Life, biology, evolution and science

Some Variants are Better

Some individuals are bound to be better than others. Perhaps their body structure allows them to escape predators better or to find food faster or to better provide for their young. For example, suppose that the faster-running animals diagrammed below are better able to escape predators than the slower ones. You would expect that more of the faster ones would survive and reproduce than the slower ones.

The slower rabbits will not reproduce as much because predators kill them more than they kill the faster rabbits.

Traits Are Heritable

Those individuals that reproduce more will pass their superior genes to the next generation. Individuals that reproduce less as a result of "poorer genes" will not pass those genes to the next generation in high numbers. As a result, the population will change from one generation to the next. The frequency of individuals with better genes will increase. This process is called natural selection.

Fitness

We often hear natural selection described as "survival of the fittest." The word "fitness" used in a biological context means "reproductive." It does not have anything to do with physical fitness or strength. In the example above, it is the fastest rabbits that reproduce the most, not the strongest.

Natural Selection Produces Evolutionary Change

If the conditions discussed above are met, the genetic composition of the population will change from one generation to the next. This process is called natural selection.

The word "evolution" refers to a change in the genetic composition of a population. Natural selection produces evolutionary change because it changes the genetic composition of populations.

A variety of other mechanisms can also produce evolutionary change. For example, suppose that 65% of the eye-color genes in a population were for individuals with blue eyes and 35% of the genes were for brown eyes. If most of the immigrants entering the population carried the blue gene, the overall composition might change from 65% blue to 70% blue.

Although natural selection affects individuals, it is important to note that multicellular organisms cannot change their genes. Changes in the genetic composition of a population occur as a result of changes in reproduction or survival of individuals.

Example of Natural Selection: The Peppered Moth

There are two forms of the peppered moth (Biston betularia) in England- a dark-colored form (carbonaria) and a light form (typica).

In the early 1800's, most moths were the light form. The first dark form was reported in 1848. The dark form increased in frequency during the last half of the 1800s. By 1895, 98% of the Moths in Manchester were the dark form.

The increase in the dark (carbonaria) form of the moth occurred at a time of rapid industrialization in England- the industrial revolution. During this time, an increase in the amount of coal-burning factories caused widespread pollution. The pollution killed light-colored lichens, causing the trees to be darker. The trees in polluted areas were also covered with dark soot.

In 1896, J. W. Tutt proposed that bird predation was responsible for the increase in abundance of the dark form of the moth. He reasoned that birds had difficulty seeing the dark form on the dark trees; the moths were camouflaged and survived better. In clean areas, the trees were covered with lichens, making the pale form more difficult for birds to see. In the early 1800s, the trees were light and the light form were more difficult to see.

To test the bird predation hypothesis, H.B.D. Kettlewell released moths of each type and then measured the number that were later recaptured. The experiment was performed in a polluted area in Birmingham, England and in a clean area in Dorset. The moths were marked with a dot of paint so that he could identify them after they were released and then recaptured. In the unpolluted area, he recaptured 13.7% light, 4.7% dark indicating that the light form survived better. In the polluted area, he recaptured 13% light and 27.5% dark suggesting that the dark form survived better.

These results support the hypothesis that color change was due to bird predation. Birds ate moths that were easiest to find.

Sexual Reproduction and Evolutionary Change

Variation

Later in this course, we will discuss how sexual reproduction acts to increase variation in populations by shuffling genes. Offspring have some genes from each of two different parents and therefore are not identical clones of their parents. The increased variation due to sexual reproduction allows natural selection (and thus evolution) to produce changes in populations as described above.

Fluctuating environments

Evolutionary change due to natural selection would not be necessary if the environment never changed and the organisms within the environment were optimally adapted to the environment. For example, imagine a plant that is adapted to an environment that has an average annual rainfall of 100 cm. If the climate were to change so that the amount of rainfall decreased, individuals that could tolerate less rain would survive and reproduce better, thus establishing their drought-tolerant genes in subsequent generations. If there was no variation in the plant population, there would not be any drought-tolerant individuals and the species would likely go extinct in areas of decreased rainfall.

Sexual reproduction therefore, enables species to survive in fluctuating or changing environments because it promotes variation, which in turn allows natural selection.

What is Science?

