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A history of life, how we describe it, and a scientific look at how it came

to be.• Prebiosis:

– Clay as catalysts? Organic molecules from comets? Spontaneous cell membranes from fatty molecules? RNA as the first genetic molecule?

• Somehow, something resembling a cell that could reproduce itself came into being, and life has been reproducing itself ever since.

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Everything is related

• Our understanding of evolution is that all organisms have common ancestors.– Cell structures are very similar– Same molecules store genetic information

and use same genetic code.– All organisms use ribosomes to make proteins– Comparative molecular biology shows that

organisms supposed to be related have relative view differences in amino acids.

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Little changes, big changes

• Microevolution– Species accumulate changes in alleles– When populations become reproductively

isolated and gene flow no longer occurs, gene pools can vary.

– If environments change, species can become separate.

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Big changes, not random• Macroevolution

– Natural selection acts on existing characteristics; the best adapted to environment pass on the genes

– A “niche” is a habitat, way of obtaining nutrients, a “role” in the environment.

– When niches become available (e.g. after a mass extinction) species may change “rapidly” to fill the niche

– Outcome is not random, but• Depends on pre-exisiting traits• What best allows reproduction

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So many species

• What to do?– We name them– We group them– We order them– We look for more.

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Why do we name things?

• To distinguish one thing from another

• To communicate with others more effectively

• It forces us to examine things more closely and make distinctions

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Classical Taxonomy – the Binomial System

• Carl von Linné (a.k.a.) Carolus Linnaeus

• Binomial nomenclature – each organism gets two names, a genus name and a species name. These are always used together. You cannot use a species name without the genus name.

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If you ordered americanus in a restaurant ….

• Homarus americanus – lobster

• Ursus americanus – black bear

• Bufo americanus – American toad

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Biological Species Concept

• Biological species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups.

• Reproductive unit

• Genetic unit

• Ecological unit

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How to group species• From Linnaeus: Flora and fauna

– All living things are plants or animals– Not very satisfying

• 1969: Whittaker scheme: 5 kingdoms– Monera, Fungi, Protista, Plants, Animals

• Recent, thanks to Carl Woese and studies of rRNA genes: 3 Domains– Archaea, Eubacteria, and Eukarya

• First two domains are prokaryotes• Eukarya include Fungi, Protista, Plants, Animals

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• Kings Play Chess On Fine Grained Sand:Kingdom

Phylum

Class

Order

Family

Genus

Species

Taxon - a group of organisms at any particular level in this system

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Taxonomy: the science of classification

• Taxonomists try to group similar organisms together, primarily by evolutionary relatedness– Depends on morphological similarities– Depends on molecular similarities

• As part of grouping organisms together, taxonomists construct family trees.

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Molecular biology has had a major impact on taxonomy

• Intermediate-looking species finally grouped correctly– Bears, Pandas, red pandas, raccoons.

• Bacillus columnaris, Flexibacter columnaris, Cytophaga columnaris, Flavobacterium columnare: what’s in a name?

• Change will continue!

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Diversity

A view of Marshttp://nssdc.gsfc.nasa.gov/image/planetary/mars/vikinglander2-2.jpg

We so often take for granted the vast quantity of life we have on our little blue planet.

We’ll take a quick spin through the major groups of organisms found on our world.