The Brain: relative size, speed & complexity of sensory system (including intra-specific communication): oxygen as catalyst, food as fuel
On elephant and human brains, summarized from Not Exactly Rocket Science
Both humans and elephants show both semi-aquatic and terrestrial foraging traits, throw stones, manipulate branches or sticks, squirt water, live relatively long lives, have strong social behavior, have generally low rates of mutation yet high rate of mutations among specialized amino acids involved in "aerobic energy metabolism (AEM)" genes - which govern how mitochondria metabolise nutrients in food, in the presence of oxygen.
We already knew that the evolution of AEM genes has accelerated greatly since our human ancestors split away from those of other monkeys and apes (highly beneficial to a part-time sessile-benthic submersed forager (human ancestor, elephant ancestor) which needs both apneic and aerobic capability, but not a full-time pelagic dive chaser (dolphin) which needs maximal apneic (anaerobic) capability, nor a part-time wetland floating-food forager (congo swamp gorilla) which keeps its face always above water surface and so lacks apneic capability while not transiting far habitually so no selection for aerobic endurance.
"While other mutations were reshaping our brain and nervous system, these altered AEM genes helped to provide our growing cerebral cortex with much-needed energy.
And sure enough, elephants have more than twice as many genes with high ratios of non-synonymous mutations to synonymous ones than tenrecs do, particularly among the AEM genes used in the mitochondria. In the same way, humans have more of such genes compared to mice (which are as closely related to us, as tenrecs are to elephants). Overall, his conclusion was clear - in the animals with larger brains, a suite of AEM genes had gone through an accelerated burst of evolution compared to our mini-brained cousins. Six of our AEM genes that appear to have been strongly shaped by natural selection even have elephant counterparts that have gone through the same process.
Goodman's next challenge is to see what difference the substituted amino acids would have made to us and elephants and whether they make our brains more efficient at producing aerobic energy. He also wants to better understand the specific genes that have been shaped the convergent evolution of human and elephant brains over the course of evolution."
Both elephants and humans are very water-dependent and not well conserving of metabolic fluids (unlike full-time savanna/marine dwellers), moving from waterhole/lagoon to waterhole/lagoon, foraging opportunistically along the way.
Elephant ancestors were semi-aquatic - Telegraph
semi-aquatic ancestors of elephants
Tiny brains: "Insects may have tiny brains, but they can perform some seriously impressive feats of mental gymnastics. According to a growing number of studies, some insects can count, categorize objects, even recognize human faces — all with brains the size of pinheads. Despite many attempts to link the volume of an animal's brain with the depth of its intelligence, scientists now propose that it's the complexity of connections between brain cells that matters most...
Whales, with brains that weigh up to 20 pounds and have more than 200 billion neurons, are no smarter than people, with our measly 3-pound brains that have just 85 billion neurons. Instead of contributing intelligence, big brains might just help support bigger bodies, which have larger muscles to coordinate [Larger muscles aren't significant, see large herbivore dinosaurs with tiny brains] and more sensory information coming in.
An islanded goat evolved coldbloodedness and delayed life span and small brain/eyes:
Some animals stranded on resource-poor islands shrink size and develop lethargic metabolism while absorbing sunlight (Galapagos tortoises), others adapt to a shore-based lethargy & active aquatic lifestyle with large brain/eyes (seals, sea lions).
Discussion on baby crying relative to mother tongue:
Sports competition & aggression, instinct vs control
Brain and nerves slideshow at:
Hominid Brain to Body size: Encephalization Quotient, estimated diet
5.8 Homo sapiens - grain-meat-nut-fruit-herb/tuber-seafood-eater, boats, cooking
4.0 Homo erectus (late) - berry/nut-tuber-seafood-meat-eater, simple spears-axes
3.3 Homo erectus (early) - berry/nut/tuber-seafood-eater, sticks-pebbles
3.1 H/A habilis - mixed diet? -nut-fruit-invertebrate eater?
2.9 Australopithecus robustus - tuber-nut-berry-herb eater
2.0 Pan t. (chimpanzee) - fruit-honey-termite-meat-nut eater
1.7 Gorilla g. (gorilla) - herb-fruit-hydrocharis eater