompanied by being stupid. I think we can blame it on the rise of philosophy and philosophers.
Doesn’t it interest you at all?
I like the whole comment but absolutely agree with the point I quote. It’s a shame so little survives of very early human prehistory, apart from bones and stones…
Alan Fox,
Its the Baldwin Effect Alan. Don’t you get it?
If you need a big brain you will have a big brain, and if you have a big brain, you will need a big brain. And on, and on, it just continues increasing….
Coincidentally, the idea has recently gained new attention as it has been promoted heavily by Stephen Baldwin.
phoodoo,
Hey don’t knock the Baldwins. Alec, especially, is doing a great job on Trump.
And more people named Baldwin. Which of course increases the likelihood, that those named Baldwin will be better than those not named Baldwin, thus Baldwins will become better.
Look, if someone were to actually knock the Baldwins, then the Baldwins would experiment with being better at being knocked. Which of course would lead to Baldwins that are better at being knocked than non-Baldwins, thus increasing the genome for being knocked in Baldwins.
The feedback loop would of course continue, and The Baldwin Effect would take effect, increasing the Baldwin Effect in subsequent Baldwins.
Alan Fox,
Its pretty obvious really Alan. Its been empirically proven. Daniel Dennett would be more than happy to tell you all about it if you give him 6 bucks.
Alan,
My claim was that large human brains conferred benefits on their owners long before the rise of civilization. You asked for evidence, not realizing that the huge metabolic cost of large brains was already strong evidence for that claim.
I simply pointed out what you had missed.
keiths,
Right! If the huge brains weren’t favored, they wouldn’t exist, thus, if they exist, they are favored, so they keep increasing! Eventually they will be more favored.
Enough evidence for ya?
Remember the niche!
This Baldwin effect sounds like it could drive increasing complexity in general, not just brain complexity.
Improving the flexibility of a system, whether hardware or software, invariably entails increased complexity.
Of course the trade-off is that there are more ways for the system to fail.
Not just that, the Baldwin effect can actually drive the increase in the Baldwin effect. And thus by increasing the Baldwin effect, you have many more chances in the genome for the Baldwin effect to be effected.
There really is nothing the Baldwin effect can’t do, other than telling the genome not to be effected by the Baldwin effect.
Oh hell, it can even do that if it wanted.
I find it interesting that people can have their comments sent to guano for calling someone an asshole, but they cannot be guano’d for being an asshole.
Phailed ridicule is the coping strategy of the Lesser Phoodoo, P. minimus.
Another example from the wild can be found here.
Your claim, though correct, is trivial. Every adaptation is a result of cost vs benefit. The question that interests me is what those benefits were in the case of early modern humans.
You simply stated the obvious.
Fair Witness,
You’re discussing points that should be discussed in the moderation issues thread. The advantage is that the rules on civil discourse are not applied there.
There are several hypotheses for the selective bias towards larger brains, the development of communication skills, social living, cooperative hunting, skills like tool-making and use of fire. We have some evidence in artifacts such as arrow heads but other than that not a great deal.
No, of course not.
Exactly. If we had more details of what those niches were a half million years ago…
Since great apes also have large brains, and primates have large brains compared to other mammals (as well as mammals relative to other tetrapods, vertebrates relative to invertebrates*), there’s a larger question worth posing here: what are brains good for? Under what conditions will having a larger brain be adaptive?
It’s been suggested that one of the selective pressures driving mammalian cognitive evolution is that, for hundreds of millions of years, mammals were nocturnal insectivores. That ecological niche imposes heavy burdens in successful prediction, since the animal needs to be able to predict, based on a distant sound or smell that was caused by where the prey was, where the prey will be when the animal can get to it. So the brain has to be able to predict regularities across time and space — computationally much more difficult than darting a sticky tongue at blobs crossing the visual field.
Tomasello’s work on great apes shows that all great apes (chimpanzees, bonobos, gorillas, and orangutans) do two things that non-hominoid primates (Old World monkeys, New World Monkeys, and prosimians) don’t do: they use gestures in communication and they make tools. Tool-use requires an understanding of physical causation, and gestural communication is crucial for great ape social cognition.
On the reasonable hypothesis that the last common ancestor of Homo and Pan was much more like a great ape than like an austrolopithecine or early Homo, we can assume that from the beginning, hominids had ape-like cognitive capacities. This means that even from the very beginning of hominid evolution, about 5 mya, our ancestors were already among the most cognitively complex animals on the planet.
