Did Neurons Evolve Twice?
quantamagazine.org
quantamagazine.org
In a country where more than 50% of the population thinks that evolution is bullshit, it doesn't help to try to phrase scientific disagreements to make it sound like it is some fundamental problem being argued about, instead of the placement of one phylogenetic branch.
Now, the science itself is interesting. The DNA sequencing is quite weak evidence, from what I can see (its been 20 years since I did my PhD, though), but the radical difference in biochemistry is a good sign that, if they didn't evolve twice from scratch, at least the common ancestor probably used the cells that later became neurons in a fundamentally different way.
I am clueless about the identity of the demographic that holds this deeply entrenched idea, other than the vaguely labelled 'breathtakingly bewildered'.
When you say 'in a country where more than 50%' ... are you referring to the country that you're currently in, or the one I'm in, or the one where you assume most people who are reading this article are in, by the way?
The opposing side is known as "Creationists." They like to characterize scientifically informed people as "Evolutionists" but of course that's more misinformation. One of the various tracks of Creationist argumentation is that scientists make the "unjustified assumption that change progresses at a more-or-less constant rate" or, "that the rate of change today is the same as the rate of change way back when." They like to claim we can't know the decay rate of radioactive carbon (carbon dating, y'know) was the same a few thousand years ago (when the Earth was created) as it is today.
I mention all this because this red herring about steady evolutionary progress is one of the arguments of Creationists, and so it's annoying to see those words used in that context in a science-y article.
My inner devil's advocate wants to say that the writer meant that that idea is deeply entrenched in the general public's view of evolution, but that is very difficult to argue given the tone of the rest of the article.
Back in my undergrad days (at a small state university), during one of the very first lectures in Biology, the professor really hammered the idea that evolution is not worse -> better or simple -> complex, but rather is governed by fitness, which constantly changes with the environment (so what's really awesome and complex might wind up being very maladaptive when circumstances change). She also made the point, through several counterexamples, that humans are not the pinnacle of evolution, which strangely seemed to offend some students.
At any rate, I kind of assumed that this was standard knowledge in the scientific community if it was being taught in freshman Bio at my modest school.
I don't get this argument at all. It seems obvious that most of the time an organism gains a property it immediately dies (or fails to pass it to its offspring). They have lots of tries, they're not special.
So: "Common ancestor" my arse. They insist on drawing these diagrams as trees when they are much more complicated graphs.
The question is, do all currently living creatures with neurons trace back to a common ancestor who also had neurons, or are there several neuron-having lineages alive today, each of which traces back to a different earliest-neuron-having ancestor. In the latter case, each of those neuron-having ancestors would have shared a common ancestor, but one that did not have neurons.
The lineage of all life on earth certainly creates a more complicated graph than a tree, but at the time scale needed to create a novel feature like neurons, it certainly looks like a tree. To say otherwise, you'd have to point to a case where genetic information passed laterally between species, rather than vertically from parent to child. This probably has happened [1], but is not so common as to make all tree-shaped charts misleading.
However, it doesn't change the fact that, when viewed from 10,000 feet, the tree of life looks more like a tree than a web. Especially with regards to the question "did neurons evolve twice," very little is lost by ignoring that sometimes cousins marry, and sometimes a virus leaves a chunk of genetic material in its host.
Because they are so complicated, they are unlikely
to have evolved twice.
Of course that doesn't mean those processes wouldn't produce a completely different organism on another world, but chances are this organism would have to solve similar problems as the ones here on Earth. The need to process information and react to it in some way is not unique to our world in any way.
> So if neurons did evolve twice
Looking at all the systems organisms are using to carry information (not just neurons, but all kinds of chemical signaling) suggests that these systems perform a very basic and ubiquitous role in all ecosystems. Even if the assertion about neurons was true (which it most certainly isn't), claiming all of our biological information-passing systems as special and "unlikely to evolve twice" is stretching an implausible proposition even further.
> it is unlikely they are the Great Filter
It's unlikely anything within biology is the Great Filter, but the thing at the beginning of biology might be a candidate: it's unclear how probable the formation of a simple cell from non-biological material is. My personal hunch is that the Great Filter might really be a combination of factors, both local to us and global, and abiogenesis _might_ be one of those that globally lower the odds for life significantly.
Are you sure? We don't burn iron, we concentrate it on the surface. Ruined cities would be more concentrated ore sources than any early mines could be.
Oil is harder, but you can make biogas, so it will just mean higher fuel prices.
Yes, as for oil I was thinking more along the lines of being essential to produce machinery, and the problems when you end up walking up that chain all the way to the lowest common denominator, so to speak, or conversely the added costs which get added on top of each other. It would be a quite different world. I wonder what it would look like.
This reminds me of the beginning of the babel fish argument for the non-existence of god by Douglas Adams:
Now it is such a bizarrely improbable coincidence that anything so mindbogglingly useful could have evolved purely by chance ...
Neurons (or at least proto-neurons) are not extremely complicated, at least simple enough so that they can "do something" and then evolve.
(Not sure how/if they were able to evolve without anything to control like muscles or at least some motor mechanism, but even bacteria does that)