· like a snake, but is really

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Biologists categorize and distinguish
the millions of species on Earth through what is called a phylogeny. This is
basically a “family tree” that traces the evolutionary history of a group or
species. For example, figure 26.1 shows what looks like a snake, but is really
a legless lizard. One would think that these organisms are the same; however,
when looking at the phylogeny of snakes and lizards, one could observe that
these two organisms evolved from different lineages of legged lizards.

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Binomial nomenclature is a system
created by Carolus Linnaeus to name species based on resemblance and has two
parts to it. The first part of the name is of the genus which specifies the
species. The second part is called the specific epithet, which distinguishes
species from one another in the same genus. For example, Panthera pardus. Taxonomy is naming of biological organisms. Figure
26.3 illustrates the taxonomic system for a Panther; Species: Panther pardus,
Genus: Panthera, Family: Felidae, Order: Carnivora, Class: Mammalia, Phylum:
Chordata, Kingdom: Animalia, Domain: Archaea, Eukarya, and Bacteria. In
branching phylogenetic trees,
scientists are able to make connections in relationships within species. For
example, Figure 26.4 shows the connection and phylogeny between the leopard,
badger, otter, coyote and wolf. From this tree, one could conclude that the
badger and the wolf share a common ancestor that is more recent than the
ancestor the badger and wolf share with the leopard. Each branch point illustrates
the separation of species. From a phylogenetic tree, one can observe that it show
patterns of descent, not phenotypic similarity.  

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Homology means
to have a shared common ancestor. Homoplasy means to look the same. Cyanobacteria
are green, trees are green; this is an example of homoplasy. To question “why
are they green”, is an analogy. Analogous characters result from convergent
evolution. In figure 26.7, convergent evolution in moles is illustrated. Both
North American and Australian moles have large front paws, small eyes, and a
pad of thick skin that protects the nose. All these characteristics have
evolved in these species.

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In cladistics,
organisms are characterized based on shared derived characteristics. Figure
26.10 illustrates the three types of cladistics: a monophyletic group (clade)
includes the common ancestor and all of the descendants. A paraphyletic group
includes the common ancestor and some but not all of the descendants. A
polyphyletic group does not include a common ancestor. 

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In figure
26.13, the length of a branch can represent genetic change. The branch lengths
are proportional to the amount of genetic change in each lineage. In these
trees, branch length indicates that the gene has evolved at different rates in
different lineages. In figure 24.14, branch length can indicate time. Here,
branch points are mapped based on fossil evidence. In these trees, branch
lengths are proportional to time. Each lineage has diverged from the common
ancestor for equal amounts of time.

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When
reconstructing phylogenies, it is better to compare orthologous genes it
results from speciation and reflects evolutionary history, whereas Paralogous
genes result from gene duplication.

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A molecular
clock is a method of estimating the actual time of evolutionary events based on
the numbers of base changes in genes. It is based on the assumption that the
regions of genomes evolve at a constant rate.