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

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
We so often take
for granted the
vast quantity of life
we have on our
little blue planet.
A view of Mars
http://nssdc.gsfc.nasa.gov/image/planetary/mars/vikingl
ander2-2.jpg
We’ll take a quick
spin through the
major groups of
organisms found
on our world.
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