Evolution by Natural Selection Flashcards
Natural Selection
Nature judges existing alternatives in each generation
Those alternatives that best promote survival and reproduction are most likely to be passed on to succeeding generations
Darwin’s Argument on Population
Despite this potential for exponential growth, natural populations normally are relatively stable
Populations do not grow exponentially
Organisms must be reproducing differentially
i.e. some elephants do not produce six offspring
Darwin’s Argument
Those best suited to the prevailing environment leave the most offspring
Reproductive rates among organisms are not random
Nature selects those best able to cope with the environments
Those that are unable to cope with the environment produce fewer (or no) offspring
Darwin’s Argument Heredity
Because of heredity, offspring are like their parents
Advantages that allowed organisms to reproduce are passed on
Disadvantages that caused organisms to fail to reproduce are not passed on
Thus, offspring begin with the advantages of their ancestors
Survival of the Fittest
Coined by Herbert Spencer
Not an accurate summary of natural selection
Survival is only important insofar as it aids reproduction
Fittest is better described as those best suited to the prevailing environment
Reproduction of the sexiest
Homology
Evolution recycles traits when it constructs new adaptations
Different animals exhibit many of the same structural elements
Often times these elements have been modified for different functions
The Comparative Method
Similar structures in divergent species
Divergent structures in similar species
Universality of the genetic code
DNA
64 possible triplets of a 24-letter alphabet produce 20 amino acids plus a punctuation mark
The odds of arriving at the same 64:21 mapping are less than one in a million million million million million
Universality of the genetic code
The genetic code is literally identical in all animals, plants, and bacteria
This strongly suggests that all living things descended from a common ancestor
Adaptations
“… may be defined as an inherited and reliably developing characteristic that came into existence as a feature of a species through natural selection because it helped to directly or indirectly facilitate reproduction during the period of its evolution”
We are filled with adaptations for solving recurrent problems faced by our ancestors
Biological Adaptations
(Vision)
The visual system doesn’t interpret brightness as the amount of light that hits the retina
Coal in the light is still seen as black
Snowball in the dark is still seen as white
Psychological Adaptations
A chimpanzee and a human child are exposed to an environment rich with spoken language
One will learn to speak while the other will not
Humans have a specialized Language Acquisition Device
Reverse-Engineering the Mind
The mind is a system of organs of computation designed* to solve problems
These include understanding and outmaneuvering objects, animals, plants, and other people
The mind was designed or engineered
With this view, psychology is engineering in reverse
In forward-engineering, one designs a machine to do something
In reverse-engineering, one figures out what a machine was designed to do- Toaster example
Adaptations- Pace
Form slowly
The pace of evolution is partly determined by generation time
Generation time – the length of time from birth to reproduction
Easiest to observe natural selection in organisms with short generation times
Evolution can only select from existing possibilities
Macro-mutations
Rarely occur
Rarely favored by natural selection
Adaptations are specialized
Less specialized designs do not work as well
e.g. Number and ratio of rods and cones varies among species and is dependent on whether they are nocturnal or diurnal
Carpenter’s toolbox
Adaptations are costly
Assembling the trait during development
Maintaining the trait metabolically
Natural Selection always works with costs and benefits
Adaptations are outdated
Organisms are better adapted to the past than the present
Natural selection cannot keep up with the fast changing environment
Adaptations may fail in novel environments
Response – how genes cause the organism to adjust to environmental change (sun tan)
Susceptibility – maladaptive change in the phenotype (sun burn)
Psychological Adaptations
Just as evolution can sculpt anatomical adaptations, it can shape psychological adaptations
Each adaptation was sculpted to solve a specific recurrent problem
No general purpose mechanisms
Natural selection can’t sculpt behavior, but…
It can sculpt adaptations that influence behavior
Modular Psychological Adaptations
consisting of a set of specialized separate elements, each performing a distinctive role or task
Domain Specific Psychological Adaptations
Domain specific – designed to accept a particular kind of input and produce a particular kind of output
Sexual Selection
Reproductive rate – how many offspring an individual can produce per unit time
Sexual Selection happens because the faster reproducing sex experiences a shortage of mates
Reproductive Rates
Key point
The competition for mates will ALWAYS be less intense in the sex with the slower reproductive rate
Exceptions prove the rule
The slow sex is always the “choosy” sex
The fast sex is always the competitive sex
Intrasexual selection
Occurs as a result of competition within/among members of the same sex
Intersexual selection
Occurs as a result of choices made by one sex for features of another
Selfish
Increase the fitness of the self, but decrease the fitness of neighbors
Altruistic
Decrease the fitness of the self, but increase the fitness of neighbors
Cooperative
Increase the fitness of both the self and neighbors
Spiteful
Decrease the fitness of both the self and neighbors
Group Selection
An argument stating that altruism would be perpetuated because it is good for the group as a whole
An insignificant evolutionary force
(though not without debate)
