Click HERE for your print-friendly copy of the notes. Don't print the big font pages!

"Nothing in biology makes sense except in the light of evolution."

A Poll: Which is the most highly evolved species?

evolution is defined as change over time.

organic evolution is the genetic (and phenotypic) change of living organisms over time.

The universe is thought to be about 10-20 billion years old.

Our solar system, along with earth is about 4.5 billion years old

Life on earth first appeared approximately 4 billion years ago, with proto-humans (genus Homo) first appearing in the fossil record of the Pleistocene (about 1.8 million years ago) and humans (species Homo sapiens first showing up about 500,000 - 300,000 years ago. Modern humans (Homo sapiens sapiens) showed up around 150,000 years ago. (If you think of earth's entire history as having happened in 24 hours, modern humans have been here for less than 5 minutes of that day.)

Before humans were even aware that they'd been around that long, they were already trying to figure out where they had come from, and they had all sorts of creative ideas about the origins of life.

As long ago as 500 B.C, Greek philosophers were already toying with the idea that life was constantly changing. However, the most influential of these, Plato and his student, Aristotle, believed in an unchanging world in which all species had been created in a perfect state, with perfect interactions intact. In such a world, evolution would be counterproductive, and against the plan of The Creator.

The Old Testament account of The Creation fortified this idea. As recently as the 1700's, biology was done in a framework of natural theology: the idea that science should be dedicated to studying nature in order to figure out the Grand Plan of the Creator.

Later, many believed that living organisms could "spring" from non-living material, fully formed (spontaneous generation). (e.g., maggots from rotting meat; lice from sweat; eels from sea mud, etc.)
One seventeenth century recipe for the spontaneous production of mice directed the "cook" to place sweaty underwear and husks of wheat in an open-mouthed jar, then wait for about 21 days. Over that time, the sweat from the underwear was supposed to penetrate the wheat husks and turn them into mice. (Which are much tastier than husks of wheat?)

In 1668, Francesco Redi, an Italian physician performed experiments designed to test this idea.

He placed rotting meat in covered and uncovered jars, and noted that maggots formed only in the uncovered jar. (Light Bulb Moment: "Hey! Maggots must be fly larvae!")

In 1676, Dutch scientist Anton van Leewenhoek invents the microscope, revealing a microscopic world of wigglies. Once again, interest in spontaneous generation was revived (though on a "smaller scale")

In the late 1700's - Lazaro Spallanzani performed an experiment designed to test the spontaneous generation of microorganisms. (He boiled broth in flasks, and left one covered,one uncovered; only the uncovered one produced microorganisms.)

However, his experiments were discounted because...

2. critics said that boiling the broth might have somehow destroyed some "vital principle" in the broth and/or air, making it unfit for spontaneous generation.

In 1862, Louis Pasteur convinced the doubting scientific community with his elegant Swan-necked flask experiments.

He demonstrated that broth boiled in a swan-neck flask was protected from airborne microbes by the curve in the flask's neck, which trapped invading microbes. But if he broke off the swan neck and waited a couple of days, microbe growth occurred. There was nothing wrong with the boiled broth or its air: they were perfectly suitable for bacterial growth.
This demonstrated beautifully that spontaneous generation was not occurring.
Pasteur's experiments put the controversy to rest for good, and omne vivum e vivo ("all life from life") became the accepted aphorism.

In the late 1700's, French scientist Jean Baptiste Lamarck was studying the fossil record and living organisms, and concluded that evolution was driven by the sentiments interieurs ("felt need") of organisms.

