Working group project – the f_i term of the Drake equation: using the literature on the phenomenon of human intelligence to provide insight on the development of intelligence more generally.

 

Marc Bogonovich, 2009-05-22

 

This paper outlines a strategy for developing research questions and hypotheses. It assumes familiarity with the Drake equation, particularly the f_i term. The Wikipedia has an adequate introduction for this equation¹.

 

Background

            The f_i term of the Drake equation represents the likelihood of the development of intelligent life from non-intelligent life. Arguing that f_i  is low, Ward and Brownlee (2000) suggest that intelligent life is uncommon in the universe even if microbial life is common. Counterarguments often cite literature highlighting the importance of convergence in evolution (e.g. Conway Morris 1998) implying that intelligence is an attribute upon which lineages will converge.

            Research on the development of intelligence can be classified into two types. Those focusing on questions regarding the development of human intelligence (human intelligence phenomenon - HIP), and those with broader perspectives focusing on questions regarding the development of intelligence in general (general intelligence phenomenon - GIP). The majority of the literature addresses questions about the development of human intelligence. Such as, what are the causes of the initiation and development of intelligence in the human lineage 4-5 m.y.a to present?

            From an astrobiological perspective, while the human intelligence phenomenon is of interest, the f_i  term of the Drake equation actually hinges on answers to the more general phenomenon. As a metaphor, the development of the human lineage can be thought of as an australopithecine ringing the doorbell and entering a house. What then, causes any lineage to walk up to the door?

 

Project Overview

            I suggest a general strategy to systematically review the literature on the development of human intelligence. For each reviewed hypothesis we’ll assess if processes proffered for the development of human intelligence would be expected to operate as a more general process beyond the human lineage and its time frame. If so, how? As an analogy? Or more directly? What patterns can be found in the observations and theories on the development of human intelligence that will provide clues to the broader question inherent in the f_i term of the Drake equation? While the original f_i  term focuses on the development of intelligence after life's initiation, to narrow an already complex problem I'd like to focus on the development of intelligence after the development of multicellularity.

            There is good reason to believe that such a program could be useful. An older paper entitled, Exponential evolution: Implications for intelligent extraterrestrial life (Russell 1983), demonstrated a semi-log linear relationship between EQ (encephalization quotient – a body mass transformed estimate of brain size) and time from 540 million years ago to present ². Plotted were the most encephalized organisms on Earth at each time interval. This and other patterns presented in that paper suggest that the development of human intelligence is part of a more general process of greater encephalization over time. This paper is not well cited suggesting it has been largely overlooked (Cited 21 times, Google scholar search 2009-05-20).

 

Listed below are some of the hypotheses that exist for the development of human intelligence (HIP) that could be reviewed for their broader relevance to intelligence (GIP).

 

1) Auto-catalysis or Positive feedback: This hypothesis suggests that human intelligence developed in response to its own increasing social complexity, sexual selection, and other similar factors (Wilson 1975). In other words the human lineage developed intelligence exponentially because of feedback internally within our own lineage.

2) r-K selection: Humans are simply a species resulting from high K type selection pressures of r-K selection theory.

3) The expensive tissue hypothesis: aka Brain/gut trade-off hypothesis (Aiello & Wheeler 1995). The evolution of human intelligence involved a trade-off between nervous tissue and gut tissue, thereby altering diet significantly. Can we expect similar patterns to develop in other lineages that develop human level intelligence? If so how would this alter the dependence of animal intelligence on advances in complexity in the primary trophic level?

4) Trophic facilitation: Human intelligence and particularly its current civilization are completely dependent on angiosperms or flowering plants particularly the Poaceae, Solonaceae, and Brassicaceae (Diamond 1997). If our civilization is dependent on angiosperms, a group which did not exist 130 million years ago (much less 540mya!), could intelligence have developed prior?

5) Triune brain theory: Human intelligence was possible largely because of several distinct brain structures only accumulated over a long period of time (think mammalian brain, reptilian brain, etc. Sagan 1977). While some authors consider this an antiquated notion, its usefulness may be by way of analogy, in accumulated brain structure or tissue differentiation either at the macro or cellular scale.

6) The random walk: The level of intelligence (and complexity) is a random walk, with a 'left wall' of simplicity and an open 'right wall'. So to speak, humans have just walked in the right direction. The data exists to address this hypothesis (quotation Frank Drake³, Chyba & Hand 2005), and some work has been done (e.g. Marino et al. 2004). Importantly, depending on the random walk’s parameters, it could produce either a predictable or unpredictable time frame for the development of intelligent life.

7) The contingent walk: similar to the random walk except that intelligence may have happened much earlier in life's development, much later, or it may not have happened at all (Gould 1989, Via 2001).

