Except for New Guinean highlanders, initial European contact with all of those relict populations was universally disastrous, just as and elsewhere for centuries. Those initial contacts happened in anthropology’s early days, and studied the Andamans in the early 20th century, when they were tattered remnants of the people of a century earlier. The people were also devastated by European invasion. When the Dutch invaded what became South Africa, the Southern San were driven to extinction while the !Kung survived in the . Andamans, !Kung, and Aboriginal Australians all had/have strikingly similar religious ceremonies, which were marathon singing and dancing sessions that could last all night. Some rituals lasted for months. Their rituals are very likely what the first religions looked like, which were strenuous ordeals in which people reached frenzied states that left them exhausted. Today’s leading hypothesis is that those rituals created group cohesion that held their society together. The social glue of monkey and ape societies is grooming, but humans seem to have , and those early rituals further cemented the bonds.
What human-agency skeptics have ignored or argued around are unique features of the megafauna that went extinct the humans that preyed on them, while they examined minutia. ever before humans arrived. As , African elephants help create the biomes they live in, as terraforming agents. They were far from idle browsers and grazers, but had outsized impacts on the vegetation, soils, and geological features such as water holes. Dinosaurs may have had similar biome impacts, and it was probably a feature of that large herbivore guild. Scientists have been finding plenty of evidence that vegetation changes that human-agency skeptics attribute to climate change may well be largely the of the guild’s disappearance, not a cause. Researchers in Africa have also discovered that changes wrought by elephants created biomes dependent on elephant management. When elephants disappeared, so did the biomes that they created, which is why smaller species could also disappear when the large herbivore guild vanished. Although Australia was the only non-Antarctic continent without proboscideans 50 kya, and its guilds were comprised of somewhat smaller animals, probably reflecting inherent differences between placental and marsupial mammals, Australia's large herbivores probably had similar biome impacts.
show that some animals were mobile before the Cambrian Explosion. Sponges were probably the but they were immobile except for their flagella drawing water through them, which carried food and oxygen in and waste out. The first creatures that we would recognize as animals were probably worms crawling atop ocean sediments. As lowly as the worm might seem, it would have needed muscles, bilateral symmetry, a circulatory and digestive/excretory system, and a nervous system run by a brain; that distant ancestor probably possessed . Some early worms may have even had rudimentary eyes. And of possibly eonic importance, worms probably made the first poop. The evolution of may have been a seminal event in the organic carbon burial process. Sponges may have also been largely responsible for initially removing oceanic carbon, which helped increase atmospheric oxygen and helped ventilate the oceans. Until then, organic carbon from dead life forms would not have settled to the ocean floor, but would have floated in the water column and been recycled by other life forms. Although the hypothesis , feces sinking to the ocean floor may have been how life’s burial of carbon began, as well as robbing sulfate-reducing bacteria in the water column of their nutrients and thus enabling oceanic waters to remain oxygenated. Ediacaran fauna did not burrow into ocean sediments, but deep burrowing was characteristic of Cambrian sediments. There is debate today whether Cambrian burrowing was a of oxygenating the ocean floor.
Just as the aftermath of the appearance of complex life was uninteresting from a , as the amazingly diverse energy-generation strategies of archaea and bacteria were almost totally abandoned in favor of aerobic respiration, biological solutions to the problems that complex life presented were greatest during the Cambrian Explosion, and everything transpiring since then has been relatively insignificant. Animals would never see that level of innovation again. While investigating those eonic changes, many scientists have realized that the dynamics of those times might have been quite different from today’s, as once again may be of limited use for explaining what happened. Also, scientists generally use a rule-of-thumb called , or parsimony, which states that with all else being equal, simpler theories are preferred. , a seminal theorist regarding the scientific method, as they were easier to falsify. However, this issue presents many problems, and in recent times, theories of or speciation have invoked numerous interacting dynamics. Einstein noted that the more elegant and impressive the math used to support a theory, the less likely the theory depicted reality. Occam’s Razor has also become an unfortunate dogma in various circles, particularly , in which the of materialism and establishment science are defended, and often quite irrationally. Simplicity and complexity have been seesawing over the course of scientific history as fundamental principles. The recent trend toward multidisciplinary syntheses has been generally making hypotheses more complex and difficult to test, although and ever-increasing and more precise data makes the task more feasible than ever, at least situations in which are not interfering.
