Brain-signal proteins evolved before animals did | Hacker News Reader

Brain-signal proteins evolved before animals did

quantamagazine.org

108 pointstheafh10 comments

I always wonder about these evolutionary arguments where such and such a feature is discovered in a group of primordial precursor life forms so therefore that's when it originated.

Just to be contrary, is it not at all possible that such and such a feature "evolved" in all the relevant life forms at the same (more recent) time in response to changing external stimuli?

I remember being edified by an evolutionary biologist who stated that humans are not more "evolved" than single-celled organisms - both have been evolving for the same period of time. Both have just evolved into different niches at different levels of complexity. I hope I'm getting that right.

> discovered in a group of primordial precursor life forms so therefore that's when it originated.

It's a shorthand way of working with incomplete information. In many cases it's not possible to directly point to a concrete organism as a point of origin for a certain molecule. That's why we point to the earliest known implementation and shrug.

> Just to be contrary, is it not at all possible that such and such a feature "evolved" in all the relevant life forms at the same (more recent) time in response to changing external stimuli?

When a molecule is sufficiently complex and all other factors being equal, we tend to assume there was one common ancestor who first developed it.

It seems to me that Quanta is sometimes a bit biased towards the cosmic inevitability of intelligence, while carefully avoiding full-on Penrose mysticism. That's why the title is phrased as it is when in fact this discovery is congruous with current models.

Signal proteins evolving before the majority of systems they're currently used in is in fact well aligned with prior expectations. Once a way to synthesize a molecule has evolved, it can get re-used quite a lot for similar purposes. That's because evolution is a hill-climbing algorithm which is bad at coming up with complexity from the ground up but has no problem with complexity that has developed over extended periods.

> humans are not more "evolved" than single-celled organisms

Well, there is a directionality to evolution, and humans are way more complex than single-celled organisms. Biologists tend to avoid labels such as "more evolved" because they can be misleading and because obviously every organism around today is evolved to the same extent, namely to survive in current conditions.

> Just to be contrary, is it not at all possible that such and such a feature "evolved" in all the relevant life forms at the same (more recent) time in response to changing external stimuli?

Depends. Joints can independently evolve. Knees are unlikely.

In other words, nothing is impossible. A structure that performs any given function could evolve independently even if it looks different. The exact same structure or molecule? Unless it's one of the simplest 'solutions' to a problem, it's very unlikely without a common ancestor.

Even things that should have one solution - like eyes - can lead to many different structures. Like our "backwards" retina which is not shared with octopi.

The process you are describing is called "convergent evolution" [0].

[0] https://en.wikipedia.org/wiki/Convergent_evolution

The important question to answer for me though is whether they originated before or after muscle-like cells though. I'm a big of the saying "the brain is for moving" by, I think, Eric Kandel.

The text says "They point out that, based on their peptide sequences, both precursors are likely to be secreted molecules." How can they tell that from the sequence?

My bias, attempted a Molecular MS at Purdue.

Probably due to small weight and size as being near other known secreted moelcules.

Thanks a lot!, I though something similar but wasn't sure because while the neuropeptides are phoenixin and nesfatin the sequences are for the precursors SMIM20 and NUCB2 and maybe they could be a lot bigger although makes more sense if neuropeptides and precursors are close in size certainly.

Proteins that will be secreted have, usually at the beginning of their sequence, a signal motif (or “signal peptide”) that is recognized by the secretory machinery of the cell. The presence of the signal peptide in a protein can be predicted by computational methods such as SignalP (https://www.nature.com/articles/s41587-021-01156-3). That’s what the authors did in the paper.

Thanks a lot!, actually tried adding this on wikipedia (https://en.wikipedia.org/wiki/Evolution_of_nervous_systems#N...) because seemed important enough so I really looked at the paper and read about the signal peptide but clearly didn't understand it was the relevant element.

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