Evolutionary Theory Macroevolution

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

Graduated v. Punctuated Equilibrium Gradual Equilibrium: Gradual Equilibrium: Proposed by Darwin Proposed by Darwin Accumulation of very small changes leads to new species, new taxa, over very long periods of time Accumulation of very small changes leads to new species, new taxa, over very long periods of time

Graduated v. Punctuated Equilibrium Punctuated Equilibrium: Punctuated Equilibrium: Proposed by Niles Eldridge and Stephen Jay Gould Proposed by Niles Eldridge and Stephen Jay Gould Instead of a slow, continuous movement, evolution tends to be characterized by long periods of virtual standstill ("equilibrium"), "punctuated" by episodes of very fast development of new forms. Instead of a slow, continuous movement, evolution tends to be characterized by long periods of virtual standstill ("equilibrium"), "punctuated" by episodes of very fast development of new forms.

Why the debate? In the fossil record: In the fossil record: There are long intervals in which nothing changes for a particular organism ("equilibrium") There are long intervals in which nothing changes for a particular organism ("equilibrium") This is "punctuated" by short, revolutionary transitions, in which species become extinct and replaced by wholly new forms. This is "punctuated" by short, revolutionary transitions, in which species become extinct and replaced by wholly new forms. Instead of a slow, continous progression, the evolution of life on Earth seems more like the life of a soldier: long periods of boredom interrupted by rare moments of terror. Instead of a slow, continous progression, the evolution of life on Earth seems more like the life of a soldier: long periods of boredom interrupted by rare moments of terror.

Why the Debate? Punctuated equilibrium is more an observation than a theory of evolution. Punctuated equilibrium is more an observation than a theory of evolution. It lacks a clear mechanism. It lacks a clear mechanism. How was biological change produced as fast as the fossil record seems to require? How was biological change produced as fast as the fossil 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 Darwin! It is one of the main criticisms of Darwin—even by Darwin! “Geology assuredly does not reveal any such finely- graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against the theory.” (The Origin of Species) “Geology assuredly does not reveal any such finely- graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against the theory.” (The Origin of Species)

Darwin’s Expectation Darwin thought the gaps were because of the extreme imperfection of the fossil record Darwin thought the gaps were because of the extreme imperfection of the fossil record Also, the fossil record was just beginning to be examined Also, the fossil record was just beginning to be examined Darwin EXPECTED the intermediate forms to be found which would validate his theory Darwin EXPECTED the intermediate forms to be found which would validate his theory 140 years later, however, the gaps still exist 140 years later, however, the gaps still exist

Archaeopteryx This fossil, found during Darwin’s lifetime, fits the model of gradualism: This fossil, found during Darwin’s lifetime, fits the model of gradualism: It had feathers like a bird It had feathers like a bird A toothed jaw like a reptile. A toothed jaw like a reptile. Named Archaeopteryx it seemed to be just the kind of intermediate form which Darwin’s theory predicted, and was taken as good evidence for evolution. Named Archaeopteryx it seemed to be just the kind of intermediate form which Darwin’s theory predicted, and was taken as good evidence for evolution.

Human Fossils Human evolution also shows intermediate forms, with new ones still being found Human evolution also shows intermediate forms, with new ones still being found Lucy, Australopithecus afarensis, is 3.2 myo and was discovered in Lucy, Australopithecus afarensis, is 3.2 myo and was discovered in The Dikika infant (“Lucy’s daughter), is 3.3 myo, but still Australopithecus afarensis, and was discovered in The Dikika infant (“Lucy’s daughter), is 3.3 myo, but still Australopithecus afarensis, and was discovered in 2001.

Cambrian Explosion About half of the major animal groups appear, fully formed, in the Cambrian strata of rocks, with out any fossilised ancestors. 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, (~ 600 mya), are the oldest ones in which we find most of the major invertebrate groups. The Cambrian strata of rocks, (~ 600 mya), are the oldest ones in which we find most of the major invertebrate groups. “It is as though they were just planted there, without any evolutionary history. Needless to say, this appearance of sudden planting has delighted creationists.” (Richard Dawkins, The Blind Watchmaker, p. 229) “It is as though they were just planted there, without any evolutionary history. Needless to say, this appearance of sudden planting has delighted creationists.” (Richard Dawkins, The Blind Watchmaker, p. 229) 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 massive gap of intermediates for at least 19 different phyla. 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 massive gap of intermediates for at least 19 different phyla. A huge imperfection in the fossil record is the only explanation which evolutionists can give. A huge imperfection in the fossil record is the only explanation which evolutionists can give.

