Evolution - How Species Change

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Evolution

The Study of How Species Change

Over Time!


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Evolutionary Theory

Jean Baptise de Lamark (1744-1829) 1809, proposed an explanation of the

origin of species in his book ZoologicalPhilosophy

1. The needs of an organism determined thecharacteristics that evolved in the organism

2. Useful characteristics acquired in their lifetimecan be transferred to its offspring

This is called Use and Disuse


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Use and Disuse

How did the giraffeget a long neck?

No silly, he didntstretch it out!


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Charles Darwin (1807-1882)

Wrote Origin of Specieswhich presentedobservations thatdemonstrated all livingthings evolved fromother living things

Based on Variation and

Natural Selection


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Some of Darwin's ideas thatsupport evolution

Overproduction Within a population,

more offspring areborn then can possiblysurvive.

Competition: Numbers of individuals

in a population remainthe same fromgeneration togeneration.

A struggle for survival

is suggested

This is the basis forlife


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Survival of the Fittest Individuals who

survive are the

ones bestadapted to existin theirenvironment due

to the possessionof variations.


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ReproductionIndividuals

that survive

willreproduceand transmit

thesevariations totheir

offspring.


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Speciation As time and generations

continue, many adaptations

are perpetuated inindividuals until new speciesevolve in forms differentfrom the common ancestor


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Natural Selection

Traits which are beneficial to the survival of an organismin a particular environment tend to be retained andpassed on, increasing in frequency with in the population

Trait which have low survival tend to decrease inFrequency

When environmental conditions change, trait that wereformally associated with low survival may have greater

survival


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Problem with Darwins Theory:

He did not have any genetic

backing for his theory!


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Modern Evolutionary Theory

Supports Darwins theoryof evolution throughmechanisms of geneticinheritance

Genetic Variation isprovided by mutationsand sexual reproduction

Mutations arespontaneous . Someare harmful, some dontdo anything at all, and asmall percentage help the

species survive.


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Mutations

Definition: A random change in

the chemical natureof DNA

Mutations must occurin the sex cells inorder to be passed onto the nextgeneration.

Mutations in bodycells will only affectthe individual, nottheir offspring


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Vestigial Structures Anatomical structures which are no longer useful

have evolved to become smaller


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Comparing Structures andFunctions

Comparative anatomy Similarities in

anatomical features


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Comparison of EmbryonicDevelopment

Early vertebrateembryos closely

resemble oneanother


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Comparative Biochemistry

Their structure and function can be similareven though may not show structural

similarity The closer biochemical similarities, the

closer the relationship among organisms

Ex: nucleic acids.


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Mechanisms and Patterns ofEvolution: Geological Observations

Fossils: Law of Super-posistion Carbon Dating

Radio active decay

Common Ancestry

Divergence of modernforms of living things

from pre-existing lifeforms

This is the centralconcept in organic(species) evolution


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Concepts of Evolution

Geographic Isolation Favors speciation by

segregating a smallgroup from the mainpopulation with ageographi barrier

Ex: Islands, mountains,

rivers . In time, isolated

populations mayevolve into separate

species Ex: Darwins Finches


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Darwin's Finches


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Adaptive radiation

Rapid speciation of a single or few species to fillmany ecological niches.


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Geographic Isolation Cont.

Factors1. It may have possessed different initial gene

frequencies than the main population2. Different mutations occur with in main

population and isolated population

3. Different environmental factors

Different selecting agents (factors thatdetermine who survives) on each population


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Time Frame for Evolution

Gradualism: Evolutionary change is

slow and continuous

Punctuatedequilibrium:

Long periods ofstability interrupted bygeologically briefperiods of significant

change during whichspecies may evolve.


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The Basis of Evolution

There is grandeur in this view of life, with its

several powers, having been originallybreathed into a few forms or into one; andthat, whilst this planet has gone cycling onaccording to the fixed law of gravity, from sosimple a beginning endless forms mostbeautiful and most wonderful have been, andare being, evolved.

-- Charles Darwin


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Whats the Big Idea?

Descent with Modification organisms are altered throughdescent from an ancestor that lived in

the remote past Environments change Species change

D t ith M difi ti i lik t ith


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Descent with Modification is like a tree withmultiple branching points from a common

trunk to the tips of the youngest twigs thatrepresent the diversity of living organisms


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Homology

Homology Is the study of

similar structures indifferent species due to

their ancestry


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Anatomical HomologiesHomologous structures are anatomical similaritiesthat represent variations of a structure that waspresent in a common ancestor

Human Cat Whale Bat


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Homology in embryology (studyof development)

Reveals additional anatomical similaritiesnot visible in adult organisms

Chick embryo Human embryo


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Vestigial organs Are remnants of structures that served important functions inthe organisms ancestors

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Evolution - How Species Change