We're just a vat of chemicals fighting each other

Genetics= nature, neural structures= nurture... Human brains aren't developed at birth, it takes a couple decades for the neutral structures to develope completely and it's everything going on around the person that decides how those structures get wired (nurture)

All human behavior can be explained by wanting a little treat

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A lot of factors influence behaviour. I highly recommend a book called Behave by Robert Sapolsky.