Microevolution- Genetic changes in populations over time via natural selection (can lead to adaptations), but also via genetic drift, gene flow, bottlenecks, mutations, and other events.

Macroevolution- Evolutionary change above the species level. Origins of new species and higher taxa.

Anagenesis (microevolution)

Cladogenesis ( macroevolution)

Two general modes of speciation are distinguished by the mechanism interrupting gene flow within populations.

Allopatric speciation

  • Geological processes can fragment a population into two or more isolated populations
  • This could be a mountain range or a river

Sympatric Speciation


What causes evolutionary change above the species level? Origins of new species and higher taxa?

The sudden origin of wholly new types of organisms might occur through:

A. Transgenic Events – The lateral transfer of genetic material from one species to another, 2 mechanisms

  1. Transposable elements
  2. Symbiogenesis

B. Changes in Homeobox Genes- master regulatory genes; determine whether or not other genes will be expressed or not; controls the whole development of the organism

Transposable elements- Specialized DNA segments that move (transpose) from one location to another.

  • Within a cells DNA
  • Between individuals
  • Between Species


  • Responsible for the origin of the eukaryotic cell
  • Could give rise to different kingdoms, groups, phyla

Punctuated Equilibrium Model of Evolutionary Change

a) Gradualism Model

b) Punctuated equilibrium model

Animal Architecture and Development

There is a HUGE diversity of organisms and forms. But all animals have to accomplish the same basic physiological tasks in order to survive and reproduce.

  • Ingestion, digestion, metabolism, circulation, respiration, excretion, reproduction

A variety of Body Plans evolved to accomplish these physiological tasks

Some of the main criteria in which animals have traditionally been classified have been based on:

  • symmetry
  • tissue layers
  • body cavities
  • patterns of development


a) Radial Symmetry

b) Bilateral Symmetry

Cephalization – Formation of a head (concentration of nervous, sensory tissues at the anterior end)

Tissue Layers

Germ Layers- Embryonic tissue layers, groups of cells that behave as a unit during early stages of embryonic development; give rise to different tissue/organ systems in the adult.

Ectoderm- Outer layer (Forms the outer epithelium, nervous system)

Endoderm- inner layer (Forms the gut lining and its derivatives)

Mesoderm- Middle layer (Muscle, etc.)

  • Diploblastic animals- have 2 layers, only ecto and endo
  • Triploblastic animals- have 3 layers, ecto, meso, endo

Body Cavities- “Tube within a tube body plan”

  • The coelom likely evolved in the common ancestor of protostomes and deuterostomes
  • Bilaterians with a coelom completely lined in mesoderm (or mesodermally deriver tissue) are called coelomates
  • Bilaterians that subsequently lost their coelom are called acoelomates
  • Bilaterians that retain a coelom but lost the mesodermal lining in parts of
    the coelom are called pseudocoelomates

The coelom creates a fluid-filled container for circulation of oxygen and nutrients, and acts as an efficient hydrostatic skeleton

Patterns of Development

  1. Radial cleavage
  2. Spiral cleavage

Zygote ⇒ Eight-Cell Stage ⇒ Blastula (hollow ball)

There are two major groups of coelomate animals: the protostomes and deuterostomes, these grounps differ in

  1. The fate of the blastopore that forms during gastrulation
  2. coelom formation

Almost all animal species are protostomes

  • phylogenetic studies have long supported the hypothesis that protostomes are a monophyletic group
  • The protostome developmental sequence arose just once

Recent DNA sequence data support two major subgroups within the protostomes:

  1. Lophotrochozoa include molluscs, annelids, platyhelminthes, rotifers
  2. Ecdysozoa include the arthropods and nematodes (and others)


  • There are 13 phyla of lophotrochozoans
  • The name lophotrochozoan was inspired by the presence of
    • A feeding structure called lophophore
    • A type of larvae called trochophore
  • Lophotrochozoans also exhibit a spiral pattern of cleavage during
    embryonic development

An animal belongs to the Lophotrochozoa if you observe any of the following:
– A lophophore
– A trochophore
– Spiral cleavage

 However, not all lophotrochozoans possess all three of these

Protista (Unicellular)

  • includes protozoa

Metazoa (multicellular)

  • No “true” tissues: Parazoa(Sponges), Mesozoa
  • True Tissues:Eumetazoa
    • Diploblastic (mostly radially symmetric)
    • Triploblastic (mostly bilaterally symetric)
      • Acoelomate
      • Pseudocoelomate
      • Coelomate
        • Protostomes
        • Deuterostomes