Descriptive Science and Experimental Science

Scientists may be concerned with describing natural phenomena and they may limit their investigation to describing nature. However, they often wish to explain natural phenomena by a logical process that involves creating and testing hypotheses.

Experimental Science

The "Scientific Method" is a systematic approach to advancing knowledge. There are differences among scientists and among disciplines concerning the details of the method. Many of the steps involved in a typical scientific investigation are discussed below using research published on the peppered moth (Biston betularia).

Observation

There are two forms of the peppered moth (Biston betularia) in England- a dark form and a light form. In the early 1800's, the population was almost entirely the light form. During the 1800’s the dark form increased in frequency in urban areas. The change occurred at a time when increased pollution from coal fired factories darkened the trees. By 1895, 98% of the moths in Manchester were the dark form.

Hypothesis

A hypothesis is an explanation of an observation.

In 1896, J. W. Tutt hypothesized that bird predation was responsible for the increase in abundance of the dark form of the moth. He reasoned that birds had difficulty seeing the dark form on the dark trees; the moths were camouflaged and survived better. In clean areas, the trees were covered with lichens, making the pale form more difficult for birds to see. In the early 1800s, the trees were light and the light form were more difficult to see.

A hypothesis must be testable, and if false, it must be falsifiable.

Experiment

An experiment is a test of the hypothesis.

Experiments are useful in disproving hypotheses. Hypotheses are not proved. This idea will be discussed later.

To test the bird predation hypothesis, H.B.D. Kettlewell released moths of each type and then measured the number that were later recaptured. The experiment was performed in a polluted area in Birmingham, England and in a clean area in Dorset. The moths were marked with a dot of paint so that he could identify them after they were released and then recaptured.

The bird predation hypothesis (above) predicts that the light form should survive better in the clean area and the dark form should survive better in the polluted area. An estimate of survival can be obtained by using the number of moths recaptured. Obviously, moths that were taken by predators were not recaptured; only survivors were recaptured.

Experimental Design

Scientists often perform experiments by doing some sort of a manipulation. In the example above, one group of mice was given a hormone and the other group was not. The group of mice that wasnot given the hormone is referred to as a control group. A control serves for comparison. If the average weight of the control mice had been the same as that of the group given the hormone, it would be necessary to conclude that the hormone did not cause a change in growth.

Many experiments are controlled as described above. A controlled experiment is not one in which variables are controlled, it is usually not possible to control all of the factors that may affect the outcome of an experiment. In a controlled experiment, the control group experiences the same environment as the experimental (manipulated) group. If an environmental variable affects the experimental group, it also affects the control group equally. In the example above, the researcher wanted to determine if a hormone caused mice to grow larger. It is possible that the temperature of the room also affected mouse growth. The control mice were kept in the same room as the experimental (hormone) mice. If the mice receiving the hormone were heavier, the weight difference was not due to temperature because the control mice were kept at the same temperature.

Results (Data)

The data are often numbers (measurements, counts, etc.).

1. Biology is the scientific study of life.

2. The general process of science is said to be characterized by this sequence of stages.

B. Observation

1. Scientists believe nature is orderly and measurable.

2. Science also considers that natural laws do not change with time.

3. Phenomena can therefore be understood from observations.

4. Actual science research may also involve chance (e.g., Alexander Fleming’s discovery of penicillin).

*This principle of science is known as NATURAL CAUSALITY, by its nature it excludes supernatural phenomenon*

C. Hypothesis

1. Inductive reasoning allows a person to combine isolated facts into a cohesive whole.

2. A hypothesis is a possible explanation for a natural event - must be testable

Examples of hypotheses, check those that are valid and can be tested

_____Bluebirds sing to attract mates.

_____ Bluebird songs are beautiful.

_____ Only male bluebirds sing.

_____ Sparrows will leave territories where they hear bluebird songs.

_____ Bluebirds hate sparrows.

D. Experiments/Further Observations

1. Testing a hypothesis involves either further observations or conducting an experiment.

2. Deductive reasoning involves “if, then” logic that predicts what will happen based on the hypothesis.

3. An experimental design is proposed that tests the hypothesis.

4. Scientists may use a model (globabl warming, but models are not always valid)

5. If a model cannot be tested, it always will remain a hypothesis.

E. Data

1. Data are the results of experiments, and are observable and objective.

2. Data are often displayed in a graph or table.

3. Often the data must be inspected for the probability the data could show a relationship by chance; this

is a measure of “significance.”

