Selection Types  -MOVIE    Genetic Drift  -MOVIE

 

 

 

As we try to catch up with the missed lecture... please be sue to  review all the  specifics of the Scientifi Method, the use of the Null Hypothesis and how it expands possibilitied of continued research...  and allows for "proof by contradiction" refuting the negative notion  eg. that humming birds spend the same  amount of time around flowers with colour... and in so doing (potentially opening up for the possibility  -however small-   that if "colour" is important, may be there might be some greater differences with different colours, UV light (perhaps) etc....

While all this sounds very mundane and more than a little tedious, it does provide the very foundation of our Scientific Approach, and allows for an "objective" validation of any querky notion that we can come up with.

 

“The whole of science is nothing more than a refinement of everyday thinking.”

- Albert Einstein

 

    ...How we refine our everyday thinking, however, is fundamentally based upon the questions we ask, and how we go about finding the answers to those questions

It is also critical that -in an "ideal world" - valid scientific questions are unencumbered by fluctuating social mores, and potential missinterpretation that result: as exemplified by Copernicus (1530's); Galileo (early 1600's)...  More recently un-scientific interventions of lecture/classes/text books in Science that try to downlplay or minimize Scientiifc discourse offer more closer to home examples, such as  Cobb County school board (early 21st century)...

Of course... there are (and should be) social limits (?)... human cloning??.

The Bush administration's moritorum (back in 2000) on the use of placental tissue and already destroyed human embryos to provide STEM cells for STEM cell research is potentially more of interest to open bioethical discussion....

As one of the previous fires shows, the Earth’s early atmosphere lacked free oxygen, and was predominantly made up of, carbon dioxide (CO₂), methane (CH₄), carbon monoxide (CO), ammonia (NH₃), free hydrogen and water vapor. Oxygen came along, apparently as a bi-product, and accumulated in relative abundance AFTER (or as a result of?) simple life forms (prokaryotes?) evolved the ability to use WATER as a source of hydrogen ions, in photosynthesis.   Increasing atmospheric oxygen subsequently allowed the further biological development of these prokaryotes. Thereafter, the increasing oxygen in the environment potentiated the evolution (development) of a somewhat distinctive branch of living organisms -the eukaryotes ?- and the potential for multicellular organismal existence.   Review: Temporal view of living organisms

Physical changes that have aparently occurred on and in the Earth over these times, have also included a gradual cooling and weakening of the forces that caused the immense,and -as we shall see- continental drifts that occured, as we shall see have been quite significant continental drifts.

Throughout Earth’s history, they would suggest, the continents have shifted, sometimes separating, at other times colliding.

There is a considerable body of evidence to suggest that a meteorite may have been at least partially the cause of the somewhat abrupt mass extinction at the end of the Cretaceous period.. or alternatively...Volcanoes in the Deccan Traps... Even so, there are though to be at least 5 different major mass extinctions in the life of this planet

The ages of rock layers in Earth’s crust can be determined from their position -relative to one another and the presence of somewhat novel metals such as iridium and other radioactive element. more rocks.

Much of what we know about the history of life on Earth comes from the study of fossils embedded in the ages of rock layers in the Earth’s whose age crust can be determined from their position -relative to one another and the presence of somewhat novel metals such as iridium and other radioactive elements. more rocks.

As with the universe, radioisotopeshave supplied the key for assigning absolute ages to rocks, giving rise to our perspective on "Relative Time", Thus, changes in geological time can be related to the metronomic (or consistent) isotopic changes in the environment.

³²P 14.3 days, ³H 12.3 years, ¹⁹²Ir 73.83 days ¹⁴C 5,700 years and ⁴⁰K 1.3 billion years

The fossil record, although only partially complete (little more than 300,000 fossil species have yet been described), reveals broad patterns in the evolution of life.

Fossils records show that many evolutionary changes are also gradual (in geological time). While these changes do explain some of the changes that have occurred through geological time, they also demonstrate that an incomplete record -in a similar way to faulty reasoning (such as circular arguments or the use of "invalid probes") can sometimes falsely suggest or even conceal times of rapid change, or completely redirect potential heritable linkages.

 

 

Review:         

 

But we are getting a little ahead of ourselves....

In the early to mid 19th century, at about the same time that a researcher called Sir Charles Lyell was appreciating the idea that the age of fossils somehow related to the age of the rocks in which they were found......

Darwin began his "Voyage of the Beagle" (1831)

and his first opus: The Origin of Species  1859, and the crucial determination.....

As a result of his travels, Darwin developed his idea of "evolution by natural selection" by carefully observing nature, especially during his voyage around the world, and comimg up with a rationale for how he understood that these variations could exist..

He based his theory (little "t")on well-known facts and some key inferences.  Obviously, he had no examples of the action of natural selection, so he based his arguments on his current knowledge of artificial selection by plant and animal breeders of the day.

Modern Genetics has since elucidated the mechanisms of heredity, which have provided a solid base that supports and substantiates (to a large extent) Darwin’s theory.  These findings, along with others over the subsequent years, began to change the "t" into a "T".

In essence, Darwin looked at various traits of the wild life that he observed, both in South America and on the islands.  He noted, similarities and differences, and wrestled with the ideas of how these similarities came about. He understood, the importance of potentially "informative", shared traits, and how an appreciation of changes in these traits can lead toward distinctions and similarities. 

... and how these traits change can also be highly informative.

Natural selection, which is the variation of heritable traits that can determine the success of the "reproductive efforts" of animals (life foms) within a given population and can lead to changes in the Genetic makeup or "gene pool" of populations.

The book mentions three distinct types of "selective mechanisms"and uses uses the colouration of lizards against a changing background to distinguish among the three fundamentally different types of selective pressure....resulting in Stabilizing, Directional, and Disruptive effects upon phenotypes. Of course there are many examples of other simliar selective pressures.

Directional selection: cliff swallows in Nebraska, which depend on insects for their livelihood.  Severe cold snaps give (as occurred in May  1996), totally devastated the population, killing up to 2,000 birds (presumably through lack of food).  When scientists analyzed all the dead birds, they determined that birds with a small wing span (less SA to Vol ratio) and assymetrical wing shapes (less manouverability) were disproportionately represented in the dead birds.

 

 

 

"Stabilizing effects":  If other external forces were to select against the swallows becoming...too large for example (perhaps the ability to fit into a home with in the mud-nests of the cliff, then the "average" sized bird would begin to predominate.