Why the Gap? Perhaps the evolutionary ancestors of the Cambrian organisms were small and soft-bodied, and hence hard to fossilize. Perhaps the evolutionary ancestors of the Cambrian organisms were small and soft-bodied, and hence hard to fossilize. But fossilized micro-organisms have been found in Precambrian rocks around the world But fossilized micro-organisms have been found in Precambrian rocks around the world Many entirely soft-bodied animals have been found fossilized in Cambrian rocks. Many entirely soft-bodied animals have been found fossilized in Cambrian rocks. There does not seem to be a good reason why such a massive gap should exist. There does not seem to be a good reason why such a massive 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 which there is no fossil evidence, they take the fossil record to show that the Cambrian animals did not evolve gradually from a common ancestor, and came into being through intelligent design. Instead of hypothesising a large number of Precambrian animals for which there is no fossil evidence, they take the fossil record to show that the Cambrian animals did not evolve gradually from a common ancestor, and came into being through intelligent design.

What about DNA? Macroevolution, the evolution of large changes over time, still acts on DNA at the molecular level Macroevolution, the evolution of large changes over time, still acts on DNA at the molecular level Body plans are divided into systems, subsystems, subsubsystems…. Body plans are divided into systems, subsystems, subsubsystems…. Changes (mutations) in a subsubsystem gene: Changes (mutations) in a subsubsystem gene: if selected for might not show any evidence in the fossil record if selected for might not show any evidence in the fossil record E.g. hemoglobin modification in malaria hot spots E.g. hemoglobin modification in malaria hot spots Or they might create a gradual change that creates an intermediate form Or they might create a gradual change that creates an intermediate form 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 any intermediate form If selected for, will create a dramatic jump in the fossil record without any intermediate form E.g. a mutation which forms 6 legs instead of 4 E.g. a mutation which forms 6 legs instead of 4

Back to the Tree of Life By comparing the DNA sequences of major genes (like cytochrome c) between organisms, we can determine how distantly they are related By comparing the DNA sequences of major genes (like cytochrome c) between organisms, we can determine how distantly they are related We can then construct trees showing evolutionary relationships between organisms We can then construct trees showing evolutionary relationships between organisms This helps determine whether homologous structures are present because of descent or lifestyle (convergent evolution) This helps determine whether homologous structures are present because of descent or lifestyle (convergent evolution) E.g. legless lizards E.g. legless lizards

Embryology Ontogeny describes the origin and the development of an organism from the fertilized egg to its mature form. Ontogeny describes the origin and the development of an organism from the fertilized egg to its mature form. Phylogeny is a species’ evolutionary history—it’s geneological lineage over millions of years Phylogeny is a species’ evolutionary history—it’s geneological lineage over millions of years “Ontogeny recapitulates phylogeny”—Haeckels “Ontogeny recapitulates phylogeny”—Haeckels i.e., the development of an organism exactly mirrors the evolutionary development of the species, i.e., the development of an organism exactly mirrors the evolutionary 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 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. 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, 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 stages, only to later disappear. E.g., embryos of the baleen whale still develop teeth at certain embryonic stages, only to later disappear. 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 embryos at early stages of development. 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 embryos at early stages of development.

Haeckel’s Embryology Drawings

Macroevolution in Summary The fossil record shows punctuated equilibrium, which seems to discredit Darwin’s ideas of gradualism The fossil record shows punctuated equilibrium, which seems to discredit Darwin’s ideas of gradualism Genetic evidence suggests that if a change occurs in a major system, we shouldn’t expect intermediate forms to exist Genetic evidence suggests that if a change occurs in a major system, we shouldn’t expect intermediate forms to exist Embryological development loosely mirrors evolutionary history, showing relationships between very diverged organisms Embryological development loosely mirrors evolutionary history, showing relationships between very diverged organisms E.g. fish and humans E.g. fish and humans