Chapter 17: Introduction to Darwinian Evolution

Evolution

• Accumulation of inherited changes within populations over time

• NOT changes in an individual in its lifetime• Changes in characteristics of populations over

many generations

2 perspectives:

• 1) MICROEVOLUTION: short-term adaptations of population to changes in the environment

• 2) MACROEVOLTUION: long-term formation of different species from common ancestors

Contributing Scientists

• Jean Baptiste de Lamarck– 1st – organisms undergo change because of

natural phenomena– Organisms endowed with vital force to change

toward complexity over time– Organisms could pass traits acquired during their

lifetimes to their offspring• Giraffes – stretch necks• Discredited when basis for heredity discovered

• Thomas Malthus– Population growth not always desirable– Outstrip food supply– Famine, disease, war – stop growth• “struggle for existence”

– strong and constant check on human population growth

• Charles Lyell– Slow geological processes Old Earth

• Charles Darwin– HMS Beagle – South America – 5 years– Naturalist – plants, animals, fossils, geology– Galapagos Islands – compared species to

mainland and other Galapagos Islands– Artificial selection: breeders develop varieties in a

few generations• Dogs, plants• Similar process in nature – model for natural selection

Fig. 22-9

Kale

Kohlrabi

Brussels sprouts

Leaves

Stem

Wild mustard

Flowersand stems

Broccoli

Cauliflower

Flowerclusters

Cabbage

Terminalbud

Lateralbuds

Fig. 22-5

NORTHAMERICA

EUROPE

AFRICA

AUSTRALIA

GREATBRITAIN

SOUTHAMERICA

ATLANTICOCEAN

PACIFICOCEAN Cape of

Good Hope

Tierra del FuegoCape Horn

TasmaniaNewZealand

Ande

sEquator

TheGalápagosIslands

Pinta

MarchenaGenovesa

Santiago DaphneIslands

PinzónFernandina

IsabelaSan

Cristobal

SantaFe

SantaCruz

Florenza Española

– Favorable variations would be preserved, unfavorable eliminated

– adaptation : evolutionary modification that improves the chances of survival and reproductive success in a give environment

– Accumulation of modifications maybe new species

– Time required for new species to originate• Old Earth

Fig. 22-6

(a) Cactus-eater (c) Seed-eater

(b) Insect-eater

Fig. 22-2

American Revolution French Revolution U.S. Civil War1900185018001750

1795

18091798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)Hutton (gradual geologic change)

Lyell (modern geology)Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

Natural Selection (Darwin)

• Better adapted organisms are more likely to survive and become parents

• Population changes over time; frequency of favorable traits increase with each generation

4 observation for Natural Selection• 1) Variation – each individual is unique– Some advantageous traits - inherited

• 2) Overproduction – each species can produce more offspring than can survive

• 3) Limits on Population Growth – (struggle for existence) more individuals than resources competition

• 4) Differential reproductive success – (survival of the fittest) better adapted individuals will survive and reproduce

Fig. 22-10

Evidence for Evolution

• Fossil Record• Comparative Anatomy• Biogeography• Developmental biology• Molecular evidence

Fossil Record

• Fossils – remains/traces of previously existing organisms– Sedimentary rock, bogs, tar, amber, ice– Conditions slow or prevent decay– Covered quickly – water, sand– Hard body parts– Record biased – location, body

Dating Fossils

• 1) Relative Age – position in rock– Index fossils – • characterize a specific layer over large geographical

areas• Existed short time, preserved in large numbers

– With this info arrange rock layers and fossils in chronological order and identify comparable layers in widely separated locations

Fig. 22-3

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

• 2) Absolute Age – – Radioisotopes – emit radiation – nucleus changes

into nucleus of different element with decay– Half-life – time required for ½ of the atoms to

change to a different atom– Potassisum-40 (1.3 billion years)– Uranium-235 (704 million years)– Carbon-14 (5730 years)

Comparative Anatomy• Similar structures related organisms (common

ancestor)• Homologous structures – features derived from

same structure in a common ancestor– Ex: limb bones of mammals, modified leaves– Similar structure, different function

• Homoplastic features (Analogous features) – structurally similar features that are not homologous but have similar functions in distantly related organisms– Ex: wings of insects/birds, spines and thorns– Same function, evolved separately (different structure)

Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

PhalangesHuman WhaleCat Bat

Fig. 22-20

Sugarglider

Flyingsquirrel

AUSTRALIA

NORTHAMERICA

– Show organisms with separate ancestries may adapt in similar ways to similar environmental demands Convergent evolution• Ex: aardvarks, anteaters, pangolins

• Vestigial structures – organs or parts of organs that are seemingly nonfunctional and degenerate, undersized or lacking some essential part– Remnants of parts that were functional in ancestors– Ex:

• Human - appendix, coccyx, 3rd molars, ear muscles• Whales/pythons – hind limb bones• Pigs – vestigial toes• Kiwi – wingless bird – vestigial wing bones• Burrowing/cave-dwelling – vestigial eyes

Vestige usually not harmful so selective pressure to completely eliminate is weak

Biogeography

• Study of past and present geographical distribution of organisms

• Not all animals/plants found in all environments where they could survive

• Spread from origin• Continental drift / Pangaea

Developmental biology

• Genetic similarities reflect shared evolutionary history

• Vertebrates – embryological development similar common ancestor– (segmentation, gill pouches, aortic arches)

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

Molecular evidence

• Confirms structural and fossil evidence• Universal genetic code• Similar amino acid sequences, proteins,

nucleotides• More similarities common ancestor• Phylogenetic trees - diagrams showing lines

of descent– Derived from differences in DNA sequences– Whales and hippos closely related

Evolution is happening NOW!

• Can be observed in our lifetime• Ex:– Resistant Bacteria– Finch beaks– Guppy study