psych
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Introducing Evolutionary Theory
Lectures 2 & 3 Dr. Francine Dolins University of Michigan-Dearborn
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Topics of Discussion
o Issues and pitfalls in evolutionary thinking: think critically!
o Before Darwin o Darwin’s Theory of Evolution by Natural Selection o Genes and the Modern Synthesis o Average and Inclusive Fitness and ‘The Selfish Gene
Theory’ o Ethology and understanding evolution of behavior
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Armchair Thinking or “Just so” stories
Excerpt, Buss (2002), Evolution of Desire
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Before Darwin
o species seen as immutable (unchangeable); created by higher being
o explanation: n differences between species —physical & behavioral
characteristics n similarities between species —physical & behavioral
characteristics, and in embryological development n the functionality/ apparent purposefulness of parts of
organisms o Lamarck — inheritance of acquired characteristics
n giraffes necks: how did they get to be so long? n Epigenetics: support for Lamarck in the 21st century!
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Galapagos Finches …Darwin on beetles…
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Darwin’s influences and theory o H.M.S. Beagle, Galapagos Islands and its finches
n http://www.britannica.com/EBchecked/topic-art/223745/74641/Fourteen-species-of- Galapagos-finches-that-evolved-from-a-common
o Why variation of traits in birds that were alike and inhabited the same environment?
o Thomas Malthus: An Essay on the Principle of Population (1798) population growth & decline.
o Darwin applied Malthus’ principles: n Larger populations exist than can survive and reproduce leading to
a struggle for survival. n Those with favorable traits selected for, survive, and pass on those
traits to offspring. n Certain favorable traits become more prevalent in a population. n We refer to this population as a “gene pool”.
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Darwin’s influences and theory continued The Theory of Natural Selection (Darwin, also Alfred Russell
Wallace) based on: n variation — in physical & behavioral characteristics/traits of
an individual (the ‘tapestry’ of evolution) n adaptation — favorable traits selected for by the environment
promoting better survival and passing on of genes n inheritance — only some of these variations are inherited n selection — based on the adaptive nature of traits n competition for limited resources (mates, food, nest sites,
etc) within & between species n reproductive success is the measure or currency of evolution
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What is ‘Selection’ o FOUR types of selection in Evolution:
n Natural n Sexual n Kin n Group n (Artificial selection: only human-induced, not part of evolution)
o The mechanism of selection is adaptation to a given habitat or environment = an ecological niche.
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Evolution by Natural Selection Thus, Evolution by Natural Selection is:
A biological process in which, from the variation of characteristics in a given population, favorable traits are selected for that enhance an individual’s adaptation to its environment.
These traits, and therefore these adaptations to surviving in a given environment, are passed on to viable offspring, increasing the frequency of these genes in the gene pool and the population.
Why a “given” population” Why “viable” offspring?
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Mechanisms of Natural Selection within a lifetime and over generations
o William Hamilton (& George Williams) o AVERAGE FITNESS: sum of an individual’s own reproductive
success during their lifetime (e.g., how many viable offspring survive to reproduce)
o INCLUSIVE FITNESS: sum of an individual’s own reproductive success (= average fitness) + the reproductive success of genetic relatives + the reproductive success of relatives over generations, weighted by the degree of relatedness
o e.g. 0.5 for siblings; 0.5 for offspring; 0.25 for grandchildren o ‘The Selfish Gene Theory’(Richard Dawkins, 1976):
=> Evolution works on the molecular level n to express ideas of Hamilton & Williams about average and
inclusive fitness
Natural Selection in Humans
http://news.sciencemag.org/sciencenow/2012/04/n atural-selection-is-still-with-.html
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Darwin’s theory: some important points • Evolution is not ‘forward-looking’, ‘intentional’ or ‘goal-directed’; a blind watch-
maker (Dawkins) • Evolution is gradual [What is ‘gradual’? Everything is relative!]
o evolution can be relative, occurring in ‘spurts’ with periods of stasis [Punctuated Equilibrium; Stephen Jay Gould]
o each and every step in the gradual evolution of a feature or trait must be ‘advantageous’ (ultimately, in respect of reproduction) — e.g. ‘partial wings’, ‘partial eyes’
o The problem of the dung beetle: Crypticity - What is the good of looking 1/3rd like a piece of dung? [Stephen Jay Gould]
• Evolution does not work to perfection but is often “optimal” • All species can be seen as being connected by the same lineage: a large bush, not a
ladder. [See sketch of Darwin’s evolutionary tree] • Evolution is not a moral process (e.g. infanticide). • Evolution works by reproduction (e.g. sexual reproduction to maintain variation in
populations).
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Darwin’s evolutionary tree
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The great ape evolutionary tree (from Corballis, 1999)
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Genes and the modern synthesis o Introduction
n natural selection is not the only form of evolution, but it’s the only one we know that produces complex design
n Darwin didn’t have a coherent theory of inheritance, & didn’t know the nature of the mechanism of inheritance ...
o genes n Gregor Mendel and his experiments with variations in sweet
pea plants n genotype, phenotype (see next slide); DNA; Crick & Watson n the units of inheritance — the vehicles for the transmission of
information through lineages of organisms n the information that genes transmit constitutes the instructions
for the design of those organisms
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Genotype and Phenotype
o Genotype = the make-up (total) of one’s genes (a “genome”)
o Phenotype = the make-up of one’s genes + the interaction with the environment; n all observable characteristics n e.g., hair and eye color n including some behaviors
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Ethology and the evolution of behavior
o Behavior leaves behind no fossils o Darwin: theory applies to behavior as well as to physical
structures n all behavior depends on physical structures n artificial selection/ breeding of species for behavioral
characteristics
o Ethology: the study of behavior in the subject’s natural environment n e.g., imprinting & Konrad Lorenz n Niko Tinbergen & the 4 ‘whys’ of behavior: (see next slide)
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Niko Tinbergen & the four ‘whys’ of behavior
n immediate causes: according to the behavior’s SURVIVAL VALUE and CAUSATION of the behavior
n developmental causes: DEVELOPMENT of the behavior
n adaptive function: according to the behavior’s FUNCTIONAL VALUE
n evolutionary origins: EVOLUTIONARY HISTORY of the species
Why is a behavior shown?
