topics: |  brain | neuro-science | evolution

My review

Although Carl Sagan came to fame on
his work as a physicist, he is
perhaps better known as a Science
popularizer, the "billions and
billions" man of Cosmos.  However,
beyond explorations in cosmology and
the nature of the universe, he also
had interests in biology and the
evolution of intelligence (related to
his interest in whether such
intelligence could arise in other
parts of the universe).  He was also
a gifted writer, with an intuition
for organizing his thoughts in a way
that would make you sit up and think
(see the cosmic
calendar analogy below).  His
cogent account of how the brain
evolved, though dated, still remains
an exciting read covering the basics
even at the beginning of the 21st
century.

He is presenting a physicalist view
of mind, "the workings [of the brain - what we sometimes call 'mind' -
are a consequence of its anatomy and physiology and nothing more".  Harold
J. Morowitz comments on the Reductionist stance (excerpted in
The Mind's I):
   As a further demonstration of this train of thought, we note that Sagan's
   glossary does not contain the words mind, consciousness, perception,
   awareness, or thought, but rather deals with entries such as synapse,
   lobotomy, proteins, and electrodes.

This book is based on Jacob Bronowski Memorial Lecture in Natural
Philosophy which Sagan gave at the University of Toronto in 1975.

Introductory quotations

Mankind is poised midway between the gods and the - Plotinus

This extensive quote from Darwin's Descent of Man is worth re-quoting; it
illustrates a civilized man's difficulty with the hypothesis, while
going ahead with the hypothesis.

   I am aware that the conclusions arrived at in my work will be denounced
   by some as highly irreligious. The main conclusion, that man is
   descended from some lowly organized form, will, I regret to think, be
   highly distasteful to many. But there can hardly be a doubt that we are
   descended from barbarians. The astonishment which I felt on first seeing
   a party of naked wild hairy men on the shores of Terra del Fuego will
   never be forgotten by me, for the reflection at once rushed into my mind
   —such were our ancestors.

   These men were absolutely naked and bedaubed with paint, their long hair
   was tangled, their mouths frothed with excitement, and their expression
   was wild, startled, and distrustful. They possessed hardly any arts, and
   like wild animals lived on what they could catch; they had no
   government, and were merciless to every one not of their own small
   tribe. He who has seen a savage in his native land will not feel much
   shame, if forced to acknowledge that the blood of some more humble
   creature flows in his veins. For my own part I would as soon be
   descended from that heroic little monkey, who braved his dreaded enemy
   in order to save the life of his keeper, or from that old baboon, who
   descending from the mountains, carried away in triumph his young comrade
   from a crowd of astonished dogs - as from a savage who delights to
   torture his enemies, offers up bloody sacrifices, practises infanticide
   without remorse, treats his wives like slaves, knows no decency, and is
   haunted by the grossest superstitions.

   Man may he excused for feeling some pride at having risen, though not
   through his own exertions, to the very summit of the organic scale: and
   the fact of his having thus risen, instead of having been aboriginaIIy
   placed there, may give him hope for a still higher destiny in the
   distant future. But we are not here concerned with hopes or fears, only
   with the truth as far as our reason permits us to discover it; and I
   have given the evidence to the best of my ability. We must, however,
   acknowledge, as it seems to me, that man with all his noble qualities,
   with sympathy which feels for the most debased, with benevolence which
   extends not only to other men but to the humblest living creature, with
   his god-like intellect which has penetrated into the movements and
   constitution of the solar system - with all these exalted powers - Man
   still bears in his bodily frame the indelible stamp of his lowly origin.

Introduction

The introduction chapter pays homage to Jacob Bronowsky whose
Ascent of Man stands as a superb example of
science popularization.  Then Sagan unveils his thesis that the mind is a
mere "consequence of its anatomy and physiology and nothing more" - which
challenges thousands of years of dualist tradition both in the east and the
west.  The rest of the book attempts to justify this based on research
available then, many missing pieces of which are still being filled in.

==Chapter 1: The cosmic calendar==

The opening chapter Cosmic Calendar, poses a beautiful analogy of the process
of evolution, where the entire liftespan of the universe is compared to a
single year.  The analogy is indeed a thought provoking way of looking at
evolution, and although it is widely popular, it still holds considerable
punch for anyone seeing it for the first time.

Looking at the 15 bn year age of the universe as a single year, we find that
the first signs of life would come around September 25.  The first mammals
would show up on December 26, the first flowers on Dec 28, and man would have
made his appearance only on December 31 at 22:30 (10:30 pm), with little more
than an hour remaining on the clock.

    All of recorded history occupies the last ten seconds of December 31; and
    the time from the waning of the Middle Ages to the present occupies
    little more than one second.

Somehow, the force of this analogy keeps buzzing in the mind.  You can
combine this with any number of other facts.

Calculating the hours, minutes and seconds

The math works out as follows.  Taking the age of the universe as 15 bn
years (todays best estimate is closer to 20bn years), we have:

15000000000 / (365.2 * 24 * 60* 60)
1000/ (15000000000 / (365.2 * 24 * 60* 60))
	1 day = 1.5 x 10^10 / 365 = 4.1 x 10^7 (4.1 e7)
	1 hour = 1.7 e6
	1 minute = 2.9e4 = 29K years [35.4 minutes = 1mn years]
	1 second = 476 years
	1 millisecond = 0.5 years
---
	2.1 milliseconds = 1 year
	2.1 seconds = 1K years
	3.5 minutes = 100K years
	0.18 microseconds = 1 month = 175 microseconds
	5.8 microseconds = 1 day

Birth of Christ or 2K years ago - is about 4 seconds back.  11:59.56

Mammals appeared around the end the Permian - about 250 mya - so that
would be 250 x 35.4 =  = 8850 minutes = 6.1 days before Dec 31 midnight,
i.e. about Dec 25 evening.  However, today it is thought that these early
fossils constitute the Mammaliformia,  not the direct mammalian ancestors,
but some related creature.

