EvolutionEvolution

Earlier TheoriesEarlier Theories

WHY EVOLUTION?

• Evolution as a PROCESS is a SETTLED THEORY accepted by biologists all over the world.

• Evolution provides a framework for understanding all aspects of biology (classification e.g. simple to complex organisms, adaptation e.g. function, environment & structure)

WHY EVOLUTION? Cont.WHY EVOLUTION? Cont.

Evolutionary biology provides tools for many studies in genetics/genomics

- Relationships between groups,

- Research,

- Resolving legal issues such as

DNA fingerprinting & Sources of AIDS infections,

Evolution is NOT the process of Evolution is NOT the process of superior animals triumphing over superior animals triumphing over

inferior ones, but is rather a inferior ones, but is rather a series of alternative strategies series of alternative strategies that have arisen in response to that have arisen in response to

changing environments. changing environments.

No organism is better or worse than No organism is better or worse than another. another.

Arthropods (crabs, spiders, insects etc.) are Arthropods (crabs, spiders, insects etc.) are more successful than vertebrates when one more successful than vertebrates when one considers the number of species, number of considers the number of species, number of individuals, and number of adaptations to individuals, and number of adaptations to different environments and habitats.different environments and habitats.

In a similar way, humans are more In a similar way, humans are more successful than other modern apes in successful than other modern apes in having a large number of individuals having a large number of individuals adapted to living in different environments.adapted to living in different environments.

EARLY THEORIESEARLY THEORIES• Describe the two “laws” of Lamarck

• History and observations of Darwin ideas/theory

• Application of the theories with examples

• Why Lamarck`s theory was rejected

• Differences

Jean-Baptiste LamarckJean-Baptiste Lamarck

French Biologist French Biologist (1744-1829)(1744-1829)

Professor of “Worms Professor of “Worms and Insects” in Parisand Insects” in Paris

The first scientific The first scientific theory of evolutiontheory of evolution

Lamarck theoryLamarck theory Use and disuse of organsUse and disuse of organs Changes in the environment create new Changes in the environment create new

needs that cause organisms to modify needs that cause organisms to modify their existing organs to meet the need. their existing organs to meet the need. Repeated use of the organ would cause it Repeated use of the organ would cause it to enlarge and become more efficient. to enlarge and become more efficient. Disuse of a organ would cause it to Disuse of a organ would cause it to degeneratedegenerate

Inheritance of acquired characteristics

The modification an organism acquired during its life time could be pass on to its offspring.

Explain that Lamarck’s theory is not accepted by Explain that Lamarck’s theory is not accepted by most life scientists todaymost life scientists today

Acquired characteristicsAcquired characteristicsare are not not inheritedinherited/do/do

not cause any change to the DNA of an organism'snot cause any change to the DNA of an organism'sgametes (sperms or ova)gametes (sperms or ova) OROROrganisms did not evolve because they Organisms did not evolve because they

wantwantto evolveto evolve

ORORLamarck believed in Lamarck believed in determinismdeterminism (internal drive (internal drive

ofoforganisms to change)organisms to change)

LamarckLamarck -- All giraffes had short All giraffes had short

necksnecks originally originally-- Giraffes frequently Giraffes frequently

stretchedstretched/used their /used their necks to reach necks to reach

-- for leaves of tall treesfor leaves of tall trees -- necks become longernecks become longer- - The long necks acquiredThe long necks acquired

in this wayin this waycould be passed on to the could be passed on to the next generationnext generation /were /were inheritedinherited

How did Lamarck explained the long necks of giraffes?

Snake

Jean Baptiste de LamarckJean Baptiste de Lamarck• Two “Laws”

1. Law of use and disuse: Use or disuse causes structures to enlarge or shrink.

DISUSE & USEDISUSE & USE

2. “Law” of inheritance of acquired 2. “Law” of inheritance of acquired traitstraits

• Acquired traits can be inherited • All such changes are heritable

MisuseMisuse

Legs of snake Legs of snake disappeared disappeared because it did not because it did not use them in its use them in its gliding movement; gliding movement; also their bodies also their bodies became thin and became thin and long to allow them long to allow them to crawl through to crawl through narrow spacesnarrow spaces

Lamarck`s “Law” rejected Lamarck`s “Law” rejected His idea was that there is a ladder of life His idea was that there is a ladder of life

with superior forms (humans of course) near with superior forms (humans of course) near the top and lower forms on lower rungs the top and lower forms on lower rungs (plants near the bottom). (plants near the bottom).

