Lamarckism Revisited

  The concept that traits acquired during an individual's lifetime can be passed on to offspring and therefore affect evolution—a theory most associated with the French scientist Jean-Baptiste Lamarck (1744-1829)—was relegated to the dust bin by the advent of Darwinism.  After Darwin, a new orthodoxy prevailed for more than a century.  In present-day terminology, it held that only traits already embedded in genes are passed on, and evolution occurs exclusively by natural selection of mutations in the genome.  Such mutations are purely random events, caused by errors in DNA transcription or by environmental factors.  Any suggestion of "directed" mutations—beneficial, nonrandom changes in the genome provoked by an organism in response to specific environmental challenges—was decried.  Further, the notion that changes in and inheritance of traits could occur through other than genetic means was anathema.

  That orthodox Darwinian viewpoint has been challenged in the past 30 years or so.  Modern studies have shown that directed, nonrandom genomic mutations can occur; that acquired non-genomic attributes can be inherited; and that both are subject to natural selection in the same way as are random genomic mutations.  These new insights and much else are discussed in a remarkable, but lengthy and hard-to-read book by Eva Jablonka and Marion J. Lamb, Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral and Symbolic Variation in the History of Life.

  I will skip over Jablonka-Lamb's first dimension, genetics, for it is the Darwinian dimension, with which I assume you are familiar.  The second dimension, epigenetics, is the most astounding to me.  It turns out that molecular "markers" can attach themselves to the genome as a result of environmental impact or stress.  They do not change the genome, but can turn genes on and off, thus changing the expression of an individual's genetic traits.  What is surprising is that these epigenetic factors can be passed on to offspring.

  The earliest-discovered and most common epigenetic marker is methylation of DNA.  Small methyl (CH₃) groups can become attached to bases in the DNA sequence because of environmental influences and stress, but they do not change the DNA other than by turning genes on or off.  Remarkably, the methylation remains in daughter cells after cell division.  Even more remarkably, when methylation affects sperm or egg cells, it is inherited by an embryo and thus passed on to the next generation.  To quote from Jablonka-Lamb:

"[B]ecause it provides an additional source of variation, evolution can occur through the epigenetic dimension of heredity even if nothing is happening in the genetic dimension.  But it means more than this.  Epigenetic variations are generated at a higher rate than genetic ones, especially in changed environmental conditions, and several epigenetic variations may occur at the same time.  Furthermore, they may not be blind to function, because changes in epigenetic marks probably occur preferentially on genes that are induced to be active by new conditions.  This does not mean that all induced changes are adaptive, but it does increase the chances that a variation will be beneficial.  The combination of these two properties—a high rate of generation and a good chance of being appropriate—means that adaptation through the selection of epigenetic variants may be quite rapid compared with adaptation through genetic change."

This one astonishing paragraph was to me worth the price of the book.

  Less compelling to me, but still impressive, are Jablonka and Lamb's asserted third and fourth dimensions of evolution—behavioral and symbolic.  If I understand these dimensions correctly, they overlap with and extend what the British evolutionary biologist Richard Dawkins called "memes"—an analog of genes.  Just as a gene carries information about biological traits, a meme carries information about socio-cultural ideas, symbols, and practices that are passed from generation to generation but not necessarily to direct offspring.  That many memes are acquired under the influence of the environment and unrelated individuals, and propagated by social interaction rather than genetics, doesn't sound extraordinary—we know that species, especially Homo sapiens, pass on a vast repertoire of behaviors derived from their environment and social groupings.  More startling, however, is evidence Jablonka and Lamb cite indicating that acquired memes may also be inherited through bio-chemical means; for example, a mother's particular food preferences have been shown to be reproduced in her offspring through placental affects on the fetus.  The important point Jablonka and Lamb make is that memes as well as genes are subject to evolutionary selection: those that are advantageous for survival will persist, those that aren't will vanish.

  The focus of the Jablonka-Lamb book is therefore on information transmission as the basis of evolution, not only the biological information of the genome and its epigenetic markers, but also the behavioral and symbolic information of cultures. 