F. Conclusion

1. Whether the data support or reject the hypothesis is the basis for the “conclusion.” - avoid the word "prove"

2. The conclusion of one experiment can lead to the hypothesis for another experiment.

3. Science findings are reported in scientific journals so results are available to the research community (peer review).

4. The experiments and observations must be repeatable or the research is suspect.

G. Scientific Theory

1. The ultimate goal is to understand the natural world in scientific theories, conceptual schemessupported by a broad range of data.

2. The terms “principle” and “law” are also used for generally accepted theories.

Basic theories of biology are:

a. Cell theory: all organisms are made of cells.

b. Biogenesis theory: life only comes from life.

c. Evolution theory: living things have a common ancestor and are adapted.

d. Gene theory: Organisms contain coded information that determines their form, function, and

behavior.

Other Theories.

e. Germ Theory - proposes that microorganisms are the causes of many diseases

f. Heliocentric Theory - the sun is the center of the solar system, planets revolve around the sun

g. Law of Gravity - masses attract each other

H. A Controlled Study

1. Some investigations are managed where conditions can be kept constant, as in the case of the nitrogen fertilizer and pea plant experiment).

a. A variable is a factor that can cause an observable change.

b. The experimental variable is the step that is deliberately manipulated (nitrogen fertilizer).

c. A dependent variable is component of an experiment that changes due to the experimental variable (yield).

2. Study I

a. The hypothesis that pigeon peas will increase winter wheat production, compared to nitrogen fertilizer, is tested in clay pots using both treatments and a control group without treatment.

b. Although both treatments exceed the control in wheat growth, the fertilizer-only treatment exceed the use of pigeon peas.

3. Study II

a. To test the hypothesis that pigeon pea residues will build up over time and will increase winter wheat production, compared to nitrogen fertilizer, the test is continued.

b. The fertilizer-only treatment no longer exceeded biomass production with the use of pigeon peas.

c. All results and conclusions were then reported in a science journal.

4. Study III

Observation: Babies are born with severe birth defects, mothers of these babies report taking the drug thalidomide during pregnancy for morning sickness.

Question: Does thalidomide cause birth defects?

Hypothesis: Thalidomide causes birth defects.

Experiment:

Control group: Mice not given thalidomide during pregnancy

Variable (Experimental Group): Mice given thalidomide during pregnancy

In this experiment, mice born from both the control and variable group will not have birth defects. This experiment was performed long before thalidomide was marketed and prescribed to pregnant women.

Does these mean that the hypothesis is not supported?

I. A Field Study

1. Observations led the researcher to the hypothesis that male bluebirds vary their aggressiveness toward other males depending on the time during the cycle of breeding.

2. To test the hypothesis, a male bluebird model was placed by the nest while the male was gone and observations were made upon his return.

3. A control consisted of a model of a robin placed in the same position for some nests.

4. Resident male bluebirds did not bother the control model but were aggressive toward the male bluebird model depending on the stage in nesting.

5. The conclusions confirmed the researchers hypothesis and were published in a science journal

The germ theory of disease is a theory that proposes that microorganisms are the cause of many diseases. Although highly controversial when first proposed, germ theory was validated in the late 19th century and is now a fundamental part of modern medicine and clinical microbiology, leading to such important innovations as antibiotics and antiseptics

What is a Theory?

A Theory is an explanation for natural events that is based on a large number of observations. Can also be referred to as a PRINCIPLE or a LAW.

Scientific Theories join together well supported and related hypotheses

Its important to realize that theories EXPLAIN what we observe. For instance, the Germ Theory explains why we get sick and why we get infections, in short it uses observation of viruses and bacteria as well as data from those who get ill to create a theory on what causes the illness.

Theories must explain a wide range of observations

Theories must be falsifiable

Theories can be changed if new evidence presents itself

Keep in mind that scientists do not "believe" in something. Instead, they have levels of confidence in explanations for natural phenomena.

If the Theory of Evolution is valid, why isn't Creationism (God created life) a theory?

Keeping in mind that there is nothing wrong with religious beliefs, things like creationism are not considered scientific because they do not meet the criteria of a scientific theory itself.