For example, he would explain that the long necks of giraffes were due to their stretching for food, and passing their stretched necks on to their offspring.
Similarly, the big, beefy muscles developed by the village blacksmith with all his hammering and slinging of heavy metal objects would be expected to be passed on to his offspring.
Lamarck claimed that evolution was driven by "use vs. disuse"
- a used structure will become larger, stronger and more important.
- a disused structure will atrophy and become vestigial. (look it up)
- essentially, he argued that traits acquired during an organism's lifetime could be passed on to its offspring, and this was a driving force of evolution.
- His work was published in 1809, and was widely accepted.
Also in the late 1700's, a French anatomist named George Cuvier was developing the science of Paleontology, the study of fossils.
- He noted that deeper strata of sedimentary rock had diversity of organisms more different from present day life than more recent strata. His reason: catastrophism.
- Cuvier was a staunch creationist, and insisted that the various signs of change in the fossil record were merely confirmation of catastrophic events such as floods and massive destruction wrought by the Creator.
- He proposed that huge,natural disasters had wiped the earth clear of life (locally), and that new life migrated into the devastated places from surrounding areas.
Surprise! Early European scientists were creationists who believed that the world was made in seven days by a Supreme Being.
And among these creationists was a young student named Charles Darwin.

The Darwinian Revolution

Who was this man called Darwin? Where did his ideas come from? To understand a bit more, let's look at the historical context of his work.

In addition to the abovementioned scientists, Darwin had other influences...
James Hutton, a Scottish geologist, challenged Cuvier's view in 1795 with his idea of gradualism, proposing that large changes in the earth's surface could be caused by slow, constant processes such as erosion.
Charles Lyell added to this by saying that such earth processes had been going on constantly, and could explain the appearance of the earth. This proposal, termed uniformitarianism, was a strong basis for Darwin's later theory of natural selection.
Thomas Malthus, a religious scholar, wrote "An Essay on the Principle of Population" in which he suggested that much of humanity's suffering (disease, famine, homelessness and war) was the inevitable result of overpopulation: humans reproduced more quickly than their food supply could support them.

People already knew about artificial selection (humans breeding animals and plants for desired characteristics). Darwin thought: Should nature not operate in a similar way?

The stage was set for the Darwininan Revolution!

Voyage of the Beagle

1809 - Darwin was born in Shrewsbury, England. From the beginning, he loved bugs n slugs, and spent most of his time outside or reading nature books.

His father, a well-known physician, thought that no good life could await a naturalist, and so sent young Charles, at the age of 16, off to the University of Edinburgh medical school. Young Charles hated med school, and dropped out after making mediocre grades.

With his father's blessing, he enrolled at Christ College at Cambridge University with plans to become a clergyman. (This isn't as odd as it sounds, since most scientists of his day were members of the clergy.)

He fell in with the biologists and became the star pupil of The Reverend John Stevens Henslow, Professor of Botany.

1831 - With the help of Darwin's uncle, Henslow convinced both Captain Robert Fitzroy of the H.M. S. Beagle and Darwin's father to let Charles go on the five year voyage as an "unpaid gentleman scholar and naturalist."

So at the age of 22, Darwin set sail. While the Beagle's crew mapped South American coastlines, he went ashore and collected every living things he could lay his hands on.

1836 - Darwin returned to England, settled down, married his cousin, Emma, and proceeded to write. Unfortunately, he was a bit too meticulous, and slow to formally publish. In The World of Science, this can lead to potential disasters.

1858 - Darwin was nearly scooped by Alfred Wallace, a young British scientist studying plants in Malaysia. (Alarmed at Darwin's failure to publish his ideas, his friend Charles Lyell had warned him about this possibility!)

Lyell and some colleagues presented both Wallace's and Darwin's work at the meetings of the Linnaean Society of London on July 1, 1858. Wallace's and Darwin's ideas were identical, but Darwin's had been written first, and with much more completeness than Wallace's. Today, Darwin is given credit as the Father of the Theory of Evolution by means of Natural Selection, though Wallace is always given a footnote of respect.

