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.

“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.”

CLADOGRAM ( partial) of VERTEBRATES: DESCENT WITH MODIFICATION

“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

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.

“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

PAX6/Eyeless Expression inInsect 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 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

ORIGIN OF FEATHERS FROM SCALESThrough Repetition of SHH-BMP Interactions

(Harris, M., et al., 2002)

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

Perpetual Change – The Fossil RecordBurgess Shale Fossils, Canada

Dinosaur Provincial Park, Canada

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

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