about myself - 國立臺灣大學 · darwin's hypothesis – variation is inherited g r o w t h t o...
TRANSCRIPT
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Lecture 5/23
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About myself
• 林雨德
• Dept. of Life Sciences
• Office hour: by appointment
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About the course
• I will give the next 5 lectures for this course.• You will turn in an exercise sheet every
lecture.• There will be a quiz every week on the
material from the previous week. The last quiz will be given in the final exam.
• All quizzes will be in English, and take about 15 minutes.
• There is no final exam per se for my lectures.
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About discipline• You need to come to lectures to earn credits
for quizzes and exercises.• I will not give make up quizzes, unless you
can provide official documents that justify your absences.
• Coming in late, leaving early, or having a cell phone ringing are annoying behaviors. Be respectful.
• All lectures will be posted on website after the lecture.
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Get a piece of paper, print your name and ID#,
and be ready to write down the answers to the exercises during the lecture.
Do not look up answers in the textbook.I want your own thoughts.
You are free to discuss with your neighbors.
Turn in the paper at the end of class.
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Genes Within Populations
Chapter 21
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Exercise: Why are there so many different species?
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God must be very fond of beetles!
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Charles Darwin
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Falkland IslandsMarch 1833March 1834
April 1832
Jan. 1836
Sept. 1835GalapagosIslands
July 1834
Dec. 1831
Oct. 1836
Darwin’s 5-year journey on HMS Beagle
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Darwin’s historical visit to the Galapago islands
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Darwin saw thateach island had its own kind of giant tortoises.
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Darwin saw thatsimilar finches had different types of beaks.
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Falkland IslandsMarch 1833March 1834
April 1832
Jan. 1836
Sept. 1835GalapagosIslands
July 1834
Dec. 1831
Oct. 1836
Darwin’s other observations & collections over the 5-year journey
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Species must have changed with time in respond to the environments.
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Evolution: change through time(decent with modification)
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How do species changed through time.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lamarck's hypothesis – variation is aquired
stretching stretching
reproduction
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Jean Baptiste Lamarck
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• Acquired traits (e.g., bigger biceps) do not change the genes transmitted by gametes to offspring.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
reproduction
reproduction
reproduction
Darwin's hypothesis – variation is inherited
growth
to adult
growth
to adult
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• Individuals within a population differ among each other. (individual variations)
• Populations grow rapidly, yet natural causes (food, predation, etc.) set limits.
• Individuals with advantageous traits are selectedover less ones. (differential reproduction & survivorship)
• Individuals with advantageous traits produce offspring with advantageous traits. (variation is inherited)
• Thus, the population change through time.
The process of natural selection
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Not only could populations change with time, but over long period of time new species could come in place.
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Exercise: How do finches evolve into different species?
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1858--Alfred Wallace had a similar thought as Darwin’s.
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1859--Darwin published ‘On the Origin of Species by Means of Natural Selection’.
The controversy started.
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Populations of living things change with time (microevolution).
Gradual accumulation of changes leads to speciation: the occurrence of new species (macroevolution).
Evolution: Change through time
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Individuals within a population differ from each other. HOW?
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– Population = members of the same species that occupy the same area.
– Each new generation, genetic mechanisms (mutations, independent assortment, crossing–over, random recombination) create new variations of individuals within a population.
Genetic variation in nature
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– The proportion of different variations may change over time (i.e. microevolution), due to various reasons.
– One of the reason is that different variations do well under different environment. That is,the environment (nature) is a selection agent-- natural selection.
Microevolution
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darkercoloration
lightercoloration
Natural selection –Different phenotypes/genotypes do well under different environments
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What are phenotypes & genotypes?
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• Individuals within a population differ in their phenotypes and genotypes. (individual variations)
• Populations grow rapidly, yet natural causes (food, predation, etc.) set limits.
• Advantageous phenotypes are selected over less advantageous ones. (differential reproduction & survivorship)
• Alleles conferring advantageous phenotypes increase in frequencies. (frequencies of different genotypes changed over time).
• Individuals with advantageous phenotypes and genotypes. produce offspring with advantageous phenotypes and genotypes. (variation is inherited)
The new synthesis of natural selection
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Survival of the Fittest
• Fitness is generally defined as the number of surviving offspring left in the next generation. It is a relative measure. Natural selection favors phenotypes with the greatest fitness.
• Differential reproduction & survivorshipis the key feature of natural selection.
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12 13 14 15 16
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12 13 14 15 16Length of adult female water strider (mm)
Num
ber o
f egg
s la
id p
er d
ayLi
fe s
pan
of a
dult
fem
ale
(day
s)N
umbe
r of e
ggs
laid
dur
ing
lifet
ime
Several fitness measurement
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Individuals do not evolve, populations do.