Two other factors worth thinking about here:
1. Is the brain is getting bigger because the whole animal is getting bigger, or whether the brain is getting bigger while the body size remains mostly unchanged. The latter is more strongly indicative of selective pressure for larger brains than the former.
2. Is brain size simply a matter of positive allometry, like cervid antlers? The massive antlers of the Irish elk were not selected for — rather, there are developmental constraints in cervid biology such that antler size increases faster than body size as body size increases. My understanding is that brains are not subject to positive allometry, but it’s a consideration that would need to be ruled out.
* This is not to besmirch the octopi, who arrive at mammal-like intelligence through a completely different neurophysiology (no myelin!), neuroanatomy (no centralized brain!) and evolutionary pathway.
Alan,
It’s obvious to those who understand evolution well, but it wasn’t obvious to you. Hence your unnecessary request for evidence, when the high metabolic costs associated with large human brains should already have persuaded you of their value.
You’ve (hopefully) learned some important things from this thread:
1. Large human brains were evolutionarily valuable long before the advent of civilization.
2. That they were retained by natural selection, despite their high metabolic cost, is conclusive evidence of that value.
3. This is evident even before you consider the specific ways in which they contribute to reproductive success.
It is obvious. What is not so obvious is what those values were, between a half-million and three hundred thousand years ago and why the rapid expansion effectively stopped.
I try to learn something new every day.
Yes, The new evidence pushes this back to 300,000 years ago. Why do you think that is? Or are you, like phoodoo, not interested.
Trivially true. As I keep saying. What was that value? Why did it tail off around 300,000 years ago?
Yes, as I said, trivially true.
There’s a clue in that plants are without sensory or motor systems. Sensory systems seem linked to motility.
Metabolic rate is, I’m sure key to the ability to pay for a larger brain, thermo-regulation must be a factor.
Frans der Waal has done some great work on animal cognition too. Not just chimps but macaques and elephants (you just need robust mirrors)
.
Fair conjecture!
Yes, I’ve seen that argument put forward with elephants and cetaceans.
My new fact for the day! Positive allometry.
Different niche and different, though fascinating, sensory skills. Talking skin.
Alan,
Calling it “trivially true” doesn’t change the fact that you missed it altogether. That’s why you asked for additional evidence when a sharper person — one who recognized that the high metabolic cost was itself evidence — wouldn’t have needed any.
Why is it so hard to admit your mistake? It’s just one of many, and I doubt that anyone is surprised.
keiths,
I’m sure you can keep the “Admit your mistake” shtick up till the cows come home. The simple fact is that cost and benefit of an adaptation is central to selection. Something not mentioned specifically does not make it “missed”. Have the last word.
Alan,
You asked for evidence because you didn’t realize that you already had it. It was just a mistake. It’s not the end of the world.
You’re making this far harder for yourself than it needs to be.
Just for the record, I did think it was perfectly obvious that you were taking for granted the general point that large brains had to be adaptive, on metabolic grounds (because there’s a cost to having a metabolically expensive organ, so there must be compensating benefit).
I took you to be asking what the specific evolutionary benefits were and why cognitive evolution manifested when and as it did in the hominid line.
That is, I didn’t see you make any mistakes. It’s just the difference between the general principle that brains must be adaptive and asking what specifically they are adaptive for, esp. in the hominid case.
(Presumably, what large brains are adaptive for in great apes and hominids is not the same as what large brains are are adaptive for in cetaceans and elephants, since the niches are so different!)
As for why cognitive evolution seems to have plateaued (about 300,000 years ago) — I took this to be one of your questions — one constraint worth noting is the size of the birth canal.
If human infants were born with larger brains, they couldn’t pass through the birth canal (or do with even greater difficulty). If the birth canal were larger, that would interfere with efficient walking and running. If infants were born at an earlier stage of development, they would be even more prone to infection, other systems wouldn’t be developed as much, and so forth.
In other words, the constraints of primate embryology and the constraints of hominid locomotion together put a hard ceiling on how large hominid brains can be.
KN, to Alan:
KN,
This isn’t difficult.
My claim was that large brains were beneficial long before the advent of civilization. Alan challenged me, asking for evidence to support that claim.
His mistake was in failing to realize that the high metabolic cost of large brains is already sufficient evidence for that claim, even before you consider the ways in which the benefits play out.