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Well I think the bigger issue for gazelles is energy density period - brains are calorie hogs and it doesn't take much cunning to track down grass. Grass eating is the opposite direction in a food strategy - going for abundant but low density food instead of chasing higher density.

A diverse diet is a bit of a hallmark of intelligence in itself in that they are able to use their brains to get more food to make it worth the investment - similarly to complex group behavior I guess.

Hermit crabs for instance are shockingly intelligent for crustaceans, especially for ones of their size. I know that improperly shut lids which while closed have enough play - they cold push from the inside causing them to rotate on their axis and let them escape. That isn't quite tool use but recognizing tools unlike anything in nature and how to manipulate them to get what they want.

Hermit crabs have both and live in large social groups and eat a diverse diet as well.

Speaking of Hermit Crabs, I was also blown away by their communal shell exchange process.

Many hermit crabs will come together and work as a team to change shells in hierarchy. If you've never seen it, you are in for a treat.

https://www.youtube.com/watch?v=f1dnocPQXDQ

That was fascinating, thank you for sharing.

I feel like there's something taboo, something indecent about seeing a hermit crab out of its shell.

That one crab was caught with its pants down for a moment.

Also big herds probably discourage engaging in complex group behaviors: Just blindly follow the flock and you'll be ok most of the time.

When you're saying "Big brains" I assume you mean a higher level of cognition and awareness in some general sense, not a physically larger brain.

First I think you're getting the cause/effect of evolution backwards. For example, primates did not evolve hands so they could better grasp branches, but rather they better grasp branches because they evolved hands and so had a higher rate of survival.

So the question isn't so much "what causes complex intelligence" (your proposal being hands) but rather "why hasn't complex intelligence appeared for something like the gazelle family tree?"

It's an interesting hypothesis to say that perhaps it's because they don't have hands, but there are innumerable other factors that could also be an influence, I doubt it comes down to a lack of hands.

I'm not a biologist though so take what I'm saying here with a gigantic grain of salt.

"primates did not evolve hands so they could better grasp branches, but rather they better grasp branches because they evolved hands and so had a higher rate of survival."

We agree that it can be difficult to distinguish causation from correlation, and in this case you may be right that the survival advantage conferred by better grasp of branches might have been a "bonus" or helpful side-effect, rather than an adaptive trait directly informing our ancestors' evolution. But I don't think it's so clear-cut or obvious.

I think the distinction being made is between evolution and design. In evolution traits do not come about for a reason, they occur at random, but they persist if they are advantageous.

Yes. But there's an illusion of intentionality. Because [pausing, looking at my hands] it's all just so bloody amazing.

But on the other hand, some of the kludginess is also bloody amazing. Spiders, for example. The gut passes through the "brain". So there's a tradeoff between "brain" size and eating. And so they employ external digestion, and suck liquid.

Well, a couple of things start to make sense about the kludginess, if you start with the single-cellular origin, and then pile up layers of specialized tissue, with some cells permanently buried within the organism, never to be exposed to an external environment.

The first part is that brains are just plain weird, and perhaps one of the weirdest aspected of any multicellular organism. More than half of all known life forms don’t have brains. So, brains usually aren’t a priority.

Second, the gut is often regarded as a brain-like organ in many vertebrates, and so, with arthropods and crustaceans, it’s interesting that the the two might be more tightly coupled. It probably cheapens the endocrine feedback loop.

Third, external digestion actually comes across as less freakish and uncivilized underwater. On land it has a messy, disgusting sensibility, but in the ocean it’s kind of on par with a smokey cooking fire at a camp site, especially when considered from a single celled animal’s perspective.

When you consider that crabs and lobsters are the ancestral relatives of insects and arachnids, the low prioritization of a brain, and externalized digestion start to look more and more normal.

Crabs and lobsters don't use external digestion but eat their food not terribly different from what we do. So it looks like spiders evolved their system later.

Yes, they're not close relatives. Closer than us and them, but not that close. So yes, external digestion is largely a spider thing. However, crabs and lobsters do "chew" very thoroughly before swallowing. As do some spiders without external digestion.

In all invertebrates, "brains" (to the extent that they're present) are ring ganglia, with the gut going through the center. So arguably they all face that tension between brain development and the ability to eat. Vertebrates, conversely, have ~parallel guts and central nervous systems, so there's no conflict.

The thing with octopuses is that their ring ganglia are mode widely spaced. Having no exoskeleton helps with that, I guess.

This kind of nitpick seems a bit unnecessary, and I think it's particularly strong because people are contending with intelligent design nonsense.

When you talk generation to generation, the gradual tiny mutation each time did indeed allow primates to grab the branches a little better and so they had a higher rate of survival and the causation matters.

But when you talk about the end product (the hand), it is fair to say that primates (as the product of those millions of tiny iterations) evolved to better grab branches, imo.

It should be noted though that intelligence isn't linked to brain size, except for in the case of hominids compared to other hominids. There is also not a direct correlation to increased intelligence and survivability except for competition between individuals.

Corvids are among the most intelligent animals in the world. In many cases far more intelligent than many ape species. Their brains are the size of almonds, at largest. Whale species are intelligent but their brains are incredibly massive. Whales aren't 10-100x more intelligent than humans because of brain mass.

https://en.wikipedia.org/wiki/Corvidae

The intelligence level of Neanderthals is unknown but they had a cranial volume approximately 22% larger than modern humans. The common knowledge is that Neanderthals went extinct because they were stupid and eventually killed off by human invaders. The current evidence is that Neanderthals and humans overlapped in Europe for roughly 5000 years and heavily interbred with humans. The most likely cause of extinction had nothing to do with intelligence. They likely died off because the evidence indicates they were less social and reproduced less frequently. If anything they may have been comparatively too smart for their own good.

