Dec 22, 2015
Lamarck’s evidence and inference Comparisons between
current species and fossils: lines of descendents
Use and disuse Inheritance of
acquired characteristics
1. All species produce far more offspring than required just to replace parents. This would result in exponential growth if populations were not limited. ("Essays on Population" by Thomas Malthus)
2. Populations do not, however, increase exponentially. They generally remain stable in size.(Field observations at home and on the voyage of the Beagle)
3. The resources in the environment are limited. (Field observations)
1. Because of the limited resources in the environment, there is competition among individuals. Only a small fraction of the individuals born can survive.
Darwin’s evidence and Darwin’s evidence and inferencesinferences
Darwin’s evidence and inferences
4. There is variation within species and populations. Some individuals possess characteristics that are better suited to the environment than others. (Field observations)
5. Most physical, and some behavioral characteristics are inherited.(Breeding experiments with pigeons. "Artificial selection")
2. Those individuals with the best characteristics for the particular environment will do a better job of producing and providing for offspring than will others with less "fit" characteristics.
Darwin’s evidence and inferences
6. Geologic processes are very, very slow. (Principles of Geology by Charles Lyell, work by Hutton, as well as Darwin's own studies of geology)
3. The earth must be very, very old. Over very great periods of time, "good" characteristics have time to accumulate and less fit ones have diminished.
Homologous vs. analogous structures vs.Vestigial structures
Evolution
Macroevolution:Changes ABOVE the species level
Can change
Gene pool
Can remain constant (equilibrium)
Microevolution:Change in the genetic makeup of a population
Variation
Within populationsPolymorphisms
Between populationsGeographic variation (clines)
Evolutionary fitness Darwinian vs. relative fitness Altering frequency of
phenotypes
Preservation of Genetic Variation Diploidy Balanced polymorphism
Heterozygous advantage (sickle cell trait) Frequency dependent selection (fitness
declines if a characteristic becomes too common)
Common moths at a disadvantage since the jays recognized it quickly
Neutral variation Mutations arising in noncoding regions,
pseudogenes, or parts of a coding region may not be selected for or against
Sexual selection Sexual dimorphism arises since they
influence mating success (not REPRODUCTIVE success)
Intrasexual vs. intersexual selection (mate choice)
Advantage/disadvantages of sex?
Preservation of allele frequencies
Hardy-Weinburg Theorem Allele frequencies remain constant from
generation to generation if only Mendelian inheritance is at work (segregation and recombination)
H.W. equilibrium – Population state in which allele frequencies are not changing, so genotype frequencies can be predicted
Conditions for PRESERVING Hardy-Weinberg equilibrium Large population size No gene flow No new mutations Random mating No natural selection
The goal of natural selection? Evolution is limited by its
ancestry Adaptations are often
compromises Chance and natural selection
interact (natural selection is not random)
Selection can only edit existing alleles (new alleles do not arise ON DEMAND)
Small genetic changes can result in large morphological changes
Anagenesis vs. Cladogenesis Evolutionary theories
must explain how new species form (macroevolution) in addition to evolution of adaptations in a population (microevolution)
Adaptations ABOVE the species level can help define higher taxa
What is a species?
More importantly what evidence do we use to distinguish species
Reproductive isolation
Read through the following definitions of a species: biological, morphological, paleontological, ecological, phylogenetic
Discuss as a group which one you think should be used when classifying species and why
Allopatric speciation
Sympatric speciation
Adaptive radiation
Punctuated equilibrium
Small genetic changes can result in large morphological changes
Small genetic changes can result in large morphological changes
Species selection
Phylogeny and Systematics Problem: Organism classification and
evolutionary history Phylogeny: “tribe” “origin”: Evolutionary
history of a species or group of species Evidence:
Fossil record systematics (analytical approach using
morphological or biochemical similarities) Molecular biology represents best method for
VERY closely related species
Sorting homology from analogy Example: Bat and birds have wings. Is this the
result of divergent evolution (homologous structure) or convergent evolution (analogous structure)?
We need to example the actual bone structure and complexity of it
Homoplasies: analogous structures that evolved independently
Molecular homologies and molecular clocks
Sequences must first be aligned (problem with deletion mutations?) Problems with molecular
systematics? Molecular homoplasy
Molecular clocks Calibration: Graph number of nucleotide
differences against known evolutionary branch points (fossil record)
Neutral theory DNA coding for rRNA vs. mtDNA
Classification Binomial: genus + specific
epithet Homo sapiens Taxon (plural taxa): A
taxonomic unit
Phylogenetic trees Cladograms A branched diagram
that depicts the evolutionary hypothesis
Depicts pattern of shared characteristics but not evolutionary history
If shared characteristics due to homology, then it is the basis of a phylogenetic tree
Origin of Life Evidence supports this sequence of events
that led to life on earth… 1. Abiotic synthesis of small organic
molecules 2. Joining of monomers to form polymers 3. Packaging of polymers to form
“protobionts” 4. Origin of self replicating molecules that
made inheritance possible
1. Abiotic synthesis of organic molecules First conditions on earth
Lot’s of water vapor (eventually condensed to form oceans)
N2, nitric oxides, CO2, CH4, NH3, H2, H2S
Reducing atmosphere with energy from UV rays and lightning (postulated by Oparin and Haldane in 1920’s
Oceans were a “primitive soup” of organic molecules
Current conditions on earth Mostly N2, CO2, and O2 O2 comes primarily from
biological splitting of water in cyanobacteria
Evidence: Stromatolites (3.5 billion years old)
Oxidizing atmosphere
1. Abiotic synthesis of organic molecules Miller-Urey
experiments
2. Abiotic synthesis of polymers Chains of amino acids can
form spontaneously on hot sand, clay, or rock
3. Formation of protobionts Aggregates of abiotically
produced molecules surrounded by a membrane
“Laboratory” evidence: When lipids or other organic molecules are added to water liposomes form, which can do all the functions of a cell membrane (shrink and expand, transport materials, carry a voltage)
4. Origin of self replicating molecules
Chech and Altman: RNA plays catalytic role in protein synthesis and can carry out enzymatic like reactions (ribozymes)
Diversity and selection of RNA molecules
Dyson:
Possible scenario Other scenarios?
Fossil and geology records
Index fossils (order in which fossils were laid down, but not age)
Radiometric dating Based on decay of
radioactive isotopes Half-life: # of years it
takes for 50% of material to decay
A brief history of life
Kingdom classification