Evolutionary TheoryEvolutionary Theory

MacroevolutionMacroevolution

Tree of LifeTree of Life

A phylogenetic "tree A phylogenetic "tree of life" constructed by of life" constructed by computer analysis of computer analysis of cyochrome c molecules cyochrome c molecules in the organisms in the organisms shown.shown.

Graduated v. Punctuated Graduated v. Punctuated EquilibriumEquilibrium

Gradual Equilibrium:Gradual Equilibrium: Proposed by DarwinProposed by Darwin Accumulation of very Accumulation of very

small changes leads to small changes leads to new species, new new species, new taxa, over very long taxa, over very long periods of timeperiods of time

Graduated v. Punctuated Graduated v. Punctuated EquilibriumEquilibrium

Punctuated Equilibrium:Punctuated Equilibrium: Proposed by Niles Proposed by Niles

Eldridge and Stephen Jay Eldridge and Stephen Jay GouldGould

Instead of a slow, Instead of a slow, continuous movement, continuous movement, evolution tends to be evolution tends to be characterized by long characterized by long periods of virtual periods of virtual standstill ("equilibrium"), standstill ("equilibrium"), "punctuated" by episodes "punctuated" by episodes of very fast development of very fast development of new forms.of new forms.

Why the debate?Why the debate?

In the fossil record:In the fossil record: There are long intervals in which nothing changes There are long intervals in which nothing changes

for a particular organism ("equilibrium")for a particular organism ("equilibrium") This is "punctuated" by short, revolutionary This is "punctuated" by short, revolutionary

transitions, in which species become extinct and transitions, in which species become extinct and replaced by wholly new forms. replaced by wholly new forms.

Instead of a slow, continous progression, the Instead of a slow, continous progression, the evolution of life on Earth seems more like the evolution of life on Earth seems more like the life of a soldier: long periods of boredom life of a soldier: long periods of boredom interrupted by rare moments of terror. interrupted by rare moments of terror.

Why the Debate?Why the Debate? Punctuated equilibrium is more an observation than a Punctuated equilibrium is more an observation than a

theory of evolution. theory of evolution. It lacks a clear mechanism. It lacks a clear mechanism. How was biological change produced as fast as the fossil How was biological change produced as fast as the fossil

record seems to require? record seems to require? No good answers to this question have been found No good answers to this question have been found

But, this IS what is observed in the fossil record.But, this IS what is observed in the fossil record. It is one of the main criticisms of Darwin—even by It is one of the main criticisms of Darwin—even by

Darwin!Darwin! ““Geology assuredly does not reveal any such finely-Geology assuredly does not reveal any such finely-

graduated organic chain; and this, perhaps, is the most graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against obvious and serious objection which can be urged against the theory.” (the theory.” (The Origin of SpeciesThe Origin of Species) )

Darwin’s ExpectationDarwin’s Expectation

Darwin thought the gaps were because of the Darwin thought the gaps were because of the extreme imperfection of the fossil recordextreme imperfection of the fossil record

Also, the fossil record was just beginning to be Also, the fossil record was just beginning to be examinedexamined

Darwin EXPECTED the intermediate forms to Darwin EXPECTED the intermediate forms to be found which would validate his theorybe found which would validate his theory

140 years later, however, the gaps still exist140 years later, however, the gaps still exist

Archaeopteryx Archaeopteryx

This fossil, found during Darwin’s lifetime, This fossil, found during Darwin’s lifetime, fits the model of gradualism:fits the model of gradualism: It had feathers like a birdIt had feathers like a bird A toothed jaw like a reptile. A toothed jaw like a reptile.

Named Named ArchaeopteryxArchaeopteryx it seemed to be just the it seemed to be just the kind of intermediate form which Darwin’s kind of intermediate form which Darwin’s theory predicted, and was taken as good theory predicted, and was taken as good evidence for evolution. evidence for evolution.

Human FossilsHuman Fossils Human evolution also Human evolution also

shows intermediate forms, shows intermediate forms, with new ones still being with new ones still being foundfound

Lucy, Australopithecus Lucy, Australopithecus afarensis, is 3.2 myo and afarensis, is 3.2 myo and was discovered in 1974.was discovered in 1974.

The Dikika infant (“Lucy’s The Dikika infant (“Lucy’s daughter), is 3.3 myo, but daughter), is 3.3 myo, but still Australopithecus still Australopithecus afarensis, and was afarensis, and was discovered in 2001.discovered in 2001.

Cambrian ExplosionCambrian Explosion About half of the major animal groups appear, fully formed, in About half of the major animal groups appear, fully formed, in

the Cambrian strata of rocks, with out any fossilised ancestors. the Cambrian strata of rocks, with out any fossilised ancestors. The Cambrian strata of rocks, (~ 600 mya), are the oldest ones The Cambrian strata of rocks, (~ 600 mya), are the oldest ones

in which we find most of the major invertebrate groups. in which we find most of the major invertebrate groups. ““It is as though they were just planted there, without any It is as though they were just planted there, without any

evolutionary history. Needless to say, this appearance of evolutionary history. Needless to say, this appearance of sudden planting has delighted creationists.” (Richard Dawkins, sudden planting has delighted creationists.” (Richard Dawkins, The Blind WatchmakerThe Blind Watchmaker, p. 229), p. 229)

For evolution to be true, there must be a gap here – not just a For evolution to be true, there must be a gap here – not just a small gap of one or two intermediate forms – but a truly small gap of one or two intermediate forms – but a truly massive gap of intermediates for at least 19 different phyla. massive gap of intermediates for at least 19 different phyla.

