|posted 1 September 2003|
William H. Calvin, A Brief History of the Mind (Oxford University Press 2004), chapter 12. See also http://WilliamCalvin.com/BHM/ch12.htm
William H. Calvin
The Major Transitions in Evolution
adapted and expanded from those of
1. Bagging those replicating molecules inside a cell membrane.
2. Centralizing replicating molecules onto chromosomes.
3. The division of labor between DNA’s information storage and RNA’s construction activities.
4. A beyond-the-bacterium cell, the live-together-or-die-together eukaryote confederation of organelles.
5. Sex (Don’t leave variation to chance mutations: shuffle those genes with every generation).
6. Making various specialized cells from the same DNA.
7. From solitary cells to coexisting in groups (about a billion years ago).
8. From primate socialization to having protostructure and protolanguage abilities (perhaps a million years ago).
9. From unstructured short sentences to coherent higher intellectual functions (the transition to the modern mind was perhaps 50,000 years ago).
10. The superhuman transition. (Pending?)
What’s Sudden About the Mind’s Big Bang?
The moderns somehow got their act together
Major transitions don’t have to be fast, only profound. They are something like phase transitions (ice to water, water to steam) – revolutionary, not just evolution as usual.
Many of the past major transitions are about coming-together successes, rather like corporate mergers. Most happened more than a billion years ago. The last transition is usually stated as simply language or “the mind’s big bang.” I subdivide it, myself, into proto- and then the real thing; still, they are both in the last million years or so.
Protostructure and protolanguage probably developed slowly. Was the behaviorally modern transition from the proto version particularly quick?
Maybe speed doesn’t matter. The archaeologists still might show that it was really spread out in stages. And speed is sometimes merely in the eye of the beholder: if your unit of time is geologically slow, then something that takes a few million years (such as the demise of the dinosaurs) looks quick. Get data with better time resolution, and you may discover a gradual ramp or a series of events.
But speed does matter, should two processes be operating in parallel or in opposition. That’s because the faster one becomes what later processes build atop. Absolute speed might not matter, but relative speed often does. So of all the candidates for the last transition so far, which ones have the right stuff to be the quickest?
The first thing that I was taught by my high-school journalism teacher was to always cover, in the course of writing a story, the five W’s and the H: Who, what, when, where, why, and how. This brief history of the mind is a summary of all of them, but why and how are sometimes a little tricky, given our usual tendency to focus on one “cause” at a time and suppose that it is in opposition to other candidates. Or to assume that they are chained in sequence. (Of course, all might be needed, like the stones in an archway.)
Why and how are both about the process by which one thing turns into something else. How usually focuses on the here-and-now mechanics of the change, while why usually directs our attention to the setup phase and provides a rationale for things operating as they do now. Yet why questions are usually just how questions operating on a longer time scale, and focusing on whole populations rather than the individual.
Among anthropologists, the first why’s that come to mind are social. Increasing group size allows wider cooperation and occupational specializations – but they also challenge you to keep track of who-owes-what-to-whom. Gossip might become very important, a payoff for protolanguage. Animals that live in larger social groups have bigger brains.
A growing cultural toolkit, both vocabulary and staged toolmaking, can build combinations – but then you have to judge the coherence amidst more ambiguity. Just as the invention of money vastly expanded the barter economy, so researchers have suggested a similar expansion for social stuff that falls short of syntax itself. I agree they are reasonable, that such things could be like a common currency being invented. My question is whether something else got there first. (That’s often the issue in evolutionary arguments. There may be a number of reasonable candidates, things that ought to have been useful, but some are surely slow and no one can yet judge which is the fastest track.)
We now have a few how candidates for the mind’s big bang, things that operate on the neurophysiologist’s favorite time scale, the milliseconds-to-minutes span of thought and action:
And on a different level of explanation, that of the childhood development time scale’s how and the many-generations evolutionary why, we have an “EvoDevo” candidate for the first appearance of whichever the crucial one is, something capable of producing a runaway acceleration into the creative explosion:
Undoubtedly more candidates will be forthcoming on each time scale and at other levels of organization, but these five will do to illustrate the task of analyzing the how and why candidates for their contributions to the transition we call the mind’s big bang.
“Essential but not sufficient” probably operates here. They all may have been essential for being behaviorally modern but only one may have changed rapidly at the transition and finally made possible the flowering of the modern mind. The question is not when the last one was added to the archway but which has the growth curve that becomes steeper and steeper because things build on themselves.
A word about linear versus exponential growth. In linear growth, nothing changes the base on which the next round operates. If the truck factory’s annual output grows from 50 to 100 trucks in 25 years, there is nothing that says it will redouble in the next 25 years. If the trend continues, it may just go from 100 to 150 trucks annually – not redoubling to 200, because the existing trucks do not (we hope) beget more trucks.
But suppose that the average mother doubles her output of children surviving childhood from, say, two to four. If her girls are just as successful at parenting, there are eight children after another 25 years. And another redoubling to 16, and 32, and so on. When the next generation is some multiple of the present generation, it is called exponential growth over the generations. When the average mother has three children, as in Kenya today, the population doubles in about 23 years if the death rate and emigration do not change. You see the same exponential growth in epidemic disease spread: more active cases means even more people exposed in the next round. The incidence can keep doubling and redoubling every month until acquired immunity or isolation procedures slow down the growth rate.
There are a lot of things potentially involved with the expansion of the human mind. Some grow over time. But do they grow exponentially, because the base-on-which-to-grow itself increases in the next generation? Does success breed even more success?
