jeremydon at aol.comspamenot <Jeremy Donovan> wrote:
> >
> > Limerent Mollusk "Zählt"@Iangefrauen.de, anonymous as usual, crossposting to a
> > variety of unrelated groups as usual,
... and just what's wrong with: "sci.med.psychobiology, sci.med.physics,
sci.med.pathology, bionet.neuroscience, alt.dreams.toltec, alt.idiots" [??!!]
> > opinionates thusly:
> > > Jesus Christ, dude, not to burst your bubble or anything, but most of
> > > us were absorbing the more interesting & pragmatic bits of this kind of
> > > data
> > >
> > Don't be silly; you could not burst my bubble. :-) I'm happy to learn you
> > imagine yourself such a genius, but you could not be aware of what "most of us"
> > know, so it merely makes you look dull to pretend. I've been reading science
> > books for many years and I still learned a few things from that material.
"'Intelligence', as we usually use the term, depends
fundamentally on both rationality and emotion."
-- Paul Grobstein
http://www.sciam.com/news_directory.cfm
> > More to the point, you are disrupting a potentially informative thread merely
> > to make the egomaniacal point that "YOU already knew that". Which may well be
> > a lie anyway... :-)
Good Point! GOAL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > > way back when you were still infatuated with Castaneda's early works
> > > of psuedo-fictional phenomenology. Where you saw nothing but "tonal" &
> > > "nagual" & "sorcery", we were measuring "men who mistook their wives for
> > > their hats!" Sheesh!
> > >
> > Whoopie for you. There are still plenty around here who have no idea what you
> > even mean by "men who mistook their wives for their hats", and a signficant
> > number of those who do know have nevertheless quickly invented some kind of
> > metaphysical caca to divert the blow so as to completely avoid having to
> > *really* think about it (I'm tempted to put money on it that this category
> > includes you...).
THE MAN WHO MISTOOK HIS WIFE FOR A HAT
http://www.oliversacks.com/hat.html
> > Btw, the book I'm quoting from was published in 1999, the
> > year AFTER CC died, and a good deal of the information in it was only
> > discovered or confirmed that very year, so no one could possibly have read some
> > of this stuff "way back when".
Yes, data much too recent. Give us latest please. We want it! You know we do!
> > > Then you saw the error of your ways, net-published a big old whupp-ass on
> > > Cleargreen's mindfuck (to your everlasting credit),
> > > <http://www.sustainedaction.org/Explorations/core_myths_are_intertwined.htm>
> > > and like all true-believers-scorned who then establish a scorched-earth
> > > policy toward their former infatuations, get it out of their system, and
> > > move on the wiser for it, you, instead, maintained your same old holier-
> > > than-thou punk-ass-bitch attitude as if you were light years beyond all
> > > mere mortals.
> > >
> > Merely your assertion again, devoid of content. I harbor no illusions as to my
> > own status as one more mortal. However, thanks for mentioning that particular
> > article of mine. In retrospect, it laid out the situation pretty accurately,
> > I'd say.
"We're all Bozos on this Bus."
> > > You'll never change (get it) until the known, unknown &
> > > unknowable righteously and unmistakenly tweaks your bulbous clown nose:
> > > "HONK!" [Re-invent & recapitulate the wheel all you like, please, it's fun,
> > > just do it with the realization that thou ain't the first upon these vigin
> > > shores...]
> >
> > I have not implied I am the first anything.
We think it's your comical dictator attitude, "in print", & the
inevitable self-righteous introductions to your posts that set up
a resistance to free-minded people. Personally, we don't care,
just had some weird, "too much time on our hands", recently. Sorry!
Anyway, facist dictators are not popular with a significant
portion of the population. Who knows why?! Something to do with
evolution, no doubt. Perhaps you'll do a study on the Mass
Psychology of Facism and deliver a synthesis for our edification.
Seriously, you post very interesting stuff. You're bright &
articulate. Heavy-handedness, though, is a communications
nightmare. We know, 'cuz all the assorted stupidities in our
lives have allowed us a most miserable, bioelectric & moist insight!
