7/30/2019 Chapter 22 in-Class Notes PDF

1/2

Chapter 221/19/12

Aim: Is there evidence that evolution has taken place?

Yes, several types. Look at todays living (extant) populations (species).

1. Darwins Finches: 13 species of Finches that live on the Galapagos islands, can nolonger interbreed with one another and produce fertile offspring. This means that

they are separate and distinct species. Each of the populations has unique traits(adaptations) that were selected for over time.

2. Industrial Melanism: idea originally proposed by JW Tutt (1896).

He studied the peppered moth. THe moth has two naturally occurring phenotypes -

Dark

Light

Pre-industrial England: very clean air, very little pollution (dirt, dust, soot). Lightcolored buildings & tree bark. Light colored moth selected for, dark color selectedagainst. More light colored moths.

Industrial revolution takes place: machinery produces pollution (dirt, dust & soot)changes color of buildings & trees (get darker). Now dark color selected for & lightcolor selected against because environment changed.

3. Artificial selection: a breeder picks parents with a desirable set of traits(phenotype), mates them together & chooses the offspring that have the desiredcombinations. (combination of characteristics). Done in agriculture as well - increasecrop yield/output/harvest.

4. Fossil Record: a record (the remains) of organisms that were, at one time, alive onour planet. Use the fossil record to establish a sequence of events that took placeover time. 2 ways to accomplish this using fossils;1. Relative Dating: in undisturbed rock layers (strata). The further (deeper) you go

into the Earth the older, and more simple the fossils become.2. Absolute (radiometric) dating: use radioisotope to establish the age of the fossil

(as accurately as possible)

Most commonly used radioisotope is Carbon-14 (14C)

Radioisotope decays (changes) over time

14C > 14N happens at a predictable, and measurable rate (1/2 life)

1/2 (half) life - the amount of time it takes for 1/2 of the radioisotope to changeinto its stable compound.

14C - 1/2 life: 5730 yrs.

10g 14C 5730 yrs> 5g of 14C and 5g of 14N 5730 yrs> 2.5g 14C & 7.5g14N

At a certain point, the amount of radioisotope that remains is too small to bemeasured. 14C = about 50,000 years for older fossils - use other radioisotopeswith longer 1/2 life.

Uranium 238 (238U) = 1/2 life of 4.5 billion years.

In this case, date the rock layer (where you find the radioisotope).

Problems with using the fossil record:

Finding fossils is difficult

Not all organisms that ever lived become fossils.

7/30/2019 Chapter 22 in-Class Notes PDF

2/2

Organisms may be degraded by the environment

erosion makes many fossils unrecognizable

gaps exist > fossil record is incomplete5. Anatomical record: compare anatomical structure of organisms. Looking for similar

structures, which may indicate a common ancestor.

1. Homologous Structures (homology): structures that are similar and developsimilarly (embryo), but have slightly different functions.

points to a common ancestor

divergent evolution: sometime in the past when the organisms were related,the environment changed and the organisms split and became distinctbecause of different adaptations.

2. Analagous Structures: have a similar function, but are completely different instructural arrangement and embryological development.

Ex:

Bird wing & insect wing

Fish fins and whale flippers

Similar adaptations were selected for because the organisms occupied asimilar niche in their environment > convergent evolution: similar adaptationsare selected for because of an organisms role in a region regardless of wherethey are on the planet.

3. Vestigal structures: evolutionary left overs, or relics. Used to serve a purpose(were adaptive) but now no longer have a purpose

Ex: pelvic bones in whales/snakes6. Embryological development: look at development in the embryos. Similar

developmental sequence may indicate a common ancestor.

Ontogeny recapitulates phylogeny - Embryological development supports howorganisms are classified.

Molecular clock: the greater the number of amino acid differences, the longer it hasbeen since we diverged.

7. Biochemical Evidence: look at base sequence in RNA & DNA - as well as amino acidsequence in polypeptides.

common proteins to use include:

Hemoglobin

Cytochrome C