u/Jayjay4547

In the short time that my post "Maybe hominins walked of the woods with spears" survived here, it drew a response from yourupinion, who was punting for a "sanctuary" variation of the aquatic ape hypothesis. In his variation, early hominins retreated into water when threatened, where they held an advantage by being bipedal, as bipedal kangaroos have been observed when reacting to dingoes.

The argument I had been making was Dart's "Killer ape" redivivus, and like the AAH, can be labelled an umbrella theory. But with the logic reversed. According to Dart (1925), his Taung Child would have been hopelessly vulnerable in the Southern African savanna context "where competition was keener between swiftness and stealth " but, having hands free, and with precocious intelligence, had used their hands as "organs of offence and defence". By which he later proposed, they had used bones found at other fossil sites as weapons. While the AAH sees hominins as out of place on the dry savanna, Dart placed them on the dry savanna as found, but saw them incomplete, unless one associated them with other objects. He looked for material evidence from other fossils like antelope jaws.

My little riff is that he should rather have asked what weapons would have been most effective, which would have been thrusting spears, although they would very seldom have been preserved for the fossil record. A thrusting spear keeps an attacker at a distance, which would have had developmental consequences.

Another mistake I think Dart made, was to see an inevitable bloody murderous future in a weapon-using hominin. Other plant eaters on the savanna who deter their predators using horns, teeth of hooves, are not warlike, so why should hand weapons have led hominins towards warfare? Granted that the Taung Child lived near the nick point where human encephalization started abruptly, and granted that it might have been sparked by competition between groups of hominins replacing competition with predators in the food web. Granted also that encephalization has something to do with the evolution of language. Dart should have noticed that the horrors committed during the great 20^(th) century wars were committed by men who returned in peacetime to decent behavior. They had been motivated by the societies they were embedded in.

That motivation towards warlike behavior was achieved through ideology, as means to persuade groups to behave towards other groups in a particular way. And that motivation is partly achieved through spectacle, as in the Nazi rallies of the 1930's. What is now transmitted through speech and text might have started as dramatic expressions of what had happened or should happen, in encounters with the Other. According to that logic, language evolved as an economical refinement of what started as already-structured and highly consequential dramatic expression. And individual groups hosted populations of alternative ideologies, as coherent plans of how to behave, which competed and survived according to their practical outcomes for the group.

According to the conventional picturing of "the ascent of man", as humans became more intelligent, they took to using stone tools, then clubs and finally spears. Over the same period, they became more strictly bipedal. ChatGPT, DeepSeek and Gemini concurred that bipedalism freed our hands for gathering things and for using tools, for walking efficiently, and to stay cool.

These explanations from AIs trained on the scientific literature, are all about independent marginal advantages, and they aren't that interesting; their point is to teach that evolution can involve small advantages that add up. Also, none invoke outside actors, unless one counts inanimate factors like climate change. Evolving humans are visualized as the only actors on a bare stage where only the backdrop changes.

I want to sketch out an alternative explanation: humans evolved to walk on their back legs because that enabled them to forage on the food-rich savanna by the defensive use of spears.

The main technical problems with that explanation are:

(a)     There is no direct evidence of spears earlier than the Schöningen spears found in a coal mine that had been a bog where horses had been hunted 350,000 years ago by almost modern man.

(b)     Weapon use is associated with intelligence, while bipedalism evolved millions of years before distinctively human intelligence.

It can also be considered a category mistake to focus narrowly and specifically on spears, when they are just one type of weapon, weapons are just one type of tool. humans are distinctively tool makers, and anyway the earliest tools found are stones. But that also offers an opportunity to  explore an opposite hypothesis built on relations with external actors.

(a)     THE "NO EVIDENCE" PROBLEM.

If early hominins did use spears, those would very seldom appear in the fossil record, because of the active food web for metabolizing lignin. Discarded spears would need to be quickly-buried below the savanna's biotic stone line that marks the limit of this activity, often between 10cm and 1m deep. A possible source of evidence could be long-lived striations on exposed granite outcrops on which sticks might have been scraped over many generations, to smooth and sharpen them.

Evidence from contrasting body plans of savanna primates.

One line of evidence that early hominins used spears comes from contrasting the hominin body plan with that of baboons, whose fossils were found associated with hominins at six South African cave sites. Arboreal monkeys and apes both settled the savanna, both were plant eaters, of comparable size, the hominins were doubtless as highly social as baboons. Several monkey lineages adapted into the dog-like baboon body plan that is common on the savanna, extending the common primate defense of biting by evolving longer jaws and longer canines, especially in the males. Those canines are conventionally attributed to sexual selection but they are also powerful inter-specific (aposematic) signals, recognizable by how seldom a human would try to grab a trapped baboon.

 

The strangeness of the contrasting hominin body plan is easily overlooked seeing that obligatory bipeds make up a third of the mammalian biomass on Earth. However, they belong to only a handful of related extinct hominin species, and to only one living species, out of over 6,000. To reverse the thought experiment about grabbing a baboon, what could make the baboon fear to bite a human would be a weapon in the human's hand.

