Evolution By Natural Selection

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adaptation

Back 1

feature of an organism created by the process of natural selection

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natural selection

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process that produces adaptations, based on the 3 postulates

*NON RANDOM DIFFERENTIAL REPRODUCTION

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morphology

Back 3

form & structure of organism

and field of study that focuses on form and structure

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equilibrium

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steady state in which composition of population doesn't change

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stabilizing selection

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selection pressures that favor average phenos

--> reduces amt of variation but doesn't change the mean value of the trait

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trait

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characteristic of an organism

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character

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trait/attribute of phenotype of organism

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species

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group of organisms classified together @ lowest level of taxonomic hierarchy

-biological vs ecological species concept

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fecundity

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biological capacity to reproduce

(not same as fertility)

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continuous variation

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phenotypic variation in which there's a continuum of types

ex- height in humans

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discontinuous variation

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phenotypic variation in which there's discrete # of phenos w/ no intermediate types

ex- mendel's pea color

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convergent evolution/analogy

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evolution of similar adaptations in unrelated species

ex- camera eyes in vertebrates and mollusks

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placental mammals

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gives birth to live young (developed for period of time in uterus, nourished by blood delivered to placenta)

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marsupials

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mammal that gives birth to live young (continue developing in pouch with mammary gland)

ex- kangaroos, opossums

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blending inheritance

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model of inheritance (accepted during 19th cent)

*hereditary material of mom and dad thought to combine irreversibly in offspring

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for any 2 categories in Linnaeus' hierarchy, they are either...

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1. non-overlapping
(birds and bats)

2. one fits entirely w/i the other
(bats in mammals)

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Lamarckian inheritance

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idea that organism can pass on to offspring characteristics that it acquired during its lifetime

ex- giraffe striving for higher leaves develops long neck

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influences on Darwin's theory

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1. Malthus- essay on principle of population

2. observation of variability in nature

3. artificial selection

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DARWIN'S 3 POSTULATES

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1. variation within population

2. struggle for existence

3. heritability

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variation (1st postulate)

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organisms w/i pop vary, variation affects ability of organism to survive and repro

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struggle for existence (2nd postulate)

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ability of pop to expand is infinite, ability to environment to support is finite

-competition

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heritability (3rd postulate)

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variations transmitted from parents to offspring

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Daphnia example of natural selection

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variation- even before bacteria became problem, some daphnia more resistant than others

heritability- clones from diff periods differed genetically

struggle- toxin-resistant strains outreproduced less resistant strains

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MISUNDERSTANDING: Adaptations generally benefit individuals' survival and reproduction, even at expense of the species' well being.

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but evolution changes composition of population NO PERSONAL EVOLUTION

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MISUNDERSTANDING:
Natural selection is a circular argument (traits that persist are the ones that persist)

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traits that persist are the ones that engineer would consider better designed

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MISUNDERSTANDING: Natural selection is equivalent to random chance.

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variation is generated randomly but next generation's traits ARE SELECTED not random

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MISUNDERSTANDING: Natural selection usually acts to cause evolution.

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actually...usually acts to prevent it

STABILIZING SELECTION- keeping distribution of traits the same

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MISUNDERSTANDING: Natural selection makes traits all at once.

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nope...builds complex adaptations step by step

ex- eyes, winds

(simple but effective intermediate forms)

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MISUNDERSTANDING: Natural selection makes changes toward greater complexity.

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doesn't mean progress/global improvement

ex- blind cave fish

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problems darwin couldn't solve

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what maintains variation?

how can nat select extend range of variation?