History of Evolution

Mary Anning?

• became known as an expert on fossils in the early 1800s

• her gender and socioeconomic status precluded her from joining scientific societies and sharing her discoveries

History of Evolutionary Biology

1. Ancient Thought

2. Fossils and pre 18th century thought

3. Uniformitarianism/Pre-Lamarckian Evolution

4. Lamarck and Lyell

5. Between Lamarck and Darwin

6. Darwin and Wallace

7. Late 19th Century

8. Mendelians vs Biometricians (1900-1915)

9. Theoretical Evolutionary Genetics (1915-1930)

10. Modern Synthesis (1930-1950)

11. Era of Big Ideas (1950-1980s)

12. Molecular Revolution (1990 – now)

What are the 3 Ancient Ideas about evolution?

1. Ancient Greece (600-300 BC)

2. Taoism (China, 300 BC)

3. Islam (9th Century)

Ancient Idea: Ancient Greece (600-300BC)

• Anaximander: early philosopher who proposed that humans evolved from non-human species, land organisms originated in the water

• later, more influential philosophers (Plato, Aristotle) proposed a more static view of the universe

Ancient Idea: Taoism (China)

• World is constantly changing- contrast with more static western view

• Zhuang Zhou proposed speciation 300 BC)

Ancient Idea: Islam

• Islam-al Jahiz (9th century): book of animals discusses struggle for existence

• Ibn Khaldun (14th century): humans developed from a “world of monkeys” by species becoming more numerous

Fossils and pre-18th century thought

• who influenced western philosophy?

• what did they emphasize?

• static perception?

• what did they think of fossils?

• western philosophy was heavily influenced by Plato and Aristotle

• emphasized perfection of creation and great chain of being

• static perception: why change things if the world is already perfect

• fossils were assumed to be remains of organisms still living elsewhere

What was the 18th century known as?

• Age of Reason: an era that laid the foundation for modern science. Many ideas about evolution were developed during this time

What ideas developed during the 18th century and who developed them?

1. Comte de buffon: a french scholar who proposed change over time, but suggested that different species had different ancestors (limited evolution from many different ancestors, no common ancestor of all life)

2. Cuvier: studied fossils and age of the earth, proposed that fossils are extinct organism, catastrophism= evolution proceeded through very big changes

3. Erasmus Darwin (Charles Darwins grandfather): wrote poetry about the formation of new species and natural history

Who is James Hutton and William Smith?

• James Hutton and William Smith were geologists in a British scholar group called the Uniformitarianists

• Uniformaterianists: claimed that the geological processes taking place now operated similar in the past; the earth was very old

• ex: formation of mountains and layers of rock, sedimentary rock layers have different fossils, erosion, sedimentation, volcanic activity,

• suggesting that the earth was shaped by slow, continuous change

What did Hutton and Smith argue/find?

• Hutton argued for the constancy of the geological process

• Smith found that layers/order of rock strata were consistent in different places and had the same kind of fossils regardless of where he found the layers

Who is Lyell?

• Lyell: an english geologist published the Principles of Geology (1830s), a comprehensive synthesis of uniformatarian ideas with geological phenomena (age of earth, rock layers)

Who is Lamarck?

• Lamarck: a french scholar who proposed (1809) that organisms evolve new traits through a combination of environmental pressure and inheritance of acquired characteristics

Mid- 19th Century before Darwin/Wallace?

• who were important people during this time?

• William Charles Wells: wrote an essay on natural selection (1813)

• Patrick Matthew: proposed natural selection (1831)

• Matthew was upset when Darwin published the Origin of Species bc he argued he thought of it first and claimed he was the discoverer of natural selection

How were Darwin and Wallace different from the scientists before them?

• Darwin and Wallace had extensive field experience outside of England (low biodiversity, lots of human modification)

• explored environments with high biodiversity and unaffected by humans (ex: voyage on the Beagle, time in Amazonia and SE Asia

• observing nature in the wild shaped their thinking

• Joint paper presented in 1858, but neither attended the presentation, Darwin was spurred to publish the Origin of Species in 1859

Evolution After Darwin

• did society accept the idea of evolution and natural selection?

• Evolution was widely accepted by scientists fairly quickly

• however, natural section was less accepted bc it requires variation within populations; such variation contradicted the prevailing explanation of heritability of the time: Blending

• this lack of knowledge of genetics hindered advances in the late 19th century, leaving natural selection to be accepted by mainly naturalists (Wallace, Bates, Hooker)

What was rediscovered in the 1900s?

• 1900s: Mendelian (particulate) inheritance was rediscovered. This led to serious conflict between Mendelists and Biometricians

• The disagreement between biometricians and Mendelists was about how evolution works and how traits are inherited.

Biometricians- what do they believe?

Biometricians:

• natural selection causes evolution

• observed quantitative traits in populations of parents and offspring, less emphasis on mechanism of heritability

• studied traits using statistics

• Evolution happens gradually

• Traits (like height or size) show continuous variation (a range, not just categories)

• Natural selection slowly shifts these traits over time

👉 Example: Human height — there’s a smooth range from short to tall, not just “short” or “tall”

Medelists- what do they believe?

Mendelists:

• inheritance causes evolution

• observed dominant and recessive alleles, assumed dominant alleles would “win out” and become more frequent in a population over time

• Traits are inherited as discrete units (genes)

• Variation is not continuous, but comes in distinct categories

• Evolution can happen in sudden jumps (mutations)

👉 Example: Flower color being either purple or white

Unification Evolution and Genetics

• when was this conflict resolved?