<snip>
> > links all the time, and the way you crosspost idiotically
<snip>
and just what's wrong with: sci.med.psychobiology, sci.med.physics,
sci.med.pathology, bionet.neuroscience, alt.dreams.toltec, alt.idiots
[??!!]
> > > Later -- Limerent Mollusk
> >
> > There will be no later. Not for us. You've just guaranteed it.
""Shudddderrr""
> > I have a simple policy now: Life is short and valuable. If you want to talk
> > to me, then you identify yourself and behave like a human being.
> >
> > Addendum to that policy:
> > ANYONE who crossposts as if on LSD and/or adopts some ridiculous sock puppet
Preparatory arrangements - LSD-25 Synthesis:
http://www.egodeath.com/lsdsynth.htm
> > name, from now until the end of time merely goes directly into my killfile
> > after the FIRST post, regardless of content or the usual lack thereof. No
> > muss, no fuss, no complexity.
"The killfile is the last refuge
of a desperate reader." -- Jerry Stratton
http://www.hoboes.com/html/NetLife/Children/Augustine.html
> > -Jeremy
> >
_________________
>crsds at att.net wrote:
> >
> > Ok let's all sing it together, ready?
> > "Nobody Mr. Nice Guy, no more Mr. Clean.
> > He's sick, he obscene." :)
>> ### - how about::)
"slider" <slider at nospam.com> wrote:
> She came in through the bathroom window
> Protected by a silver spoon
> But now she sucks her thumb and wanders
> By the banks of her own lagoon :)
"Row, row, row your boat
Gently down the stream.
Merrily, merrily,
merrily, merrily,
Life is but a dream."
Jeremy Donovan's original, very interesting, insightful & unedited post:
***********
What follows are my notes and comments on a Scientific American series book on
the evolution of the brain. I would recommend reading them carefully and
patiently, for I have tried to make some important points as simply as
possible. I have condensed more than 150 pages of material:
At the ends of the billions of neurons in your brain are branches called
dendrites that look like trees (dendron is Greek for tree). At the ends of
these dendrite branches are chemical receptors. The gaps between the dendrites
of different neurons are called synapses. Neurons send chemical messages to
each other across these gaps.
Looking at pictures of the vast interconnecting networks of neurons in the
brain, I am reminded, whimsically, of the root systems of plants.
The main purpose of the root systems of plants is to find and secure adequate
water. Is there a correlate with some similarly simple purpose for our brains?
Yes, in a way...
In most animals, the brain is located near the *entrance* to the gut. In many
arthropods, the brain actually surrounds the stomach. In vertebrates, such as
humans, the brain is located just above the mouth. This consistency of
location suggests that perhaps the most basic purpose of brains is to regulate
the intake of good food and the rejection of toxic substances.
Looking at all the evidence he could find, Darwin inferred that all living
things had descended from some ancient common form. This is as close to
'nonduality' as I can come. While I see no reason to believe individual
animals live on after their death and decay (and see good reasons to suspect
they do not), what is clear is that LIFE does live on.
Each living creature, including YOU of course, is a 'leaf' on a 'branch' in an
unbroken 'tree' of ancestry which reaches back billions of years to the most
primitive living forms. And inside YOU still reside many of the first
structures LIFE ever developed on this planet.
Basically, brains exist among animate organisms because resources vary and are
limited. An immobile organism, such as a plant, has no need for a brain.
The E.coli bacteria which live in your intestines are single-celled, and lack a
brain. However, they have more than a dozen receptors on their surface, and
very basic internal biochemical mechanisms which allow storing and evaluating
information about what is detected around them. Some surface receptors detect
food while others detect toxins, and E.coli are capable of adjusting their
movements based on what substances are detected in only two ways: they can
keep swimming ahead, or go into a 'tumble' to turn in a new direction.
Internal chemical signals trigger the use of tiny 'flagella' (whip-like tails)
to swim in two different ways to accomplish this.
This is what 'decisions' are like, at the one-celled level. :-)
A particular one-celled organism which lives in salt marshes derives its energy
from orange light, and has receptors enabling it to swim toward orange light.
