2014 By Gary Vey
A farmer I know often goes out to shoot possums that
invade his garden in the middle of the night. His dog chases them up a tree
and, with a flashlight reflecting in their eyes, they are easy to spot and
dispatch. But not always. Increasingly, more possums are apparently learning
not to look at the light and they remain invisible -- and continue to live. He
joked that this was an example of natural selection, with nature favoring the
successful strategy for survival.
On the surface this seems to make sense. But does it
really?
Offspring inherit lots of characteristics from their
parents' DNA. There are genes for size, hair color and brain development -- but
was there somewhere in the possum's genes that stored the strategy of not
looking at the hunter's flashlight?
This is not a new question. Survival behaviors of
animals have been studied by many researchers, but their inherent programming
has never been fully explained. How exactly is this strategy coded and passed
on from one generation to the next? Can DNA do this?
The most famous study of survival strategies is
outlined in Richard Dawkin's book,The Selfish Gene. Let's take
look.
Evolutionay Stable Strategies (ESS)
One
of the most interesting ideas in The Selfish Gene originated
from another researcher, Maynard Smith. He described what he termed
Evolutionary Stable Stategies, or ESS. These are programmed behaviors which
specific species use when they are threatened. These strategies are not
taught or learned. They are carried out unconsciously by each organism in a
particular species, suggesting that they are imparted to each generation at
birth through genes.
Smith listed five main strategies which are observed
in the animal kingdom (including humans):
The Hawk -- If threatened, attack and fight to
the end. This strategy is to fight an opponent with the maximum
effort, unrestrained and for as long as it takes to either win the
battle or to quit because of death or injury. Dog and cock fights are
examples of this kind of aggressive strategy. While one party will always win,
the other party will suffer extreme losses, and possibly death.
The Dove -- If threatened, threaten back but
never fight. Run away if attacked.This strategy involves making
threatening gestures but inflicting no real harm to the opponent. The threats
are usually a kind of ritual or symbolic "gesture" which continues
until one of the animals doing this gets tired, bored or simply gives up. No
one is injured, one party wins, but often there is a loss of energy and
time if each animal has equal stamina.
The Retaliator -- If threatened, act like a dove. But
if seriously attacked, respond like a hawk and fight to the end. In
this strategy, the animal reacts differently to the threat, depending on
which strategy is being used against it. If it encounters a dove, it will
respond with a dove strategy and threaten with gesture. But if it encounters
a hawk, it will act like a hawk, aggressively fighting to the end. By acting
initially as a dove, actual conflict and injury is avoided when the threat is
small. But if there is to be a fight, the risk of injury or death is
significant.
The Bully -- Act like a hawk when threatened
(and hope the opponent is scared away). But if challenged, run away like a
dove. This strategy works pretty well as the animal can
"fake" that it is willing to fight to the death. And if it comes to
a fight, it runs away to safety. The survival potential of the bully is
pretty good, unless it encounters a real hawk.
The Prober Retaliator -- Act like a retaliator with most
encounters...but be unpredictable and sometimes switch to the hawk strategy
-- even if the opponent is a dove! This is perhaps the most
successful strategy for some animals because the outcome of an encounter with
them is uncertain. Other animals will think twice before challenging them.
Do any of these strategies sound familiar to you?
They are exhibited in human competition, such as gaming (poker), government
policies and even war games. The last one, Prober Retaliator, is the tactic
used by many terrorist organizations.
Not every strategy is the best for all animals. The
strategy used by a particular species is determined by which outcome enables
optimal survival and more replication of its own kind. It varies depending on
the size and strength of the animals, the potential enemies it might
encounter and the environment it lives in. Somehow, each species finds the
precise strategy that maintains its numbers in a stable, viable population.
When it is carefully analyzed, it is always the best choice
for that particular species.
While these strategies are interesting in
themselves, the fact that they seem to be intelligently designed and
unconsciously implemented by the species is even more so. But... designed by
whom? And transmitted to each generation by what means?
