Chapter 16: Darwin’s Theory of Evolution

16-1 Darwin’s Voyage of Discovery•1831, Darwin set sail on HMS Beagle•Ship’s naturalist -observer/collector of plants, animals, & fossils•Left from England, sailed around South America, across Pacific, around Africa, and back to England•Most famous for observations made at Galapagos Islands•Biological evolution – change of populations of organisms over time

• Darwin noted 3 patterns of biodiversity:•Species vary globally – different, yet ecologically similar animal species inhabited separate, but ecologically similar, habitats around the globe (rheas, ostriches and emus)•Species vary locally – different, yet related animal species occupied different habitats within a local area (tortoise shell shape - Galapagos)•Species vary over time – fossils of extinct animals were similar to living species

16-1 Darwin’s Voyage of Discovery

• Darwin noted 3 patterns of biodiversity:•Species vary globally – different, yet ecologically similar animal species inhabited separate, but ecologically similar, habitats around the globe (rheas, ostriches and emus)

16-1 Darwin’s Voyage of Discovery

• Darwin noted 3 patterns of biodiversity:•Species vary locally – different, yet related animal species occupied different habitats within a local area (tortoise shell shape - Galapagos)

16-1 Darwin’s Voyage of Discovery

• Darwin noted 3 patterns of biodiversity:•Species vary over time – fossils of extinct animals were similar to living species

16-1 Darwin’s Voyage of Discovery

16-2 Ideas That Shaped Darwin’s Thinking

Darwin was influenced by:

• James Hutton - proposed that layers of rock form very slowly– Some rocks move up, while others are buried to

create mountains and valleys.– Natural forces such as rain and temperature

shaped the landscape– These processes happen very slowly over

millions of years

•Charles Lyell – said earth was several million years old

•Earth changed over time due to geologic forces (volcanoes, earthquakes, wind, erosion, etc.)

•Darwin reasoned that if Earth changed, those who lived on it would have to adapt/change to survive.

16-2 Ideas That Shaped Darwin’s Thinking

•Jean-Baptiste de Lamarck suggested that organisms acquired traits during their lifetime to adapt to their environment and passed those acquired traits onto their offspring.

•WRONG – only traits found on genes can be passed onto offspring!!

16-2 Ideas That Shaped Darwin’s Thinking

•Thomas Malthus – an economist that said the human population was limited by the supply of food and living space.

•Darwin reasoned that the same limits could apply to organisms in nature.

16-2 Ideas That Shaped Darwin’s Thinking

• Natural Variation – differences among individuals of a species.

• Farmers depend on natural variation for selective breeding– Only the largest hogs would be bred.

• Artificial Selection – humans selected the variations that they find useful.

16-2 Ideas That Shaped Darwin’s Thinking

•Darwin published his findings in 1859 in a book entitled The Origin of Species by Means of Natural Selection.

•He was motivated to publish his book in 1859 because Alfred Wallace had independently come up with the same conclusions

16-3 Darwin Presents His Case

Adaptations vs. Variations•Variations – differences that exist within a population that may have no effect on fitness

•Ex: length of your thumb

•Adaptations – a variation that all members of a population have inherited because that trait improves fitness

•Ex: an opposable thumbs

16-3 Darwin Presents His Case

•Sources of variation:•Mutations – individual genes change

•Ex: ATC AGC

•Events during meiosis – during meiosis, chromosomes get mixed up (crossing over) in making eggs & sperm

•Random fusion of gametes – which sperm fertilizes which egg – determined by chance

16-3 Darwin Presents His Case

•Three types of adaptations:•Structural – physical features of an organism

•Ex: long tongue to get food, sharp teethCamouflage

•Behavioral – actions an organism takes •Ex: migration, tracking prey, storing nuts, growing towards light

•Physiological – functioning/biochemical processes

•Ex: venom, ink of octopus, protein in web, respiration rate, digestive enzyme, blood clotting

16-3 Darwin Presents His Case

• Populations become modified through natural selection

• Natural selection - the process by which environment acts on a population, determining which organisms are most “fit.” Those organisms who are most “fit” survive and reproduce more often than those who are not.

• Fitness – reproductive success (“survival of the fittest”)

16-3 Darwin Presents His Case

•Darwin noticed similarities between species seen on mainland and island chains•Thought similarities could be explained by descent with modification – species came to new environment, then changed over time as the species adapted to its new environment.

16-3 Darwin Presents His Case

• Fossils• Anatomy

• Analogous structures• Homologous structures• Vestigial structures

• Embryology• Biochemistry• Direct observation

16.4 Evidence of Evolution

Fossil Evidence

•Fossils - the remains of past life

•Ex: shells, bones, teeth, imprints

•Tell us age, habitat, diet, & lifestyle of organisms.

•Record is incomplete – many organisms leave no fossils behind

16.4 Evidence of Evolution

Anatomical Evidence – Homologous Structures• All vertebrate forelimbs contain the same sets of bones –

suggests they evolved from a common ancestor.• Homologous structures - structures that are similar

because they develop from same tissues early in development; may or may not have same jobs• Ex: frog, lizard, bird, whale, cat, bat, and human

forelimbs

16.4 Evidence of Evolution

Bones of vertebrate forelimbs

Anatomical Evidence – Analogous Structures• Analogous structures - used for the same purpose but are not due to a common ancestor

• Ex: bird wing & insect wing

16.4 Evidence of Evolution

• Vestigial structures – have no function in the living organism but may have been used by its ancestors.

• Ex: human appendix, python leg bones

16.4 Evidence of Evolution

Cormorant – flightless bird

•Embryology – the more similar the embryos are at certain stages of development, the more closely related they are thought to be.

16.4 Evidence of Evolution

Biochemical Evidence

• Universal genetic code – organisms use the same triplet code and the same 20 amino acids in proteins

• All organisms have certain organic molecules in common.

1.Hemoglobin - carries oxygen in blood

2. Cytochrome c - protein for cell respiration found in almost all living cells

3. Hox genes – control development

16.4 Evidence of Evolution

Significance of biochemical differences

•Direct observation – We’ve seen evolution occur in cases like:

•The Grant’s studies of finches on Daphne Major in the Galapagos•Bacteria becoming resistant to antibiotics•Insects that become resistant to pesticides

16.4 Evidence of Evolution