The photoreceptive pigment utilized is similar in molecular structure to
rhodopsin, the photoreceptive pigment utilized by our own eyes.
Another free-swimming algae uses blue-green light to orient itself. It also
utilizes a receptor pigment similar to rhodopsin. It has two flagella which
move together as if doing a 'breaststroke'. It can bend these flagella using
'sliding microtubules', enabling it to change its swimming direction in more
complex ways than E.coli. These flagella work exactly like 'cilia', which are
common structures in YOUR body.
In a human eye, the rhodopsin pigment migrated into cilia which reside on the
retina of the eye. We call these modified cilia 'cones', and they are the
first step involved in allowing us to see the world in color. The receptors
enabling YOUR sense of smell also happen to be modified cilia.
Multicellular organisms can make more complex decisions. They separate
themselves from the environment at large, and control the flow of information
within by using chemical signals. A common method of conveying information in
the most ancient and primitive life forms was to utilize the passage of sodium
or potassium ions through cell membranes. The very same method is still used
in YOUR brain.
Brains contain billions of neurons, cells specialized for processing
information. Just like single-celled organisms, neurons have receptors located
on the cell surface for different chemicals.
Just like single-celled organisms, neurons integrate, reduce, and store a
diverse array of incoming information, but instead of then swimming in one
direction or another, they FIRE (or are inhibited from firing) in a certain
way.
E.coli evaluates information from a dozen receptors to make a simple binary
decision.
Individual neurons (even individual human beings) also evaluate and reduce a
large number of information sources in order to make simple decisions.
The most common internal chemical messengers in one-celled organisms are amino
acids. The receptors in your neurons are also sensitive to amino acids.
There are 20 amino acids. DNA is made up of long sequences of 'triplet
combinations', where each 'triplet' is made from 4 possible basic chemical
building blocks (an example sequence might look like: ggg ttt att ggg agt
tac... where g is guanine, t is thymidine, a is adenosine, and c is cytidine).
There are 4x4x4 = 64 possible triplet combinations. Of these, 61 code for one
of the 20 amino acids, and three are 'stop sequences'. A complete sequence of
these triplet combinations makes up a chain of amino acids which codes for a
protein. We call these sequences of complete amino acid chains 'genes'.
Since LIFE began, genes have been replicated from generation to generation,
passing on vital instructions on how to build LIFE. Alterations in the
sequences are called mutations.
'Junk DNA' makes up most of our DNA, and it consists of genes that have been
rendered inactive through mutations. By providing information about genes that
were active in the past, junk DNA may also prove to be an important source for
reconstructing evolutionary history.
In addition to the DNA in the chromosomes of the cell nucleus, there is also
DNA in the mitochondria which reside in the cellular fluid. Mitochondria
produce ENERGY for cells through the oxidation of carbohydrates, and are
transmitted from mother to offspring. Mitochondria may have originally come
from bacteria which invaded the one-celled organisms ancestral to all life,
which were in turn UTILIZED by the invaded organisms as an energy source (see
Lynn Margulis).
Brains use an enormous amount of energy.
The dendrites of your neurons contain a lot of mitochondria, because it
requires generating a lot of energy for neurons to maintain ionic equilibrium
with the surrounding brain fluids, which are constantly in flux as a result of
opening and closing neuronal membranes.
In a neuron, information derived from chemical messengers (neurotransmitters)
flows from receptors at the ends of fine dendrites into main dendrites and then
to the cell body, where it is converted into all-or-none signals which are sent
back out. These all-or-none-signals are called 'action potentials'.
The cell body generates 'action potentials' by opening voltage-sensitive sodium
ion channels in the axon membrane. This sends an 'action potential' (like an
electrical wave) down the axon (like a big wire) to the terminal of a dendrite,
where it again triggers the release of certain neurotransmitters into the
synaptic gap (to be picked up by the dendrites of adjacent neurons and so
on...).
Your nervous system uses both analog and digital signals.
The dendrites of a neuron may integrate thousands of neurotransmitter inputs,
each of which has a small influence on the overall electrical voltage within
the dendrite. This is similar to analog information flow.
