Geology Reference
In-Depth Information
What Would You Do
?
among evolutionary lineages, but overall they are overwhelm-
ingly united in their support for the theory. And despite stories
holding that scientists are unyieldingly committed to this idea
and unwilling to investigate alternative explanations for the
same data, just the opposite is true. If another scientifi c (test-
able) hypothesis offered a more fruitful approach, scientists
would be scrambling to investigate it. There is no better way
in the sciences to gain respect and lasting recognition than to
modify or replace an existing widely accepted theory.
Suppose someone told you that evolution is “only a theory
that has never been proven” and that “the fossil record
shows a sequence of organisms in older to younger rocks
that was determined by their density and habitat.” Why is the
fi rst statement irrelevant to theories in general? What kinds
of evidence could you cite to refute the second statement?
Chapter Summary
Jean-Baptiste de Lamarck's proposal of inheritance of
acquired characteristics was the fi rst formal explanation
for the theory of evolution to be taken seriously.
In 1859, Charles Robert Darwin and Alfred Russel Wal-
lace published their views on evolution and proposed nat-
ural selection as the mechanism for evolutionary change.
Darwin's observations of variation in natural populations
and artifi cial selection, as well as his reading of Thomas
Malthus's essay on population, helped him formulate the
idea that natural processes select favorable variants for
survival.
Gregor Mendel's breeding experiments with garden peas
provided some of the answers regarding how variation is
maintained and passed on.
Genes are the hereditary determinants in all organisms.
This genetic information is carried in the chromosomes
of cells, but only the genes in the chromosomes of sex cells
are inheritable.
Sexual reproduction and mutations account for most
variation in populations.
Evolution by natural selection is a two-step process. First,
variation must be produced and maintained in inter-
breeding populations, and second, favorable variants
must be selected for survival.
An important way in which new species evolve is by allo-
patric speciation. When a group is isolated from its parent
population, gene fl ow is restricted or eliminated, and the
isolated group is subjected to different selection pressures.
Divergent evolution involves an ancestral stock giving rise
to diverse species. The development of similar adaptive
types in different groups of organisms results from paral-
lel and convergent evolution.
Microevolution involves changes within a species,
whereas macroevolution encompasses all changes above
the species level. Macroevolution is simply the outcome
of microevolution over time.
Scientists are increasingly using cladistic analyses to
determine relationships among organisms.
Extinctions take place continually, and times of mass
extinctions resulting in marked decreases in Earth's bio-
logic diversity have occurred several times.
The theory of evolution is truly scientifi c because we can
think of observations and experiments that could sup-
port or falsify it.
Much of the evidence supporting the theory of evolution
comes from classifi cation, embryology, genetics, bio-
chemistry, molecular biology, and present-day small-scale
evolution.
The fossil record also provides evidence for evolution in
that it shows a sequence of different groups appearing
through time, and some fossils show features that we would
expect in the ancestors of birds or mammals, and so on.
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Important Terms
allele (p. 474)
allopatric speciation (p. 477)
analogous structure (p. 484)
artifi cial selection (p. 472)
body fossil (p. 485)
chromosome (p. 475)
cladistics (p. 480)
cladogram (p. 480)
convergent evolution (p. 478)
deoxyribonucleic acid (DNA) (p. 475)
divergent evolution (p. 478)
fossil (p. 485)
gene (p. 474)
homologous structure (p. 484)
inheritance of acquired characteristics
(p. 470)
macroevolution (p. 480)
mass extinction (p. 482)
meiosis (p. 476)
microevolution (p. 479)
mitosis (p. 476)
modern synthesis (p. 476)
mosaic evolution (p. 481)
mutation (p. 476)
natural selection (p. 472)
paleontology (p. 470)
parallel evolution (p. 478)
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