"All four ways of transmitting information introduce, to different degrees and in different ways, instructive mechanisms into evolution.  All shape evolutionary change. …  As molecular biology uncovers more and more about epigenetic and genetic inheritance, and as behavioral studies show how much information is passed on to others by nongenetic means, evolutionary biologists will have to abandon their present concept of heredity, which was fashioned in the early days of genetics."

For those of us who have been raised in the pure-genetics tradition, this is a big gob to swallow.  We were taught to ignore Lamarck and to disdain the USSR's ideologically motivated Lysenko;  now, it seems, some of their ideas may turn out to have merit.

Eusociality

  Certain invertebrate species such as ants, in which individuals subordinate their own needs to those of the group, are said to be eusocial.  The term has also been applied more loosely to some vertebrate species, particularly Homo sapiens.  Unlike ants, though, humans act selfishly for their own survival and reproductive benefit as well as altruistically for the benefit of groups to which they belong.

  Eusociality is the thought-provoking subject of my book club's latest selection, The Social Conquest of Earth by E. O. Wilson of Harvard University.  Wilson is one of the world's leading biologists and probably its leading entomologist.  His lifelong study of eusociality in insect colonies led him to study it in humans, in order to explain how we came to dominate the biosphere.  In describing the difference between eusociality in ants and humans, Wilson wryly observed that "Karl Marx was right, socialism works, it is just that he had the wrong species."

  A warning before I proceed: Wilson is one of the originators and a strong proponent of a controversial sociobiological theory which asserts that eusociality is dependent on evolution of groups as groups, a level of evolution above that of individuals.  As did Darwin with ant and bee colonies, he sees the group as a macro-organism, subject to forces of natural selection.  It is a top-down theory, in which the group selectively chooses as members those who express a set of innate altruistic traits favoring the group's success in competition with other groups.  Wilson is an equally strong opponent of an alternative evolutionary theory called kin selection, a bottom-up theory, which posits that altruistic behavior in groups evolves only because individuals in the groups already share family genes, and accordingly at times act selflessly to assure the perpetuation of their genes in others if not in themselves. 

  The argument literally rages.  Evolutionists Jerry Coyne of the University of Chicago and Richard Dawkins of Oxford have unsparingly attacked Wilson [1,2].  In the remainder of this posting, however, I'll summarize some key points of Wilson's book as well as I can—it is not always easy for a layperson to follow.

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  The development of eusociality is quite rare.  Of the many millions of invertebrate species, only a score or so have independently achieved it, the remaining species competing largely at the level of individuals rather than groups.  (Think flies and ants.)  Among vertebrates, eusociality is even rarer, having occurred in just a handful of species, including Homo sapiens.  Its appearance in ants has led to their dominance over the insect world, in humans to their dominance over the world at large.

  What is amazing, Wilson maintains, is that eusociality has occurred at all, for the evolutionary maze that leads to it is so extensive and full of twists and dead ends, that for any species to wend its way through the maze is something of a miracle.  After all, eusociality must get its rudimentary start in a species where the rule is selfish natural selection at the individual level, and selflessness/altruism the exception.  Still, ants and their precursors negotiated the maze successfully over many millions of years, as did the line of hominins leading to Homo sapiens in a somewhat shorter time.  Wilson describes the process as involving a long sequence of small evolutionary pre-adaptations over hundreds of thousands to millions of years, leading to a tipping point where the random mutation of as little as a single gene in an individual could start the final conversion to full eusociality.

  Eusociality in humans is of course very far from the extreme of the genetically homogeneous, fixed-caste behavior of ants, yet goes much farther than the social behavior of other vertebrates.  A critical competitive advantage of humans vis-à-vis other vertebrates is that they build defensible, multigenerational, task-allocating cooperatives to which members may have no genetic kinship.  Each community, Wilson says, selects for inclusion individuals who express a desirable subset of altruistic behaviors, most of which were already deeply ensconced in the human genome at the time Homo sapiens emigrated from Africa some 60,000 years ago.  The chosen subset reflects the evolved culture of the group.