• who set up a framework to allow us to predict how evolution would occur under different conditions?

• this conflict was resolved by 1915-1930, as basic theoretical ideas about genetics and evolution were developed

• Wright, Haldane, and Fisher set up a framework to allow us to predict how evolution would play out under different conditions

• this was not immediately appreciated bc of Math

What was the Key ideas of their framework? (4)

1. Alleles make up genotypes (AA, Aa, aa)

2. Both alleles and genotypes have frequencies within a population

3. Both alleles and genotypes have fitness values

4. Allele and genotype frequencies can change in predictable ways

Allele and genotype frequencies can change in predictable ways- what ways?

• Selection (differences in fitness)

• Genetic drift (chance changes)

• Migration (movement between populations)

• Mutation

• Nonrandom mating

• Meiotic drive (allele affects outcome of meiosis)

Modern Synthesis (1930s-1950s)- what is it?

Modern Synthesis: successful integration of genetics with Darwin’s postulates, leading to a reformulation of the Theory of Evolution

What were the two propositions made during the Modern Synthesis era (1930-1950s)

1. Gradual evolution results from small genetic changes that are acted upon by selection

2. the origin of species and higher taxa (macroevolution) can be explained in terms of natural selection acting on individuals (microevolution)

• alleles associated with higher fitness increase in frequency from one generation to the next

1950s-1980s

• what happened during this period?

• name?

• how was research affected?

• Era of Big Ideas (1950s-1980s)

• having a common conceptual framework allowed for explosion of new ideas (entire field of behavioral ecology, neutral theory of molecular evolution)

• Tomoko Ohta: Japanese population geneticists that developed the nearly neutral theory of molecular evolution

• despite the flood of new ideas this period was hampered by technical limitations, making ideas difficult to tests

• ex: it would be hard to test the effects of groups vs individual selection without models observing relatedness and group structure

1990s- Now

• what is this era known as?

• what has allowed researchers to test hypotheses that were impossible before?

• what is there a greater emphasis on now?

• “The Golden age of evolutionary biology”

• “Molecular Revolution”

• molecular techniques have allowed researchers to test hypotheses that were previously impossible

• much greater emphasis on rigorous hypothesis testing

Only Illustration in Origin of Species

• what does evolution consists of?

• what can evolution produce?

• Crucial contribution: evolution consists of change over time plus splitting/origins of diversity

• this process can produce not only differences over time, but also increased diversity

Taxonomy & Phylogenetic systematics- what are they?

• Traditional classification of organisms based grouping on morphological similarities

Taxonomy

• Taxonomy: naming of organsims grouped into progressively more inclusive sets (a hierarchy)

• Taxon: can refer to any level in the hierarchy (taxa is plural)

Easy way to remember

• Taxonomy = the system/process of classifying organisms

• Taxon = one specific group within that system

Think:

• Taxonomy = filing system

• Taxon = one folder in the system

Phylogenetic Systematics

• naming is based on evolutionary relationships and classification is tree based, reflecting branching events

• clade: a group of organisms that includes a single common ancestor and all of its descendants (aka a monophyletic group)

Paraphyletic Groups

Many traditional taxa names represent paraphyletic groups

Paraphyletic: group includes some, but not all the descendants of a common ancestor

ex: Fish

• a common ancestor

• but NOT all descendants

Monophyletic Groups

• evolutionary history should be based on monophyletic groups

• groups includes all descendants of a common ancestor

A monophyletic group includes:

• a common ancestor

• and all of its descendants

What do nodes represent?

• how do we study relatedness?

• nodes represent the most recent common ancestor between 2 groups

• they show us points of divergence

• the order of organisms along the branch tips does not tell us their relatedness

• we must investigate the nodes and branching patterns

Sister Taxa

• sister taxa: share a unique common ancestor not shared with other groups

• sister taxa are each others closest relatives in the tree

• share the most recent common ancestor

• branch off from the same point on the tree

Different ways to depict phylogenies

• Phylogenies can be presented in different ways in publications

• all show branching patterns. when interpreting these trees, use the nodes as your guide

• ex: we see the lion, leopard, and jaguar grouped together in every tree

Reduced Phylogenies

• trees can be reduced by depicting less species

• phylogenies can depict subsets of species, and dont necessarily show every possible species in a group

What is Polytomy?

Polytomy: three-way split, rather than a bifurcattion, can indicate uncertainty in a lineage

Which traits are informative for phylogenies?

• what do they need to reflect?

How do we decide with traits to use in constructing a tree?

• The traits need to reflect common ancestry and evolutionary history.

• The types of homologous traits that are useful in phylogenies are synapomorphies

Synapomorphies

• a shared, derived character used to define clades

• synapomorphies identify monophyletic groups

• derived traits are evolutionary novelties

• A shared derived trait inherited from a common ancestor

• Used to determine evolutionary relationships and identify clades

• Considered an evolutionary novelty because it is a newly evolved trait

How do we decide what is derived?

• an ancestral trait is present in the common ancestor of organisms

• in contrast, derived traits are evolutionary novelties

new traits that did not exist in the ancestor but appeared later during evolution.

• some derived traits are unique to one species, or they are shared