A History of A History of EvolutionEvolution

Evolution is a process that results in Evolution is a process that results in heritable changes in a population heritable changes in a population spread over many generationsspread over many generations VariationVariation Natural SelectionNatural Selection EvolutionEvolution

AristotleAristotle 384-322 BC- believed living 384-322 BC- believed living

things could be arranged in a things could be arranged in a hierarchy- hierarchy- Scala Naturae- Scala Naturae- a a ‘ladder of nature’‘ladder of nature’

Simplest creatures on the Simplest creatures on the bottom rung, man on the top bottom rung, man on the top rung, other arranged in betweenrung, other arranged in between

Scientists supported this until Scientists supported this until late 19late 19thth century- it explained century- it explained why organisms seemed perfectly why organisms seemed perfectly adapted to their environment, adapted to their environment, role in naturerole in nature

The idea of evolution isn’t new- The idea of evolution isn’t new- School of Greek Philosophy, founded School of Greek Philosophy, founded

by Anaximander (611-547 BC) by Anaximander (611-547 BC) proposed an atomic theory and an proposed an atomic theory and an evolutionary theory similar to modern evolutionary theory similar to modern viewsviews

However, this work was unknown in However, this work was unknown in Europe during formation of the Europe during formation of the science of Biologyscience of Biology

Georges de Georges de BuffonBuffon 1707-1788- proposed species 1707-1788- proposed species

might undergo change in the might undergo change in the course of timecourse of time

Suggested that in addition to Suggested that in addition to the creatures of the world, the creatures of the world, there might be “lesser there might be “lesser families conceived by nature families conceived by nature and produced by time”and produced by time”

These changes occur through These changes occur through a process of a process of improvement/degenerationimprovement/degeneration

Erasmus Erasmus DarwinDarwin 1731-1802- grandfather of 1731-1802- grandfather of

DarwinDarwin Suggested species have Suggested species have

historical connections with historical connections with one anotherone another

Animals may change in Animals may change in response to their response to their environmentenvironment

Polar bear- ordinary bear, but Polar bear- ordinary bear, but living in the Arctic ‘modified’ living in the Arctic ‘modified’ it- those traits were passed it- those traits were passed onon

James James HuttonHutton 1726-1797- geologist- 1726-1797- geologist-

proposed that earth’s proposed that earth’s features were created by features were created by slow, gradual processes, slow, gradual processes, not sudden violent eventsnot sudden violent events

Important for 2 reasonsImportant for 2 reasons Earth had a long history- Earth had a long history-

long enough for long enough for evolutionary changesevolutionary changes

Stated that change itself is Stated that change itself is the normal course of eventsthe normal course of events

William William SmithSmith 1769-1839- studied fossil 1769-1839- studied fossil distribution scientifically-distribution scientifically-

Noticed the order of Noticed the order of geologic strata, collected geologic strata, collected fossils from each layerfossils from each layer

Each stratum, regardless of Each stratum, regardless of location, contained location, contained characteristic fossils- used characteristic fossils- used to identify layersto identify layers

Implies present surface had Implies present surface had been formed layer by layerbeen formed layer by layer

Georges Georges CuvierCuvier

1769-1832 – Recognized 1769-1832 – Recognized that fossils showed many that fossils showed many species had existed (but no species had existed (but no longer exist) longer exist)

Proposed extinction of Proposed extinction of species due to catastrophes. species due to catastrophes.

Couldn’t explain where new Couldn’t explain where new species came fromspecies came from

Vocal opponent of Vocal opponent of evolutionary theory.evolutionary theory.

Jean Baptiste Jean Baptiste LamarckLamarck 1744-1832 – Worked out a 1744-1832 – Worked out a

systematic concept of systematic concept of evolution.evolution.

1801 he proposed that all 1801 he proposed that all species, including species, including Homo Homo sapiens, sapiens, are descended are descended from other species.from other species.

Everything derived from Everything derived from an earlier, less complex an earlier, less complex species.species.

Inheritance of acquired characteristics- Inheritance of acquired characteristics- characteristics of organisms become characteristics of organisms become stronger/weaker, larger/smaller, stronger/weaker, larger/smaller, more/less through use or disuse. These more/less through use or disuse. These changes are transmitted from parent to changes are transmitted from parent to their progeny – ex. Giraffes neck!their progeny – ex. Giraffes neck!

Evolution was a universal principle – Evolution was a universal principle – unconscious striving upward on the unconscious striving upward on the Scala Naturae Scala Naturae that moved all that moved all organisms to more complexity. organisms to more complexity.

Charles Charles LyellLyell 1797-1875 – Geologist 1797-1875 – Geologist

provided new evidence to provided new evidence to support Uniformitarianism.support Uniformitarianism.