works for animals that are no more than a couple of millimeters thick, but for larger animals a respiration system was necessary. The rise of the arthropods has been an enduring problem for paleobiologists. Why was the arthropod so successful, particularly in the beginning? Segmented animals dominated Cambrian seas, and segmentation provides for repeated features. Segments obviously became important for locomotion but, for arthropods, segmentation appears to have conferred the more important advantage of distributed oxygen absorption. Each trilobite leg had an attached gill, and leg motion constantly drew fresh oxygenated water over each gill. Arthropods never developed the kinds of lungs that vertebrates have, or the pump gills of fish and other aquatic animals. Early arthropods breathed by moving their legs. Peter Ward’s recent hypothesis is that segments were first used for respiration, to provide a large gill surface area, and using the segments for locomotion came later. For trilobites, the same functionality that pushed water over gills was also coopted for food intake. Also, the leg-mounted gill was necessary because of an arthropod’s body armor; oxygen could not be absorbed through tough exoskeletons.
The moon rocks retrieved by astronauts are still being tested, as new experiments and hypotheses are devised. In 2012, which resulted from testing moon rocks for the ratios (both are stable isotopes), and it has brought into question the hypothesis that the Moon was formed by a planetary collision more than four billion years ago. The titanium ratio was so much like Earth’s that a collision with Earth forming the Moon has been questioned (as very little of the hypothesized colliding body became part of the Moon). The collision hypothesis will probably survive, but it may be significantly different from today’s hypothesis. , as well as , and their ages confirm that geologists have derived, and meteorite dates provide more evidence that our .
Mass spectrometers have been invaluable for assigning dates to various rocks and sedimentary layers, as radioactive isotopes and their daughter isotopes are tested, including , , , and . Also, the ratios of elements in a sample can be determined, which can tell where it originated. Many hypotheses and theories have arisen, fallen, and been called into question or modified by the data derived from those increasingly sophisticated methods, and a few examples should suffice to give an idea of what is being discovered.
Another major advance happened in the late 20th century: the ability to analyze DNA. was discovered in 1953. In 1973, . In 2003, . was accomplished in 2005, for orangutans in 2011, and for in 2012. The comparisons of human and great ape DNA have yielded many insights, but the science of DNA analysis is still young. What has yielded far more immediately relevant information has been studying human DNA. The have been identified. Hundreds of falsely convicted Americans have been released from prison, and nearly 20 from , due to Human DNA testing has provided startling insights into humanity's past. For instance, in Europe it appears that after the ice sheets receded 16,000 to 13,000 years ago, , and for all the bloody history of Europe over the millennia since then, there have not really been mass population replacements in Europe by invasion, migration, genocide, and the like. Europeans just endlessly fought each other and honed the talents that helped them conquer humanity. There were , but other than hunter-gatherers being displaced or absorbed by the more numerous agriculturalists, there do not appear to be many population replacements. In 2010, suggested that male farmers from the Fertile Crescent founded the paternal line for most European men as they mated with the local women. DNA testing has demonstrated that all of today’s humans are , of whom a few hundred and conquered Earth. The , as well as genomes of other extinct species, and for a brief, exuberant moment, some scientists thought that , -style. Although dinosaur DNA is unrecoverable, organic dinosaur remains been recovered, and even some proteins have been sequenced, which probably no scientist believed possible in the 1980s.
Those interrelated and often mutually reinforcing lines of evidence have made many scientific findings difficult to deny. The ever-advancing scientific toolset, and the ingenuity of scientists developing and using them, and particularly the multidisciplinary approach that scientists and scholars are increasingly using, have made for radical changes in how we view the past. Those radical changes will not end any time soon, and what follows will certainly be modified by new discoveries and interpretations, but I have tried to stay largely within the prevailing findings, hypotheses, and theories, while also poking into the fringes and leading edges somewhat. Any mistakes in fact or interpretation in what follows are mine.
Scientific practice is ideally a process of theory and experimentation that can lead to new theories. There are three general aspects of today's scientific process, and it , which used to formulate his theory of evolution. First, facts are adduced. Facts are phenomena that everybody can agree on, ideally produced under controlled experimental conditions that can be reproduced by other experimenters. Hypotheses are then proposed to account for the facts by using inductive (also called ) logic. The hypotheses are usually concerned with how the universe works, whether it is star formation or evolution. If a hypothesis survives the fact-gathering process – often by predicting facts that later experiments verify – then the hypothesis may graduate to the status of a theory. Scientific theories ideally can be , which means that they can be proven erroneous. The principle of hypothesis and falsification is primarily what distinguishes science from other modes of inquiry.