A huge imperfection in the fossil record is the only A huge imperfection in the fossil record is the only explanation which evolutionists can give. explanation which evolutionists can give.

Why the Gap?Why the Gap? Perhaps the evolutionary ancestors of the Cambrian organisms Perhaps the evolutionary ancestors of the Cambrian organisms

were small and soft-bodied, and hence hard to fossilize. were small and soft-bodied, and hence hard to fossilize. But fossilized micro-organisms have been found in Precambrian rocks But fossilized micro-organisms have been found in Precambrian rocks

around the worldaround the world Many entirely soft-bodied animals have been found fossilized in Many entirely soft-bodied animals have been found fossilized in

Cambrian rocks. Cambrian rocks. There does not seem to be a good reason why such a massive There does not seem to be a good reason why such a massive

gap should exist.gap should exist. Non-evolutionists take the fossil record more at face value. Non-evolutionists take the fossil record more at face value.

Instead of hypothesising a large number of Precambrian animals for Instead of hypothesising a large number of Precambrian animals for which there is no fossil evidence, they take the fossil record to show which there is no fossil evidence, they take the fossil record to show that the Cambrian animals did not evolve gradually from a common that the Cambrian animals did not evolve gradually from a common ancestor, and came into being through intelligent design.ancestor, and came into being through intelligent design.

What about DNA?What about DNA? Macroevolution, the evolution of large changes over time, still Macroevolution, the evolution of large changes over time, still

acts on DNA at the molecular levelacts on DNA at the molecular level Body plans are divided into systems, subsystems, Body plans are divided into systems, subsystems,

subsubsystems….subsubsystems…. Changes (mutations) in a subsubsystem gene:Changes (mutations) in a subsubsystem gene:

if selected for might not show any evidence in the fossil recordif selected for might not show any evidence in the fossil record E.g. hemoglobin modification in malaria hot spotsE.g. hemoglobin modification in malaria hot spots

Or they might create a gradual change that creates an intermediate Or they might create a gradual change that creates an intermediate formform

Changes in a main system gene, however:Changes in a main system gene, however: If selected for, will create a dramatic jump in the fossil record without If selected for, will create a dramatic jump in the fossil record without

any intermediate formany intermediate form E.g. a mutation which forms 6 legs instead of 4E.g. a mutation which forms 6 legs instead of 4

Back to the Tree of LifeBack to the Tree of Life

By comparing the DNA sequences of major genes By comparing the DNA sequences of major genes (like cytochrome c) between organisms, we can (like cytochrome c) between organisms, we can determine how distantly they are relateddetermine how distantly they are related

We can then construct trees showing evolutionary We can then construct trees showing evolutionary relationships between organismsrelationships between organisms

This helps determine whether homologous structures This helps determine whether homologous structures are present because of descent or lifestyle are present because of descent or lifestyle (convergent evolution)(convergent evolution) E.g. legless lizardsE.g. legless lizards

EmbryologyEmbryology OntogenyOntogeny describes the origin and the development of an organism from describes the origin and the development of an organism from

the fertilized egg to its mature form. the fertilized egg to its mature form. PhylogenyPhylogeny is a species’ evolutionary history—it’s geneological lineage is a species’ evolutionary history—it’s geneological lineage

over millions of yearsover millions of years ““Ontogeny recapitulates phylogeny”—HaeckelsOntogeny recapitulates phylogeny”—Haeckels

i.e., the development of an organism exactly mirrors the evolutionary i.e., the development of an organism exactly mirrors the evolutionary development of the species, development of the species,

This theory is discredited today in its absolute form. This theory is discredited today in its absolute form. However, the phenomenon of recapitulation, in which a developing organism However, the phenomenon of recapitulation, in which a developing organism

will for a time show a similar trait or attribute to that of an ancestral species, will for a time show a similar trait or attribute to that of an ancestral species, only to have it disappear at a later stage, is well documented. only to have it disappear at a later stage, is well documented.

E.g., embryos of the baleen whale still develop teeth at certain embryonic E.g., embryos of the baleen whale still develop teeth at certain embryonic stages, only to later disappear. stages, only to later disappear.

E.g. the emergence of a structure which could develop into pharyngeal gill E.g. the emergence of a structure which could develop into pharyngeal gill pouches if it were in a lower vertebrate, appears in almost all mammalian pouches if it were in a lower vertebrate, appears in almost all mammalian embryos at early stages of development. embryos at early stages of development.

Haeckel’s Embryology DrawingsHaeckel’s Embryology Drawings

Macroevolution in SummaryMacroevolution in Summary

The fossil record shows punctuated equilibrium, The fossil record shows punctuated equilibrium, which seems to discredit Darwin’s ideas of which seems to discredit Darwin’s ideas of gradualismgradualism

Genetic evidence suggests that if a change occurs in a Genetic evidence suggests that if a change occurs in a major system, we shouldn’t expect intermediate major system, we shouldn’t expect intermediate forms to existforms to exist

Embryological development loosely mirrors Embryological development loosely mirrors evolutionary history, showing relationships between evolutionary history, showing relationships between very diverged organismsvery diverged organisms E.g. fish and humansE.g. fish and humans