I had always taken evolution more or less for granted. The
evidence in support of it is pretty overwhelming, and the remaining gaps in the
theory are pretty small. But when I took a biophysics class about 15 years ago
and learned about the incredible complexity of the nervous system, I was taken
aback. It’s easy to think about the evolution of something like a wing, where
intermediate steps might lead to the ability to make longer jumps or glide
before flight is eventually possible. But our neurons require several ion
channels to send electrical impulses, and some of the steps towards even a
primitive nervous system offer no apparent benefit, making it difficult to
understand how they could have evolved. Eventually I had to accept that this
was a mystery that we couldn’t answer yet.
While it’s not yet entirely clear what the value of some of
the early steps towards a functioning nervous system was, there has been some recent
research that shows how it evolved. Voltage-gated sodium channels (a key
component of what allows a neuron to generate an electrical impulse) have
recently been found to exist in early organisms before neurons existed (http://www.pnas.org/content/109/suppl.1/10619.abstract).
There has also been work showing how some of the proteins used in neurons also
were developed before neurons (http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000506).
It can be tempting to avoid thinking about gaps in dominant
scientific theories (whether unexplained steps in evolution, the inability of
the standard model in particle physics to explain gravity, remaining areas of
uncertainty in climate change modeling, etc.). But I love keeping an eye open
for new research into topics that I remain unsatisfied by. I’m encouraged that
while we’re still not entirely clear why
these early components of neurons spread, we at least have evidence showing how the neuron evolved.
