Theories for Evolution

Chapter 15-2

Biological Evolution

• The change of populations of organisms over time

Jean Lamarck1744-1829

• Similar species descended from a common ancestor

• To explain how species changed: he hypothesized that acquired traits were passed to offspring

• Acquired trait: not determined by genes; it arises during organisms lifetime as a result of behavior or experience

LamarckAcquired Traits

Examples

• Giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks.

• Shore birds got their webbed foot by repeatedly stretching the membrane between their toes

To Lamarck this means…

• If you have a nose job, your kids will inherit the new nose!

• In real life, what nose will your kids get? (the old one or the new one?)

• Answer: the old one!

Is this logical?

• What determines that traits are passed to their children?– DNA

• If you change your appearance, will your children inherit the new appearance– No, because your DNA did not change

Charles Darwin1809 - 1882

• A naturalist (studied and preserved biological specimens that he collected)

• 5 year voyage around the world aboard the HMS Beagle to collect specimens from South America and the South Pacific

Charles Darwin

• Theory of evolution by natural selection– Nature will select the organisms that have

variations that allow them to better survive (survival of the fittest)

– Darwin collected different species that were very similar and hypothesized that they shared a common ancestor

insects

finches

Darwin’s Book: On the Origin of Species by Natural

Selection

• Described his theory of evolution

• Caused a lot of controversy and angered the church

• The church initially believed that evolution is a sin against God

• Before Darwin died, the church accepted his theory and he was buried in a famous church in England

Survival of the fittest by means of natural selection

• Variations may give certain organisms advantages to survive, while other organisms died

• Nature selects those organisms that will die or survive

Darwin explains why giraffes have longer necks than their ancestors

• Overproduction – too many giraffes

• Struggle or compete for food

• Variation in length of neck exists naturally

• Longer neck…reach food...survive

• Longer necked giraffes survive and reproduce to eventually originate a new species of giraffes

Charles Darwin

• Darwin’s theories are accepted today as the most accurate explanation for evolution

Hugo De Vries

• Added the concept that mutations in DNA are what cause organisms to change or have variations

• Evolution is changes in

DNA that is then inherited

Adaptations

• A trait that increases an organisms chances of survival

Fitness

• An individual with high fitness is well adapted to its environment and reproduces more successfully than individuals with low fitness

Adaptive Advantage

• A favorable trait that fits their needs and environment

Evolution in Process

Chapter 15-3

Evidence for EvolutionHomologous structures

• Similar shape

• Different function

• Shared origin

• Example forelimbs: arms of human, wings of bats, wings of penguins, arms of alligators

Evidence for EvolutionAnalogous structures

• Different shape & internal anatomy

• Similar function

• Different origins

• Example: wings of a humming bird and wings of a moth, both allow the organism to hover

Vestigial Structures

• A structure that had a use in an ancestor but has no use in a particular organism today

• Examples: – Appendix in humans– Tail bones in humans… we have no tails– Tiny leg bones in snakes…they have no legs– Wings in penguins…they do not fly– Nipples on boys…they do not produce milk

Embryology

• The study of an organism from creation to birth• Vertebrate embryos are similar to one another• Embryos have

– tails that vanish into their spines– gill slits, like fish to breath that vanish into ears– coats of hair that fall off at birth

Embryos go through stages of heart development

• 2 chambers like fish hearts

• 3 chambers like reptiles

• 4 chambers like birds and mammals

Patterns of Evolution• Co-evolution: change of two or more

species in close association with each other

–Predator/prey

–Animals/plants they eat

Convergent Evolution: environment select phenotype even though ancestry is different (analogous structures)

Divergent Evolution: two species become more and more different over time due to different habitats (homologous structures)