Underlying Principles of Zoology Laws of physics and chemistry apply. Principles of genetics and evolution

important. What is learned from one animal group

can be applied to others. The two central principles for zoology

are; Evolution Chromosomal inheritance

Darwin's Theory of Evolution (Ernst Mayr’s 5 central theories of “Darwinism)

Perpetual change: changes across generations are a fact documented in the fossil record.

Common descent: branching lineages form a phylogeny that is confirmed by expanding research on morphological and molecular similarities.

Multiplication of species: splitting and transforming species produces new species.

Gradualism: small incremental changes over long periods of time cause gradual evolution but current research is still studying whether this explains all changes.

Natural selection: based on variability in a population, the inheritance of that variation, and differential survival of those variants, explains adaptation.

Natural Selection Observation 1. The reproductive

potential of every species is theoretically limitless.

Observation 2. Nevertheless, populations generally remain relatively constant in size. They are not increasing exponentially.

Observation 3. Natural resources are limited.

Natural Selection Inference 1. There is competition

for survival among members of a population.

Observation 4. Individuals in a species display variability.

Observation 5. Much of this variability is inherited.

Natural Selection

Inference 2. Because of their differing adaptations, varying organisms will have differential survival and reproduction rates.

Those with the best traits in a given environment will reproduce more and pass these traits on to their offspring.

Natural Selection

Inference 3. Over time, natural selection will result in the development of novel adaptations and new species.

Natural selection is random with respect to the mutations that result in variability, but selective in increasing beneficial traits in populations.

Evidence for Darwin’s Theories of Evolution Fossil record (see text) Common Descent Homology (very important concept in

reconstructing phylogenetic history of a species). Homologous structures are those that arise

the same way embryologically. Homology implies relationship = descent with modification.

Analogy. Structures with similar form, but arising

independently as a response to similar environmental pressures.

Haeckel’s generalization “Ontogeny recapitulates phylogeny.”

Many exceptions. Free-living embryos have to adapt to their

environment and diverge from ancestors. Development is conservative, but the timing

of changes necessary to give different adults varies.

Nevertheless, similarity in embryological stages is a strong argument in favor of Darwin’s theory of common descent.

Terms to note when reading

Gradualism vs. punctuated equilibrium

Allopatric speciation Adaptive radiation Neo Darwinism. Add chromosomal

theory of inheritance to what Darwin knew.

Two theories of taxonomy Traditional evolutionary phylogeny

(phylogenetic tree) Phylogenetic systematics =

cladistics (provide cladograms) Differences between these are not

based on differences in evolutionary principles, but in how these principles are used.

Relationships between taxons and trees or cladograms

Monophyly. Monophyletic taxons

include the most recent common ancestor of all of the members of the group and all of the descendants of that ancestor.

Relationships between taxons and trees or cladograms

Paraphyly. Paraphyletic taxons

include most recent common ancestor of group, but not all of the descendants of that ancestor.

Polyphyly. Polyphyletic taxons do

not include the most recent common ancestor of the group. Groups evolved same feature independently.

Relationships between taxons and trees or cladograms

Two theories of taxonomy

Both traditional and cladistic views accept monophyletic groupings and reject polyphyletic groups from their classifications.

Differ regarding acceptance of paraphyletic groups. These are accepted in traditional view.

Traditional evolutionary phylogeny

Higher taxa ranked by: common descent. amount of evolutionary change shown

on a phylogenetic tree. Each taxonomic group must:

have a single evolutionary origin Be unique with respect to adaptive

features.

Traditional evolutionary phylogeny Based on adaptive zones (distinct ways

of life). Enter new adaptive zone when change

sufficiently in structure (morphology) and behavior, e.g. fly rather than walk.

Recognize paraphyletic taxa. Problem because distorts patterns of common descent in order to group taxa according to unique adaptive features.

Phylogenetic Systematics/Cladistics

All taxa must be monophyletic. Exclusion of paraphyletic taxa

complicates things, but makes sense. Use sister group concept to avoid

statements re what evolved from what.

Gets clearer when we get to vertebrate groups.