Nitpick, article quotes scientists that talks about brain size relative to body being a factor in intelligence, not brain size alone.

I thought that always as a strange argument. Why would relative size matter for intelligence? At least if one thinks of compute capacity this shouldn't matter.

probably because relative size is a good proxy for evolutionary "resources" being allocated to brains.

why absolute size doesn't matter as much as we think it should is a really good question, but clearly our modern transition from "the nervous system is like a steam engine" to "the brain is like a computer" is only an improvement and not actually a good model yet.

So, when "one thinks of compute capacity" one arrives at the wrong answer instead of one that fits the evidence and statements of the evidence seem like "a strange argument".

Because not all of the brain is 'compute'. Lots of it seens to be allocated to map 1:1 with body areas (or probably the number of nerves in those body areas). I guess you could see this as IO.

Both absolute size and relative size are poor approximations, but relative size gets closer.

Large animals aren't just scaled up versions of smaller animals. Large animals use the space for more complicated digestive tracts. Their larger appendices allow them to have more joints with more degrees of freedom, and longer appendices and higher speeds require a higher resolution from their eyes to perceive sufficient detail. Skin with more surface area also means many more cells for sensing heat, pressure, damage, etc across the entire skin.

All of this means the brain of a larger creature needs more "IO ports", more neurons to compute sensible outputs for them even for routine tasks, and more neurons to break the wealth of data into a form usable by a cognitive process or an instincutal reaction (mapping to area of body, computing averages over time and over multiple inputs, correlating different types of senses, etc).

All of these differences have different scaling factors. The amount of neurons to count to 5 stays the same, the amount of neurons to process skin sensations scales approximately with skin area, or the square of animal diameter, but the amount of neurons to control motor functions or the digestive tract can grow much faster. Overall, putting brain size in relation to animal size or mass is a decent first approximation and works in practice.

I sometimes feel like we talk about evolution wrong. Here, for example; it's not like gazelles couldn't take advantage of being smarter, there are plenty of advantages to be had if you can outsmart your predator, it's just that the smarter gazelles weren't ever smart enough for that to matter.

It's more about if it's possible for minute intelligence improvements to produce higher survival chances. For a gazelle, the intellect leap needed to be substantial, and random genetic mutations weren't going to get there. For an octopus, each little intellect bump meant little survival bumps too.

You could formulate this argument simply as a differential equation.

d(SurvivalGazel) = 0.001 dIntelligence

d(SurvivalOctopus) = dIntelligence^2

Surely survivability has to decrease with intelligence otherwise all intelligence would rise over time.

We have an expression (aphorism), something like "clever enough to be dangerous".

Intelligent enough to experiment, but not too realise the dangers involved is relatively common in humans; the societal system in the past mitigated the dangers by pairing younglings with adults who can tell them when they're being dumb.

That's part of it, but there's also the fact that bigger brains qhoch lead to being smarter have downsides in terms of resource usage (needing to eat more, or reduce physical movement), which might not pay off for the smarter gazelles as it might make them slower and thus more likely to be eaten...

So why aren't all birds as smart as crows? They have similar anatomy.

What I've read is that crows are smart for the same reason that dolphins are smart ("social intelligence"). Crows also tend to live in flocks/groups, unlike many other bird species.

Not a great source, but here's an excerpt explaining that they tend to grow up in groups:

But growing up is a different story. During younger years, they often live in larger flocks dubbed juvenile gangs. "It's exactly how it sounds: they're basically a bunch of teenagers trying to compete with each other," Brown says. And it's these relationships they have to keep tabs on.

https://cosmosmagazine.com/social-sciences/why-are-crows-so-...

The octopus is a counterpoint to this, being very intelligent but absolutely solitary.

But it has excellent hands.

Humans may be unique in having both complex social structure as well has hands.

Arguably elephants fall somewhat into this category...

I've often wondered whether elephant-like aliens would make sense, exactly because of this.

I guess Niven and Pournelle had the same idea for Footfall.

Dolphins are also very social creatures which certainly goes alongside their intelligence as an evolutionary pressure — especially with regards to their group hunting strategies, like humans and wolves.

Most primates don't do a whole lot with their hands that's different than say what birds do with their beaks. Chimps are not building iPhones out there. Intelligence is also needed to plan, and notice & remember patterns of food & threats. Those don't necessarily involve hands.

What about birds? Crows display surprisingly intelligent behaviour, like understanding water displacement or fashioning tools from sticks or wire.

Evolution is not a directed process. It is essentially a load of small random mutations, and the random evolutions that improve the organism's fitness get passed on.

So, yeah octopodes are really cool, but it's not correct to say that octopodes evolves intelligence and chromo-camouflage in some sort of direct way because they needed to become intelligent: what would have happened was over a very long time, certain families or society started being born with more than above intelligence, which allowed them to get better access to food and mates, which meant they were fitter, which meant they may pass on their advantageous traits their children, who would carry it on the their children etc.

Evolution doesn't happen "because" of something. Wales didn't evolve into marine mammals because they needed more food. Yes, they needed more food but their evolution just randomly moved their species towards the water.

For example a terrestrial wale may have been born with the ability to hold its breath, just by chance. Eventually every terrestrial wale has inherited that ability, and then the process repeats, with another mutant wale evolving thicker blubber which would allow it to obtain more food, spend longer in the water end pass on their trait for blubber.

OP isn't claiming that evolution is directed. He's simply illustrating the magnification effect of existing bodily structure on intelligence mutations.

OK I think I've just ended up reading OP in a such a way that it appeared OP was saying that primates evolved opposable thumbs because they needed opposable thumbs, as if evolving opposable thumbs suddenly resulted in primates thinking "you know what would be awesome? If we could touch the pads on our hands together."

There isn't a "because".