That might be stretching "external memories" a bit far, for hype's sake. Not that slime molds aren't fascinating, but what's with the hyperbolic word choices?
I suppose the fact that the information is being stored at the location it describes, instead of in a central location, makes it a bit weird?
"weird" is emotional response. I think that function is the appropriate criteria here. Functionally, it is serving as memory. There's no magic difference between inside the body and outside of it.
Richard Dawkins' The Extended Phenotype http://www.amazon.com/Extended-Phenotype-Reach-Popular-Scien... is a good read on this sort of stuff (it's a little bit more technical than his other books, but still readable by someone without a biology background).
Similarly, many plants "lean" to point towards the sun. Are they "remembering" where the sun is with the increased growth on the far side?
You can (successfully) argue that it can be an accurate description. It is. I would argue that it's deliberately choosing words that invoke more interest (be it scientific or "OMGWHAT") than accuracy.
If they had put the sun there first, then yeah, that would be external memory. That's the difference.
Another option: (micro-)evolution. Is an amoeba's resistance to a chemical "memory", or an environment-selected random mutation? Again, technically it can be viewed as memory, but it's diluting the term so far as to make it a catch-all for any kind of information, ever, to get someone to click on a link.
Well, it's not being used later on to make decisions, is it?
I suppose I will go with that for my definition of memory: the agent makes a change to the state of the world (external) or to its own state (internal) and that change later affects its action.
Using that definition, my answer re the amoeba is yes.
I can see why it seems too broad. But I don't know a better definition. I suppose one could stipulate that consciousness is required. But I don't think that would be a standard position.
No, you have a point there. I missed that part. Though I just realized your new definition implies this: a river has memory.
To each their own :) I'll still call it too broad, but that's pure opinion.
Nice point... well, I'm all ears for a better definition :)
I doubt that most people would consider Hansel and Gretel's trail of breadcrumbs a form of 'external memory.'