BIL 106 - Lecture 2

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Which species is the most highly evolved?

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 billions years old.

Our solar system, along with earth - 4.5 billions 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 (species Homo sapiens sapiens showed up around 150,000 years ago.)

Before humans were even aware that we had been around that long, they were already trying to figure out where we 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, and even 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.

The early idea that living organisms could "spring" from non-living material, fully formed, is termed SPONTANEOUS GENERATION. (e.g., maggots from rotting meat; lice from sweat; eels from sea mud, etc..)

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. ("Hey! Maggots must be fly larvae!")

In 1676, Dutch scientist ANTON VAN LEEUWENHOEK 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 Neck 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. Nothing wrong with the boiled broth or its air!
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)
- His work was published in 1809, and was widely accepted.
In other words, Lamarck claimed that traits acquired during an organism's lifetime could be inherited by that organism's offspring.

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! All the 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.)

On the Origin of Species by Means of Natural Selection

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 Cuvier, 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 theory, uniformitarianism, was a strong basis for Darwin's later theory of natural selection.
THOMAS MALTHUS - a religious scholar who 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).

Why should nature not operate in a similar way?

The stage was set for the Darwininan Revolution!

A tale of Charles Darwin.

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

His dad, a famous 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. HATED IT.

Dropped out after making mediocre grades

Enrolled at Christ College at Cambridge University with plans to become a clergyman. (This isn't as weird 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 Rev John Henslow, Professor of Botany.

1831 - with the help of Darwin's uncle, Henslow convince both Captain Robert Fitzroy of H.M. S. Beagle and Darwin's dad to let Charles go on the 5-year Beagle voyage as "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 and got married and wrote up all his work.

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.

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.

SO WHAT IS THIS THEORY OF NATURAL SELECTION, ANYWAY? It can be broken down into four basic tenets, or ideasS

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.

The popular phrase "survival of the fittest" that's often ascribed to Darwin was a phrase originally used by Herbert Spencer, (27 April 1820 - 8 December 1903) an English philosopher, in his 1851 work Social Statics. (The phrase was later used by Social Darwinists, but that's another story.) The phrase "survival of the fittest", when applied in the colloquial sense, is not truly meaningful when applied to Darwin's theory.

The fittest organisms are those that leave the most genes to the next generation, nothing more and nothing less. Survival doesn't always ensure fitness, and fitness doesn't always ensure survival.

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 "fit" the environment in which they forage, seek mates, escape predators, destroy pathogens, etc.

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.

Scientists who study the processes and mechanisms that lead to such speciation events are EVOLUTIONARY BIOLOGISTS.

Over the course of the next few weeks, we will be studying Zoology in the context of Evolution, the change in genetic composition of populations over time.

To understand a little more about how evolution works, let's refer to this GENETICS PRIMER.

Genetics is only one area of BIOLOGY, and like all other areas of biology, it is a NATURAL SCIENCE.

The Natural Sciences (Physics, Chemistry, Biology, Geology, etc.) are all governed by the necessity of their adherents to utilize

The Scientific Method

...to add to the knowledge of their field.

The Scientific Method is a precise set of rules followed by researchers/investigators in the natural sciences.

The difference between a Miracle and a Fact
is exactly the difference between a mermaid and a seal.

-- Mark Twain

As eminent German philosopher Karl Popper wrote in his famous essay, Science as Falsification, it is vulnerability to falsification--not constant verification--that is the mark of truly powerful theory.

The Scientific Method consists of the following steps...

OBSERVATION - The investigator notes a phenomenon that poses a problem/question.
HYPOTHESIS FORMULATION - The investigator poses the question in such a way that it can be tested by rigorously designed experiments or field observations.
- Null hypothesis - Stated in terms of "no difference between observed results and expected results" of an experiment.
- Alternative hypothesis - The opposite of the null, and actually the statement of interest. (We'll give an example in class!)
PREDICTION - The investigator makes a statement about what s/he believes is true about the hypothesis.
EXPERIMENTAL DESIGN - The investigator designs an experiment which will yield data to either support or refute the hypothesis.
DATA COLLECTION - The experiments are run, and data are collected.
DATA ANALYSIS - The data are subjected to rigorous analysis via quantification and statistical tests to determine whether any deviation from the expected result is truly meaningful, or merely due to chance.
CONCLUSION - Investigator accepts or rejects the null hypothesis.

"The process known as the Scientific Method outlines a series of steps for answering questions, but few scientists adhere rigidly to this prescription. Science is a less structured process than most people realize. Like other intellectual activities, the best science is a process of minds that are creative, intuitive, imaginitive, and social. Perhaps science is distinguished by its conviction that natural phenomena ,m including the processes of life, have natural causes--and by its obsession with evidence. Scientists are generally skeptics." (from Biology by Neil A. Campbell

So don't confuse The Scientific Method with Science, in general. And also note that if something is outside the realm of scientific testability, the wise scientists will not presume that it is not true, or that it does not exist. It is simply outside the realm of Science, and may not be answerable with the Scientific Method.

As we tour through the scientific discoveries of genetics this semester, recall a couple of definitions (that will serve you well in your own fields, too!):

Induction - reasoning from a specific case to the general.
Deduction - reasoning from a general observation to a specific conclusion. For example:
- If all organisms are composed of cells
- and humans are organisms
- ...then humans are composed of cells.

A common theme in scientific endeavors is the use of HYPOTHETICO-DEDUCTIVE reasoning: The formulation of hypotheses (a tentative answer to a question) and the execution of experiments from which one may deduce a general answer to the hypothesis.

Important aspects of hypotheses...

A hypothesis is nothing more than a POSSIBLE EXPLANATION of a particular phenomenon.
A hypothesis is based on past experience about the phenomenon. It's an "educated guess."
Multiple hypotheses make good science. (If you have only one possible answer, you may bias your experiment and your analysis.)
Hypotheses should be testable via experimental procedures or field studies based on the hypothetico-deductive approach.
Hypotheses can be refuted (proven wrong, or falsified), but they CANNOT BE PROVEN CORRECT. (It is impossible to perform enough experiments to be certain that the answer will always be the same, and that the same explanation will hold true.)

Let's try it ourselves and see! Think of a question in genetics, and we'll run it through the process to see how it goes.

What's "Theoretical" about Darwin's Idea?

It fails to separate Darwin's two main claims
- extant species evolved from ancestral forms
- natural selection is the main mechanism by which this occurred
Darwin's conclusions are based on HISTORICAL EVIDENCE.
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 (the geographical distribution of related species) and other types of evidence.
Darwin's original hypothesis was that this evolution--as evidenced by the above--occurred by means of natural selection.

The only part of Darwinian thought that's "theoretical" is that evolution has occurred by means of natural selection. Scientists do not question that evolution has occurred (all physical evidence clearly says that it has), but only how it has occurred. And Darwin's hypothesis was that it has occurred by means of NATURAL SELECTION.

Also remember that in science, the term THEORY has a very precise meaning that is quite different from the colloquial use of the term.

A THEORY is an hypothesis whose predictions have stood up to thorough and rigorous testing with experiments and observations. Such has been the case with Darwin's hypothesis, and so it has been elevated to a THEORY.

Still, neither a hypothesis nor a theory can be "proven" with the scientific method, and a good scientist refuses to let even the most powerful theory become DOGMA (something held as an established, unquestioned opinion). New evidence should always be examined with an open mind, as even a powerful theory is always subject to modification and revision.

(Note: A theory that is ultimately proven to hold true in all cases becomes a LAW. There are very few laws in natural science, most of them in Physics, such as the Laws of Thermodynamics.)