By contrast, after integrating information from a large number of dendrites,
the cell body reduces it to a simple digital signal (an action potential) which
is then sent down the axon to be trigger the appropriate chemical broadcast to
other neurons.
You can see how this gets very complex when millions of neurons in different
brain areas which perform different functions are all sending and receiving
signals, evaluating multiple analog inputs and generating single digital
outputs.
Action potentials and voltage-gated sodium ion channels like the ones used in
YOUR brain are present in jellyfish, which are the simplest organisms to
possess nervous systems.
The development of this basic mechanism set the stage for the great
proliferation of animal life which occurred more than a half a billion years
ago, in the Cambrian period.
Early chordates developed very simple brains. The earliest vertebrates (fish)
evolved from them. Some of these early fish developed a way of insulating the
axons in the neurons in their nervous systems by wrapping them with a fatty
material called myelin. This facilitated the development of larger, more
richly connected brains.
In YOUR brain, the axons are wrapped with myelin, to facilitate the transfer of
action potentials. Myelin is not found in invertebrate life, or in jawless
vertebrates. It may have been a crucial innovation allowing jawed vertebrates
to assume more active predatory behavior, utilizing bigger brains.
Modern studies of brain size relative to body size confirm that brain evolution
appears to be linked to predatory behavior.
Some of the descendants of early fish experimented with crawling up on dry
land, and eventually some took up permanent residence there. These animals
were challenged by severe temperature changes which had not existed in the
water, and some eventually developed warm-blooded systems to deal with this
problem. The most successful of these animals became the ancestors of birds
and mammals.
The expansion of brain weights has occurred in other vertebrates and is not
unique to mammals and birds. However, the larger brain weights (relative to
body size) of mammals and birds are associated with much higher energy
requirements.
Serotonin is an important substance which regulates the responses of other
neurotransmitters. Neurons in the brainstem which emit serotonin were present
in the earliest vertebrate life, and are still present in YOUR brainstem. The
brainstem occupies a remarkably constant anatomical position throughout
vertebrate evolution.
In contrast, the neocortex is the most recently evolved brain structure. It
exists only in mammals, and is found to vary extremely among different mammals.
Serotonin is made from the amino acid trytophan. Humans must obtain trytophan
from dietary sources (proteins).
The brainstem, containing the serotonergic neurons, is best thought of as the
basement of the brain. In place 500 million years ago, it is amazingly
conserved throughout evolution, yet it participates vitally in the most complex
aspects of our thinking and emotions. The serotonergic neurons are
*fundamental* to brain function.
The axons of the seritonergic neurons project richly to every part of the
central nervous system and influence the activity of virtually every neuron.
They play an important role in the integration of behavior. Our sense of
well-being and our capacity to organize our lives and relate to others defends
profoundly on the functional integrity of the seritonergic system.
Fourteen different types of serotonin receptor (14 proteins) have been
discovered so far in the brains of mammals, acting in different ways.
Serotonin receptors also exist in the gut, and in the walls of blood vessels.
Serotonin receptors exist even in yeast and molds, two primitive organisms very
unlike each other, and very unlike humans.
Judging by the mutations in DNA: Yeasts and molds diverged from a common
ancestor about 900 million years ago. Mammals and insects diverged from a
common ancestor about 600 million years ago. Mammals and birds diverged about
300 million years ago. And the primates which would become human diverged from
other mammals about 70 million years ago.
Serotonin has been fundamental to life for a billion years, and it is still
fundamental to YOU today. In addition to providing a delicate balance to the
entire nervous system, it is of primary importance in regulating "level of
physical arousal".
Serotonin levels in monkeys have been found to be highly correlated with social
status. In fact, artificially increasing serotonin levels in monkeys has been
found to be directly *causative* of increase in social status (due to it
directly giving rise to more social behavior). (This leads to interesting
questions about why ANY animal would acquire low levels of it??)
Mood disorders are associated with low serotonin, and Prozac acts on the
serotonergic system, to give one example of a drug designed to do so...
