[bkfunk]

Once I started learning more about biology, I realized that everything is just so complex. The body repurposes chemicals a lot, so you have things like serotonin being a key neurotransmitter in the brain, but also in the gut. And you have enzymes that are coded in genes, but then there are also networks of genes that are up- or down- regulated by hundreds of other genes, and sometimes only in certain types of cells or certain physiological environments. And then of course there are epigenetic and immune-modulated effects at the genome, gene network, and individual gene levels. Not to even mention all the feedback mechanisms and meta-feedback mechanisms (the drive toward homeostasis is POWERFUL), and effects of countless chemicals in our environment.

There are certainly clear-cut cause-effect relationships in biological systems, but even they will have edge cases and random chance to muddle the picture.

I would posit that the human body is far more complex than even the largest codebase, not least because it was jury-rigged together with no architect or style guide.

Also, in general, the more common the exposure, the harder it is to find a link; try finding a control group of people who have never been exposed to PTFEs, or HSV, and who also aren’t like hunter gatherers.

[senkora]

My favorite way of describing biology comes from another HN comment:

> It’s more like a vibrating causal cloud than a chain of causality.

https://news.ycombinator.com/item?id=38898335

[inciampati]

The problem is simply observational. We don't even have reliable DNA and RNA sequencing of our own bodies. And we cannot reliably observe things in a host without knowing, to some extent, what we're looking for first. Even that space is so large, it's very hard to ascertain accurately. Biology is always suffering for lack of clear observations.

Also, adding complexity is the difficulty or even literal impossibility of observing the direct interactions of elements of the system, which operate at a quantum scale, that you would disturb and do disturb when attempting to observe.

[D-Coder]

"Everything in biology is more complicated than it looks."

DNA is where we get our physical attributes (modulo environment).

No, a lot of DNA is "junk," i.e. we don't yet understand what it does.

No, a lot of functional DNA is turned on or off by the epigenome.

No, a lot of our metabolism is affected by our biome — thousand of species of bacteria that turn up or down various reactions, or produce other chemicals that we need...