Sunday, November 09, 2008

How the Leopard Changed It's Spots

How the Leopard Changed It's Spots has just introduced me to the word morphospace - "The conceptual array of all possible morphologies". This is a fantastic word for describing the design space of a procedural object. This means that you can say that "the morphospace of the stools is a strict subset of the morphospace of the chairs" with a straight face. Equally morphogen to mean a chemical that creates morphological changes...

On another tack HTLCIS makes an argument that genes just guide stable physical principles to form creatures**. That life is as much a product of natural("mathematical') patterns as the genes that guide it. I think this is slightly stating the obvious, evolution will tend to take the path of least resistance, and exploiting physical patterns is an expected trick. These physical patterns should be taken as part of the input to the evolutionary algorithm, just as much as the geographic environment of the creature.

When people build buildings, they use the most practical materials. Building a geodesic house of carbon fibre and titanium would put it in a different league to other houses, but would cost too much, be hard to design, and likely to have weaknesses we don't know about. So we stick with the thousand year old tradition of wood joists in a brick frame(our "stable maxima" in evolutionary terms) . "If genes where people and houses where cells..."

The point of the book is that just studying genes is hopeless, that understanding the paths of least resistance through the physical world ("stable physical maxima") is just as important.

But how did we settle on this set of physical patterns? are we using the complete set? or a subset defined by our environment? or our genes?

Growth and Form is going on about laws that govern at different scales in the universe (briefey mentioning sagging breasts as an example of gravity on a human scale). So at different scales different physical laws prevail. But similar geometric properties arise out of these systems at different scales - spirals etc.... Should i be looking at these different common geometric patterns and finding ways of combining them into a procedural framework? As last weeks post described, the distance-from-point partition of space (weighted Voronoi) is very common, perhaps there are others, or was that a one off common-pattern? (it's a fairly trivial property of space...). There are examples at slightly more abstract level, the legs on a table are (from a design perspective) similar to...erm...legs on a tetropod.

But we must be careful of going too far down this route. I have several books on my desk (from the Fine Arts floor of the library) about architectural theory, so far these have been descriptive rather than generative. That is they define a solution space rather than detailing how to build an actual house.

Perhaps we should be designing compuational systems in which the desired forms are stable and easily achievable. As an example, here is a complete accident that occurred while playing around with Phys2D for a side project. It is a version** of one of the bundled demos that I added a generator for three balls connected by springs (with the intention of later modelling simple cells), but note how with enough energy in the system these simple cells start joining up into chains - one ball stuck inside another cell. The was fantastic to see because it was an unintended form occurring in a complex system.

More fun from HTLCIS for my project is the idea that if genes are an undecipherable mess of information*, then the repeated physical patterns present an opportunity to understand biological life. Rather than try and evaluate the functions of genetic sequences, perhaps I should try and build a set of patterns that can build any animal with someany control mechanism standing in for genes.

Some of the chapters towards the end of the book present that argument that has always been my defn of evolution:-
phenomena that are good at existing continue to exist
so phenomena can mean:
  • parasite and the symbiote,
  • the brick
  • planets
good at existing can mean:
  • good at reproducing
  • being hard to destroy
and continues to exist can mean:
  • isn't destroyed
  • can replicate itself
  • is replicated by a symbiote (the brick)

* There are lots of fun stories of people trying to understand the output of computational evolutionary systems (section 5 here). Have you seen the size of biology textbooks? There's no way we can pretend to understand that.

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