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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)

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So, consider this essay to be a very modest attempt to call your attention to somesimple ways by which you may contribute to the welfare of animals.

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I am aware that this essay barely scratches the surface on the issue ofabuse, enslavement and cruelty that is inflicted upon animals, worldwide. Ido not have the knowledge nor the means at this time to write a complete essayabout this most disturbing facet of human behavior. All I know is that asmembers of the human race, we are guilty of turning away from the horrors doneto animals either because of our lack of knowledge, denial (as in refusing toacknowledge such ugly reality), or because of our refusal to take action due toour selfish self-absorption with our own individual problems. Every bit ofcooperation and involvement counts. Gradually, we can take steps towards thebetterment of human treatment of animals, and maybe all of these horrific storiesof animal abuse that occur in our lifetime will one day be told to futuregenerations as tales about a civilization that used to exist which was comprisedof humans consumed by greed and capable of committing satanic acts of crueltyonto all other living species;whowere insensitive to the extent of engaging in the killing of animals and calledit a "sport".