Evolution of Populations

Chapter 16 (M)

Evolution a continuing process of change in a population of organisms over long periods of time

History 1700s Scientists believed that

“Species are Fixed” and do not change

Mid 1700s fossil records lead Georges Buffon to sayEarth is older than 6000yearsDifferent species arose from variation

from a common ancestor 1800s Lamarck explained fossil

records & species diversity

Lamarck

Proposed the theory of “Inheritance of Acquired Characteristics” body changes developed during an organisms life time could be passed on to the offspring

Short neck ate up grass had to stretch neckto reach trees

Lamarck

Acquired characteristics would have to modify DNA to be inherited no evidence of this

Lamarck’s theory was rejected

Set the stage for Darwin

Variation in the population long & short necks

Long necked survived reproduced population was gradually changed to long necked animals

Darwin(1809-1882) Started his voyages at the age of 22

on the HMS Beagle Was responsible for collecting

specimens of fossils He was aware of geological formations

of land masses could explain fossils of snails from mountains

Studied his collections for the next 22 years

Darwin’s Key Observations

1. Fossils & fossil records show that organisms simpler complex

2. Overproduction of offspring3. Limited supply of resources in

an environment4. Survival in a limited

environment depends in part on features inherited from parents

Information that influenced Darwin

Charles Lyell geologist proposed that the Earth was very old and had slowly been changing for millions of years

Thomas Malthus economist social problems as a result of the exponential growth of the human population

Artificial selection by breeders

Darwin Concluded

1. Descent with Modification

2. Natural Selection

Descent with Modification

All present day organisms are related through descent from unknown ancestors in the past.

These descendants of earliest organisms spread into different habitats adapted to diverse ways of life

Natural Selection

Individuals whose inherited characteristics adapt them best to their environment are most likely to survive and reproduce

Basic Mechanism of Evolution Natural Selection

Natural Selection

Occurs over a vast period of time

Individuals undergo selection, but do not evolve Populations Evolve

Evidence of Evolution

Section 16.4(M)

Evidence

1. Fossil Records2. Comparative Anatomy3. Embryonic Structures4. DNA Homology

Fossils Remains, traces or imprints of

an organism preserved in the earth’s crustImprintMoldCastPetrified

Fossil Records1. Fossils & the order in which they

appear in layers of rocks2. Fossil records show that animals &

plants have appeared in a historical sequence, fossils found in rocks of different ages differ because life on Earth has changed through time

Each Layer represents a particular time period

Comparative Anatomy The comparison of body structures in

different species Homologous Structures Analogous Structures Vestigial Structures

Ex: common descent evident in anatomical similarities between species in the same taxonomic group

Homologous Structures

Structures that are similar & have been derived from a common ancestor, but have been adapted to different functions.

ex: humans, cats, whales, bats all mammals

Whales’ flipper does not have the same function as a bat’s wing

Homologous Structures

Analogous Structures

Body parts similar in function but have different structures

Ex: wings of insects and birds

Vestigial Structures

Body parts reduced in size & appear to serve no function

Embryonic Structures Embryos of closely related

organisms often have similar stages in development

DNA Homology

Comparison of genes and proteins shows the relationships between species

Darwin’s Natural Selection : A Mechanism of Evolution

Natural Selection Regional and timely Adapts organisms to their local

environment Environmental factors vary from

place to place & time to time adaptation in one situation may be useless in another

Example: Biston betularia peppered moth

Peppered Moth

England two varieties dark & light 1850 almost all were light industrial

revolution pollution tree trunks turned black light moths became easy prey

Dark survived & reproduced End of century almost all were dark

Biston betularia : peppered moth

Populations A group of individuals of the same species

living in the same place at the same time Mainland animal species colonizes a chain

of distant and isolated islands separate population.

These populations adapt to their local environments.

Over time, the isolated populations would become more and more different.

And over many generations, the populations could become different enough to be separate species.

Darwin’s Finches adapted to different food sources beak Structures

Variation

Differences among members of the same Species

Adaptation Inherited trait that Improves the

Chances Of Survival & Reproduction

1. Structural mimicry organism copies the appearance of another species

2. Physiological changes in the organisms metabolic process penicillin drug resistant bacteria

3. Behavioral inherited behavior pattern that allows organism to survive

Adaptation- Mimicry Monarch tastes

bitter birds avoid them because they get sick

Viceroy(extra black lines on wings) not bitter, look & act like Monarchs birds avoid them

Adaptation: Camouflage

Protective adaptation that allows an organism to blend into its surroundings

The better the camouflage, the more likely it is for the organism to survive and reproduce

Adaptation: Camouflage

Artificial Selection Selective breeding of

domesticated plants and animals to produce offspring with genetic traits that humans value.

From Wild Mustard to our Table

Pesticides- Natural Selection in Action

Spraying crops kill insect pests favored the reproduction of insects with inherited resistance to the poisons