Otoh, the most evolutionarily advanced part of the brain is the neocortex. It
contains multiple maps: multiple maps of the muscles of the body; multiple
maps of the motor functions; multiple maps of the hands, feet, and face;
multiple maps of body surface, etc. The size of different areas in these maps
depends on experience. Exercise the fine muscle controls of the fingers and
the associated areas in the maps in the neocortex grow larger. Crucial areas
of functionality occupy the largest areas, such as the muscles involved in
facial expressions and eating.
Similarly, the parts of the cortex accounting for vision have been mapped. In
these maps, more space is always devoted to the center of the retina than to
the periphery (corresponding to how we align the foveal spot in the retina with
whatever we are viewing). But vision turns out to be very complex (as one
might expect, since man is a VISUAL predator). To date, they have discovered
more than two dozen cortical areas involved in making various maps of visual
data.
Opossoms and hedgehogs resemble early mammals which lived 60 million years ago.
They have limited visual capacity, and a small number of visual cortical
areas.
One interesting question is: why are there SO MANY maps in the human neocortex
which appear to duplicate functionality? The answer appears to be that because
the brains of living animals can never just be shut down and fundamentally
reconfigured, old control systems remain in place while new systems with
additional capacity are added on and integrated. Mutations produce new cortical
areas which perform new functions, while the old systems continue to provide
the older more basic functions.
This is why the human brain is built of layers which begins with the most
primitive at the bottom (brainstem), continues with systems which evolved later
in the middle (midbrain), and ends up at the top with the most complex and most
recent feature, the neocortex. Evolution is about duplicating what worked in
the past while adding *potential* improvements for the future.
This is not to imply that mutations are always an improvement. Many mutations
have negative consequences for organisms. Several terrible diseases are a
result of mutations, for example.
In every vertebrate embryo, the central nervous system begins as a long tube,
where the major components of the brain -- the forebrain, the midbrain, and the
hindbrain -- are at first merely bulges in the anterior parts of that tube.
Depending upon the actions of master gene sequences called "the homeobox",
these 'bulges' develop differently in each vertebrate.
To make a long, complex story shorter: it has been recently discovered that the
genes which control head and brain formation in fruit flies are very closely
related to the genes that control the formation of the more anterior parts of
the brain in mammals. In fact, it has been discovered that the formation of
the most progressive part of the mammalian brain (the cerebral cortex) is
controlled by genes with ancient antecedents going back at least half a billion
years. It is also known that certain genes known as "terminal genes", which
had the ancient function of controlling the formation of the gut, are now
responsible for controlling the growth of the forebrain in mammals, once again
displaying the early intimate relationship between nutritive intake and the
evolution of the brain.
Some of the same "homeobox" genes that control brain development also control
the development of jaws and teeth. The tandem evolution of forebrain, jaws and
teeth is considered the hallmark of the major evolutionary transformations that
occurred in the earliest mammals, in the early primates, and again in early
humans.
The evolution of the axon and the action potential enabled neurons to
communicate over distances of many centimeters, which in turn made possible the
evolution of large and complex animals. Such animals first appeared during the
Cambrian explosion, about 540 million years ago.
One leading theory on WHY this occurred THEN is that at that time there was a
90-degree shift in the orientation of the poles of the earth relative to the
continental landmasses (proposed by Joseph Kirschvink and colleagues, based on
the magnetic orientation of Cambrian rocks). This (or something else that
happened at that time) caused global changes in climate. During the Cambrian
explosion, 10 rapid proliferations of life were followed in each case by a
rapid reduction as habitats were created and destroyed. These massive
oscillations may have driven the rapid evolutionary diversification which
occurred at this time.
The Cambrian animals lived in water. This influenced the way EYES developed in
living creatures, based on the spectrum of light which passes through water.
The division of labor between the receptors which became rods and cones in our
eyes occurred more than 500 million years ago.
