Natural Selection (Chapter 24) Flashcards Preview

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Flashcards in Natural Selection (Chapter 24) Deck (24):

___________________ is a genetically based trait that increases an individual’s ability to produce offspring in a particular environment.

an adaption


Evolution by natural selection occurs when __________________________

individuals with certain alleles produce the most surviving offspring in a population


What does it mean by
Populations and species evolve

meaning that their heritable characteristics change through time.  Evolution is change in allele frequencies over time.


[*] All adaptations are constrained by  - what?

trade-offs and by genetic and historical factors.



Why is evolution by natural selection is not progressive

it does not change the characteristics of the individuals that are selected―it changes only the characteristics of the population. Animals do not do things for the good of the species, and not all traits are adaptive.


•Charles Darwin and Alfred Russel Wallace made which claim

the claim that evolution has occurred, that species have changed through time. Then they proposed natural selection as a process to explain the pattern of evolution.


Which idea did idea Darwin and Wallace overturn?

that species were specially, not naturally, created


•Greek philosopher Plato claimed - what?

that every organism was an example of a perfect essence or type created by God and that these types were unchanging.



What is typological thinking?

–Typological thinking is based on the idea that species are unchanging types and that variations within species are unimportant or even misleading.


•Aristotle ordered the types of organisms into a linear scheme called the great chain of being.


–In this chain, species were organized into a fixed sequence based on increasing size and complexity, with humans at the top.


•Aristotle’s ideas were still popular in scientific and religious circles. What were the central claims?

  1. Species are fixed types
  2. Some species are higher—in the sense of being more complex or “better”—than others.


Discuss four kinds of evidence supporting the idea that species change over time.


radio dating

transitional forms of species

vestidual traits


Provide geographical evidence that related species descend from a common ancestor.

•There are often striking similarities among island species.
–For example, Darwin collected mockingbirds from the Galápagos islands.  The mockingbirds were superficially similar, but different islands had distinct species.
•Darwin proposed that the mockingbirds were similar because they had descended from a common ancestor.
•The mockingbird species are part of a phylogeny, a family tree of populations or species.
•The relationship between different species can be shown on a phylogenetic tree.


Discuss three levels of homology that provide evidence of descent from a common ancestor.

•Another line of evidence comes from homologies.

–Homology is a similarity that exists in species descended from a common ancestor.

Homology can be recognized and studied at three interacting levels: genetic, developmental, and structural


Briefly describe the evolution of cetaceans.

•Several lines of evidence support the hypothesis that whales evolved from a terrestrial ancestor:
–Some fossil cetaceans resemble extant terrestrial mammals, others resemble extant aquatic mammals, and others are intermediate.
–A phylogeny, supported by relative and absolute dating, of fossil cetaceans indicates a gradual transition between terrestrial and aquatic, whalelike forms. 
–Molecular comparisons indicate that hippos are the closest living relative of cetaceans and that they share a semiaquatic ancestor.
Some cetaceans have vestigial limbs as adults or embryos


Explain Darwin’s postulates on the process of evolution by natural selection.


•While many researchers had proposed the fact of evolution, Darwin’s contribution was describing a pattern, natural selection, that could explain the process of descent with modification.

•Darwin broke the process of evolution by natural selection down into four steps, or postulates.

1.Individual organisms that make up a population vary in the traits they posses; size and shape.

2.Some of these differences are heritable; they are passed on to offspring.

3.In each generation, many more offspring are produced than can survive; of these, only some will survive long enough to reproduce, and some will produce more offspring than others.

4.Individuals with certain heritable traits are more likely to survive and reproduce. Natural selection occurs when individuals with certain traits produce more offspring than do individuals without those traits.


State the modern two-part synthesis of Darwin’s postulates.


•Modern biologists condense Darwin’s four steps into two statements: Evolution by natural selection occurs when:
1.Heritable variation leads to
2.Differential success in survival and reproduction.


Contrast adaptation (p 464) and acclimation (pp 471-2).

[*] adaptation is a heritable trait that increases an individual's Darwinian fitness in a particular environment relative to individuals lacking that trait. Adaptations increase fitness—the ability to produce offspring.

•Acclimation occurs when an individual’s phenotype changes in response to changes in the environment, but an individual’s genotype remains fixed, so the changes are not passed on to offspring.


Discuss an example of evolution from recent research on natural selection.

(Mycobacterium drug resistance, or size of Atlantic cod, or Galapagos finches during drought)

•Atlantic cod ( Gadus morhua) suffered a 99 percent decline in population between 1962 and 1992. Jeffrey Hutchings of Dalhousie University estimates that two billion cod were lost during this 30-year period.
–Atlantic cod with a genetic predisposition to mature at larger size or greater age were likely to be caught before they were able to reproduce.
–Cod that matured early, at a small size, had greater reproductive success.
•The result was strong directional selection for early-maturing, small adult cod.

•Small adult cod suffer a higher natural mortality, have a shorter life span, and produce fewer offspring than the large cod that were targeted by fishers
•Unlike natural predators, humans harvest other predators;
–Humans also target large age and size classes.
–Natural predators focus on “the newly born and the nearly dead,”
–Humans prefer to take large, healthy reproductive adults.
–Humans also take a far higher proportion of the harvested populations


Explain some common misconceptions about evolution (individuals do not change, evolution is not goal-directed, organisms do not act for the good of the species).

•Scientifically, there is no such thing as “higher” or “lower” organisms.

•A human is no higher than its tapeworm parasite; each is well adapted to its environment.

•All populations have evolved by natural selection based on their ability to gather resources and produce offspring. All organisms are adapted to their environment, and are related by common ancestry.

•Individuals with self-sacrificing alleles die and do not produce offspring.
•Individuals with selfish, “cheater” alleles survive and produce offspring.
•As a result, selfish alleles increase in frequency while self-sacrificing alleles decrease in frequency.
•Thus, it is not possible for individuals to sacrifice themselves for the good of the species.
•Lemmings do not throw themselves over a cliff into the sea when their populations get high.


Discuss four limitations to natural selection.

•Although organisms are often exquisitely adapted to their environment, adaptation is far from perfect.

•A long list of circumstances limits the effectiveness of natural selection.



Populations and species evolve, meaning that

their heritable characteristics change through time