In summary, becoming bipedal had great portent for evolving protohumans, and the suspicion is strong among scientists that it led to feedback loops in which tool use became advanced, which allowed for a richer diet, which helped lead to larger and more complex brains, which led to more advanced thinking and behaviors, which led to more advanced tools, which led to more acquired energy, better protection, and larger brains, and so it went. But the control of fire was a watershed event. Although better tools improved the viability of early humans, on Earth could challenge fire-wielding humans. With the control of fire, humans never had to worry again about being preyed on, nor as a threat to species viability, except by other humans. Naturally, fire was eventually used for offense instead of defense.
What is fire? That may seem too-elementary a question, but understanding what it is and where it came from is vitally important for understanding the human journey. The first fires were the quick release of stored sunlight energy that life forms, plants in that instance, had used to build themselves as they made their “decisions,” and it was from vegetation that recently died and was dry enough to burn. The energy was released from burning so fast that it became far hotter (because the molecules were violently "pushed" by the reaction that also released photons) than the biological process of making animals warm-blooded. Hot enough in fact that the released photons' (energetic enough) so that human eyes could see them, in a phenomenon called flames. Flames are visible side-effects of that intense energy release. The rapid movement of the molecules as they rocketed due to that great release of energy is the motion that powers the industrial age. Those rocketing molecules move pistons in automobile engines and , and are behind the damaging explosions of bombs and the propulsive explosions of rockets. For more than one million years, all human fires were made by burning vegetation, and wood in particular. What was fire doing? Energy stored by plants, trees in particular, was violently released by controlled fires for human-serving purposes of warmth, light, food preparation (to obtain more energy from food) and protection from predation, and it also became the heart of social gatherings. Humans have stared into fires for a million years or more.
What seems to explain invader and endemic success with those migrations is what kind of continent the invaders came from, what kind of continent they invaded, and the invasion route. Asia contains large arctic and tropical biomes, unlike any other continent. North America barely reaches the tropics and only a finger of South America reaches high latitudes, and well short of what would be called arctic latitudes in North America. Africa’s biomes were all tropical and near-tropical. The route to was straight across at the same latitude, so the biomes were similar. About the same is true of the route to Africa from Asia. Asian immigrants were not migrating to climates much different from what they left. But the route to North America was via , which was an Arctic route. Primates and other tropical animals could not migrate from Asia to North America via Beringia, and even fauna from temperate climates were not going to make that journey, not in Icehouse Earth conditions. Oligocene North America was geographically protected in ways that Oligocene Europe and Africa were not, and it already had substantial exchanges with Asia before and was a big continent with diverse biomes in its own right. It was not nearly as isolated as Africa, South America, and Australia were.
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.
Among herbivores, their mode of digestion was important. attained the , and elephants, rhinos, and horses have that digestive process. Cattle, camels, deer, giraffes, and many other herbivorous mammals are foregut fermenters and many are , which have four-chambered stomachs, while the others . While foregut fermenters are more energy efficient, hindgut fermenters can ingest more food. Hindgut fermenters gain an advantage when forage is of low quality. What they . There are drawbacks to that advantage, however, such as when there is not much forage or its quality is poor, such as dead vegetation. A cow, for instance, digests as much as 75% of the protein that it eats, while a horse digests around 25%. Live grass contains about four times the protein as dead grass. Cattle can subsist on the dead grass of droughts or hard winters and horses cannot, which was a tradeoff in pastoral societies.
