macroevolution. macroevolution the origin of taxonomic groups higher than the species level...

MacroevolutionMacroevolution

MacroevolutionMacroevolution• The origin of taxonomic groups higher

than the species level• Concerned with major events in the history

of life as found in the fossil record• Includes the origin of new design features

such as feathers and wings in birds, upright posture of humans

• Examines large scale evolutionary changes

MacroevolutionMacroevolutionmajor questions of macroevolutionmajor questions of macroevolution

• How do major novel features arise?

• What accounts for apparently progressive trends found in the fossil record?

• How has macroevolution been affected by global geological changes?

• What explains the major fluctuations in biological diversity seen in the fossil record?

Macroevolution movieMacroevolution movie

Fossil of a fish: perchFossil of a fish: perch

FossilsFossils

• Sedimentary rocks are the richest source– Formed from deposits of sand (compressed into

sandstone) or silt (compressed into shale)

• Usually form from mineral rich hard parts of organisms

• Petrification – minerals dissolved in the groundwater seep into the tissues of the dead organism and replace organic matter

• Occasionally fossils retain organic matter (DNA)

Fossils come in variety of formsFossils come in variety of forms

Dinosaur National Monument –dinosaur bone in sandstoneDinosaur National Monument –dinosaur bone in sandstone

Skulls of Skulls of AustralopithecusAustralopithecus and and Homo erectusHomo erectus

Petrified treesPetrified trees

Leaf impressionLeaf impression

Dinosaur tracks (trace fossils)Dinosaur tracks (trace fossils)

Scorpion in amberScorpion in amber

Mammoth tusks 23,000 years old (Siberia 1999)Mammoth tusks 23,000 years old (Siberia 1999)

BarosaurusBarosaurus

Limitations of the Fossil RecordLimitations of the Fossil Record• A fossil represents a sequence of improbable

events• A large fraction of species that have lived

probably left no fossils• Most fossils that were formed have probably

been destroyed• Only a fraction of the existing fossils have been

discovered• So… the fossil record is comprised primarily of

species that lived a long time, were abundant and widespread, and had shells or hard skeletons

Early Earth VideoEarly Earth Video

• Early Earth Video

The Geologic Time ScaleThe Geologic Time Scale

Geological time scale movieGeological time scale movie

25T-01-GeologicTimeScale.mov

DatingDating•Relative Dating

•Absolute Dating

•Radiometric dating (error of less than 10%)Half-life = Number of years it takes for 50% of the original sample to decay

Carbon-14 (half-life = 5600 years) Best for dating material less than 50,000 yrs old

Uranium-238 (half-life 4.5 billion years)

Evolutionary novelties (1) Evolutionary novelties (1) how do new designs evolve?how do new designs evolve?

• Higher taxonomic groups such as families and classes are defined by evolutionary novelties (such as wings in birds)

• Mechanism is a gradual refinement of existing structures for new functions

• Structures may have an evolutionary plasticity that makes alternative functions possible


• Preadaptation– When a structure evolved in one context and

becomes co-opted for another function– Natural selection can not anticipate the future,

but can improve on an existing structure– Example: feathers in birds


• Genes that control development play a major role– A slight alteration in development becomes

compounded in its effect on the adult– Allometric growth

• Differences in relative rates of growth of various body parts. A slight change in these realtive growth rates may yield a substantial change in the adult

Allometric growthAllometric growth

Genes controlling developmentGenes controlling development

• Regulatory genes can effect hundreds of structural genes, so changes here have a great impact

• Paedomorphosis = Retention of features in the adult that were juvenile in ancestral species.

Paedomorphosis moviePaedomorphosis movie

24-21-PaedomorphosisAnim.mov

PaedomorphosisPaedomorphosis in axolotl (a salamander which retains in axolotl (a salamander which retains some larval (tadpole) characteristics)some larval (tadpole) characteristics)


• Heterochrony = evolutionary changes in the timing or rate of development.

HeterochronyHeterochrony and the evolution of salamander and the evolution of salamander feet among closely related speciesfeet among closely related species

Feet are shorter with more webbing, better for climbing up a vertical surface. Possible influence of an evolutionary change in a regulatory gene which switches off foot growth earlier in tree-dwelling species


• Homeosis = alteration in the placement of different body parts

Evolutionary trends (1)Evolutionary trends (1)

• At times it appears that there are trends in the fossil record (toward greater size, more feathers, etc.)

• A trend does not mean macroevolution is goal-oriented

• No intrinsic drive toward a preordained state of being is indicated by the presence of an evolutionary trend


• Species Selection– Species that exist the longest and generate

the greatest number of new species determine the direction of major evolutionary trends

– Differential speciation may play a role in macroevolution similar to the role of differential reproduction (natural selection) in microevolution


• A trend may cease or reverse itself under changing environmental conditions.–Conditions in the Mesozoic era

favored giant reptiles, but by the end of that era the smaller species prevailed

The branched evolution of horsesThe branched evolution of horses

Hyracotherium to modern horses. Smooth progressive trend toward increased size, less toes and grazing teeth???

Not a straight line. It is just that Equus is the only survivor of a much more complicated evolutionary tree.

