Wednesday, January 25, 2012
Today in class:
-Turned in course recommendations sheet
-Turned in Lab 38
-Started Notes packet up until pg.13
Darwin and Natural Selection
- All life is connected
- The basis for this kinship is evolution
- Evolution has transformed life on Earth from its earliest beginnings to its extensive diversity today
- Evolutionary view came into focus in 1859 with Darwin's book
- One of Britain's most renowned biologists
- Published The Origin of Species 17 years later.
- Was the most influential scientist in the development of modern biology.
- 2 main points in book:
1) species living today descended from ancestral species= "descent with modification" = evolution
ex.)The diversity of bears is based on different modifications of a common ancestor from which all bears descended.
2) The mechanism for evolution is "natural selection"
-Darwin loved nature, Disliked medical school. Became a minister. Became a naturalist for a voyage around the world when he was 22 years old.
- Darwin's "Voyage of the HMS Beagle"
- Observed and collected thousands of specimens, Observed adaptations of organisms. Most of animals of Galapagos Islands live nowhere else in world, but they resemble species living on the South American mainland. It was as though the animals strayed from mainland, then diversified as they adapted to environments on the different islands.
- Darwin saw large diversity of animals on Galapagos Islands, off coast of South America
-If an ocean separated islands, it isolated 2 populations of a single species. The populations could diverge more and more in appearance as each adapted to local environmental conditions.
-After many generations, 2 populations could become dissimilar enough to be separate species-14 species in the case of the birds called Galapagos finches.(This is now called divergent evolution)
-They have beak shapes and coloration that are adapted to their environments
-The beaks are adapted to certain food sources on the different islands; the colors protect them from predators
-Q:How did Darwin explain these adaptions, or different beaks?
-A:Natural Selection! 3 main points:
1) Far more offspring are produced than the environment can hold. Overproduction leads to a struggle for existence among the individuals of a population.
2) Individuals in a population vary in many traits no two individuals are alike.
3) Those individuals with traits best suited to the local environment will have the greatest reproductive success. They will leave the greatest number of surviving fertile offspring. They will reproduce more of the same. This unequal reproductive success=natural selection.
-Nature decides what traits are most fit.
-Adaptation is the accumulation of favorable variations in a population over time.
-EX.)beaks well equipped for available food sources, and markings that reduce predation=finches survive to produce more.(Survival of the Fittest)
-Darwin also looked at "Artificial Selection" going on with farming.
-Humans have been modifying other species for centuries by selecting breeding stock with certain traits.
-These vegetables and flowers no longer look like their ancestors.
Artificial Selection in pets- have been bred for human fancy. Dog breeds-all are descendants from one ancestral population of wolves
"Humans" screened the heritable traits of populations instead of "nature" or the natural environment.
-Natural selection in action today: Antibiotic resistant forms of tuberculosis causing bacteria have made the disease a threat again in the U.S.
-Humans are connected by descent from African ancestors.
-Example of natural selection-abuse of antibiotics has sped up the evolution of antibiotic resistant bacteria.
-Evolution of pesticide resistant insects: by spraying crops with poisons to kill insect pests, humans have favored the reproductive success of insects with inherent resistance to the poisons.
-Related species of insects called mantids have diverse shapes and colors that evolved in different environments. Camouflage is an example of evolutionary adaptation.
Evolution-2 modern definitions:
A. the genetic composition of a population changes over time
B. all life descended from a common ancestor, from the earliest microbes to modern day organisms
-Darwin is ranked as the 4th most influential person of the past 1,000 yrs.
-Most scientists in Darwin's day thought:
-Earth was young(6,000 yrs old)
-Earth was populated by millions of unrelated species
-Darwin's book challenged that,and was radical for its time
An example of a camouflage is shown above, of a leaf mantid.
-Anazimander(Greek philosopher)had idea that life arose in water, and simpler forms of life preceded more complex ones.
-Aristotle(Greek philosopher)held that species are fixed or permanent, and do not evolve(are static).
-Buffon(1700s)(French naturalist) studied fossils-said Earth may be much older than 6,000 yrs. Proposed that a species in a fossil could be an ancient version of a living species.
-Lamarck(1800s)(French naturalist)said that life evolves through adaption ex.)a powerful bird's beak.
However, he had an erroneous views of how adaptations evolve:
-He said "Inheritance of Acquired Characteristics"- by using or not using body parts, one can develop certain characteristics, which can pass on to offspring.
Ex.)if you exercise beaks and get stronger you can pass that trait down to offspring.(Use & Disuse Theory) Incompatible with modern genetics.
-Lyell(Scottish geologist)-said ancient Earth was sculpted by gradual geologic processes that continue today.(Mountains,earthquakes,erosion.)Earth was very old. Gradualism principle.
-Wallace(British naturalist)(1850s)developed a concept of natural selection identical to Darwin-both were presented to the scientific community. Lamarck(shown above)
-Darwin's book evidenced 2 major points:
-Organisms on Earth today descended from ancestral species, accumulating different modifications or adaptations-"descent with modification." History of life is analogous to a tree.
-Natural selection is the mechanism for descent with modification
What is some evidence in support of evolution? (5 examples)
1.)The Fossil Record
Fossils- preserved remnants or impressions left by organisms that lived in the past
-Most found in sedimentary rocks
-Younger strata are on top of older ones; positions of fossils in the strata reveal their relative age
-Fossil record-chronology of fossil appearances in rock layers, marking passing of geologic time
-Oldest fossils date from 3.5 billion yrs ago, are prokaryotes.
-Fishlike fossils are oldest vertebrates, then amphibians, reptiles, then mammals and birds.
-Paleontologists- scientists who study fossils-found fossilized whales that connect them to their land-dwelling ancestors.
2.) Biogeography- the geographic distribution of species
Ex.)Tropical animals in South America are more closely related to species in South American deserts than to species in African tropics.
Ex.) Australia has a diversity of pouched mammals(marsupials) but few placental mammals. They are hospitable to placental mammals. Unique Australian wildlife evolved on island continent in isolation from regions where early placental mammals diversified.
-Biogeography makes little sense if species were individually placed in suitable enviroments. Instead, species are where they are because they evolved from ancestors that inhabited those regions.
3.) Comparative Anatomy- the same skeletal elements make up the forelimbs of humans,cats,whales, and bats- all are mammals.
-The functions differ, but structural similarity indicate they descended from a common ancestor- homology.
Ex.)forelimbs of diverse mammals, all have same bones
Ex.)human spine and knee joints derived from 4-legged mammals-are subject to sprains, spasms,common injuries because of our bipedal posture.
- These are some of the most interesting homologous structures which have marginal, if any, use or importance to the organism. They are historical remnants of structures which had important functions in ancestors.
Ex.) the whales of today lack hind limbs, but have vestiges of pelvic and leg bones of their four-footed terrestrial ancestors.
-Vestigial organs are evidence of evolution-shows linkage to a past ancestor.
-UP pg 19-20
-UP pg 13-16 due Monday
See you in class!