1. Creationism -tells- us what happened, and doesn't explain how, when, why or through what mechanisms

2. Creationism cannot be proven false - ie, you cannot disprove the existence of a divine creator

3. The nature of creationism means that the primary tenant (divine creation) can never be changed, much for the same reason you can't disprove it.

4. Not based on natural causes (natural causality)

What is Occam's Razor?

Ockham's Razor (Occam is the latinized and more common spelling) is a principle proposed by William Ockham in the 15th century.

The original principle stated "Pluralitas non est ponenda sine neccesitate" which translates as "entities should not be multiplied unnecessarily"

Modern times - it basically means that the simplest explanation is usually the right one.

Example: A paper clip is placed on a scale, the scale reads 600 pounds. The following hypotheses can be proposed

The paperclip weighs 600 pounds

The scale is broken

There is a miniature black hole producing a gravitational pull on the paperclip at that moment, creating such a force to make the paperclip weigh 600 pounds

Though all three hypothesis may be correct, in fact we could probably make up a dozen other explanations, occam's razor would suggest that the simplest explanation is probably the correct one (the scale is broken)

Statistical Testing

Is it possible that the data above could have been due to chance and not really to the effect of bird predation? Statistical analysis allows you to calculate the probability that the data could have come out as they did if there really was no effect of predation.

If the probability that the results could be due to random chance is less than 0.05, we conclude that the difference is real; it is not due to chance. If the probability is greater than 0.05, we conclude that the difference is due to chance.

In the example above, a statistical analysis revealed that it is very unlikely that data could have produced the observed results due to chance.You must accept or reject your hypothesis. In this case, the data suggest that the hypothesis should be accepted. Otherwise, it needs to be modified to account for the data.

Publish

Scientists generally do not regard information unless it has been published in a peer-reviewed or refereed journal. Typically, the scientist writes a report on the research and submits it to a journal editor. The editor distributes copies of the article to several peer reviewers that are recognized experts in the field. After reviewing the research, the peer reviewers recommend whether the paper should be published or not.

Junk science has not undergone this peer review process. Politicians, journalists, and others interested in swaying public opinion may mislead the public by presenting junk science as sound science or by presenting it along with sound science.

Do Scientists Prove Hypotheses?

Suppose that a pet store owner observes that the mice in her colony grow slowly. She hypothesizes that they grow slowly because she does not give them enough food. To test this hypothesis, she uses two groups of mice. One group is given more food than they can eat while the other group receives the normal amount.

Suppose that all of the mice in her experiment grow slowly. Her hypothesis that she does not give them enough food must be incorrect. She rejects her hypothesis and decides to test an alternative hypothesis.

An alternative hypothesis is that the mice grow slowly because she does not give them enough water. She tests this hypothesis by giving the mice in one group more water than they can drink and giving the mice in another group the normal amount.

Suppose that mice in the group that received the extra water grow faster. She accepts her hypothesis that lack of water caused the poor growth. She has not proved her hypothesis. Perhaps it is not the water but instead, a mineral in the water that causes faster growth when given in higher amounts.

Science advances by rejecting false hypotheses. In the above experiment, she has not proved that it was the lack of water that caused poor growth. There may be other factors involved that she does not know about.

When a hypothesis is disproved it is rejected and an alternative hypothesis is accepted. However, you cannot be 100% sure that the hypothesis is false. You may reject a hypothesis that is true. Statistical techniques are used to reduce this type of error.

Theory

Hypotheses that have been tested by different investigators numerous times and have not been disproved become theory.

Modeling

Models are often used to describe natural phenomena. Models may be as simple as a diagram or a verbal explanation. Others may involve sophisticated mathematical equations and require computer analysis.

Mathematical models are often developed to explain complex phenomena. For example, a model could be developed to show nitrogen cycling in a montane (mountain) watershed. The model may have many variables and involve mathematical calculations. Complex models are often computerized (computer modeling). Example - climate models are often very sophisticated and require fast computers to analyze.

Mathematical models enable researchers to make predictions. For example, we could ask what will happen to Earth's temperature if carbon dioxide in the atmosphere increases by 100 ppm? The solution can be found by entering this number into the model and performing the calculations. The model must reflect what really happens in nature. If the model is not realistic, the predictions will not be accurate.