are created by undisturbed organism remains that become saturated with various chemicals, which gradually replace the organic material with rock by . Few life forms ever become fossils but are instead consumed by other life. Rare dynamics lead to fossil formation, usually by anoxic conditions leading to undisturbed sediments that protect the evidence and fossilize it. Scientists estimate that only about 1%-2% of all species that ever existed have left behind fossils that have been recovered. Geological processes are continually creating new land, both on the continents and under the ocean. Seafloor strata do not provide much insight into life’s ancient past, particularly fossils, because the process in “mere” . The basic process is that, in the Atlantic and Pacific sea floors in particular, oceanic volcanic ridges spew out basalt and the plates flow toward the surrounding continents. When oceanic plates reach continental plates, the heavier (basaltic) oceanic plates are subducted below the lighter (granitic) continental plates. Parts of an oceanic plate were more than 100 mya and left behind plate fragments. On the continents, however, as they have floated on the heavier rocks, tectonic and erosional processes have not obliterated all ancient rocks and fossils. The oldest “indigenous” rocks yet found on Earth are . have been dated to 3.5 bya, and fossils of individual cyanobacteria have been dated to 1.5 bya. There are recent claims of finding . The oldest eukaryote fossils found so far are of . The first amoeba-like vase-shaped fossils date from about 750 mya, and there are recent claims of finding the first animal fossils in Namibia, of sponge-like creatures which are . Fossils from might be the first animal fossils, and some scientists think that animals may have first appeared about one bya. The first animals, or , probably descended from . The is a tail-like appendage that protists primarily used to move and it could also be used to create a current to capture food. Flagella were used to draw food into the first animals, which would have been sponge-like. When the first colonies developed in which unicellular organisms began to specialize and act in concert, animals were born, and it is currently thought that the evolution of animals probably only happened . In interpreting the fossil record, there are four general levels of confidence: inevitable conclusions (such as ichthyosaurs were marine reptiles), likely interpretations (ichthyosaurs appeared to give live birth instead of laying eggs), speculations (were ichthyosaurs warm-blooded?), and guesses (what color was an ichthyosaur?).
For this essay’s purposes, the most important ecological understanding is that the Sun provides all of earthly life’s energy, either (all except nuclear-powered electric lights driving photosynthesis in greenhouses, as that energy came from dead stars). Today’s hydrocarbon energy that powers our industrial world comes from captured sunlight. Exciting electrons with photon energy, then stripping off electrons and protons and using their electric potential to power biochemical reactions, is what makes Earth’s ecosystems possible. Too little energy, and reactions will not happen (such as ice ages, enzyme poisoning, the darkness of night, food shortages, and lack of key nutrients that support biological reactions), and too much (such as , ionizing radiation, temperatures too high for enzyme activity), and life is damaged or destroyed. The journey of life on Earth has primarily been about adapting to varying energy conditions and finding levels where life can survive. For the many hypotheses about those ancient events and what really happened, the answers are always primarily in energy terms, such as how it was obtained, how it was preserved, and how it was used. For life scientists, that is always the framework, and they devote themselves to discovering how the energy game was played.
To revisit the Neanderthal split from about 500 kya, stayed in West Asia and Africa. When evidence of came to light, some scientists placed the beginning of the at about 500 kya. Stone tools have recently been dated using , which works for stone tools heated by fires, and using . That method measures water absorption into the surface of obsidian tools. For dating artifacts before the appearance of behaviorally modern humans about 70-50 kya, will not work, but successful. Neanderthals dominated Europe and today’s Middle East while home was Africa, and they also ranged to Europe and West Asia. Whether existed for only a half-million years or a million is controversial today, but what is not very controversial is that it is probably the direct ancestor of both Neanderthals and , and the first members of our species appeared in Africa about 200 kya. There is evidence that other descendants of may have existed, and . It also could have been a Neanderthal descendant. As with the discovery of the “” of Flores Island, it will not be surprising if scientists find more species that branched off of those early human and protohuman lines and died out when behaviorally modern humans spread across Africa and Eurasia.
Growing the human brain was about more than energy. There is speculation that meat protein helped human evolutionary brain development, and there is also evidence that oils help. There are surely nutritional requirements besides calories, but calories comprise the vast majority of nutrition. About 80% of what is called human nutrition consists of calories. If animals can obtain enough energy, the other dietary constraints are usually minor issues.
However, all that scientists have determined so far for DNA's function is providing the “blueprint” for making proteins. Proteins have , and the science of studies the highly complex way that genes express themselves. DNA provides the foundation for life’s structures, and as with , the FOXP2 gene is highly conserved in humans, which means that it does not change. Similar to , those genes form the foundation of the biological structures built from them, and if the foundation is damaged, the resulting house will be defective. Epigenetics and other factors are important, but if the foundation is sufficiently flawed, the house may not stand at all.