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A maze of possibilities
There is some evidence that strategic behavior can be
transmitted by genes. A classic example is Tryon's experiment on the
maze-running ability in rats [1][2]. Tryon managed to breed two groups of rats
by selectively mating the "best" maze runners with each other and,
conversely, the "worst" maze runners. After seven generations he
could show that he had produced two distinct heredity groups with a vast innate
differences in their maze running abilities. This was believed by many to be
proof that behavior was inherited, and therefore a product of DNA. But his
results were soon challenged.
When the "worst" maze runners were subjected
to an enriched environment with more objects to explore and more social
interactions to enjoy, their maze running abilities were restored. What's more
interesting is that their offspring continued to have improved maze running
abilities -- even without the stimulating activities [3]. In just one
generation this "inherited" deficit was erased. This result suggested
that the maze running ability was the product of an interaction of genes and
environment, where the genetic effect is only seen under some environmental
conditions. If that is true, how can genes change so quickly -- even in the same
organism?
Small changes have big results
Scientists continued to examine how small genetic
changes could alter complex behavior. Their first success was in explaining how
an animal could be programmed to be more "hawkish" or
"dovish". As reported in Principles of Neural Science (1992):
"Most animals, including humans, become
aggressive when threatened, such as when their territory is invaded, their
offspring are attacked, or sexual interactions are prevented. The importance of
serotonergic transmission in aggressive behavior is clearly evident in studies
of mice in which the gene for the serotonin 1B receptor has been ablated by
targeted deletion.
When mice lacking serotonin 1B receptor are isolated
for four weeks and then exposed to a wild-type mouse, they are much more
aggressive than wild-type animals under similar conditions. The mutant mice
attack intruders faster than wild-type mice or mice lacking only one copy of
serotonin 1B receptor gene, and the number and intensity of attacks is
significantly greater than that of the wild-type mice. Thus, the serotonin 1B
receptor plays a role in mediating aggressive behavior in mice... [4]
While the mechanism for generalized behavior
strategies (like being more or less aggressive) seemed to implicate genes and
their ability to alter certain neurotransmitters, it was still not known how
genes could also modify specific behaviors -- like making the
possum turn its eyes from the hunter's flashlight.
Some amazing examples of genetically encoded, complex
behaviors have been studied in monozygotic twins -- siblings with the exact
copies of their DNA -- who were separated at birth and reared in different
environments.
Identical Twins Reared Apart
Human monozygotic (MZ) twins account for 1
in 250 live births. The origin of MZ twins is attributed to two or more
daughter cells of a single zygote (fertilized egg) undergoing independent cell
divisions, leading to independent development and births.
Although they are considered genetically identical
at birth, significant differences between MZ twins may exist, becoming more
evident with age. But the main focus of study has been on the remarkable
similarities which involve complex behaviors, personality and interests.
These are, after all, strategies that humans use to survive conflicts.
The Minnesota Twins, as they are known, are perhaps the most reported
case involving two male babies who were monozygotic twins, separated at when
they were only 4 months old, and each adopted by a different family.
At age five, Lewis learned that he had a twin, but
he said that the notion never truly "soaked in" until he was 38
years old. Springer learned of his twin sibling at age eight, but both he and
his adoptive parents believed the sibling had died. The two were finally
reunited at age 39. The similarities the twins shared not only amazed one
another, but researchers at the University of Minnesota as well. The very
fact that you had twin siblings separated at birth bearing the same name,
both 6 feet tall and weighing exactly 180 pounds is pretty incredible. But
there's more.
Consider these
coincidences:
- As youngsters, each Jim had a dog named "Toy."
- Each Jim had been married two times -- the first wives were both
called "Linda" and the second wives were both called
"Betty."
- One Jim had named his son "James Allan" and the other
Jim had named his son "James Alan."
- Each twin had driven his light-blue Chevrolet to Pas Grille beach
in Florida for family vacations.
- Both Jims smoked Salem cigarettes and drank Miller Lite beer.
- Both Jims had at one time held part-time posts as sheriffs.
- Both were fingernail biters and suffered from migraine headaches.
