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

•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…..?????

Carol von Linné (1707 – 1778)“Father of Taxonomy”

Immutable 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

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

ACCORDING TO DARWIN…

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

What is biological fitness???

Biological fitness:

The contribution an individualmakes to the gene pool

of the next generation relative to contr ibutions of other

individuals

Offspring should be fertile

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

•Genetic variation exists in sexually reproducing populations

•Different alleles are available in the population thus producing different phenotypes.

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.

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

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

Homologous Structures

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

Homologous Structures