On Dec 31:
   10:15(am) : Apes appear at
   21:24    : first Humanids (9:24pm)
   22:48    : Homo erectus
   23:54    : Modern man (homo sapiens)
   23:56:30 : Language (<100K ya, if you believe in FOXP2 genetic evidence )
   23:59:48 : Writing (6K ya, assuming 4000 BCE)
   23:59:53 : Vedas composed (3.5Kya, assuming 1500 BCE)
   23:59:56 : Christ born (2Kya)

Using the 20bn years figure for the age of the universe would reduce
these differences from the present moment by 1/4th.  Modern man would then
appear at 23:55:30.

Chapter 2, Genes and brains

Here Sagan considers the complexity of biological life
forms.  One measure of complexity is in terms of information content; and
here it considers the gene, which is (very approximately, ignoring expression
factors which influenced by environment etc.) the program that builds an
organism.  A chromosomme may have 5 billion nucleotides, and since each can
have four proteins, 20 bn bits of information.   p. 23-24

[I am not sure I agree. 5 bn nucleotides may be in 4^(5bn) states, which
corresponds to 2^10bn, which is 10bn bits and and not 20bn.  Maybe I am
missing something.  Also, there are other constraints on the genes that is
ignored, as well as large areas of inactive genes.]

This corresponds to four thousand books, each with 500 pages, with
approx. 300 words per page and 6 alphabets per word.

With longer genome lengths, the probability of mutation increases, so the DNA
length drops in higher evolved forms.  Nonetheless, something caused the
information capacity of the brain to grow dramatically in the last 4 million
years or so.

Disproportionate region of the motor cortex  (approx. 1/3d) goes for the
motor / sensory control of the hands and fingers.

Expts by Penfield on memory excitation from electric impulses; chilled the
brain of hammsters - kind of induced hibernation.  After thawing, hamsters
remembered about mazes they had been trained for.   . p. 31-36

Average brain volume: 1.37 liter ~ 1.37 kg; at birth, baby's brain = 12% of
body mass (exceptional).
male brain ~ 1.4+, woman brain ~ 0.15 kg smaller - may be insignificant
huge diff between brain size of byron/cromwell/turgenev, vs anatole
france.

Brain size vs body mass

 

Brain mass in proportion to body mass (from Jerison). The largest brain is
in a blue whale (9kg, 6+ times the human brain) , but man has the highest
offset from the average line (about 40 degrees) - i.e. human brain size as
a proportionn re-done in dark for birds/mammals, vs light for
fish/reptile/dinosaurs - show clearly higher ratios for the former. p.38-39

Pygmy shrew, 100mg brain in 4.7g body - is comparable to human ratio - but
too small to really compare.

Other chapters

Subsequent chapters look at other aspects of brain evolution and function:

   Chapter 3,'''The Brain and the Chariot'': Considers  anatomical details of
	brain volution

   Chapter 4 , Eden as a Metaphor: The Evolution of Man - considers
	human evolution and the role of language

   Chapter 5, The Abstractions of Beasts : language and tool use in
	chimpanzees and other animals

   Chapter  6, Tales of Dim Eden:  The evolution and dominance of mammals
	(dinosaurs figure prominently in the story), and moves on to dreams
	and its relation to the limbic system, which may have evolved well
	before the neocortex in higher mammals and primates.

   Chapter 7,Lovers and Madmen: Reports on experiments on
	split-hemisphere patients.  In some patients with severe epilepsy
	(grand mal), the two hemispheres are	disconnected by cutting
	through the corpus callosum.  When shown the word "BOOK" in the L
	visual field, they are able to recognize it and right it out with
	the left hand.  But when asked to say what it was that they wrote,
	they may give the incorrect answer "cup".  Other aspects such as the
	separation of musical and verbal skills are addressed.  Handedness,
	which is getting increasing attention in explaining brain function
	and evolution (see Chris McManus'
	Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures),
	is mentioned briefly.

   Chapter 8: The Future Evolution of the Brain:

	p.201:
	A friend of mine who has spent time with the Pygmies says that for
	such activities as the patient stalking and hunting of mammals and
	fish they prepare themselves through marijuana intoxication, which
	helps to make the long waits, boring to anyone further evolved than a
	Komodo dragon, at least moderately tolerable.

	Ganja is, he says, their only cultivated crop.  It would be wryly
	interesting if in human history the cultivation of marijuana led
	generally to the invention of agriculture, and thereby to
	civilization.

 	  [This may actually be true.  Note that explorations in ancient Iraq
	   and Egypt indicate a preponderant concern for making and consuming
	   beer.  Perhaps this was indeed what happened - ten millennium ago,
	   agriculture may have originated so as to obtain barley and other
	   grains for beer; bread may have been a byproduct.  see Ian
	   Horsey's excellent History of Beer and Brewing).

  Chapter9: '''Knowledge is Our Destiny: Terrestrial and Extraterrestrial
   	Intelligence''' speculates on the possibility of extra-terrestrial life.  .

Links

Discovery Education has a good <website relating to the cosmic calendar.
The chapter 1 itself can be read as a "search inside" on amazon).

For another very readable popular history, also focused on the brain, written
around the same time, see Robert Jastrow's The Enchanted Loom: Mind in the Universe.
Modern representations of evolutionary time often use a spiral, (e.g. see
the geological timeline in Atlas of Life on Earth.