Evolution by Natural Selection

How did life originate? Why are all the species we see on earth in existence? 3 main ideas

Creationism

Seeding theory

Evolution by natural selection Evolution by natural selection

In the distant future... Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. --Charles Darwin, 1859

Landmarks in the History of Evolutionary Thinking

Evolution Before Darwin Change over time in organic structures (evolution) Change over time in organic structures (evolution) Characteristics seemed to have a purpose (porcupines, turtles, skunks) Characteristics seemed to have a purpose (porcupines, turtles, skunks)

Jean Pierre Antoine de Monet de Lamarck ( ) Two causes of species change: 1. Progress toward a higher form 2. Inheritance of acquired characteristics

Darwin’s Theory of Natural Selection The explanatory challenge: The explanatory challenge: 1. why change takes place 2. how new species emerge 3. what the functions are of parts

One clue: Malthus: more organisms produced than survive and reproduce, leading to “a struggle for existence”

More individuals produced than can possibly survive

Struggle for Survival

Natural Selection Variation Variation Inheritance Inheritance Differential Reproduction Differential Reproduction

The key to natural selection: Differential reproductive success because of heritable variants; everyone has ancestors, but not everyone leaves descendants

Natural selection provided 3 key answers Explained change over time (descent with modification) Explained change over time (descent with modification) Explained apparent purposive quality of component parts Explained apparent purposive quality of component parts United all species into one grand tree of descent (including humans) United all species into one grand tree of descent (including humans)

Problems That Troubled Darwin 1. Phenomena that seemed inexplicable on the theory of “survival selection” 2. The existence of sex differences.

Objections to Natural Selection No theory of inheritance at the time No theory of inheritance at the time Hard to imagine utility of intermediate stages, and natural selection requires each step to benefit Hard to imagine utility of intermediate stages, and natural selection requires each step to benefit Beliefs at the time that species were unchanging Beliefs at the time that species were unchanging

Three Products of Evolutionary Processes 1. Adaptations 1. Adaptations 2. Byproducts 2. Byproducts 3. Noise 3. Noise

Adaptations 1. inherited characteristics 1. inherited characteristics 2. reliably developing in most or all species members 2. reliably developing in most or all species members 3. produced by natural or sexual selection… 3. produced by natural or sexual selection… 4. because they solved an adaptive problem— functionality 4. because they solved an adaptive problem— functionality 5. must have contributed to reproductive success, directly or indirectly 5. must have contributed to reproductive success, directly or indirectly 6. need not be present at birth (teeth, breasts, beards, desires, etc.) 6. need not be present at birth (teeth, breasts, beards, desires, etc.)

One Example of Adaptation: Umbilical Cord

Byproducts Characteristics that do not solve adaptive problems Characteristics that do not solve adaptive problems Do not have functional design Do not have functional design Are “carried along” with characteristics that do have functional design Are “carried along” with characteristics that do have functional design

Examples of Byproducts: belly button

More Examples of Byproducts belly button belly button heat from light bulb heat from light bulb white color of bones white color of bones Attributing intentionality to objects that do not have intentionality (sun, clouds) Attributing intentionality to objects that do not have intentionality (sun, clouds)

Noise: random effects due to mutations or perturbations during development Examples: shape of belly button; perturbation in roundness of glass bulb

Adaptations are the primary products of natural and sexual selection

Sexual Selection Intrasexual Competition Intrasexual Competition Intersexual Selection Intersexual Selection

“The sight of the peacock gives me nightmares” – Charles Darwin

Intrasexual Competition competition among members of the same sex for mating competition among members of the same sex for mating

Thought experiment: Examples in humans of intrasexual competition?

Intersexual Selection: Preferential Mate Choice a form of sexual selection in which members of one sex are differentially attracted to members of the opposite sex

Intersexual Selection: Preferential Mate Choice

Two Kinds Of Causal Questions Proximate: HOW a mechanism develops and operates Proximate: HOW a mechanism develops and operates Ultimate: WHY a mechanism evolved— evolutionary forces that led to the creation of the mechanism; the adaptive problem it evolved to solve. Ultimate: WHY a mechanism evolved— evolutionary forces that led to the creation of the mechanism; the adaptive problem it evolved to solve.

Causal Question Why are men taller than women on average?

Proximate and Ultimate Answers to Questions Why are men taller than women on average? Why are men taller than women on average? Why do people grow calluses? Why do people grow calluses? Why do people like to eat pizza? Why do people like to eat pizza? Why do people get jealous? Why do people get jealous?