As one of my manifestations of intellectual contrarianism, I like to collect historical examples of times when a largish group of scientists thought that a complicated theory was the best way to explain a set of facts, but then a more simple explanation turned out to be much better.
I especially like examples of this in neuroscience, where people are wont to postulate complicated theories about the way that we think.
There is perhaps no better example than the debate between the reticular theory of the nervous system and the neuron doctrine.
The reticular theory postulated a form of exceptionalism in the nervous system: that axons and dendrites seen on light microscopy were not attached to cells but were in fact a separate, non-cellular entity, forming their own protoplasmic network.
The neuron doctrine is, at least in hindsight, much simpler, postulating that axons and dendrites are extensions of cells, as occurs in other types of biology.
The reticular theory had many proponents, including Camillo Golgi and Franz Nissl, and lasted from 1840-1935. It’s easy to dismiss it now, but it was a reasonable idea at the time.
Now, though, it’s an good example of how theories that postulate that the brain is extremely complicated and different than other types of biology do not have a good track record.