Biol 121- 2010.03.08- Evolution- Evidence for Evolution (Ch. 24).docx

23 views2 pages
22 Apr 2012
Biol 121 225
Freeman 484-490 Mar 8, 10
Evolution 2- Ch. 24, Evidence for Evolution
Main points of Darwin’s theory?
1. Evolution “descent with modification”
-all organisms have a common ancestor Linnanean hierarchy, “tree of life”
-two species in a family are more closely related than those in different families in the
same class
-the environment changes traits in a population over time/over generations (allele
frequency changes in a population)
2. Natural selection the mechanism of evolution
-genetic variation exists
-performance affects reproductive success higher fitness
-competition differential survival
-natural selection occurs through interaction between environment and existing
genetic variation in a population
-it causes a change in the population resulting in increase in those better suited for
-variable population because of adaptation of population to environment
variation + selection = adaptation
Evidence for evolution
1) Evidence for change through
a) Fossil record
i) Extinctions
-the fossil record
-extinct species can be noticed in fossils containing shells, bones, leaves, bird tracks,
dung, etc
-this was used as evidence by Darwin who then said that species were not static,
immutable entities
-his reasoning: since species have gone extinct, array of species living on Earth
changes over time
ii) Transitional forms
-when a species evolves over generations, it may enter many transitional forms
-transitional form = fossil species with traits that are intermediate b/t those of older
and young spp.
-was known as the “law of succession” when there were resemblances b/t fossils
found in rocks underlying certain regions and the living spp. found in the same
geographic area
-Evolution of whales: Whales evolved from terrestrial mammals to the aquatic
mammals of today
-transitional forms had shorter legs with time, as well as a flatter body
-eventually, legs disappeared and became small fins
b) Changes in living organisms
i) Vestigial trait
-a vestigial trait is a reduced or incompletely developed structure that has no function
or reduced function, but is clearly similar to functioning organs or structures in closely
related species
-for example, humans have tailbones (coccyx) but we don’t have tails
-also, appendix in human is reduced version of cecum digestive organ in other
ii) Artificial selection
-spindly flowering stalk (Brassica aleracea)
-if you select individuals with largest and most compact flowering stalks and breed
them, and do so for a few generations, you will get broccoli
-basically, you can breed/cross individuals that have a specific trait of interest
Unlock document

This preview shows half of the first page of the document.
Unlock all 2 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.