Theory of Evolution

Ch. 15

(15-1) Evolution

• Change of organisms over generations w/ a strong natural modification process

• “Change over time”

Scientific Theories

• Explain data• Generations of predictions• Falsifiable

Lamarck’s Theory

• Use & Disuse: parts of body that are used extensively become larger & stronger while those that are not used deteriorate– Acquired traits

Lamarck (cont.)

• Ex: – Webbed foot = stretching of membrane b/w

toes (water birds)• 1st to say:

– Organisms change over time– New organisms are modified descendants of

older types

Darwin & Wallace’s Theory

• Natural Selection: organisms best suited to their environment reproduce more successfully than others

• “Survival of the fittest”

Charles Darwin’s

• Voyage on the Beagle

Darwin’s Studying Ground

Darwin’s Observations

• 13 similar but separate species of finches– Specialized for food

• Similarities lead to belief of a common ancestor

Darwin’s Conclusions

1. Descent w/ modification2. Modification by natural selection

Descent w/ Modification

• Newer species are modified descendants of older species

• All species descended from 1 of a few original types of life

Modification by Natural Selection

• How evolution occurs• Environment limits pop.’s growth• Not all individuals in a pop. are identical &

environment affects them differently

Natural Selection (cont.)

• Individuals w/ favorable traits reproduce more often than those w/ unfavorable traits

• Thus favorable traits will be passed down more often

Adaptation

• Inherited trait that inc. an organism’s chance of survival in a particular environment– Based on genes

Fitness

• Ability to survive to propagate their genes (have babies)

Lamarck vs. Darwin

(15-2) Evidence of Evolution

1. Biogeography• Geographical distribution of species

2. Fossil Record• Type & order of fossils

Evidence (cont.)

3. Homologous structures• Similar b/c of common ancestry

4. Comparative embryology• Study of structures that appear during

embryonic development

5. Molecular biology• DNA & proteins

Biogeography

• New organisms arise in same geographic area where similar forms already lived

• Ex: kangaroos only in Australia

Fossil Record

• Fossils: impressions of organisms from the past mineralized in rock

• Links b/w modern forms & ancestors

Distribution of Fossils

• Law of superposition: lowest layers of rock are oldest

• Fossil-bearing strata show when organisms became extinct

• Mass extinction: brief period in which large #’s of species disappeared

Homologous Structures

• May have different functions but have similar anatomy

• Shows a common ancestor• Ex: bird beaks & forelimbs

Common Ancestor

Analogous Structures

• Similar look & function, but different embryological development & anatomy

• Ex: bird & insect wings

Vestigial Structure

• Part of an organism w/ little or no function, but had a function in an ancestral species

• Ex: human tailbone & appendix

Comparative Embryology

• All vertebrate embryos go through a stage in which they have gill pouches & tails

Molecular Biology

• The more similar the sequence, the more closely related 2 species are to each other

• DNA, RNA, proteins (amino acids)

Amino Acid Chart

(15-3) Patterns of Evolution

1. Coevolution2. Convergent Evolution3. Divergent Evolution

• Pattern & speed result from changes in the environment

Coevolution

• Change of 2 or more species in close association w/ each other

• Ex:– Predator-prey– Parasite-host– Plant-animal pollinator

Convergent Evolution

• Organisms appear to be similar but are not closely related

• Environment selects similar phenotypes• Ex: shark & porpoise

Divergent Evolution

• 2 or more related populations become more dissimilar in response to different habitats

• Adaptive radiation– Galapagos finches

• Artificial selection– Domestic dogs

Divergent evolution of Grand Canyon squirrels

Peppered Moth Evolution