In Part I we have established that “good” and “evil” are relative and judged individually by our own personal and cultural values. Hence, we found that we need to come up with general values that transcend culture, time and species to approximate a definition of “goodness” that is as universal as humanly possible.
What I believe we can agree upon is that the smallest common denominator of all living beings is the pursuit of happiness and well-being . “Good” for us is what makes us and our loved ones happy, so one can argue that “best” ist what brings pleasantness to as many beings as possible. 
But we need to be careful with this. Happiness is relative, too, but most would agree that pain is a bad thing – after all it makes us unhappy, whether it is of physical or emotional nature. However, machine learning taught me that pain is a learning signal we need to embrace and follow to have a chance of succeeding in pretty much anything. Used properly, it can be a very good tool helping us to see and adapt to reality.
“Pain + Reflection = Progress”Ray Dalio 
This is why short-term gratification and avoidance of pain are rarely conducive to long term happiness  – they keep you from seeing what needs to be seen and from doing what needs to be done.
Moreover, it is dangerous to limit happiness to just one species or even just one single group of people. We cannot be ignorant of the fact that everyone and everything are interdependently linked to one another, especially in our futuristic globalized world. Viewing the whole picture from all angles you will realize: what is good for the whole is best for you, too. The short-sighted use of insecticides protects our harvest in the short term, but kills off the bees in the long run, ultimately starving us to death by a lack of pollination.  Only in a healthy ecosystem can any being flourish, to which it has to contribute its part.
This is why I’d like to suggest that “good” is that which serves life in its totality. The Victorian philosopher Herbert Spencer agreed, saying the best behavior is the one leading to the greatest length, breadth and completeness of life. 
“To be ‘good’ something must operate consistently with the laws of reality and contribute to the evolution of the whole. […] Reality optimizes for the whole – not for you.”Ray Dalio 
Still, we should not forget that there is no such thing as “good” or “evil” in an absolute sense – those remains human constructs dependent on perspective.
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 https://www.youtube.com/watch?v=FJcHN6wzViA, as of 2020-03-31
 Ray Dalio: Work & Life Principles, 2017
 https://www.pbs.org/newshour/science/loss-honey-bees-pollinators-mean-malnutrition-millions-around-world, as of 2020-03-31
 Will Durant: The Story of Philosophy, the Lives and Opinions of the Greater Philosophers, 1926
 Dalai Lama: Ehics for the new Millenium, 1999