What Makes Humans Different From Animals? - The Dodo
The Human Difference: How Humans are Unique …
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.
SparkNotes: The Crucible: Context
But the branch of the that readers might find most interesting led to humans. Humans are in the phylum, and the last common ancestor that founded the Chordata phylum is still a mystery and understandably a source of controversy. Was our ancestor a ? A ? Peter Ward made the case, as have others for a long time, that it was the sea squirt, also called a tunicate, which in its larval stage resembles a fish. The nerve cord in most bilaterally symmetric animals runs below the belly, not above it, and a sea squirt that never grew up may have been our direct ancestor. Adult tunicates are also highly adapted to extracting oxygen from water, even too much so, with only about 10% of today’s available oxygen extracted in tunicate respiration. It may mean that tunicates adapted to low oxygen conditions early on. Ward’s respiration hypothesis, which makes the case that adapting to low oxygen conditions was an evolutionary spur for animals, will repeatedly reappear in this essay, as will . Ward’s hypothesis may be proven wrong or will not have the key influence that he attributes to it, but it also has plenty going for it. The idea that fluctuating oxygen levels impacted animal evolution has been gaining support in recent years, particularly in light of recent reconstructions of oxygen levels in the eon of complex life, called and , which have yielded broadly similar results, but their variances mean that much more work needs to be performed before on the can be done, if it ever can be. Ward’s basic hypotheses is that when oxygen levels are high, ecosystems are diverse and life is an easy proposition; when oxygen levels are low, animals adapted to high oxygen levels go extinct and the survivors are adapted to low oxygen with body plan changes, and their adaptations helped them dominate after the extinctions. The has a pretty wide range of potential error, particularly in the early years, and it also tracked atmospheric carbon dioxide levels. The challenges to the validity of a model based on data with such a wide range of error are understandable. But some broad trends are unmistakable, as it is with other models, some of which are generally declining carbon dioxide levels, some huge oxygen spikes, and the generally relationship between oxygen and carbon dioxide levels, which a geochemist would expect. The high carbon dioxide level during the Cambrian, of at least 4,000 PPM (the "RCO2" in the below graphic is a ratio of the calculated CO2 levels to today's levels), is what scientists think made the times so hot. (Permission: Peter Ward, June 2014)