Thursday, July 29, 2010

Survival of the Fittest?

My brother-in-law John recently sent me a very interesting book The Thin Bone Vault: The Origin of Human Intelligence.  It was published on the eve of Darwin’s 200th birthday last year by Frederick Menger, an Organic Chemistry professor of Emory University.  Menger’s lucid writing style helped me expand and update my extremely limited and superficial understanding of the fascinating but complex subject of evolution biology, a field that has been going through rapid advances in last few decades.  This though provoking book takes readers through just enough details and facts to confront one of the most challenging questions: how do modern humans, the only surviving homo sapiens, become so “smart” so quickly (in a matter of 10’s of thousands of years) after a less than impressive history of walking around naked on earth for few million years?  And has the widely accepted Darwin’s Natural Selection really provided a satisfactory framework in explaining how life and intelligence come to be?    

Creationists and supporters of Intelligent Design would be quick to reject the Evolution Theory and insisted that life and universe is created by a supernatural entity; a quick answer that could explain all the unexplainables.  Menger addressed this controversy early in his book.  I found his view pointed, objective, honest, and worth repeating here: “Science is theologically neutral; it depends upon observation and experimentation; and it accepts as little as possible on faith. Religion, on the other hand, is a system of belief; it is not amenable to experimental testing; it addresses issues of morality and values on which science has nothing to say. The two domains are time-honored but completely different. They are pursued for different reasons. They serve different functions.”

Below is what I have learned from reading Menger’s wonderful book.  Many of us are nodoubtedly familiar with the “classical” theory of evolution which was first presented systematically in Darwin’s 1859 landmark book The Origin of Species.  The concept of Natural Selection and the popular quote of “survival of the fittest” can be seen frequently today in many contexts.  Of course, contrary to the popular paraphrasing “survival of the fittest”, what really counts is the reproductive advantage not survival which is merely necessary.  Further, it does not suggest perfection and instead, “good enough” is more the rule rather than exception.  The fact is that Darwin’s natural selection however incomplete and imperfect it may be, remains the ONLY rational and uncontrovertible framework of evolution biology today.   By the way, Menger’s gave a succinct summary of the three premises upon which the concept of natural selection is based: 1)favorable traits in competitive environment are more likely to survive, reproduce and be passed on, 2)inheritable differences may take place randomly and spontaneously, 3)new species may appear after a very long time through graduate and minute changes.

Did Darwin’s natural selection close the book on evolution theory?  The answer is a definite “no”.  There have been continuing debates and enhancements on evolution theory by scientists although none has invalidated the theory.  As recent as earlier this month, there was a report on a research study that has identified more than 30 mutated genes of Tibetan people that allow them live more easily with the low oxygen Tibetan Plateau at an average altitude of 14,000ft.   The significance of the finding is at the rate of the evolution of these genes:  it took place within the last 150 generations when Tibetans migrated to Tibetan plateau about 3,000 years ago.  If it were due to random mutations alone, as one of the research leads Professor Rasmus Nielsen of UC Berkeley put it: "For such a very strong change, a lot of people would have had to die simply due to the fact that they had the wrong version of a gene."  This provides an encouraging evidence to support the idea of Directed Mutation by neo-Darwinism that “Natural selection tends to increase the frequency of those rare mutations or genetic changes that happen accidentally to impart survival or reproductive advantage to the organism.”

Mengers brought a more troubling open issue however that natural selection cannot explain how some complex traits came to be without any obvious and immediate use (such as survival like the Tibetans’).   Human intelligence – the unique and distinguishing feature of humans in the animal kingdom – is such an example.  Here is Menger’s one sentence summary of the current evolutionary dilemma: “ Natural selection is faced with the problem of explaining how a complex set of genes, controlling an expensive trait with no obvious benefit, came into permanent existence in such a short time period within every member of a small population (that was dispersed and geographically isolated over the entire planet) who had a low reproductive output and a low mutation rate."

