Evolution is a change in a species over time.
Summary of Darwin’s Theory
Darwin’s theory of evolution presented a new view of life, summarized below. This view, profoundly different from any thing known in nineteenth-century England, continues to be upheld by research today. Many would still agree with Darwin, who wrote, “There is grandeur in this view of life, that from so simple a beginning, endless forms most beautiful and wonderful have been and are being evolved.”
1. Individual organisms in nature differ from one another. Some of this variation is inherited.
2. Organisms in nature produce more offspring than can survive, and many of those that survive do not reproduce.
3. Because more organisms are produced than can survive, members of each species must compete for limited resources.
4. Because each organism is unique, each has different advantages and disadvantages in the struggle for existence.
5. Individuals best suited to their environment survive and reproduce most successfully. The characteristics that make them best suited to their environment are passed on to offspring. Individuals whose characteristics are not as well suited to their environment die or leave fewer offspring.
6. Species change over time. Over long periods, natural selection causes changes in the characteristics of a species, such as in size and form. New species arise, and other species disappear.
7. Species alive today have descended with modifications from species that lived in the past.
8. All organisms on Earth are united into a single tree of life by common descent.
Natural Selection. Survival and reproduction of those organisms best adapted to their surroundings. Suggested by Charles Darwin requires three things.
Variation – Organisms in a species are slightly different due to mutations and sexual reproduction.
Overproduction - More offspring are produced than can be supported by the environment.
Competition - organisms must struggle with one another in order to get what they need to survive, food, territory, mates …
The best-adapted members of a species survive to reproduce. Survival of the fittest.
Inheritance of Variations _ Organisms
Environment and evolution – Organisms evolve due to changes in their environment. Example the peppered moths.
Lamarck Acquired characteristics (use and disuse). Theory that traits acquired in an organisms lifetime could be passed on to offspring. Example giraffe’s neck. Traits would develop if they were used, atrophy if not used.
22-4 Gradualism / punctuated equilibrium – Used to explain missing information in the fossil record
Evidence of Evolution
1. Anatomical Evidence-
Homologous body parts, body parts which are similar in shape and structure. Example Lion Leg, bat wing, Dolphin Flipper.
Lamark showed how closely organisms were related through homologous structures.
2. Fossil Evidence-
Fossils are imprints or remains of plant or animals that existed in the past. Fossils of organisms that are different or that no longer exist show life has changed.
3. Radioactive Dating-
One method used by scientists to measure age.
Half Life – The time it takes for ˝ of a radioactive element to decay. Example C14 ˝ life is 5770 years.
When scientists use the rock layer in which fossils are found to determine relative age.
Sedimentary rock – layers or mud or sand that harden slowly over time. Lower layers are older than upper layers, thus showing earths history.
5.Fossil Record – Collecting and comparing fossil evidence to form a history or record of life on earth.
6.Embryological Evidence – embryos of different organisms are very similar in early stages of development. Example Fish, chicken, rabbit and human. “Ontogeny recapitulates phylogeny” similar development is due to common ancestor.
7. Chemical Evidence – All living things share basic chemical reactions and control through DNA. The closer organisms are related the closer their DNA matches, this is a kind of molecular clock.
All primates had a common ancestor. Primates are the order of animals that includes apes, monkeys and humans.
Human evolution – Australopithecus afarensis (LUCY) to Homo erectus (upright man) to Homo sapiens (wise man) a. Neanderthal which died out b. Cro-Magnon which lead to modern man.
Check out www.becominghuman.org