The History of Evolutionary Thought

Aristotle ( B.C.) Ladder of Life »2 types of animals – those w/ blood & those w/o Animals classified by their way of life Plants by structure Observation of various marine life anatomy was remarkably accurate Distinguished whales from dolphins

Natural Selection Summarized: Darwin’s theory suggests that in a species: There is a tendency towards overproduction Variation exists Variations are inherited Individuals survive in their environments with varying degrees of success Best adapted, survive and pass favorable variation on to next generation In time, great differences arise, until a new species evolved from an old species

Jean-Baptiste Lamarck ( ) His name is associated merely w/ a discredited theory of heredity – he died in obscurity & poverty Darwin & Lyell give him great credit Law of use/disuse Law of acquired characteristics

LAMARCK’S THEORY

ACCORDING TO DARWIN…

Alfred Wallace ( ) Studied the way geography limited or facilitated the extension of species range How ecology influenced the shaping of adaptations In 1858, shared with Darwin on the Theory of Evolution by means of Natural Selection

Charles Darwin ( ) Voyaged around the world Wrote On the Origin of Species which reveals his ideas on Evolution by means of Natural Selection

Linnaeus was classifying organisms based on what they looked like. This made it difficult to classify organisms that seemed to share characteristics with both kingdoms that Linnaeus proposed, Plants and Animals. For example, fungi including mold and mushrooms do not move (or do they?) so they seem to be plants but, unlike plants…..?????

LionCatDogManCatbird PhylumChordata ClassMammalia Aves OrderCarnivora PrimataPasseriformes FamilyFelicidae CanidaeHominidaeMinidae GenusFelis CanusHomoDymetella Speciesleodomesticuscarolinensissapiensfamiliaris

Homologous Structures Structures that have different mature forms in different organisms but develop from the same embryonic tissues.

A kind of evolution wherein organisms evolve structures that have similar (analogous) structures or functions in spite of their evolutionary ancestors being very dissimilar or unrelated.evolutionorganismsanalogous

Classifying organisms often starts at the cellular level

Cladistics (phylogeny) A system of classification based on the study of evolutionary relationships history of groups of organisms.

An Example of Cladogram Construction for Vertebrates Trait Outgroup (lobed- finned fish) FrogTurtle Kangaroo MouseHuman Dorsal Nerve Cord Yes LegsNOYes Nature of Egg Requires water Hard shell prevents drying Develops inside the mother Nature of development In egg Marsupial Placental HairNo Yes reduced Presence of pouch No YesNo Bipedal posture No YesNoYes

Coevolution Mutual evolutionary influence between two species Typically evolution of two species totally dependent on each other. Exert selective pressure on the other, so they evolve together. Extreme example of mutualism.

What is biological fitness???

Evolution of Populations

Populations are the units of evolution

Population A group of individuals of the same species living in the same place at the same time.

Biological definition of a species A group of populations whose members are capable of interbreeding and producing fertile offspring.

Population genetics  An important turning point for evolutionary theory the 1920’s.  Developed in the 1920’s  A field that combines Darwin’s and Mendel’s ideas by studying how populations change over time.

The Gene Pool  In studying evolution at the population level, geneticists focus on the GP  Total collection of genes in a population at any one time.

The Gene Pool

Sources of Genetic Variation Mutations Gene Shuffling Crossing over Sexual reproduction

Single Gene Traits The number of phenotypes produced for a given trait depends on how many genes control the trait

Polygenic traits are controlled by two or more genes

Natural Selection can affect the distributions of phenotypes in 3 ways: Directional selection Disruptive selection Stabilizing selection

Directional Selection When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end.

Disruptive Selection When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle.

Stabilizing Selection Takes place when individuals near the center of a curve have higher fitness than individuals at either end

Isolating Mechanisms Behavioral Geographic Temporal THE PROCESS OF SPECIATION

Behavioral

Geographical

Temporal

The Hardy–Weinberg principle states:  Both allele and genotype frequencies in a population remain constant or are in equilibrium from generation to generation unless…  Disturbing influences happen such as non-random mating, mutations, selection, limited population size, random genetic drift and gene flow.  Genetic equilibrium is a basic principle of population genetics.

Hardy-Weinberg principle is like a Punnett square for populations, instead of individuals.

p 2 + 2pq + q 2 = 1; p + q = 1