• Darwin----natural populations are variable, not just imperfect copies of a "blueprint"
• Population concept of species

Ontogeny: The embryonic and post embryonic history of an organism

Does "ontogeny recapitulate phylogeny"?

• Ernst Haeckel's (1834-1919; 1866) "biogenetic law"
• An organisms embryology (ontogeny) repeats (recapitulates) the entire evloutionary history of an organism (phylogeny)
• ontogeny recapitulates phylogeny
• Ontogeny gives general indications of the sequence of juvenile forms seen in the ancestors, but it is not a complete guide to phylogeny

• Subtle and continuous in some organisms (growth of a human)
• Abrupt and major in others (metamorphosis in insects)
• The constrains of skeletal material
• Endoskeleton
• Exoskeleton

Accretion- adding on discrete growth layers to the skeleton as the organism grows

• (e.g. Tree rings, growth lines in mollusks; can be read as annual or seasonal bands)
Addition- adding of discrete parts which grow very little after they are formed
• (e.g. the chambers of a foraminifera)
Molting- shedding of an exoskeleton (e.g. trilobites)
• Discontinuous growth because growth is rapid in the brief time after molting and before the new exoskeleton hardens
Modification- continuous remodeling and adding to existing skeletal elements. (mammals)

1. Growth Series
2. Study cross-sections of organisms
Isometric growth: growth in which dimensions change at the same relative rate. When these variable are plotted against one another the result is a straight line

Allometric growth (allometry): growth in which at least one dimension changes much faster than another.

Principle of similitude: body size increase = surface area squared and volume cubed.

• If an organism has surface-dependent functions (like gills), the surfaces increase at a slower rate than the overall increase in body size. Growth pattern must accommodate for this relationship.

HETEROCHRONY: evolution by changing developmental timing

Paedomorphosis: retention of juvenile features into sexual maturity
• Progenesis: stopping development at an early stage
• EXAMPLE: GO TO THIS LINK
• Neoteny: slowing down developmental timing
Paramorphosis: addition of ontogenetic stages beyon the adult reproductive stage
• Acceleration: increased rate of growth so that more stages are added in a shorter time
• Hypermorphosis: shutting off growth at a letter stage so that growth continues past the "usual" endpoint

Population: a group of individuals living closely together so that they are capable of interbreeding (gene pool).

Ecophenotypic variation: any changes due to differences in the environment (nutrients, light temperature, chemistry, etc.)

Sexual dimorphism: Phenotypic differences between males and females of the same spcies.

1. Analogy with living relatives
2. Ratios of males to females
3. Coincident distribution in time and space

Thanatocenosis: death assemblage

Biocenosis: life assemblage