Download scheme for the human species is illustrated in ` Vestigial structures

Species
Genus
Family
Order
-
Domain
Figure
pat{:erm
be fossils of transitional forms between them
and there are. Transitional species are defined as
those that show a mixture of features from both
their ancestors and their descendants. There are
transitional fossils between fish and amphibians,
reptiles and birds, hippos and whales, and apes and
humans.
' fl,ogical inf,erence. Modern evolutionary theory
evolution to occur, only two processes
are required. One is mutation
a change in the
states that for
genetic material
-
of an organism. The other is
natural selection, defined as a change in the genetic
composition of a population of organisms caused
by differences in reproduction between individuals.
Both mutation and natural selection can be directly
observed, so evolution is inevitable.
F{ierarchical classification. If all organisms are
related by descent, it should be possible to classify
them into a nested pattern of groups within groups.
Each group is defined by an agreed set of similar
characteristics. The application of this hierarchical
scheme for the human species is illustrated in
3
of
-
Homo sapiens
Horzo
Hominidae Great apes
Primates Aoes. monkevs, lemurs
-
Chordata Animals that have a notochord
Animatia Multicellular eukaryotes that eat other organisms
.-
Eukaffa
Organisms with cells that contain a nucleus
Qr.garTislals qaul 8le aflassi$ieci im a
gTnou,rgls
Humans
Mammalia Chordates that have nrammary gland
Phylum
Kingdom
-
-
-
hierarthicel fashiotl
fim
a ruesteol
trulthim glreug'rs.
' Vestigial structures. Vestigial structures are
defined as structures that are reduced in complexity
and function compared with similar structures in
other organisms. These structures occur at both the
anatomical level in the form of vestigial organs and
at the molecular level in the form of pseudogenes.
There are many examples of vestigial anatomical
structures that have no known functions, such as
reduced pelvises and hind limb bones inside the
skins of pythons and whales, and the wisdom teeth,
appendix and coccyx of humans. Pseudogenes are
genes that have lost their original protein-coding
ability. About 600/o of the 1000 smell receptor genes
in humans are pseudogenes
- we rely far less on
smell and more on sight than our ancestors did.
Dobzhansky was correct: evolution does make
sense ofbiology.
Figure 3.
Eiogeography. Location provides a better index of
biological similarity than does similarity of climate
because geography reflects descent from common
ancestors. For example, both the North and South
American continents share the same range of humid
forests, arid mountains, grassy plains, marshes,
lakes and rivers as does the European continent. But
there are few species of animals or plants that occur
naturally in both locations.
No',,emher 2C't2
o Evolution is the change in the genetic composition
of organisms between generations.
o Natural selection is the change in the genetic
composition of organisms between generations
caused by differences in reproduction.
o A scientific theory is a conceptual model that
explains whole sets of facts and withstands falsifiable
predictions.
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