A certain master regulatory gene called Pax-6 controls formation of the eye in
fruit flies, mice, and humans. The mouse version remains sufficiently
unchanged over evolutionary time that it can actually induce eye development in
fruit flies. These findings suggest that Pax-6 existed in the common ancestor
of flies and mammals, and thus existed even before the Cambrian period. Pax-6
is also found in nematodes, which do not have photoreceptors or eyes at all.
In nematodes, Pax-6 regulates formation of the head, so it is likely that this
was the original function of the gene, but that it later came to play a
specialized role in eye formation.
Amphioxus is the non-vertebrate chordate which may have been the common
ancestor of both flies and mammals.
Amphioxus is a primitive sea creature whose 'eye spot' has an internal
structure very similar to the developing eye in vertebrates. Comparing the
brain of amphioxus to the brain of a primitive vertebrate, one also finds major
similarities. In particular, structures corresponding to frontal eyes, the
pineal gland, and the hypothalamus are all present in amphioxus. Again, there
is a similarity of location of the serotonergic neurons between amphioxus (in
the dorsal nerve cord) and primitive vertebrates (in the hindbrain), indicating
how old and basic this system is.
Comparison of amphioxus and early vertebrates also yields the conclusion that
the midbrain and the telencephalon (olfactory structures and the cerebral
cortex) originated in the earliest vertebrates.
The earliest vertebrates were jawless fish which appeared about 470 million
years ago. They were small predators. Over and over again in evolution, the
originators of new modes of life have been small predators, and key innovations
at each stage conferred a selective advantage in predation.
Examples of early key innovations: gills, pharyngeal muscles (later the
formation of jaws), the cerebellum (supports the stability of the retinal image
during active movement), changes in hemoglobin which release oxygen more
effectively (the brain is especially dependent upon a large supply of oxygen),
and a keen sense of smell (important not only in predation but also
reproduction).
Early brain development in vertebrates was dominated by processes related to
smell. More recent brain development, such as in humans, has been more related
to vision. Vision maps to space geometrically (topographically) whereas smell
does not.
The oldest visual structure in the brain of all vertebrates is the map of the
retina on the roof of the midbrain. In fact, the midbrain is an important
center for the integration of spatial information from all the senses in all
vertebrates.
The other group of animals (besides mammals and birds) that evolved large eyes
and brains is the cephalopods: the nautilus, squid, octopus, and cuttlefish.
Brain size falls within the lower part of the mammalian range. The evolution
of the sensory systems in cephalopods shows remarkable parallels with
vertebrates even though their common ancestor was very primitive.
Cephalopods appeared about 500 million years ago, and the early ones resembled
the chambered nautilus that today lives in the depths of the Indian Ocean.
They are also predators, and like other early predators have well-developed
respiratory systems and a good sense of smell. More advanced cephalopods like
the octopus have magnificently developed eyes related to their more active
predatory life-style. In fact, octopus eyes can detect features of light of
which ours are incapable. Their major limitations are that they did not
develop myelin and the hemocyanin in their blood can only carry about 1/4 the
oxygen as our hemoglobin, thus limiting brain size. But their cerebellum
developed similarly to ours, enabling them to stabilize visual images.
The larger brains of mammals and birds are a crucial part of a large set of
mechanisms for maintaining a constant body temperature. Because all chemical
reactions are temperature dependent, having a constant temperature allows
precise regulation and coordination of complex chemical systems.
However, maintaining constant body temperature requires a tenfold increase in
energy. Such animals must find much larger amounts of food.
The first amphibians crawled out of the water about 370 million years ago.
About 300 million years ago the first reptiles appeared. Their innovation was
eggs that could be laid on land, allowing them to move further inland.
The earliest reptiles were small predators which preyed upon insects. (The
first mammals were also insect predators.)
Very soon after the origin of reptiles there arose a basic division into three
separate lineages: 'synapsids', which led to mammals; 'anapsids', which led to
turtles; and 'diapsids', which led to dinosaurs, birds, and reptiles other than
turtles.
The basic distinctions among these three groups are related to shape of the
skull and arrangement of the jaw muscles, both related to predatory behavior.