- Each Jim enjoyed leaving love notes to his wife throughout the
house.
- Both Jims had abilities in mechanical drawing and carpentry
The Jims, like other identical twins, are not carbon
copies of each other. Some obvious differences were discovered. Each styled
his hair differently; one Jim wore it combed straight, hanging down over his
forehead and the other Jim wore it combed back and sported sideburns. One Jim
more clearly conveyed himself through speech, while the other was better
suited to writing. While both Jims had been married twice, one Jim had taken
vows with a third wife (called "Sandy").
Daphne and Barbara are also examples of subtle behaviors that are
apparently transmitted through genes.
Daphne Goodship and Barbara Herbert first met when
they were 40. Debbie was raised Jewish and Sharon was raised Catholic.
According to Barbara, "We discovered we had a
miscarriage the same year, followed by two boys and a girl in that
order."
They joke that they've also cooked the same meal
from the same recipe book on the same day, without knowing it. Daphne
and Barbara have been called the "giggle twins" because they laugh
and fold their arms the same way.
Identical twins Tom Patterson and Steve
Tazumi met four years ago. Tom is from rural Kansas, he was raised
Christian and his parents were janitors. Steve, raised as a Buddhist, lives
in Philadelphia. His father was a pharmacist.
However, Tom and Steve chose the same careers.
"It's phenomenal," says Steve. "He owned a body building gym
and I owned a body building gym. We're both 100 percent into fitness."
But there are differences in these twins, too. Steve
says he's more party oriented while Tom is more family oriented.
Heredity vs Environment
Although there is ample documentation for these
similar personality traits in identical twins, it is not without some
controversy. In her book Identical Twins Reared Apart: A Reanalysis,
Susan Farber noted that many of the cases studied were based on subjects who
were recruited by asking television viewers to refer people who were
identical twins. She claimed that these twins would have been the most
obvious to look and act similar. In other words, the selection was not
unbiased. She attempted to set the record straight and based her own research
on a study that selected twin births from the Danish registry, between 1954
and 1959, and found 12 identical twins that were reared apart.
Farber summarized her review by stating that
identical twins who shared the same home life were almost 80% similar, while
those reared apart were only 60% alike. Although this certainly proves that
environment has a role in shaping behavior, it still makes a strong case for
genetics. In the examples above, interests, professions, and even the way we
laugh seems to be encoded in our genes. Yet, the environment can modulate
this genetic expression. How is that achieved?
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Epigenetics: the new frontier
If the genes can be likened to long list of
instructions, we have learned that some of these instructions can be marked
"to do" (activated) or "ignore" (inhibited). Scientists
have recently come to understand that, although the list itself remains intact,
the various instructions undergo activation and inhibition in a
process called epigenetics.
This process is vital when a single fertilized egg
(zygote) divides and the cells differentiate to become muscle, tissue, nerve
cells skeletal cells, etc. Each different type of cell requires a different set
of proteins and different sets of instructions are activated or inhibited.
These sets of instructions stabilize and continue over the life of the cell and
over many generations as the cell divides and reproduces.
Epigenetics is the result of turning a set of DNA
instructions on (activated) or off (inhibited).
The process is well understood for the methylation
process, where a molecule containing one atom of carbon and three atoms of
hydrogen (CH3) attaches to specific genes to turn them off (inhibit) and
prevent their instructions from being used to make specific proteins.
The histone modification of genes is less understood
but involves a molecule that attaches to part of the gene, causing it to
deform and interfering with its ability to make a specific protein --
essentially turning it off.
The attachment of these switching molecules is
achieved through the control of ion charges at the specific site. The charges
then facilitate the molecular bond and inhibit the gene from replicating and
producing its specific protein [8].
The production of specific proteins is critical to
life and even minor changes at the genetic level can have dramatic
consequences. Much of our genetic code is not completely understood and
so-called "junk DNA" may contain instructions that have very
specific roles to play in our behavior and thinking.
In our earlier example of the possum, it is possible
that some kind of epigenetic change causes increased light sensitivity,
making the possum turn its head to avoid the glare of the hunter's flashlight.