 

(b)     THE PROBLEM OF INADEQUATE INTELLIGENCE

Bipedalism evolved during a period from Sahelanthropus about 7 million years ago, close to the last common ancestor with forest-dwelling apes. Over that period lasting till Australopithecus africanus, hominin brain volume was increasing at about 14 cc/million years, 20 times slower than in the subsequent so-called encephalization. So, if early hominins used hand weapons, that could have had little to do with growing intelligence. That goes against the conventional position that weapon use requires big brains because it needs advanced planning.

The tiny Pom Pom crab contradicts that association between brains and weapons. It holds one stinging anemone in each claw, and it manages them intensely. When threatened, it pushes the stinging anemones at the threat. It trims the anemones and takes food from them, keeping them small. If it loses one anemone it tears the other into two and attaches half to the other claw, where it regenerates. When it molts or when it wants to clean its front it first attaches an anemone to one of its legs and later retrieves it. If it loses both anemones, it immediately tries to replace them. So, this is an obligatory relationship. These complex behaviors evolved with only the transmission of instincts and without any brain to speak of. And that habit affected its body plan, so that its claws are only useful for holding anemones.

Preadaptation of forest apes for defensive spear use.

It’s easier to reconstruct how forest apes would have preadapted grassland hominins for weapon use than it is to imagine how pom pom crabs could have picked up the use of stinging anemones, if we narrow our specification of what those weapons could have been.

Modern chimps use sticks to dig up tubers on the forest floor. It would be natural for a forest primate with a digging stick to try to keep an attacker away from it. The stick would then function as a spear, more particularly a thrusting rather than a throwing spear.

Two uses of spears

Two kinds of spear use have importantly different effects. A thrown spear can strike distant prey that is trying to escape, and if it lodges in the body, further movement is so painful that it slows or stops the animal. That is useful in hunting. Later humans are much better adapted for throwing spears than the australopiths were.

The thrusting spear has more complex defensive uses. It can stop an attacker, keep it at a distance and take the initiative from it, allowing time for others to join in the defense. If an attacker charges down a spear that has been grounded, its own momentum would impale it. Which is why an even much heavier attacker would lose the advantage of its weight.

A thrusting spear can also be pushed at the attacker, with as much effect as a desperate spear-holder’s vigor can achieve.

So, unlike the throwing spear and the African knobkerrie, which is the next more difficult effective weapon to make, the thrusting spear is both a stopper and a striker.

The brain as a working organ.

According to this argument so far, the high intelligence quotient of ancestral apes would have been irrelevant to hominins having uniquely adapted into obligatory spear use. That issue might be addressed by treating the brain more as a working organ than as the seat of intelligence. Consider these EQ values: Sloth 0.4 , Capuchin 2.8, Dolphin 4.5.  Those numbers could be interpreted like this: The South American sloths and capuchin are both predated by eagles, but the sloth relies on being hard to find, while the monkey relies on sensing an eagle quickly and responding by fleeing quickly amongst branches. The dolphin's large brain enables it to rapidly process sonar echoes from the fish it is hunting. The high EQ of baboons and hominins enabled them to rapidly process actions during a mobbing attack on a predator.

 

Viewed from that perspective, the human EQ of 7 enables us to rapidly parse sentences, which has plugged us into the intelligence of the group. Until AI arrived to "help" us with that.

Google's AI Overview told me that humans are bipedal for reasons of energy efficiency, thermoregulation, to free the hands, and for visibility. I know about those, I came across the thermoregulation thesis in a1988 New Scientist article by Peter Wheeler. But I have a question: How would those have affected the impression that early bipedal hominins made on their predators? Savanna mammals innately message each other that they are hard to kill and good at killing. What would have made the australopiths hard to kill? How about, if they carried weapons, more specifically thrusting spears?

Thrusting spears are both stoppers and strikers: they frustrate an attack, take initiative from the attacker, and keep the attacker at a distance from the body. They are also the simplest weapon to make from a bush, needing just two cuts and some scraping.

A Google image search for "Ho. floresiensis spears" shows those tiny-brained bipeds spearing Komodo dragons, although no wooden spears have been found associated with them. Naturally, because exposed wood is metabolised by a whole food web. Then equally, evidence that australopiths used spears can come from their environmental relationships, their body plans and later human habits.

If you were to meet a bunch of men with spears, wouldn’t that make you try to avoid them, more than just meeting a bunch of men carrying food?

AI Overview ended by telling me: "This upright posture sparked a massive feedback loop in human evolution. A rotated pelvis altered the birth canal, allowing hominins to give birth to babies with larger, more complex brains, while also freeing up the hands to develop more advanced tools." OK, but even more, those babies, unlike the young of other primates, also remain immobile for several years, which requires them and their mothers to be well defended, which necessitates a defended troop.

Has that proposition ever been decently unpacked?