01 06-01-2016 evidence for evolution

8/18/2019 01 06-01-2016 Evidence for Evolution

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Variation

Formation of “distinctly different groups”

How it is generatedMutation, Recombination,Gene duplication, Plasticity, Culture etc

How it changes within a groupover generations

Individual do not affect eachother’s absolute fitness Allele level: Pop GenTrait level: Q Gen

Individual s affect each other’s absolute fitness • Cooperation and conflict• Parent-offspring conflict• Sexual selection• Evolution of eusociality

Process:Speciation, Macroevolution

Pattern:Phylogeny, Phylogeography

A rough organization of different topics in evolution aka A roadmap for BIO 422

Usage of evolutionary theory• Breeding• Antibiotic resistance• Evolutionary Medicine• Algorithm


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• What do we mean when we say that “evolution” happens?

• Why do we think “evolution” happened?

Today’s discussion


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Three alternative theories of species diversity

Creationism

Every species was created in their final form and have remainedunchanged.

Transformism (Lamarck)Every species were created separately but have changed after that.

DarwinismLife originated once (or very few times). Descent with modification issufficient to explain the species diversity that we see today.


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Evidence for origin of “species”


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Biological species concept• Species are groups of actually or potentially interbreeding natural populations,

which are reproductively isolated from other such groups (Mayr, 1940).• The biological species concept cannot be applied to fossils or asexual organisms.

Phylogenetic species concept• “A species is an irreducible (basal) cluster of organisms, diagnosably distinct from

other such clusters, and within which there is a parental pattern of ancestry anddescent” (Cracraft 1989).

• It applies to sexual and asexual species, but it can be difficult to determine the

degree of difference required for separate species

Morphological species concept (Darwin’s views)• A species is defined by phenotypic characteristics.•

It applies to both sexual and asexual species.

What is a species???


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Evidently, the concept of “change” is very different across these three definitions. Therefore, the kind of evidence needed for each will also be somewhat different.


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Change happens….

Therefore, if you define evolution as “change” and species as“sufficiently different groups”, then this amount of differencesuggests strongly that evolution happens. But if you take BSC then itdoes not work.

Can variations within species be sufficiently large to produce reproductive isolation?


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Ring species of salamanders in California

variations within species can besufficiently large to produce reproductive

isolation.

Note that the notion of ring species apparently challenges BSC but not the Darwinianconcept of species.


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Fossil evidence for species transformations


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Can new species be produced directly from existing species?

Artificial hybridization


11/23New species can be produced from old ones.

Natural hybridization


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Evidences for common ancestry


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Argument fromunity of type

Differencebetweenanalogy,

“Darwinian -homology”(unity of type)and evolutionary

homology


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Even better example of unity of type: genetic code

Three theories for the (near) universality of genetic code:

1. Chemical constraints:1. None found. Some mutations can make the UAG t-RNA bind to an amino

acid, indicating that there are no chemical constraints.2. Anti-codon and amino acids found on opposite ends of t-RNAs.

2. Convergent evolution

3. Common ancestry: seems the best solution

Note that this is an appeal to parsimonious reasoning.


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Hierarchical classification of “unity of type” is possible

Does it show common ancestry by itself?


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By itself this is not remarkable, but…. When hierarchicalclassificationsconstructed out ofmany unrelatedtraits, lead to verysimilar trees, thenthat demands anexplanation.Common ancestry isagain the mostparsimonious one.

In this case, >34million trees arepossible


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Interestingly, at least for major groups, the determined order alsocorresponds well with fossil records

Again, ancestry provides the most parsimonious explanation


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Existence of vestigial organs, pseudogenesand primitive forms during development

1. Tough to show that an organ does not have a function.2. Common ancestry gives a parsimonious explanation for this, but if you are ready to accept

“mysterious are the ways of the lord” and the notion that there might be slops in themaster plan, then I do not see how this is NOT reconcilable with the other two notions.

Primates can not manufacture vitamin Cas the enzyme required for the last stepis present but inactivated.


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Existence of transitional forms

Appeal to parsimony supports common ancestry

Angular

Quadrate

Articular

Dentary


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To summarize:

1. The evidence for origin of new species is direct and

uncontroversial.

2. Each strand of evidence for common ancestry, by itself,has to appeal to parsimony.

3. However, taken together, they make a very strong casefor believing in common ancestry.

4. The last statement (perhaps) is the reason for whichthe debate lingers. The other possibilities are politicalgains and stupidity, which (perhaps) can not be fullyignored.

C S


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REFERENCES

Chapter 3 of Mark Ridley’s Evolution offers the most coherent arguments for the

process of evolution and much of the treatment here is modeled after that book.Many authors make a case for common ancestry, without showing what theobservations mean for the other competing theories. This chapter avoids thatlogical pitfall and is a must-read to understand how to interpret evidences.

I have also used “The evidence for evolution” by GC Myer (not to be confusedwith Ernst Mayr!!) for some diagrams and examples.

A nice treatment of the issue is in “Why evolution is true” by J.A. Coyne. Thatbook should be read by anyone who would like to take a less formal look at thetopic.


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01 06-01-2016 evidence for evolution

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