Myth 2: A Hypothesis is an Educated Guess
The definition of the term hypothesis has taken on an almost mantra- likelife of its own in science classes.
CORRECTION: Because science relies on observation and because the process of science is unfamiliar to many, it may seem as though scientists build knowledge directly through observation. Observation critical in science, but scientists often make about what those observations mean. Observations are part of a complex process that involves coming up with ideas about how the natural world works and seeing if observations back those explanations up. Learning about the inner workings of the natural world is less like reading a book and more like writing a non-fiction book trying out different ideas, rephrasing, running drafts by other people, and modifying text in order to present the clearest and most accurate explanations for what we observe in the natural world. To learn more about how scientific knowledge is built, visit our section .
Studies have shown that humans and chimpanzees have the same basal metabolism, so the first possibility is considered very unlikely in our ancestors, although large brains in general . The subject of reducing energy output has an intriguing hypothesis: bipedal motion allowed humans to move by using less energy than our pre-bipedal ancestors. Human bipedal locomotion requires only a quarter of the energy that chimpanzee locomotion does, and chimps use about a quarter of their metabolism walking, although whether this was a key evolutionary event is controversial. Even though protohumans would have taken advantage of bipedal walking to range farther than chimps (humans can average 11 miles a day, while chimps can only achieve six), thereby using a relatively larger proportion of their energy on locomotion; bipedal locomotion energy savings alone might largely account for the growing brain’s energy needs. was developed to account for the required energy, which proposed that energy to fuel the growing brain came from reducing digestion costs, which was initially provided by eating more meat.
Many traits of apes, including humans, are evident in monkeys. , which is when species have genders of different shapes and sizes, is a . But it is , especially apes, and is why men are larger and stronger than women. Its : how females choose their mates. A prominent hypothesis is that early monkey troupes had males as sentinels guarding the territorial perimeter and protecting the female-dominated core where offspring were cared for and where food was. A defensible food source was the key attribute of any simian territory. Most primates are , and extreme territorial behaviors can be seen in monkeys and apes, including murder, with its apotheosis in humans.
The study of intelligence is a young science, and the relationship of brain size (both absolute and relative) and structure to what is called intelligence is currently subject to a great deal of research and controversy, and even the is hotly debated. The appeared with mammals, and is the key structural aspect of brain evolution that led to human intelligence. The attempts to determine which , and those suspected of being the most intelligent have passed the test, including all great apes, cetaceans, elephants, and even a bird. Humans do not pass the mirror test until about 18 months of age. There is great debate between those embracing "rich" versus "lean" interpretations of behavior and intelligence observations among animals, in which seemingly complex thinking can be an illusion.
A has challenged The Expensive-Tissue Hypothesis, at least as far as robbing energy from the digestive system to fuel the brain. The study compared brain and intestinal size in mammals and found no strong correlation, but there was an inverse correlation between brain size and body fat. But since human fat does not impede our locomotion much, humans have combined both strategies for reducing the risk of starvation. Whales have bucked the trend, also because being fatter does not impede their locomotion and provides energy-conserving insulation. A human infant’s brain uses about 75% of its energy, and baby fat seems to be brain protection, so that it does not easily run out of fuel. However, the rapid evolutionary growth of an energy-demanding organ like the human brain seems unique or nearly so in the history of life on Earth, and comparative anatomy studies may have limited explanatory utility. There are great debates today on how fast the human brain grew, what coevolutionary constraints may have limited the brain’s development (, , ), and scientific investigations are in their early days.
The chimpanzee and human lines seem to have split , and some recent estimates are as low as 4.6 mya. The species perhaps the dates to about seven mya, but the findings have also been used to argue for pushing the . Whatever the timing that scientists eventually agree on, the splits of orangutans first, gorillas second, and chimpanzees last (and the bonobo split arguably about a million years ago) almost certainly will not change. The between 5.8 and 5.2 mya may have been the reason for the split, as the resulting droughts from those Mediterranean Sea drying episodes further shrank the African rainforest. As with so many other evolutionary events, the line that led to humans began to leave the trees as the losers of rainforest life and adapted to new environments probably out of necessity, not a sense of adventure and opportunity. Those apes pushed to the margins learned to walk upright and learned to eat new foods such as roots.
Around 10.5 mya, after Eurasian forests began thinning out, African rainforests began losing their continuity, broke up into isolated patches, and woodlands and grasslands appeared along rainforest edges. Whether the around 9-10 mya as the Miocene cooling progressed, or , is currently controversial. However, by seven mya the evolutionary line to humans was firmly established in Africa, as the forests that could support apes in near-African Eurasia disappeared, and the last of those lines went extinct about eight mya. The from the human line about seven mya, but . Whatever the timing really was, there is little scientific debate whether humans and gorillas descended from the same line and that that ancestor lived in Africa. The show that great ape DNA and human DNA are very similar. Chimpanzees and bonobos, our closest surviving cousins, share more than 98% of their genes with humans. About . in common with humans, and . Humans also that other great apes retained.
In the mid-Miocene cooling’s early stages, beginning about 14 mya, apes were richly spread across Eurasia and were adapted to the hardier diets that less-tropical biomes could provide, and one from Spain 13 mya . It largely lived on the ground and had a relatively upright posture. Its discovery threw previously accepted ideas of ape evolution into disarray. The idea of apes ancestral to humanity living beyond Africa is a recent one, but is gaining acceptance. Important new fossils are found with regularity, as with all areas of paleontology, but the most plentiful funding is for investigating human ancestry. A , with features common to both orangutans and African apes, led to questioning whether some key ape features are ancestral or . One early finding is still highly controversial as to where it fits into the evolutionary tree, as it had ape and monkey features but lived 10 million years after the hypothesized ape/monkey split. The great ape lineages are the subject of considerable controversy today, and the human ancestral tree is regularly shaken up with new findings.
Monkeys, apes, and humans have many traits in common, and one is that members of "out-groups" are fair game. Chimpanzees are the only non-human animals today that form ranked hunting parties, and they are also the only ones that form hunting parties to . Distinct from the killer ape hypothesis, which posits that humans are instinctually violent, the chimpanzee violence hypothesis proposes that chimps only engage in warfare when it makes economic sense: when the benefits of eliminating rivals outweigh the risks/costs. Macaque wars and revolutions appear spontaneously, but chimp wars have calculation behind them, which befits a chimp’s advanced cognitive abilities; they plan murderous raids and carry them out. It is quite probable that the advancing toolset of protohumans was used for coalitionary killing when perceived benefits exceeded assessed risks/costs. Just as with , these traits probably also existed in our last common ancestor. Other animals also engage in intra-species violence, which includes spiders when key resources are scarce and contested, and when ant colonies have power imbalances, they can trigger invasion and extermination by the larger colony. But human and chimpanzee warfare is uniquely organized and calculating.
Few people on Earth today have much understanding of the relationship between . Most people think that money runs the world, when it is only an accounting fiction. Money by itself is meaningless, and financial measures of economic activity can be highly misleading. I noted long ago that scientists had little respect for . that obscured the role of energy while exalting money. What a coincidence. Understanding this essay's first half will help with comprehending the last half, and the connections between energy, ecosystems, and economics should become clear.