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Natural section is only one of the mechanism that may cause the evolution
of populations.
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Allele frequencies may change through time due to following mechanisms…
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The 5 mechanisms of evolutionary change-- Mutation
• Mutation creates new alleles, thus change allele frequencies.
• It’s the ultimate source of genetic variations.
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T
AG
G
G
GC
C
UV light DNAAllele A
Allele A no more
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• Movement (emigration & immigration) of alleles from one population to another change allele frequencies.
The 5 mechanisms of evolutionary change-- Gene flow
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Allele A
Allele B
CarryAllele A
+ Allele A
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• Assortative mating - phenotypically similar individuals preferentially mate with each other, and causes frequencies of particular alleles to increase disproportionately.
The 5 mechanisms of evolutionary change-- Nonrandom mating
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Self-fertilization
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• Frequencies of particular alleles may change by chance alone.
– bottleneck effect - drastic reduction in population size
– founder effect - few individuals found a new population
The 5 mechanisms of evolutionary change-- Genetic drift
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Genetic Drift - Bottleneck Effect
Original Reduction Rebound New
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Genetic Drift - Founder Effect
Bye!
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Consequences of natural selection-- some examples
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Coat color matching to avoid predators
Pocket mice in the Tularosa Basin of New Mexico
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1.0
0.8
0.6
0.4
0.2
44 42 40 38 36 34 32 30Latitude (degrees North)
Enzyme types change to optimize metabolism
Mummichog along the coast of North America
Freq
uenc
y of
col
d-ad
apte
d al
lele
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Pesticidemolecule
Insect cellmembrane
Target site
Target site
Insect cells with resistance allele at pen gene:decreased uptake of the pesticide
Insect cells with resistance allele at kdr gene:decreased number of target sites for thepesticide
Resistanttarget site
Cell membrane target site change to increase
resistance to insecticide.
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Exercise: Reconsider this question.How do finches evolve into different species?
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Exercise: Do they increase, maintain, or decrease genetic variation?
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You got to have variation to have evolution
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Variation is the spice of life !
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Natural selection can maintain variation, sometimes
• Negative frequency-dependent selection– Phenotype fitness depends on its frequency
within the population. If selection favors rare phenotypes, variation will be maintained.
• Oscillating selection– Selection favors different phenotypes at
different times.
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20 40 60 80 100
Color form frequency
Dark brownMedium brownLight brown
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Per
cent
of c
olor
form
take
n by
fish
pre
dato
rs
Negative frequency-dependent selection
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Three Modes of Natural Selection
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Modes of Natural Selection
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DIRECTIONALSELECTION
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Selection on beak size of finches
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beak depth
1976
1978Averagebeak depth,1978
Averagebeak depth,
1976
Beak depth (mm)
Shift of average beak depth during drought
5 6 7 8 9 10 11 12 13 140
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Num
ber
of in
divi
dual
s
Selection on beak size of finches
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711977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k de
pth
Selection on beak size of finches
72Mean beak depth of parents (mm)
Medium ground finch8
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9
10
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Bea
k de
pth
ofof
fspr
ing
(mm
)
Beak size variations are heritable
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Peppered Moths and Industrial Melanism
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Industrialization favored melanism
• Until the 19th century, peppered moths had predominately light-colored wings. Subsequently, dark individuals became predominant because industrial smog helped turn lichens on tree trunks dark.
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Pollution control reversed the trend
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STABLIZINGSELECTION
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2 3 4 5 6Birth weight in pounds
7 8 9 10
Perc
ent o
f birt
hs in
pop
ulat
ion
Percent infant mortality
Selection on Birth Weight
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DISRUPTIVESELECTION
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Selection on Color in Guppies
• Guppies are found in small streams in S. America and nearby Trinidad.
– Due to dispersal barriers, guppies can be found in pools below waterfalls with high predation risk, or pools above waterfalls with low predation risk.
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Selection on Color in Guppies
Predator
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Evolutionary Change in Spot Number
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Pocket mice in the Tularosa Basin of New Mexico
Another disruptive selection
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Limits to Natural Selection
• Selection requires genetic variation– Intense selection may remove variation
from a population at a rate greater than mutation can replenish.
• Gene interactions affect allelic fitness (epistatic interactions)
– Selection to increase a good gene may increase a bad gene in the same time.
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Limits to Selection
• Genes have multiple effects (pleiotropy)– Selection to increase a desired effect may
increase an undesired bad effect in the same time.• Selection requires genetic variation
– Intense selection may remove variation from a population at a rate greater than mutation can replenish.
• Gene interactions (epistasis)– Selection to increase an allele, which have good
effect in individual A, but bad effect in individual B.