Darwin made some profound observations, from which he inferred some brilliant conclusions...

observation #1. All species have huge potential fertility
observation #2. Except for seasonal fluctuations, populations tend to maintain a stable size.
observation #3. Environmental resources are limited.
inference #1: The production of more individuals than the environment can support leads to a "struggle for existence," with only a fraction of offspring surviving in each generation.
observation #4: No two individuals in a population are exactly alike
observation #5: Much of the observed variation in a population is heritable
inference #2: Survival in this "struggle for existence" is not random, but depends, in part, on the hereditary makeup of the survivors. Those individuals who inherit characteristics that allow them to best exploit their environment are likely to leave more offspring than individuals who are less well suited to their environment.
inference #3: Unequal reproduction between suited and unsuited organisms will eventually cause a gradual change in a population, with characteristics favorable to that particular environment accumulating over the generations.

The Theory of Evolution by Means of Natural Selection can be broken down into four basic tenets, or ideas

OVERPRODUCTION

2. Those offspring are variable in appearance and function, and some of those variations are heritable. (The tenet of HERITABLE VARIABILITY)

3. Environmental resources are limited, and those varied offspring must compete for their share. (The tenet of COMPETITION)

4. Survival and reproduction of the varied offspring is not random. Those individuals whose inherited characteristics make them better able to compete for resources will live longer and leave more offspring than those not as able to compete for those limited resources. (The tenet of DIFFERENTIAL REPRODUCTION)

Note that evolutionary fitness is nothing more and nothing less than differential reproduction due to organisms' differing abilities to cope with environmental limitations.

Any trait exhibited by an organism may be

adaptive - increases the likelihood that the individual will leave offspring
maladaptive - decreases the likelihood that the individual will leave offspring
neutral - does not affect the likelihood that the individual will leave offspring

A trait can be classified into one of these three categories only in the context of the environment in which the organism exists. Hence, evolutionary fitness is determined by the environment, and organisms are selected to "match" the environment in which they forage, seek mates, escape predators, destroy pathogens, etc.

As we already know, a species is a group of similar organisms that can mate to produce fertile, viable offspring. Different species are, by definition, reproductively isolated from one another. (More on this later.)

This means that at some time during their common ancestral history, two related species were derived from a single ancestral species. By definition, the ancestral species became extinct when its descendants diverged and became reproductively isolated.

Let's Keep Our Terminology Accurate

There is no such thing as an "evolutionist" or a "Darwinist". Neither evolution nor Darwin are philosophies or schools of thought. Evolution is an observable, testable phenomenon. Darwin was a person who elucidated one means by which evolution can occur.

Scientists who study the processes and mechanisms that lead to evolution evolutionary biologists.

Darwin's Idea: Is it "Just a Theory"?

You will sometimes hear the uneducated dismiss Darwin's idea as "only a theory." Such a person may ask, "Do you believe in evolution?"

For the student of natural sciences, what is the appropriate response to this question?

The "Only a Theory" argument is flawed in that it fails to separate two important things:.

1. extant species evolved from ancestral forms (an observable phenomenon supported by copious physical evidence)
2. natural selection is the main mechanism by which this occurred (Darwin's claim)

Darwin's conclusions are based on observable evidence, and are subject to falsification with carefully-designed experiments. This cannot be said of other most ideas about the origin of life, including the one now being marketed as "Intelligent Design."

An hypothesis is a tentative explanation for an observable fact.
The observable fact is that evolution has occurred, as documented by fossils, homologies between related species, biogeography and other evidence.
Darwin's hypothesis was that this evolution has occurred by means of natural selection.
Darwin's hypothesis has never been falsified, despite decades of scientific challenge and observation of natural selection in action.
When an hypothesis cannot be falsified despite a long history of testing, that hypothesis may be elevated to the level of a theory: An extremely powerful idea that--although still subject to testing, refinement and revision--is generally believed to be correct.
If anyone out there can suggest a valid way to subject the "theory" (it's not) of Intelligent Design to falsification, I'll be interested to hear it. Until then, I.D. remains outside the realm of science, but rather in the realm of faith.
(On the other hand...)