The Theory of Evolution

Darwin and the development of the theory

The Theory of Evolution

What is a SPECIES? Group of similar organisms

– Structurally– biochemically

Can interbreed successfully in nature– Offspring are healthy– Offspring are fertile (can reproduce)

These organisms are not new species…Why?

Mule Liger

Variation Variation – differences between

individual members of a population

Members of a species are very similar, but differences can be observed, or not, make each individual unique.

May be caused by mutations

Mutations Changes in DNA base sequences

Most are either neutral or harmful

Those that allow the organism to survive better in a particular environment are good and are more likely to be passed on to future generations.

Most variations are not caused by mutations

Sexual reproduction combines genes from different parents

Crossing over during meiosis can produce variations

Adaptation An inherited trait that increases

the population’s chances of survival and reproduction in a particular environment.

Allows organisms to fit best into a particular niche (habitat and role)

Biodiversity The variety and abundance of species

that makes up a biological community. Pine Barrens forests have little

biodiversity – a limited number of species can survive there.

Tropical rain forests have great biodiversity – many species in a concentrated area.

Organisms have changed over time to produce so many different forms

of life

Theories accepted before Darwin

1769 – Bonnet – theorized that fossils were from animals/plants that lived before catastrophes that made them extinct.

Jean Baptiste Lamarck Use and disuse Inheritance of acquired

characteristics

Darwin and his theory Charles Darwin lived

in early-mid 1800’s.

Went on voyage around the world as the ship’s naturalist – collected specimens of plants and animals during the 5+year-journey.

Darwin’s Voyage

Galapagos IslandsDarwin’s route

Darwin Returned Home to Think! These influenced his development of the theory:

– Evidence that the 13 different species of finches found in the Galapagos Islands were the descendents of one species.

– HERE ARE JUST A FEW BEAK TYPES:

Artificial selection – farm animals and plants

– Population control – population limited by resources and nature controls it by killing off some members during natural disasters, illness (epidemics), blights in plants, etc.

– Geologic evidence of slow changes

Darwin’s Theory of Evolution by Natural Selection

1. There is variation within a population2. Some variations are good (helpful)3. Not all young produced in a generation

can survive– This leads to a struggle for existence.– Survival of the fittest.– Those that survive and reproduce are those

with the good variations.

Evidence supporting Evolution

Fossils – remains of plants or animals that lived before – can show structures

Homologous Structures – similar in structure, but have different

functions

Vestigial Structures Inherited But, reduced in size and often not

used.– Examples

Snake legs (they’re so reduced in size that they are not apparent).

Human appendix –no function, except can cause problems.

Human coccyx – tail bone.

Analogous Structures Similar in function, but very different in

structure – indicate organisms are not closely related

Insect wings Bat wing Bird wing

Embryological Evidence

If organisms have similar embryos, they are more closely related than those with less similar embryos

Sea lamprEy pond turtle chicken cat human

Origin of Species Speciation – evolution of one or

more species from a single ancestor species. can be from:

– isolation – usually because of a geographic barrier such as a canyon, mountain, or island

Divergent Evolution Isolated populations of a species

evolve independently of each other.

– Ex – polar bears and brown bears

Convergent Evolution Natural Selection produces

analagous (similar) adaptations in different organisms in response to similar environments: – African Serval cat & south american maned wolf

– See text p 242– These animals have similar ears, legs, acute

hearing, habitat, and Occupy similar niches

Coevolution Species that interact closely often

adapt to one another:

Adaptive Radiation Many different species evolve from

one ancestral species – each new species has a different niche

Evolution Observed: Peppered Moths

Light moths

Dark moths

Light tree Dark tree

Less pollution More pollution

The End