The History of Evolutionary Thought

Aristotle (384-322 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 (1744-1829)

• 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 (1823-1913)

• 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 (1809-1882)

• Voyaged around the world 1831-1836

• 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…..?????

Lion Cat Dog Man Catbird

Phylum Chordata Chordata Chordata Chordata Chordata

Class Mammalia Mammalia Mammalia Mammalia Aves

Order Carnivora Carnivora Carnivora Primata Passeriformes

Family Felicidae Felicidae Canidae Hominidae Minidae

Genus Felis Felis Canus Homo Dymetella

Species leo domesticus carolinensis sapiens familiaris

            

                     

           

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.

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)

Frog Turtle Kangaroo Mouse Human

Dorsal Nerve Cord

Yes Yes Yes Yes Yes Yes

Legs NO Yes Yes Yes Yes Yes

Nature of Egg

Requires water

Requires water

Hard shell prevents drying

Develops inside the

mother

Develops inside the

mother

Develops inside the

mother

Nature of development

In egg In egg In egg Marsupial Placental Placental

Hair No No No Yes Yes reduced

Presence of pouch

No No No Yes No No

Bipedal posture

No No No Yes No Yes

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.

p2 + 2pq + q2 = 1; p + q = 1