Zoology and Evolution
Zoology
• The scientific study of animals
• What is an animal?
Evolutionary Tree of Life
Animals
• Multicellular eukaryotes
• Heterotrophs (consumers)
• Develop through a blastula stage
• Motile at some stage of their life
Choanoflagellate Protozoan
• Simple colonial flagellates
• No specialization
• Precursor to Metazoa
Spherical Colonies of Choanoflagellates
• Reproduction of the whole cell aggregate through gametes
• Cell specialization
Animal Kingdom Includes Very Diverse Organisms
Cell level of specialization
• Porifera
Tissue level of specialization
• True tissues– Endoderm– Ectoderm
• Example– Cnidaria
Organ level of specialization
• Tissues form organs
• Three germ layers– Ectoderm– Mesoderm– Endoderm
• Example– Platyhelminthes
Complete alimentary canal
• Mouth and anus
• Example– Nematoda
Internal body cavity - Coelom
• Organs suspended inside body cavity
• Example– Annelida
Invertebrates – Animals without a backbone
Vertebrates – animals with a backbone
Evolution
• Process of organic development and change– Continual process– Driven by the environment– Organisms have built in potential for change
Perpetual Change
Common Descent
• Phylogeny– Common descent through branching lineages
• Evidence– Homologies – similarity between organism that
occur because of common ancestry• Structural
• Genetic
Skeletal Homologies
Similarities because of common descent
Skeletal Homologies
Similarities because of common function
Evolutionary Relationships Revealed During Embryonic Development
Multiplication of Species
• Reproductively distinct populations of organisms– Usually but not always differ in form– No interbreeding between species in the wild
• Species split and develop into new species
Gradualism and Punctuated Equilibrium• Gradualism
– Small changes accumulate over time
– Steady rate of change
• Punctuated equilibrium– Bursts of rapid change
followed by little change
– Rate of change varies
Natural Selection
Responses to Selection
Sexual Selection
• Results in some sexual dimorphism
Potential for Variation
Modern View
• Microevolution– Small-scale changes– Change within a species
• Macroevolution– Large-scale changes– Formation of new species