Theory is deterministic. He imagined that all Theory is deterministic. He imagined that all organisms had organisms had an internal drivean internal drive to ascend to ascend the ladder during evolution. Those that the ladder during evolution. Those that started earlier (or had a stronger drive) started earlier (or had a stronger drive) would be higher than those that evolved would be higher than those that evolved later. He did not think of evolution in a later. He did not think of evolution in a tree-like form.tree-like form.

Lamarck`s “Laws” rejected (Cont.)Lamarck`s “Laws” rejected (Cont.) He imagined that when an organism tries to He imagined that when an organism tries to

use an organ for some purpose REPEATEDLY use an organ for some purpose REPEATEDLY that organ will grow and, moreover, its that organ will grow and, moreover, its offspring would start with an already offspring would start with an already enlarged organ. For example a giraffe would enlarged organ. For example a giraffe would stretch for high leaves throughout its life and stretch for high leaves throughout its life and this would result in its offspring being borne this would result in its offspring being borne with a longer neck and legs. with a longer neck and legs.

That there is no way that an event going on That there is no way that an event going on during an organisms life can causes directed during an organisms life can causes directed changes in its HERITABLE MATERIAL.changes in its HERITABLE MATERIAL.

Charles Darwin (1809 -1882)Charles Darwin (1809 -1882)

English NaturalistEnglish Naturalist College dropoutCollege dropout Traveled around the worldTraveled around the world Best known for Best known for On the On the

Origin of Species Origin of Species (1859)(1859) Abundant evidence for Abundant evidence for

evolutionevolution Proposed a mechanism: Proposed a mechanism:

natural selection natural selection

Envisaged evolution as a treeEnvisaged evolution as a tree

A radical and novel view

Summary of Charles Darwin’s theory

1. More individuals are born than survive to reproduce.

2. Variety exists among individuals of a species.

3. ‘Fitter’ individuals are more likely to reproduce = “Survival of the fittest”: Natural selection

eliminates less well-adapted individuals.

4. If characteristics are inherited, species slowly evolve. = adaptation, or ‘microevolution’ eventually giving rise to new species = speciation, or ‘macroevolution’.

Summary of Charles Darwin’s theory

1. More individuals are born than survive to reproduce.

2. Variety exists among individuals of a species.

3. ‘Fitter’ individuals are more likely to reproduce = “Survival of the fittest”: Natural selection

eliminates less well-adapted individuals.

4. If characteristics are inherited, species slowly evolve = adaptation, or ‘microevolution’ eventually even giving rise to new species = speciation, or ‘macroevolution.

Evidence

Th

en

Now

Summary of Darwin’s theory Summary of Darwin’s theory

Based on Based on Natural SelectionNatural Selection observations:observations:

Fraction of offspring survive to maturityFraction of offspring survive to maturity Natural resources are limited Natural resources are limited Population size fluctuate around carrying Population size fluctuate around carrying

capacitycapacity A population has variations of similar traits A population has variations of similar traits Traits best fitted to environment are passed Traits best fitted to environment are passed

on to next generation - unsuitable traits on to next generation - unsuitable traits disappear disappear

How would Darwin account for the long How would Darwin account for the long necks of the giraffesnecks of the giraffes

As a result of genetic variationAs a result of genetic variationin the giraffe in the giraffe population population

some giraffes have longer neckssome giraffes have longer necks than others than others Environmental changeEnvironmental change/competition for /competition for

resources occurred causing those with shorter resources occurred causing those with shorter necks to dienecks to die

and those with longer necks to surviveand those with longer necks to survive This is natural selectionThis is natural selection/survival of the fittest/survival of the fittest The genesThe genes/genotype for longer necks/genotype for longer necks were passed on to subsequent generationswere passed on to subsequent generations

most of which now have long necksmost of which now have long necks

Differences: Theories of Differences: Theories of evolutionevolution

Lamarck’s theory Lamarck’s theory 18091809

Darwin’s theory Darwin’s theory 18591859

Tabulate differencesTabulate differencesLamarckLamarck

Variation because Variation because individual changeindividual change

Individuals in Individuals in population changepopulation change

Because they Because they want to adapt to want to adapt to the environmentthe environment

Change acquired Change acquired inherited from inherited from parent to offspringparent to offspring

Darwin• Offspring showed

variation when produced

• Change because of environmental factors

• Natural selection – best suited

• Best suited characteristics are passed inherited from parent to offspring