Social Spiders have Bigger Brains--BECAUSE they are Social

Of the 50,000 species of spiders in the world, the vast majority are anything but social – even frequently eating prospective or actual mates. However, a handful live together comfortably in colonies...exploration of the differences between these spiders and their counterparts has shown parallels with the genes that make other social creatures.

One of the conditions for social animals is that they have a bigger brain size, said Professor Alexander Mikheyev [one of the authors]...Not only do they need to store information about the physical environment, but also the social one.

However, as Mikheyev noted, spiders don’t have brains, instead distributing their neurons throughout their bodies. In Nature Communications, Mikheyev and co-authors note social spiders’ nervous systems are more developed than those of their closest solitary counterparts.

https://www.iflscience.com/some-spiders-are-evolving-sociability-and-it-s-making-them-smarter-66380

Truly fascinating study. However the explanation of the observations, which may well be true, seems to be of the Kiplingesque "Just So Story" sort. Here is the original (open source) article in Nature

I have unhappiness with the apparent speciesism which I see as motivating the above assertion that spiders don't have brains. Is this really factually, correct?

When looking at anatomy, physiology and behavior many see everything only through the lens of human, primate, mammalian or vertebrate referents. I'm not a scientist, but my undergraduate degree was Zoology and I've continued that interest all my life. A quick interweb search turns up many references to spider brains.



The above graphic [which, as do many image links, doesn't seem to work here] is from a wonderful Australian site which states:

The structures that comprise the cellular masses of a spider's nervous system are almost entirely found in the cephalothorax with just a few relatively minor ganglia...in the abdomen. The piece of neurological tissue that serves as a spider's brain is the supraoesophageal ganglion which is positioned just above the digestive tract...most important function of this brain is to process sensory information, especially that from the eyes...a spider's brain does appear to have at least a small capacity to learn from past experiences...

I take the question of "does a spider have a brain" as more of a definitional demarcation, than as a clearcut PandaFact of reality.

Where is the line to be drawn between brain/not brain? The biological world is an evolutionary continuum so when did brainhood arise?

The European Molecular Biology Laboratory in a news piece https://phys.org/pdf555235760.pdf [which annoyingly autodownloads the PDF] on the evolution of the brain, mentions a (sadly paywalled Science) article] discussing neuroid cells and the presence of genes in sponges which code for synaptic transmission in other phyla of our shared Kingdom.

Some might argue this, together with the apparently demonstrated cell-cell communication, makes a case for sponges having a structure which functions as a brain. Such a claim is not made in either of the above references—nor do I advance such myself—but it does show how difficult it is to chop the world up into little pieces.

I do think many, if not most, zoologists accept that spiders have brains.

Further, this whole brain size finding thing brings to mind Mooney's The Republican Brain, leaving one wondering if this might also apply to people: Those who support a functional society versus those who do not?

Just saying...