Biogeography and Biogeography and Continental DriftContinental Drift

Earth’s crustal plates and plate tectonics (geologic processes Earth’s crustal plates and plate tectonics (geologic processes resulting from plate movements)resulting from plate movements)

Crustal plate boundariesCrustal plate boundaries

San Andreas faultSan Andreas fault

History of continental driftHistory of continental drift

PANGEA

Ghana and Brazil are separated by 3000 km of ocean, but matching fossils in both areas show the areas were once connected.

Mass Extinctions and Mass Extinctions and Adaptive RadiationsAdaptive Radiations

• Mass extinctions were followed by extensive diversification of some of the taxonomic groups that survived extinction.

• Surviving species are able to undergo new adaptive radiations into the vacated habitats and produce new diversity

Adaptive radiationsAdaptive radiations• Examples

–Flying Insects

–Mammals

Mass ExtinctionsMass Extinctions

• Why? Habitat destruction? Unfavorable environmental conditions?

• Permian Extinctions– About 250 million years ago– 90% of species were eliminated

• Cretaceous Extinctions– About 65 million years ago– Over 50% of species eliminated

Diversity of life and periods of mass extinctionDiversity of life and periods of mass extinction

Trauma for planet Earth and its Cretaceous lifeTrauma for planet Earth and its Cretaceous lifeThe The Asteroid Impact HypothesisAsteroid Impact Hypothesis

Immediate effect-Cloud of hot vapor and debris that could have killed most plants and animals in N. America in minutes?

Mass Extinction VideoMass Extinction Video

Mass Extinction Video

The Sixth Extinction The Sixth Extinction The Earth may be on the brink of a sixth mass extinction on a par with the five previous episodes

This time it appears that the cause is the activities of a growing human population.

Rate of species extinction estimated from the fossil record is about 10-100 per year. In tropical habitats alone the current rate may be 27,000 per year.

SystematicsSystematics

• Phylogeny = the evolutionary history of a species or group

• Systematics = the study of biological diversity in an evolutionary context.– Taxonomy = identification and

classification of species

Hierarchical classificationHierarchical classification

Homology/AnalogyHomology/Analogy

• Homology– Likeness attributed to a shared ancestry– Forelimbs of mammals are homologous

structures

• Analogy– Similarities due to convergent evolution, not

common ancestry– Insect wings and bird wings are analogous

structures

Homologous structures: anatomical signs of descent with modificationHomologous structures: anatomical signs of descent with modification

Convergent evolutionConvergent evolution

• Acquisition of similar characteristics in species from different evolutionary branches due to sharing similar ecological roles with natural selection shaping analogous structures.

Convergent evolution and analogous structuresConvergent evolution and analogous structures

Ocotillo of SW North America

Allauidia of Madagascar

Convergent evolution (bird beaks)Convergent evolution (bird beaks)

Systematics connects classification and phylogenySystematics connects classification and phylogeny

Molecular Biology tools for Molecular Biology tools for systematicssystematics

• Protein comparison

• DNA sequence comparison

• These can be used to access relationships even between species so distantly related that no morphological similarities exist.

Phylogenetic TreePhylogenetic Tree

• Cladogram– A dichotomous tree that branches repeatedly– Classifies organisms according to the order in

time that branches arise.– Each branch point is defined by novel

homologies unique to the various species on that branch

CladogramsCladograms

Constructing a cladogramConstructing a cladogram

Cladistics and taxonomyCladistics and taxonomy

Molecular clocksMolecular clocks

• Based on the observation that some regions of genomes evolve at constant rates.

• By comparing DNA sequences from these regions or the proteins that result, an estimate of the time since the groups diverged can be estimated.

Dating the origin of HIV-1 M with a molecular clockDating the origin of HIV-1 M with a molecular clock

Using a molecular clock method, a date for the origin of HIV infections in humans can be inferred.

HIV seems to have descended from related viruses that infect chimpanzees and sooty mangabeys.

When did the virus make the jump to the human species??

Projecting backward, the 1930s are the probable time of first human invasion by HIV.

Modern systematics is shaking some phylogenetic treesModern systematics is shaking some phylogenetic trees

Traditionally, lizards, snakes, and crocs are classified together in the Class Reptilia with birds in a separate class (Aves)

But crocodiles may actually be more closely related to birds than to lizards and snakes

Evolution of birdsEvolution of birds

Archaeopteryx

• Often you may hear critics of evolution theory claim that it is "just a theory," and that even scientists disagree about many of the details of the Earth's past and the origin of life. However, even though scientists do have heated discussions on the details, they do not disagree about the general claim of natural selection. As an example, currently there is a vigorous debate on exactly how and when birds evolved from dinosaurs. Although there is not agreement on every detail -- science is an on-going critical activity -- the evidence is solid that birds are the living descendants of theropod dinosaurs, birds are not the sole feather-bearing creatures, and feather-like structures preceded flight and hence did not evolve in connection with it. Darwin's theory predicts that a very important survival trait may initially evolve for a completely different reason than that for which it becomes a key survival trait. Feathers may have evolved in some dinosaurs for the purpose of communicating with potential mates and enemies or for moderating body temperature. Excerpt from Natural History Magazine.


http://www.npr.org/templates/story/story.php?storyId=931047

4-winged dinosaur

Possible Feather evolution

macroevolution. macroevolution the origin of taxonomic groups higher than the species level...

Documents

macroevolution slide

sandstone slide

perch slide

amber slide

barosaurus slide

macroevolution movie

homo erectus slide

geologic time scale