The earliest members of the line leading to mammals were the pelycosaurs, small
predators. Their innovative features were a more efficient chewing mechanism
and daggerlike canine teeth with which to stab prey. A very successful larger
pelycosaur was Dimetrodon, which had a huge sail rising from its vertebrae, a
solar collector which regulated temperature. Many different types of animals
'adaptively radiated' from the pelycosaurs, most of which belonged to lines
which perished within 50 million years.
But the pelycosaurs gave rise to a new group of small predators with elongated
canine teeth, called the 'therapsids'. These also 'adaptively radiated' into
many forms, and most of them were wiped out at the end of the Permian period,
248 million years ago. Near the end of the Permian period were a series of
massive volcanic eruptions which may have caused global cooling. An estimated
95 percent of all animals species died out.
Among the animals which survived were Lystrosaurus, a giant herbivorous
therapsid that was quite abundant, and two predators. One of the predators was
'a thecodont' which gave rise to birds and to the dinosaurs which displaced the
large therapsids as dominant land animals, and the other was a small therapsid
predator called 'a cynodont' because of its doglike canine teeth. The cynodont
gave rise to mammals.
Mammals expend 5-10 times as much energy as reptiles, and the bulk of it is
used maintaining a constant body temperature. But the benefits of
constant-temperature biochemical regulation exceed the energy costs, conveying
selective advantage.
In addition to increased energy intake, certain changes in brain, body and
behavior were necessary to support constant-temperature regulation -- changes
in the way food is chewed, changes in breathing, in locomotion, in parenting
behavior, in the senses, in memory, and in the expansion of the forebrain.
The cynodonts ranged in size from ferrets to wolves. They developed many
innovations in teeth which are useful for a predator. Genetically, there is a
close linkage in the evolution of the teeth and the forebrain in mammals.
Parenting behavior occurs in a few cold-blooded animals, but is universal among
warm-blooded vertebrates.
Mammary glands, the original defining characteristic of mammals, are
specialized sweat glands, indicating that they derive from an ancient system
for the evaporative cooling of the body.
Breast milk is a complex food containing more than 40 nutrients, including
sugars, fats, and proteins. There is evidence that human infants raised on
natural milk have significantly higher IQ's than infants raised on formula milk
when both are administered through bottles. This implies that breast milk is
ideal for the early functional maturation of the brain.
The ejection of milk from the mammary glands is under the control of the
hormone ocytocin, which is made in the hypothalamus in the basal part of the
forebrain. Ocytocin also stimulates maternal care in mammals. It is a member
of an ancient family of hormones that control reproductive functions in both
vertebrates and molluscs, and its expanded role in mammals illustrates again
how old components of the nervous system can assume new functions.
In mammals the huge energetic burden of sustaining the growth of infants falls
on the mother. Lactation triples the amount of food that must be eaten by a
female.
About 220 million years ago the first true mammals appeared. They were much
smaller than their cynodont ancestors, resembling the shrews that live today.
They were active predators, with major innovations in the brain, and in tooth
development.
There was also a significant innovation in hearing mechanisms (mammals can hear
*much* higher frequencies than birds or reptiles), when part of the jaw joint
evolved into delicate bones in the middle ear, and there were changes in the
hair cells of the cochlea (outer hair cells are uniquely mammalian). This
expanded ability to hear was very useful in catching insects, and in detecting
the high-frequency distress calls of mammalian infants (which remained
inaudible to many reptilian and avian predators).
Early mammals were mainly active at night, and had a simple social structure
where adults were solitary except for nursing mothers.
Another innovation which arose with mammals was having only one set of
permanent teeth. Cynodont teeth were simply replaced as they wore out. The
advantage is a more precise fit between upper and lower molars, resulting in
more efficient chewing, which fostered more efficient digestion, which
facilitated a higher metabolic rate.
The neocortex is just as much a unique defining feature of mammals as the
mammary glands. Since early mammals were warm-blooded small predators with
high metabolism, they required large amounts of food and were constantly under
the threat of starvation. The neocortex stores complex information about the
environment so that the mammal can readily find the food and other resources
needed for survival.
Stopping here due to length. To be continued...
-Jeremy
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