This subtle change in gene expression becomes a survival strategy and is
passed on to offspring.
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Scientists were surprised to discovered that
epigenetics was an on-going process, not limited to differentiating cell types.
In fact, they found that environmental factors, such as toxins, temperature or
the availability or scarcity of food, could cause epigenetic changes that
modified the behavior and form of the organism. These adaptations happened
quickly and within the lifespan of the same organism. In some cases, the
changes to "activate" or "inhibit" certain instructions
were passed to subsequent generations implying that our Darwinian concept of
multi-generation evolution needs amending. Evolutionary adaptation can occur in
a single generation!
UPDATE September 2014: The recent issue of Science has
deciphered the way in which the epigentic changes of an adult are transmitted
to their offspring through the sperm and egg! [LINK]. Back to the twins...
It was always assumed that our DNA was an unchanging
set of instructions. And because of this, MZ twins were assumed to have been
born with identical sets of genes. But scientists were curious about some cases
where one twin would develop certain types of diseases and the other did not.
When they examined the DNA of older twins they were shocked -- their DNA was different!
[5]
A study published in The American Journal of
Human Genetics, conducted by scientists at the University of Alabama at
Birmingham and universities in Sweden and the Netherlands examined the genes of
10 pairs of MZ identical twins, including 9 pairs in which one twin showed
signs of dementia or Parkinson's disease and the other did not. According to
Professor Jan Dumanski:
"These epigenetic changes -- which accumulate
over a lifetime and can arise from things like diet and tobacco smoke -- have
been implicated in the development of cancer and behavioral traits like
fearfulness and confidence, among other things. Epigenetic markers vary widely
from one person to another, but identical twins were still considered
genetically identical because epigenetics influence only the expression of a
gene and not the underlying sequence of the gene itself...
When we started this study, people were expecting that
only epigenetics would differ greatly between twins. But what we found are
changes on the genetic level, the DNA sequence itself." [5]
The study showed that the longer DNA is exposed to
environmental influences, the more likely it is to develop epigenetic
adaptations. It also suggests that these epigenetic changes can stabilize and
be passed to subsequent generations upon birth [6]. But the remarkable thing is
that these epigenetic changes can also manifest in the actual genetic code of
the DNA -- making the changes permanent -- and do this within the lifespan of a
single organism! [7] The mechanism for this appears to be something called
cytosine deaminase which can change both epigenetic code and the base DNA code.
So it appears that nature has equipped the organism
with a two tiered approach to adaptation. First, temporary changes in gene
expression can be implemented through epigenetics. These will take effect
quickly and can be passed to subsequent generations to help the organism adapt,
but they are NOT permanent. However, if these changes persist and prove
successful in the adaptation of the organism, permanent genetic mutations will
follow and constitute a form of natural selection.
Who designs these adaptive changes?
We ask the question with "who" because we
recognize that the specific genes involved in the adaptation of the organism
appear to be selected intelligently. Intelligence usually signifies sentience
and consciousness. But perhaps we err in our inquiry.
The intelligence of natural selection is not in each
specific choice of adaptation. Rather it is in the grand design of the natural
selection process which appears to involve something as yet illusive to
mechanistic science.
How does the possum adapt to the hunter's flashlight?
Initially it may be a random case of over-sensitivity to the light resulting
from some anomaly in protein synthesis. Because this anomaly proves to be a
successful strategy for survival, its epigenetic code endures until it has
reached a certain saturation in the population of possums. At this point,
presumably, some mechanism is able to make the gene expression permanent.
But there is also the possibility that the sensitivity
to light was not a random anomaly.
In the next installment of this series, we will
examine a theory which explains how the organism's cells "know" when
a particular epigenetic change has been an effective survival strategy. We will
explore the so-called mitogenetic and morphogenetic fields, how an organism
communicates with the field and how epigenetic changes can spread throughout a
species -- even when there is no physical contact or reproductive lineage.
We'll be treading on hollowed ground as we explore the
possibility that fields of energy permeate the universe, unifying and
coordinating everything.
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