So now let me ask which of the aforementioned candidates has the right stuff, an exponential growth curve that might look like a fast transition rather than like ordinary improvements:
A' The secondary use of ballistic movement planning circuitry for other things looks gradual to me. More types of use, on more and more occasions, and on longer and longer time scales – but maybe not a very steep growth curve. By itself (but see E’).
B' Making creativity “good enough” might indeed have a course of hidden improvements, where plans become more coherent but still aren’t safe enough to act on. But after they get good enough to pass this threshold, the growth looks like more and more things, more and more of the time.
C' Partitioning the cortex dynamically ought to look incremental.
D' There are threshold aspects to the ability of one cortical area to talk to another using error-correcting codes, avoiding the necessity of learning a special case for every concept to be communicated over long distances. This one looked pretty good to me when I wrote The Cerebral Code in 1996. But corticocortical codes could become more efficient, one pathway at a time. You’d just get better and better as more areas got the trick of making their pair of interconnections use error-correction features and a common code. Yes, it grows more steeply because of the two- and three-hop possibilities, but I still suspect that it builds on itself only at a moderate pace.
So none of the physiological-time-scale candidates has an obvious positive feedback that makes the growth curve get steeper and steeper over time. But the EvoDevo candidate looks to have great possibilities for explosive growth, since there is presumably a reservoir of capable but unexposed children just waiting for culture to bring structured examples to them early enough in childhood.
E' The more precocious children do better as adults and leave more variants around, some of which are even more precocious than they were. And so, over dozens of generations, even precocious two-year-olds might be successfully infected with syntax. Each mother speaking a structured language rather than protolanguage serves to “infect” a number of children growing up within hearing distance. And when they themselves have children…. You’d see an explosive growth, both locally and via lateral spread, in structured language users on the thousand-year time scale.
Precocious kids doing softwiring better, furthermore, serves as a good example of how cultural developments were likely essential – why one cannot make the usual false dichotomy between genes and culture. More culture selects for the genetically more precocious of the next generation.
Indeed, any gene changes might merely be in what promotes precocious acquisitiveness of words and their patterns. Behavior invents, anatomy follows via gene tweaks. But here the anatomy isn’t gross size (what we can measure in fossil skulls) but microscopic change affecting the plasticity of synapses between neurons. Nothing in this partial list of candidates suggests that a bigger brain might be needed for the final coming together of the committee.
Does this list of five candidates summarize how we got structured higher intellectual functions with on-the-fly creativity of quality? Is the rest of this story “just applications”? Or has this mental machinery also continued to evolve since it emerged in the middle of the most recent ice age? The story about how reading specializations are softwired into the brain shows how new cognitive tasks can achieve anatomical specializations during life. And my EvoDevo argument suggests how Darwin’s inheritance principle can gradually change acquisitiveness.
Not everything that culture invents will help softwire the brain in youth. But reading specializations certainly show that culture in childhood can sometimes build a more capable adult brain. It makes you wonder what the next round of educational improvements and cognitive challenges will do in softwiring the brain.
If language spreads like an infection, there is a useful distinction that the epidemiologists make that might help us think about the conservatism of what came before Homo sapiens sapiens.
Genes are not the only thing that a mother passes on to her offspring. The hepatitis B virus may be passed on as well. So-called vertical transmission is like inheritance in that you get it from your relatives. In horizontal transmission, you get it from unrelated persons.
Vertical transmission is slow. After all, it takes a whole generation’s time to pass it on. Things passed on this way, which include a number of cultural traits such as food preparation and the non-expert aspects of toolmaking, cannot change very rapidly. The history of toolmaking, from 2.6 million years down to 150,000 years ago, is one of conservatism and only occasional innovation.
In horizontal transmission, things can be copied, mimicked in an instant’s time. Because there are many copying errors, there will soon be a number of versions being practiced. Some will be better and will themselves be preferentially copied. Serious mimicry and real teaching make horizontal transmission of culture work even better.
Reciprocal altruism is a form of horizontal transmission that evolves atop those within-the-family forms of sharing. As Luca Cavalli-Sforza points out, sharing gets a big boost from language. (Even, I would add, from those short sentences of protolanguage.) It is expensive to share food – there are immediate costs to the giver – but sharing information is cheap. You might not want to share your knowledge of the best fishing hole, but telling someone about an ample resource – or relating who did what to whom in their absence – has little cost. When you can create long sentences without the protolanguage equivalent of an elaborate charade, information sharing gets a big boost.
The spread of culture can, of course, modify genes. For example, milk from grazing animals is a nice supplement to the diet but if the enzyme that helps digest milk works only up to the age of five or so, then this food source is useful only to young children. But there are variant genes that prolong this period of being able to digest milk. Those variants have become very common in northern Europe where reindeer milk was an important food source in winter. They have become common in some parts of Africa but not others, depending on the local cultural practices with regard to adults drinking milk.
The general principle, remember, is that behavior invents and adaptation via gene changes makes the invention more efficient. New form follows new function. Even if the invention of beyond-throwing structured stuff did not take new gene combinations, as in marching up that earlier-is-better curve, one would expect a series of subsequent genetic changes to make it more efficient.
Up-from-the-apes causes are numerous, and the five candidates for the 50,000-year transition that I have discussed were selected to show speed considerations.
But they are only the present foreground considerations, and there are background considerations that I have mentioned that would be another writer’s foreground. I am particularly impressed with adding teaching and enhancing mimicry as important aspects, and the role of beyond-the-apes attention – both joint attention and the addition of the hunter’s versatile attention span to the ape repertoire.
The “hundred” differences between apes and humans are all essential aspects of being human. They are not likely to line up in some chain of cause and effect. A web of push and pull is more likely, and attempts to identify the fast tracks must be viewed as only part of the explanatory attempt.
The River That
copyright ©2003 by William H. Calvin