  The tension in mankind between the opposing forces of individual/selfish natural selection and group/selfless selection is complex.  Genetic evolution in the former arises from competition between members of a group, in the latter from competition between groups. The two types of competition point evolutionarily in opposite directions because one requires selfishness and the other altruism.  Homo sapiens maintains a tenuous balance between the two because of what Wilson calls the "iron rule": selfish individuals beat altruistic ones, yet groups of altruists beat groups of selfish individuals. 

  The relationship between genes and culture in eusocial groups is also a critical element in group evolution, Wilson asserts, and equally complex.  In building a culture, genes make available not just one trait as opposed to another, but patterns of traits that together define the culture.  The expression of multiple traits is plastic, allowing a society to choose an ensemble from many available combinations, the choices differing among societies.  Wilson contends that the degree of plasticity itself is subject to evolution by natural selection.  These concepts add another perspective to the nature/nurture question, very different, e.g., from one presented in a book by psychologist Bruce Hood that I discussed in my posting The Self.

   A final, quintessential point.  For Wilson, the indispensible requirement for the development of human eusociality—without which group selection could not have proceeded—is the primitively evolved instinct to form tribes.  He says that people feel they must belong to tribes for their existential sense of identity, security and well-being.  Eons ago they were small bands that hunted and gathered together, built encampments, and defended each other and their young.  Today, individuals join many interlocking tribes—city, country, religion, even sports teams—each commanding loyalty, communal effort, and competition with other tribes of the same genre.  In  this sense group evolution is bilateral: groups select individuals based on group needs, and individuals choose groups based on their own needs.

  As evidence that the tribal instinct is extremely deeply embedded in the species, Wilson cites a recent experiment showing that, when pictures of out-group people are flashed in front of experimental subjects, their amygdalas—their brains' centers of fear and anger—activate so quickly and subtly that the conscious centers of their brains are unaware of the response.  Other experiments revealed that even when experimenters created groups at random, inter-group prejudice quickly established itself, subjects always ranking the out-group below the in-group.

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  Many of the ideas in Wilson's book are indeed controversial, and at times I found them alternately too detailed or too sketchy.  Still, it is a feast for thought, which has forced me to reconsider some previous musings in this blog.

  First, the deep-seated need for tribal association undermines my conjecture in a recent posting, where I discussed tribalism/clannishness and what I called their antithesis, "anticlans."  I suggested that tribalism might be ready for obsolescence in our modern, globally hyper-connected society.  I was of course out of my depth, and therefore took to wild speculation.  I asked whether the modern obsessive inclusiveness of social-networking activities could lead to a widespread "we're all in it together" anticlan behavior, which over the long run could evolutionarily trump the exclusionary, "we vs. them" behavior of clans. 

  I think Wilson would answer my question with a definitive "No."  He spends just one paragraph of his 350-page book noting that the increasing interconnection of people worldwide through the internet and globalization weakens the relevance of ethnicity, locality, and nationhood as sources of identification.  Tribes may wax and wane and sources of tribal identification may shift, but Wilson would hold that tribalism itself will survive, overwhelming anticlan behavior just as it has always defeated less-tribal species.  Bummer.

  Second, the almost-impossibility of negotiating the evolutionary labyrinth to yield a species like Homo sapiens sheds further light on my posting on the search for extra-terrestrial intelligence (SETI).  In a catalog of obstacles to the success of SETI, I listed the rarity of a star having a planet capable of hosting life at all, much less an advanced civilization that was existent at a time when electromagnetic radiation from it might be detected by us now.  If Wilson is correct about the very remote possibility that Homo sapiens could have evolved on Earth, the odds against there being a similar one extraterrestrially are even larger than I thought.  Could we therefore be alone in the Galaxy, dare I say in the universe?  We'll probably never know.  Bummer again.

  I sometimes wish that newly developing scientific theories didn't get in the way of one's fondest hopes.