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.

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"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.

Disruptive selection: can be seen in the "black-bellied seed cracking finches of West Africa, wherein the selective pressure of obtaining food, has effectively divided the population into two, quite distinctive distributions, based upon their bill type.

Both types of examples show different types of natural selective pressures that utlimately effect the resulting populationa.

All similarities and differences within and among different types of animals, therefore, when taken together, can provide a series of "near" and "distant" relationships......family trees.

A good source of information and potential answers to a variety of questions concerning the inter relationships of animals, plants etc. and their shared evolutionary history can be found at this URL:

Some of the traits that are shared among animals and plants of various species can be considered to be "informative" in that they can be used as exceptionally reliable evidence that allows evolutionary scientists to deduce (infer!!) heritable relationships and potentially build ancestries for animals that may otherwise not be fully understood.

(MOVIE) Whale evolution.....from wolves?

and (MOVIE) Lucy .......

Three important thoughts that I would like to stress from having reviewed the movies.

a) Evolutionary change in whales is not like the Tarzan movie at the end of the 90's.....

b) The use of "shared ancestries".... It is important that we understand that, according to the fossil records whales have probably descended from a "wolf-like" animal NOT from a "wolf".  Likewise "Lucy" is not an "ape" but an "ape-like hominid".

b) That the inference of bone configurations of modern (latter-day) analogues -allowing for adaptation over time- reeally can be used to relate the development of known organisms.

Ideally all of these ideas of change(s) reflect back upon Darwin's appreciation of the inhabitants of the Galapagos islands, and the finding that there are forces at work which affect "if" and "how" different animals/plants in a given population are able to survive.

Of course all this evidence pre-supposes "honesty" among scientists......which is not always the case, either as a consequence of being unable to interpret the data correctly, or even as a consequence of outright fraud.

What is also important to note... even a superficial understanding of these concepts allows us to appreciate that the primary forces of evolutionary change or exert themselves, not on individual organisms, but on populations of related individuals. 

Also implicit within this, and any understanding of evolution is that this "population of individuals" is not a number of identical clones, but a group of individuals that exhibit similar phenotypic traits (the operative word being "similar"), and that each individual has a slightly different organismal "signature" to donate to the collective "gene pool".

To put Darwin's ideas in a 21st century context with a little more clarity (gained from almost 190 years of hind-site), let's define some of the vocabulary that we might use to more readily understand some of the ramifications (consequences) of Darwin's ideas.