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Evolution
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
DIVERSITY EXISTS WITHIN POPULATIONS
Homo sapiens subgraduensis
Mechanism of Darwinian Natural Selection
1. Variation exists in the population
2. Competition for survival, most animals die before reproducing
Competition for Survival
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
DEATH IS NOT RANDOM; IT IS SELECTIVE
Changes in finch beak morphology during drought of 1976/1977
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.
THE MODERN SYNTHESIS
“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
CHARLES DARWIN
ON THE ORIGIN OF SPECIES
1859
“Community of embryonic
structure reveals community
of descent.”
“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
HOMOLOGY
“The same organ in all its
varieties of form”
Serial Homology
Derived forms within
the same organism
Special Homology
Derived forms between
different species
Versus
Sir Richard Owen
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 specialized
features 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 were
derived.”
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.”
CLADOGRAM ( partial) of VERTEBRATES:
DESCENT WITH MODIFICATION
THE DEMISE of EVOLUTIONARY MORPHOLOGY…
“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.
…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
INDEPENDENT EVIDENCE for COMMON DESCENT:
Biological genetic documentation
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.
FRANÇOIS JACOB: EVOLUTION AS TINKERING
with REGULATORY GENES in the EMBRYO
“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.”
RICHARD B. GOLDSCHMIDT:
Evolution consists of inherited changes of development
Functional biology = anatomy, gene expression
Development = d[Functional biology]/dt
Evolution = d[Development]/dt
PAX6/Eyeless Expression in
Insect and Mouse Eye Primordia
HOMOLOGOUS GENES for ANALOGOUS TRAITS
Mouse Pax 6 instructs fly compound eye formation in antenna
HOMOLOGOUS HOX GENES: DERIVATION
HOMOLOGOUS HOX GENES: EXPRESSION
MUTATIONS IN
REGULATORY GENES
CAN GIVE THE
PROTEINS NEW
PROPERTIES: UBX
ACQUIRES THE
ABILITY to REPRESS
DISTAL-LESS in the
INSECT CLADE
R. Galant and S. B. Carroll,
2002. Nature 415:910.
Ronschaugen, M. et al.
2002. Nature 415: 914.
.
HOW THE DUCK GOT ITS WEBBED FEET
Merino et al., 1999. Dev. Biol. 200: 35 - 45.
Chick
Hindlimb
Duck
Hindlimb
BMP
Gremlin
Apoptosis
Newborn
HOW THE DUCK GOT ITS WEBBED FEET. II.
Experimental Manipulation of Chick Feet
Untreated
Chick Hindlimb
Chick Hindlimb Treated
with Gremlin-Containing
Bead in Interdigital Space
ORIGIN OF FEATHERS FROM SCALES
Through Repetition of SHH-BMP Interactions
(Harris, M., et al., 2002)
Developmental Mechanisms for
Phylogeny
Shigeru 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
Perpetual Change – The Fossil Record
Burgess Shale Fossils, Canada
Dinosaur Provincial Park, Canada
Common Descent
1.6 MYA
3.4 million years – 3.4
million generations
5 MYA
19 million years – 19
million generations
24 MYA
13 million years – 13
million generations
37 MYA
21 million years – 21
million generations
58 MYA
Homologies
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
Multiplication of Species
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
Macroevolution
• Speciation events
– Microevolutionary events/mechanisms give rise
to macroevulutionary events
• Results of genetic variation
– Speciation
– Phylotypic divergence
• Major environmental changes
– Extinctions events
– Continental drift
– Ice ages