1 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.

2 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.

3 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.

4 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

5 So many species What to do? –We name them –We group them –We order them –We look for more.

6 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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8 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.

9 If you ordered americanus in a restaurant …. Homarus americanus – lobster Ursus americanus – black bear Bufo americanus – American toad

10 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

11 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

12 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

13 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.

14 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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16 Diversity A view of Mars ander2-2.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.