By focusing on human intelligence, Menger tackles this central question of biology and stresses our understanding and imagination to the limit.  We therefore are forced to reexamine notions and validity of claims many of us have casually accepted and taken for granted.   How did the human intelligence come to be?  Why humans are so much smarter than other animals? Were ancient humans as smart as modern men?  If natural selection is the ONLY mechanism, how could one explain the incredible speed of the evolution of human brains?  How could human brain adapt to the environment so quickly and acquire new traits so effectively?  Could acquired traits be inherited by off-springs and if so, how?  The list goes on and on.  By the way, Menger did not want to get bogged down in defining what human intelligence is exactly.  I agree that Descartes’ short answer suffices for the purpose here – “I think, therefore I am

Physiologically, we now know that human is smarter and posses many higher functions because we have a much larger neocortex than any other mammals (note other animals don’t even have a neocortex although it does not suggest they don’t have any intelligence.).  Incidentally, neocortex is a soft, six-layered, 2 millimeter thick sheet of neural tissue (with about thirty billion nerve cells, or neurons) that makes up the outer layer of our cerebral hemispheres.  We also know that underneath the neocortex there is the primitive brain which is common to those of reptiles (the ancestor of mammals in evolutionary tree) that regulates blood pressure, sex, emotions, and movement. 

The most impressive power of our human brains is nevertheless the incredible flexibility and adaptivity that can absorb and adapt to environmental stimuli, including ones that we have never seen or countered before.  We still don’t fully understand how it works but we can consider an analogy with our obviously limited knowledge and vocabulary, as Menger suggested, that unlike other organs, brain is born like a rather sophisticated hardware that gets “programmed” and “reprogrammed” throughout embryologic and developmental stages by some mysterious “software” responding to cultural and environmental events and interactions.

Even more curiously, as brain is so capable of adapting, could acquired traits be passed onto future generations and if so, how?  Could Jean Baptiste de Lamarck (1774–1829), a brilliant amateur biologist and pioneer of evolution theory right before Darwin, be at least partially right when he suggested “inheritance of acquired traits”?

A little digression, genetics was born when the concept of genes was first suggested by Gregor Mendel (1822–1884).  In a short span of 150 years, we have learned a great deal of the secret of life and inheritance.   Geneticists now tell us that there are over 20,000 genes in the human genome and there are about one trillion nerve cells in the human brain with about 300 trillion connections (synapses). What we can observe about a trait, the so called phenotype, is the result of genotype, transmitted epigenetic factors, and non-hereditary environmental variation where the genotype of an organism is the inherited instructions it carries within its genetic code (from Wikipedia). 

To complete an alternative that supplements Darwin’s natural selection which has been successful in explaining the development of practical traits necessary for survival, Menger introduced the emerging theory of Epigenetic Evolution (epigenetic, simply means “over, above” the classical genetic that is based upon the precise DNA sequences and their mutations).  He used an example of “oncogenes”, mutated genes causing cancer.  It turns out that with mice, such tumor cells injected in early embryological stage and placed in uterus later grew into normal tissues. It thus suggests that genes can be turned on or off depending on epigenetic factors. To complete the detail, Menger offered a self-sustaining feedback process that could account for the evolution of human intelligence based on epigenetic model.

It certainly seems plausible and reasonable that even when gene itself remains the same, gene expressions, the process by which information from a gene is used to synthesize a functional protein and RNA, can be altered by environment factors. That is, some genes could be masked or turned on and off depending on other non-genetic factors.  It would certainly explain the rapid evolution of human brain as epigenetic influences can be propagated much faster through e.g. social learning, education, etc. It does also raise interesting questions such as, if a population can and would gain advantages over time by being more educated and motivated (or in opposite direction, "wasted”)?

This would also explain the difference of the mental capabilities between the chimpanzee, our close genetic relative, and human intelligence despite their 99% similarity in genomes.  It is also encouraging to know that there is also no reason to believe humans have reached their intellectual potentials, however you define and measure it.  Of course we have not ruled out possible moments of “enlightenment” 頓悟 somewhere and sometime in the universe, like what was depicted in the awesome 1968 movie 2001: A Space Odyssey by Stanley Kubrick & Arthur C. Clarke.   In the beginning of the movie, a group of apes discovered an odd black monolith and mysteriously realized afterwards that bones could be used as a tool and as a weapon to kill their fellow apes.  The rest is history, like what people like to say. 

Perhaps, just perhaps, starting with an innocuous event, another species suddenly commence a rapid evolution of their intelligence and ultimately contend with human intelligence.  Will “survival of the fittest” be back in play then?  Talk to you soon!

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