Representation is a general process that occurs in many different ways. For example, in biology representation occurs between the information to build the animal and the physical manifestation of the animal itself: the genome of an animal represents its phenotype (Figure 3.1). In modeling with Evolvabots, representation occurs between the robot and its biological target: the robot is a representation of the target.
How does one thing represent another thing? This is a fundamental issue in cognitive science, artificial intelligence, and philosophy of the mind.[12] The most straightforward case that I can think of is when one thing is an instance of a category of things. A Tadro is an instance of an Evolvabot. As an instance, a specific Tadro represents the general category of Evolvabots. You can also flip this on its head: the category of Evolvabots represents, by definition, all instances of any kind of Evolvabot, including all the Tadros.
FIGURE 3.1. Representation in biology and in modeling with Evolvabots. In biology each animal is represented by its genome, the genetic instructions that interact over time with the environment to make the phenotype, the physical manifestation of the animal. In modeling with Evolvabots, an embodied or digital robot may represent a target, such as a vertebrate. In biology the representation is essential for development and replication of the animal. In modeling, the robotic representation is also an attempt to replicate something—in this case, particular aspects of the biological target.
We encounter this kind of categorical representation all the time when we learn. Someone shows us an example of something new to us. Hey, look at this thing called a chocolate donut! Look at it. Smell it. Feel it. Taste it. This particular donut, the donut master tells you, is one example of a whole category of foodstuffs called donuts. The category, “donuts,” includes other chocolate donuts that look and taste very much like this one, chocolate donuts that don’t look like this one (they have sprinkles) but taste similar, and donuts that neither look like this one nor taste like it either. As you can see and taste, the representation of all donuts by a chocolate donut is created in the human mind by linking the instance at hand (or is it at mouth?) with other imagined instances. The “linking” here refers to features of the donut—looks, smell, feel, and taste—that we can morph in our minds in order to create a new imaginary instance of a donut.
So if our minds do the linking between one thing and another, and this linking is the process by which we create representations, then our mind is doing the representing. Other minds, other engines of representation, are thus the judges of our efforts at representing. If no one else thinks that we’ve done a good job building an Evolvabot to represent a vertebrate, then we haven’t. More on judgment later.
To build scientifically useful Evolvabots, we need to use our minds and the minds of others to figure out, explicitly and objectively, how the Evolvabot represents an animal. Bloody obvious, eh? Maybe so. But keep in mind that we (meaning me and other nerds) often get so excited when we start to do cool stuff like build robots that we just start putting parts together, whatever’s at hand, in order to quickly build something that works. Although this can be an exciting way to start designing robots, the implicit intuitions that guide this kind of spontaneous creation can often miss the mark in terms of clearly representing the thing that we meant to represent. So before you get started: stop! Answer the six design questions![13]
We want to model the mother of all vertebrates—literally. We want the ancestor from whom all other vertebrates evolved. The only problem with this desire is that we don’t know exactly who that ancestor was or what exactly she looked like. The origins of vertebrates are shrouded in mystery (soundtrack: key low Celtic whistle). What to do?
This mystery drives crazy anyone who cares about deep evolutionary history: who were the first vertebrates, anyway? This simple question turns out to be controversial because the information that we use keeps being updated and revised. Damn those meddling scientists! We find new fossils, analyze new genes, and come up with different computer methods to reconstruct evolutionary relationships among species.[14]
Some of the newest information about vertebrate evolution when we were trying to answer this question had come from the laboratory of Frédéric Delsuc at Montreal University.[15] Delsuc and his colleagues examined 146 genes in forty species of living animals, using the similarity among the genes to cluster species into related groups. The group that clustered closest to the vertebrates was the tunicates and not a group called lancelets. This result was a surprise because adult lancelets look and behave like zippy little fish whereas some adult tunicates go by the name “sea squirt” because they are little grape-like balls attached to rocks at low tide who squirt water at finger-poking people (Figure 3.2).[16] In technical terms, any two species or groups of species that are more closely related to each other than they are to any other species or group of species are called “sister taxa,” where the term “taxa” is the plural form of “taxon,” which means any group of related organisms.
How can it be that a bag of water is the sister taxon to vertebrates? Even though adult tunicates are ugly bags of mostly water,[17] the pre-adult larvae of tunicates look like zippy little fish, sporting a sensor-filled front end and a long tail flexing with undulatory waves that push water backward and, by Newton’s third law, the larva forward. This resemblance of the larval form of tunicates to the adult form of fish has long been recognized. Walter Garstang, working in the first half of the twentieth century, proposed the then-radical idea that because the larvae of some species were more similar to the adults of others, we needed to consider the possibility that evolution might have worked by chopping off the adult stage to create new adult forms. In fact, back in 1928 Garstang proposed the idea that the larvae of ancient tunicates might have provided the basic vertebrate body plan—seventy-eight years before Delsuc’s molecular data suggested the same thing.[18]
FIGURE 3.2. Modeling the first vertebrates. Biologists use three different kinds of animals to infer what the first vertebrates might have been like. Sea squirts (three millimeters long as free-swimming larvae of the genus Botrylloides) and lancelets (about four millimeters long as free-swimming larvae of the genus Branchiostoma; twenty-two millimeters long as adults shown here) are living invertebrate members of the Phylum Chordata, the taxon that includes vertebrates. Haikouichthys is a fossil fish (about thirty millimeters long) from oceans 530 million years ago and are the earliest complete vertebrates of which we know. All three animals bear a muscular tail with a notochord for a skeleton. Sea squirts have one plan in mind: swim toward the light (positive phototaxis) and away from your parent, and then swim away from the light (negative phototaxis) and find a new place to live and turn into an adult. Images of sea squirts copyright © 2010 Matt McHenry. Interpretation of Haikouichthys based on fossil evidence (from Wikipedia Commons: Giant Blue Anteater grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.). Image of Branchiostoma licensed by Hans Hillewaert under the Creative Commons Attribution-Share Alike 2.5 Generic license.
12
For an in-depth examination of representation, see Tim Crane’s
13
In other words, make a plan. Once you have an explicit plan researched and written down—the answers to the six design questions are a good start—then keep in mind what General Dwight Eisenhower said: “In preparing for battle I’ve always found that plans are useless, but planning is indispensible.”
14
If you are interested, these issues are addressed in the fast-paced fields of phylogenetics, phylogenomics, and evolutionary developmental biology.
15
In the mid-naughties—2000s—the flux in our understanding of evolutionary relationships was widely recognized in college-level textbooks. For an excellent example, see Chapter 1 in Michael J. Benton,
16
Tunicates (also called ascidians and urochordates) are members of the Phylum Chordata, a group of related species that also contains vertebrates and lancelets. Lancelets, also called amphioxus (species name
17
The phrase “ugly bags of mostly water” was a first-contact description of humanoids uttered by a crystalline life-form in the
18
Walter Garstang, “The Morphology of the Tunicata, and Its Bearing on the Phylogeny of the Chordata,”