Worms, promiscuous connections and autistic savants
If you’ve been reading my posts, you’ve probably figured out that this blog is motivated, to a large extent, by my fascination with what mathematics can help us see about the source, targets and bewildering range of human cognition. My expectations rest on the idea that what we have come to call the human mind is necessarily grounded in those same elements whose infinite combinations produce the entire fabric of the natural world. This is not to say that the human experience of transcendence is an illusion, but rather that we have yet to grasp the full expanse of nature.
A few things that I read today point to this idea from different directions. While the topics may seem unrelated, they are each pieces of a puzzle on which I’m always working. The first, a Scientific American report, caught my attention with its title: Worm Discovery Illuminates How Our Brains Might Have Evolved. The study looked at a particular worm, the acorn worm.
These unlovely, simple little worms live most of their brainless lives buried in deep-sea beds. Researchers have probed the genetic patterns of their developing larvae and think they might have discovered a set of signals similar to the ones we use to build our central nervous system. The findings are reported online in the same issue of Nature.
“The vertebrate brain is really exquisitely complex and elaborate,” says Ariel Pani, a graduate researcher at Stanford University and co-author of the new paper. The brain is prompted into being during development by a long chain of genetically determined signals. “There are particular developmental processes in vertebrates that seem to be absent in other species”—or at least those that have been most commonly studied, such as the amphioxus, Pani notes. Thus, many scientists had presumed that these genetic tools had only emerged with the vertebrate line itself.
But the new findings challenge this idea if genetic cues in embryonic worms resemble those responsible for setting off the major divisions of the central nervous system in vertebrates. In the worm, these genetic signals direct the development of the animal’s ectoderm, which contains sensory cells.
That would mean that the vertebrate brain “didn’t invent entirely new mechanisms—it took existing ones to develop a completely new structure,” Pani explains. If the genome is the proverbial set of blueprints for an organism, the signaling centers involved in embryonic development are like the early pieces of the scaffolds. “Vertebrates have that same sort of framework and are turning it into a very fancy Frank Lloyd Wright house, and hemichordates have turned it into a little cottage.”
But many in the research community are not convinced.
The researchers have found gene interactions that are involved in body patterning dividing their heads from their tails—and not much more, says Linda Holland, a research biologist at Scripps Institution of Oceanography who was not involved in the new research. “It’s not uncommon for an animal to have part of a gene network” without possessing the entire workup, she notes.
This report pointed me to a September 2009 special issue of Scientific American devoted to origins. It contained an article by Marc Hauser (professor of evolutionary biology a Harvard) concerned with the origin of the human mind. Hauser is concerned less with the building blocks and more with what distinguishes human cognition:
Researchers have found some of the building blocks of human cognition in other species. But these building blocks make up only the cement footprint of the skyscraper that is the human mind. The evolutionary origins of our cognitive abilities thus remain rather hazy.
But these building blocks are not ones like the signaling found in the worm. They are more the communication skills or the number sense we share with other creatures.
I think that one of the more important insights into human cognition described here is what Hauser calls promiscuous interfaces – the ability to make promiscuous connections between systems of understanding anchored in different brain regions. As an example, he describes the effect of recursive operations (a powerful fuel for many imagined things including mathematical ideas).
All creatures are endowed with recursive motor machinery as part of their standard operating equipment. To walk, they put one foot in front of the other, over and over again. To eat, they may grasp an object and bring it to the mouth repeatedly until the stomach sends the signal to stop. In animal minds, this recursive system is locked away in the motor regions of the brain, closed off to other brain areas. Its existence suggests that a critical step in acquiring our own distinctive brand of thinking was not the evolution of recursion as a novel form of computation but the release of recursion from its motor prison to other domains of thought.
Promiscuous interfaces are the living tissues on the bones of mathematics.
Finally, in a February posting on the blog Bering in Mind Jesse Bering writes on autistic savants. Here, I was most intrigued by the talents of autistic calendar calculators – individuals who could correctly identify the day of the week for any date you might give them.
After conducting a series of experiments meant to probe the techniques of perhaps the fastest living autistic-savant calendar calculator (a 21-year-old man named “Donny” with an IQ of 71 who tested at a 98 percent level accuracy in naming the weekday of any date between the year 1 and the year 9999, at speeds up to 700 ms), Marc Thioux and his colleagues from the Yale School of Medicine conclude that the starting point for such an awe-inspiring capacity is the autistic child’s preoccupation with numbers and dates, in combination with a penchant for repetition and ritual.
Bering explains that:
…a mathematician, on the other hand, might explain the formulae of perpetual calendars, such as the 28-year rule (the same calendars are shared by two years 28 years apart within the same century) and Pope Gregory’s exception to this rule, in which he declared in 1582 that century years are not leap years unless they’re divisible by 400.
Researchers argue that
…calendar calculation in autistic savants involves a mix of rote memory for previous dates and, eventually (at least for some, like Donny), an implicit understanding of the underlying algorithms driving the Gregorian calendar, such as the fact that if a non-leap year starts on a Sunday, the following year will begin on a Monday. (emphasis my own)
The worm, promiscuous connections, and calendar calculators are not topics that flow easily from one to the other, but they each trigger important questions about how, for example, thought is physical, or how the body creates its complex intellectual world, or what it means to have an implicit understanding of an underlying algorithm. There is wonder in the fact that the nervous system, as David Deutsch once remarked, has developed into a physical system that can build, with increasing precision, models of the whole of our physical reality. I’m convinced that the evolution of mathematical ideas can tell us something about the evolution of cognition.