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Two levels for studying behavior o Proximate level
n Questions about HOW behavior happens n Tend to focus on the internal mechanisms of behavior
o Ultimate level n Questions about WHY a behavior occurs n Deals with the evolutionary value of a behavior
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“How” questions about proximate causes o What is the causal relationship between the animal’s genes and its
behavior? o Is the trait to some extent inherited from its parents? o Does the diet of the animal during development influence how it
acts as an adult? o What stimuli trigger the response, and how are these stimuli
detected?
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“Why” questions about ultimate causes o Has the behavior evolved over time? o If so, why did the changes take place? o What was the original step in the historical process that led to the
current behavior? o What is the purpose, the function, of the behavior? o Does the behavior help the individual to better survive in order to
reproduce?
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Causes
o Proximate n Genetic-developmental
mechanisms o Effects of heredity on behavior o G-E interactions underlying the
development of S-M mechanisms n Sensory-motor (S-M)
mechanisms o Nervous system detection of
environ. stimuli o Hormone systems for adjusting
responsiveness to environ. stimuli o Skeletal-muscular systems for
carrying out responses
o Ultimate n Historical pathways leading
to current behavior o Events occurring over
evolution from the origin of a trait to present
n Selective processes shaping the history of a behavioral trait
o Past and current usefulness of the behavior in reproductive terms
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Proximate and Ultimate not Mutually Exclusive, but Continuous
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WWW links
The BBC Evolution Web Site: http://www.bbc.co.uk/education/darwin/
The Evolutionist Online Magazine: http://www.lse.ac.uk/Depts/cpnss/darwin/evo/ interviews with a selection of today’s leading evolutionary thinkers
Darwin and Darwinism: http://www.human-nature.com/darwin/index.html
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Additional reading
o Barrett, L., Dunbar, R., Lycett, J. (2002). Human Evolutionary Psychology. Princeton, NJ: Princeton University Press. Chapter 2
o Jolly, A. (2001). Lucy's Legacy: Sex and Intelligence in Human Evolution. Boston: Harvard University Press. Section I, Chapter 2
o Buss, D.M. (1999). Chapters 1 & 2: The new science of evolutionary psychology. Evolutionary psychology: The new science of the mind. Boston, MA: Allyn & Bacon
o Cosmides, L. & Tooby, J. (1997). Evolutionary psychology: A primer. [http://www.psych.ucsb.edu/research/cep/primer.html ]
o Miele, F. (1996). The (Im)moral animal: A quick and dirty guide to evolutionary psychology and the nature of human nature. Skeptic, 4, 42-49. [http://www.skeptic.com/magazine.html]
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References and further reading
Buss, D.M. (1999). Evolutionary psychology: The new science of the mind. Boston: Allyn & Bacon. — Chap. 1
Cartwright, J. (2000). Evolution and human behaviour: Darwinian perspectives on human nature. Basingstoke & London: Macmillan. — Chapters 2 & 3 (+ Chap. 1).
Corballis, M.C. (1999). Phylogeny from apes to humans. In M.C. Corballis & S.E.G. Lea (Eds.), The descent of mind: Psychological perspectives on hominid evolution (pp.40-70). Oxford: Oxford University Press.
Darwin, C. (1859). On the origin of species by means of natural selection. London: John Murray. — edited excerpts in: Ridley, Mark (Ed.) (1994). A Darwin selection. (Revised edition.) London: Fontana Press. — pp.84-126
Dawkins, R. (1976). The selfish gene. Oxford: Oxford University Press.
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References and further reading
Dawkins, R. (1986). The blind watchmaker. London: Longman/Penguin. Ideally, you should read the whole book! But at least “Chapter 2: Good design.”
Dawkins, R. (1995). River out of Eden: A Darwinian view of life. London: Weidenfeld & Nicolson. — Chapter 1: The digital river.
Dennett, D.C. (1995). Darwin's dangerous idea. Evolution and the meanings of life. New York: Simon & Schuster. — Chapter Two: An idea is born (pp.35-60)
Maynard Smith, J. (1975). The theory of evolution. 3rd edition. Harmondsworth, Middlesex: Penguin. — Chapter 1: Adaptation; & Chapter 2: Natural selection
Sober, E. (1993). Philosophy of biology. Boulder, CO: Westview Press. — Chapt 1: What is evolutionary theory?
Sterelny, K. & Griffiths, P.E. (1999). Sex and death: An introduction to philosophy of biology. Chicago: Chicago University Press. — Chapters 2, 3 & 4
Williams, G.C. (1996). Plan and purpose in nature. London: Weidenfeld & Nicolson/ Phoenix. — Chapters 1, 2 & 3