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Left eyeof insect
Ommatidia
Right eyeof insect
Natural selection can’t work on variations without genetic basis
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1920 1940 1960
Year
1980 2000
Ken
tuck
y D
erby
win
ning
tim
e(s
econ
ds)
Natural selection can’t work on traits that run out of genetic variation
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Evolution: Change with time
Do populations of living things change with time?
(Does microevolution occur?)
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Evolution: Change with time
If you don’t believe it, you can go out and measure a population for yourself. There are countless studies that support microevolution.
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Evolution: Change with time
Do populations of living things change with time (microevolution)?
Does gradual accumulation of changes lead to speciation (macroevolution)?
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The problem is
NO ONE HAS WITNESSEDTHE OCCURANCE OF
SPECIATION
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The problem is
ALL WE HAVE ARE CIRCUMSTANTIAL EVIDENCE
THAT SPECIATION OCCURRED
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Who killed this guy?
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Is he the murderer?
No one witnessed the occurrence of the murder.
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But we have circumstantial evidence.
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You are the jury.
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Jury!
Here are the evidence for macroevolution
(speciation).
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The Evidence for Evolution
Chapter 22
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Morphology and function
The 14 finch species in the Galapagos Islands are closely related. Despite the relatedness, beak shapes are morphologically dissimilar. The close correspondence between beak shapes and food types suggested that they were shaped by evolution. Thus, different finch species are the product of evolution.
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Geospizafuliginosa
Geospizaconirostris
Geospizadifficilis
Groundand
cactusfinches
Geospizafortis
Geospizamagnirostris
Geospizascandens
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CamarhynchusparvulusCamarhynchuspsittacula
CamarhynchuspauperCactospizaheliobatesCactospizapallida(woodpecker finch)Platyspizacrassirostris
Treefinches
Vegetariantree finch
Warblerfinches
CerthideafuscaCerthideaolivacea
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Homologous structuresStructures with different appearances and functions that all derived from a common ancestor. Thus, different life forms are the product of evolution.
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Artificial selection
Artificial selection can create drastically different morphology from the original ones. Morphology could be so different that they are hardly the same species. Natural selection, as a similar process, should be able to do the same.
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Highpopulation
Bristle number in Drosophila0 10 20 30 40 50 60 70 80 90 100 110
Lowpopulation
Initialpopulation
Mea
n
Mea
n
Mea
n
Num
ber o
f ind
ivid
uals
After 35 yrs of artificial selection
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Artificial selection of agriculture plants
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Greyhound Mastiff
DachshundChihuahua
Domestication of wolves
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Simpler organisms are found in older rocks; newer rocks contain more complex organisms. It suggests that life forms are not created randomly.
Complexity of life forms
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Complexity of life forms
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Transition of life forms, such as a fossil snake with legs and a fossil aquatic mammal with four legs, provide evidence that life forms transit from one to the next.
Filling in gaps in the fossil record
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Modern toothed whales
Ambulocetus natansprobably walked on land (as do modern sea lions) and swam by flexing its backbone and paddling with its hind limbs (as do modern otters)
Pakicetus attockilived on land, but its skull had already evolved whale characteristics
Rodhocetus kasrani'sreduced hind limbs could not have aided it in walking or swimming. Rodhocetusswam with an up-and-down motion, as do modern whales
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Development (Embryology)
Different organisms exhibit similar embryological forms. It suggests common ancestor.
Early embryo development in all animals goes through similar stages, producing structures not seen in adults of the more complex organisms, e.g., pharyngeal slits in humans.
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Pharyngeal slits in distantly related organisms
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Some structure in the higher organisms do not appear to be better “designed” compared to lower organisms.
Imperfect structures
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Imperfect vertebrate eyes
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Organs with no apparent modern function, but resemble ancestral structures. It provides evidence that life forms transit from one to the next.
Vestigial structures
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Vestigial structures
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The Molecular Similarity
• For a given molecular, distantly related organisms have a greater number of differences than closely related organisms.
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Convergent Evolution
• Convergent evolution - selection that favors changes making two or more groups more similar
– similar results occur under similar selection pressure, for example, marsupial-placental convergence
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Convergent Evolution
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What’s your verdict?
Does gradual accumulation of changes lead to speciation (macroevolution)?
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Exercise:Are you a follower of me now?
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Darwin’s theory on speciation“by means of natural selection” is controversial.
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Is religion itself a product of evolution?
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Is religion itself a product of evolution?
• The God Gene: How Faith Is Hardwired into Our Genes by molecular biologist Dean Hamer.
• Hamer not only claims that human spirituality is an adaptive trait, but he also says he has located one of the genes responsible, a gene that just happens to also code for production of the neurotransmitters that regulate our moods.
• Our most profound feelings of spirituality may be due to little more than an occasional shot of intoxicating brain chemicals governed by our DNA.