Biology is the study of living organisms. Psychology is the study of the human mind and its functions. A mind is a part of an organism, not a discrete one itself. The study of the part is not the same thing as the study of the whole. Psychology is not biology. This is not a controversial thing, every person who has graduated college in the past 30 years should know this, besides it being illogical.

Your first sentence seems like it's conflating correlation with causation.

As for the second, saying psychology is ultimately biology is reductionist in a way that dismisses the context and environment biology gets expressed in. You would be a much different person if the same set of genes was born in a different place, or at a different time, or if your life circumstances were different in any mild way.

Seems a tad reductionist; by that same token, all of psychology is also physics.

I wouldn't go that far, but there are many studies that have looked at the genetic (biological) basis for brain function/behavior [0]. Once you're at the level of gene expression, which some of those studies go into, you're at a level of acetylation, methylation, etc., which is easily categorized as chemistry.

The bigger argument I get into with coworkers is the blurry line between brain function/behavior stuff and psychology.

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3030621/

> by that same token, all of psychology is also physics.

Yes, it is, which would be relevant if someone suggested there was no physical explanation for a psychological phenomenon (which is, in fact, what they are usually claiming when they claim it is not biological.)

Some people, pedantically, agree xD

https://xkcd.com/435/