 

Questions

The basic questions on the development of intelligence unspecific to humans include the following.

 - Upon the development of multicellularity, could intelligence have developed at any time, or has the likelihood of a species developing human level intelligence increased over time? Why?

 - Why and how did the human lineage develop at the time it did? Could, and what was the likelihood another lineage developed intelligence earlier? Later?

 - Presumably, intelligent life could not have developed immediately at the start of the Phanerozoic, was there a necessary incubation period, if so how long and why?

 - Are the changes in encephalization (or complexity?) within lineages indicative of a random walk over time or do many lineages show a directional trend ³ ?

 - If the above pattern is indicative of random walks, are the changes nonetheless constant enough such that the onset of particular encephalization levels within a biota is predictable?

While some of these questions have been addressed, many remain open.

 

Below are examples of more specific kinds of questions.

 - Are there any parallels in the development of plants, to the development of intelligence in animals? Or is the development of Angiosperms and fruit simply more facilitative of the development of animal intelligence rather than analogous? Or both (facilitative and analogous)?

 - Do plants have a role in the development of intelligence on Earth? Would any relationship be particular to this planet or generalizable to any primary producer, regardless of the energy source?

(obviously I like plants, but they are objectively essential for our life)

 - r-K theory posits a set of correlated traits including brain size. Has this relationship existed throughout the Phanerozoic and could it provide clues to address the basic questions regarding the likelihood of a highly intelligent species as time progressed.

 - The expensive tissue hypothesis posits a trade-off between tissue of the gut and nervous tissue within our lineage. Would similar phenomena be expected in any lineage developing intelligence? How relevant is the trade-off to organisms not at the level of intelligence of humans or our direct ancestors?

 

It will be difficult to know beforehand whether what we learn about the development of life on Earth can be extrapolated to other systems, because the ability to extrapolate will depend on the nature of the answers we get to the above questions.

 

Notes

1. http://en.wikipedia.org/wiki/Drake_equation

2. While brain size only moderately correlates with intelligence intra-specifically, an empirical relationship between EQ or brain size and learning ability and intelligence is well documented between species (Sol et al. 2008).

3. The following is a quote from Frank Drake from the Astrobiology magazine article, Is Intelligence a Biological Imperative? Aug. 26^th 2003.

http:/www.astrobio.net/news/article640.html

As I mentioned, one of the most controversial factors is f_i, the possibility of intelligence evolving, the fraction of biotas that have an intelligent species. And there is a research opportunity that has just never been carried out, because the resources haven't been available. And that is to do a much more thorough study of the fossil record to determine the real mathematically quantified path of brain evolution.

 

References

L. C. Aiello, Wheeler, P. 1995. The expensive-tissue hypothesis. The brain and digestive system in human and primate evolution. Current Anthropology 36 (2): 199-221

D. Brownlee, Ward, P. D. 2000. Rare Earth: Why Complex Life is Uncommon in the Universe. Copernicus, New York.

C. F. Chyba, Hand K. P. 2005. Astrobiology: the study of the living universe. Annu. Rev. Astron. Astrophys. 43:31–74

S. Conway Morris 1998. The Crucible of Creation. The Burgess Shale and the Rise of the Animals. Oxford University Press, Oxford.

J. M. Diamond 1997. Guns, Germs, and Steel: The Fates of Human Societies. Norton, New York.

S. J. Gould 1989. Wonderfull Life. The Burgess Shale and the Nature of History. Norton, New York.

H. J. Jerison. 1955. Brain to body ratios and the evolution of intelligence. Science 121: 447-449

L. Marino, McShea, D. W., Uhen, M. D. Origin and evolution of large brains in toothed whales. The Anatomical Record Part A. 281: 1247-1255

D. A. Russell 1983. Exponential evolution: Implications for intelligent extraterrestrial life. Advances in space research 3 (9): 95-103

C. Sagan 1977. The Dragons of Eden: Speculations on the Evolution of Human Intelligence. Random House, New York.

D. Sol, Bacher, S., Reader, S. M., Lefebvre, L. 2008. Brain size predicts the success of mammal species introduced into novel environments. American Naturalist 172: s63-s71

P. Ulmschneider 2006. Intelligent Life in the Universe. Principles and Requirements Behind its Emergence. Adv. Astrobiol. Biogeophys. 2^nd Edition. Springer, Berlin, Heidelberg.

S. Via 2001. Are we alone? Lessons from the evolution of life on Earth. Annals of the New York Academy of Sciences 950: 225-240

E. O. Wilson 1975. Sociobiology: The New Synthesis. Harvard University Press, Cambridge.