Uniformitarianism – Slow, Uniformitarianism – Slow, steady, cumulative effect of steady, cumulative effect of natural forces produced natural forces produced continuous change in the continuous change in the course of Earth’s history.course of Earth’s history.

Since process was slow, Since process was slow, results being barely visible results being barely visible in a lifetime, must have in a lifetime, must have been going on for a very been going on for a very long time.long time.

Thomas Thomas MalthusMalthus Influenced both Darwin Influenced both Darwin

and Wallace with his and Wallace with his work on populationswork on populations

Warned that human Warned that human population was population was increasing so rapidly increasing so rapidly that food supplies that food supplies would run outwould run out Food supplies and other Food supplies and other

factors keep populations factors keep populations in checkin check

Alfred Russel Alfred Russel WallaceWallace Biologist, naturalist, explorerBiologist, naturalist, explorer

Studied geographical Studied geographical distribution of animal distribution of animal species- biogeographyspecies- biogeography

Influenced by Malthus, Influenced by Malthus, realized that species diverge realized that species diverge from similar ones due to from similar ones due to environmental pressures environmental pressures

Developed his own theory of Developed his own theory of evolution, very similar to evolution, very similar to Darwin’sDarwin’s

Charles Charles DarwinDarwin 1809-1882 – The father of 1809-1882 – The father of

evolution.evolution. Naturalist – accompanied Naturalist – accompanied

HMS Beagle as ship’s HMS Beagle as ship’s naturalist.naturalist.

Explored fossil beds in S. Explored fossil beds in S. America.America.

Collected specimens of plant, Collected specimens of plant, animal life he encountered.animal life he encountered.

Observed that varieties of Observed that varieties of animals differed on east and animals differed on east and west coast.west coast.

Galapagos Islands –sailors could tell island Galapagos Islands –sailors could tell island origins of tortoises based on appearance.origins of tortoises based on appearance.

Also noted that island finches varied in size, Also noted that island finches varied in size, shape of bodies, beak, type of food eaten.shape of bodies, beak, type of food eaten.

Observed that islands were young, plants, Observed that islands were young, plants, animals on islands differed from those on animals on islands differed from those on mainland, and from each other.mainland, and from each other.

Influenced by Malthus, Influenced by Malthus, realized that populations realized that populations could easily reach limits of could easily reach limits of resourcesresources

Something had to keep Something had to keep populations in check- 1 pair of populations in check- 1 pair of elephants => 19 million elephants => 19 million elephants in 750 years, but elephants in 750 years, but average number of elephants average number of elephants remains constantremains constant

Natural selection- Natural selection- environment ‘determines’ environment ‘determines’ which individuals survive and which individuals survive and reproducereproduce

Natural selection is analogous to Natural selection is analogous to artificial selection used by breeders of artificial selection used by breeders of cattle, dogs, crops, etc. Humans choose cattle, dogs, crops, etc. Humans choose individual specimens for breeding based individual specimens for breeding based on desirable characteristicson desirable characteristics

Natural selection- environment ‘decides’Natural selection- environment ‘decides’ Individuals with certain hereditary Individuals with certain hereditary

characteristics survive and reproduce, characteristics survive and reproduce, other individuals with other traits are other individuals with other traits are eliminated, population slowly changes.eliminated, population slowly changes. EX- horses that can run faster, escape EX- horses that can run faster, escape

predators survive, reproduce, offspring, in predators survive, reproduce, offspring, in turn, might be fasterturn, might be faster

Inherited variations are Inherited variations are a matter of chance- not a matter of chance- not produced by produced by environment or ‘creative environment or ‘creative force’ or unconscious force’ or unconscious striving of the organism. striving of the organism.

Variations, in Variations, in themselves, have no themselves, have no goal or direction- often goal or direction- often have positive or negative have positive or negative adaptive value- more or adaptive value- more or less useful to an less useful to an organisms survival and organisms survival and reproduction.reproduction.

It is the operation of It is the operation of natural selection – natural selection – interaction of interaction of individual organisms individual organisms with their with their environment- over a environment- over a series of generations series of generations that gives direction to that gives direction to evolution. A variation evolution. A variation that gives even a slight that gives even a slight advantage makes that advantage makes that organism more likely organism more likely to leave surviving to leave surviving offspring.offspring.

Essential difference Essential difference between Darwin, between Darwin, predecessors is predecessors is variation- Darwin found variation- Darwin found variation to be part of variation to be part of the fabric of evolutionary the fabric of evolutionary process. Species arise process. Species arise when differences among when differences among individuals within a individuals within a group are gradually group are gradually converted in to converted in to differences between differences between groups as the groups groups as the groups become separated in become separated in space and time.space and time.