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Precursors to Darwin
• Jean Baptiste de Lamarck– Evolutionary change proceeds via inheritance
of acquired characteristics– ie. Giraffe’s ancestors stretched their necks and
subsequent generations inherited longer necks– ie. Loss of a digit would result in loss or
reduction of digit in subsequent generations
Precursors to Darwin
• Incorrectness of Lamark’s hypothesis– Somatic changes do not alter the genes passed
on to offspring– ie. The loss of a digit does not remove the dna
from the genome that specifies development of a digit.
Precursors to Darwin• Charles Lyell
– Geologist who first explained the significance of geological formations/strata
– Realized that geological changes must require great time spans
– Formulated uniformitarianism• Physical and chemical processes are the same now as they
have always been
• Natural processes occurring now, have always occurred
Darwin’s Synthesis
• Five Tenets– Perpetual change (derived from Lyell’s work)
– Common descent (derived from observations from Beagle and other journeys)
– Multiplication of species (corollary to common descent)
– Gradualism (derived from Lyell and lack of any other mechanism)
– Natural selection (Darwin’s most original contribution)
Mechanism of Darwinian Natural Selection
1. Variation exists in the population
2. Competition for survival, most animals die before reproducing
Mechanism of Darwinian Natural Selection
1. Variation exists in the population
2. Competition for survival, most animals die before reproducing
3. Survival of those most fit for the environment
Mechanism of Darwinian Natural Selection
1. Variation exists in the population
2. Competition for survival, most animals die before reproducing
3. Survival of those most fit for the environment
4. Offspring are from the survivors
5. Offspring inherit the genes that made their parents fit for the environment.
“Evolution is a change in the genetic composition of populations. The study of the mechanisms of evolution falls within the province of population genetics.” --Theodosius Dobzhansky. 1951
THE MODERN SYNTHESIS
“Community of embryonicstructure reveals communityof descent.”
CHARLES DARWIN
ON THE ORIGIN OF SPECIES
1859
“Embryology rises greatly in interest, when we look at the embryo as a picture, more or less obscured, of the progenitor, either in its class or larval state, of all the members of the same great class.”
The embryos of the organisms in a phylum reflect the evolutionary progenitor of that phylum
Sir Richard Owen
HOMOLOGY
“The same organ in all its varieties of form”
Serial HomologyDerived forms within the same organism
Special HomologyDerived forms between different species
Versus
ANALOGY Forms similar due to
same function
KARL ERNST von BAER:
“The general features of a large group of animals appear earlier in development than do the specializedfeatures of a smaller group…The early embryo is never like a lower animal, but only like its early embryo.”
DARWIN (1874):“Thus, if we may rely on embryology, ever the safest guide in classification, it seems that we have at last gained a clue to the source whence the Vertebrata werederived.”
AGGASIZ (1874):
“One could hardly open a scientific Journal or any popular essay on Natural History without meeting some allusion to the Ascidians as our ancestors.”
“It is difficult, even if possible, to say whether the differences or the resemblances have a greater zoological value (because we have no clearly defined standard of zoological value).”
-A. Sedgwick, 1894.
THE DEMISE of EVOLUTIONARY MORPHOLOGY…
…AND THE EXODUS TO GENETICS
"Morphology having been explored in its minutest corners, we turned elsewhere...The geneticist is the successor of the morphologist."
-W. Bateson, 1894
GENETIC EVIDENCE for DESCENT WTH MODIFICATION MOLECULAR SYNAPOMORPHIES
Phylogenetic tree made from interspersed DNA elements. Four transposon insertions, at loci 4-7, define a clade of whales and hippos.
“Small changes modifying the distribution in time and space of the same structures are sufficient to affect deeply the form, the functioning, and the behavior of the final product--the adult animal. It is always a matter of using the same elements, of adjusting them here or there, of arranging various combinations to produce new objects of increasing complexity. It is always a matter of tinkering.”
FRANÇOIS JACOB: EVOLUTION AS TINKERING with REGULATORY GENES in the EMBRYO
RICHARD B. GOLDSCHMIDT: Evolution consists of inherited changes of developmentFunctional biology = anatomy, gene expression Development = [Functional biology]/t
Evolution = [Development]/t
MUTATIONS INREGULATORY GENES CAN GIVE THE PROTEINS NEWPROPERTIES: UBXACQUIRES THE ABILITY to REPRESSDISTAL-LESS in theINSECT CLADE
R. Galant and S. B. Carroll,2002. Nature 415:910.
Ronschaugen, M. et al.2002. Nature 415: 914.
.
ChickHindlimb
DuckHindlimb
BMP Gremlin Apoptosis Newborn
HOW THE DUCK GOT ITS WEBBED FEETMerino et al., 1999. Dev. Biol. 200: 35 - 45.
HOW THE DUCK GOT ITS WEBBED FEET. II. Experimental Manipulation of Chick Feet
UntreatedChick Hindlimb
Chick Hindlimb Treated with Gremlin-Containing Bead in Interdigital Space
Developmental Mechanisms for PhylogenyShigeru Kuratani et al. 2001. Phil. Trans. Roy. Soc. London B 356: 1615-1632
Tenets of Evolutionary Theory• Perpetual change
• Common descent
• Multiplication of species
• Punctuated equilibrium
• Natural selection
Common Descent
58 MYA
37 MYA
24 MYA
5 MYA
1.6 MYA
21 million years – 21 million generations
13 million years – 13 million generations
19 million years – 19 million generations
3.4 million years – 3.4 million generations
Phylogenies• Shared traits –
synapomorphies– Homologous structures
• Anatomical• Genetic
• Ratite birds skeletal homologies– Those homologies
present in the most groups are most ancestral
– Those in few or one define species
GENETIC EVIDENCE for DESCENT WTH MODIFICATION MOLECULAR SYNAPOMORPHIES
Phylogenetic tree made from interspersed DNA elements. Four transposon insertions, at loci 4-7, define a clade of whales and hippos.
Ontological Homologies• Homologies of embryonic
structures and developmental patterns
• Vertebrate embryos– Pharyngeal arches
– Somites
– Segmentation of CNS
• Subtle changes in developmental expression of genes can drastically alter morphologies – Speciation and phylogenic
event
Subcomponents of Evolutionary Theory
• Microevolution– Genetic change
• Macroevolution– Major events
Microevolution• Genetic variation
– Alleles – different versions of genes– Polymorphism – degree of variation in alleles– Allele frequencies – occurrence of allele variety– Changes in allele frequencies due to
• Genetic drift• Non-random mating• Migration• Natural selection processes
Microevolution – Genetic Drift• Random fluctuation in allele frequencies
• Dramatic changes in genetic variation within a population or species
Greater affect on small populations – they have less inherent variation to start with
Microevolution – Nonrandom Mating
• Individuals with a particular genotype mate preferentially with individuals of the same genotype
• Result – their common alleles become more frequent within the resulting population
Microevolution - Migration
• Influx – efflux of individuals with a particular genotype into a population increase/decreases frequency of their alleles
Microevolution – Natural Selection
• Environmental factors select for particular phenotypes and their underlying genotypes
• Alleles that give rise to selected phenotype increase in frequency in population
Natural Selection
• Environmental conditions provide a selective pressure
• Alleles producing selected phenotype increase in population
• Disruptive selection is a strong speciation event