Evolution Notes

evolution--process of change through time

Evolution includes the change in characteristics of populations through generations.

Thus, existing life forms have evolved from earlier life forms.

Evolutionary theory is a unifying principle for the biological sciences.

It provides an explanation for the differences in structure, function, and behavior

among life forms.

Through radioactive dating with uranium, geologists

estimate the age of the earth at about 4.6 billion years. (It is assumed that the earth

is at least as old as the oldest rocks and minerals composing its crust.)

fossils: direct or indirect remains of organisms preserved in media such as sedimentary rock, amber, ice, or tar

Fossils have been found that indicate organisms existed well over 3 billion years ago. These organisms were simple, single-celled organisms.

Law of Superposition: the higher up you go in an undisturbed rock stratum, the

younger the rock layers become

** Upper, undisturbed strata generally contain fossils of more complex organisms,

whereas, the lower strata contain fossils of simpler life forms.

(Tendency toward increasing complexity over time.)

** When comparing fossils in undisturbed strata, fossils can be found in

upper strata which, although different from fossils in lower strata, resemble

those fossils. This suggests links between modern forms and older forms, as

well as divergent pathways from common ancestors.

adaptations--changes in organisms which make them better suited to their environment

Gene mutations can be caused by such agents as radiation and chemicals. When they occur in sex cells, the mutations can be passed on to the offspring; if they occur in other cells, they can be passed on to body cells only. The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience.

biological adaptation -- changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment

Theory of Natural Selection

Darwin--(1859) Book--"On Origin of Species"

--stated his theory of Natural Selection

-- Natural selection and its evolutionary consequences provide a scientific explanation of the fossil record of ancient life-forms, as well as the molecular and structural similarities observed among the diverse species of living organisms.

(Theory of Natural Selection)

1. Overproduction -- Within a population more offspring are born than can possibly survive.

2. Competition -- since the number of individuals in a population tends to remain constant from generation to generation, a struggle for survival is suggested

3. Survival of the Fittest -- The individuals who survive are the ones best adapted to exist in their environment due to the possession of variations that maximize their fitness.

4. Reproduction -- Variations assist or hinder individuals in their struggle for survival.

The best adapted individuals survive and reproduce, passing on the favorable variations to their offspring.

5. Speciation -- as time and generations continue, adaptations are perpetuated in individuals and new species may evolve from a common ancestor.

adaptive variations--those variations which assist an organisms survival

(Weaknesses of Darwin's Theory)

1. Darwin didn't explain how variations arose.

2. He did not distinguish between hereditary and environmental variations.

3. Darwin believed that both environmental and hereditary variations were inherited.

Some Sources of Variation in Modern Natural Selection Theory

1. The genetic basis for variation within a species is provided by mutations and sexual reproduction. (crossing over and recombination)

2. Mutations are spontaneous and provide the raw material for evolution.

(Modern Natural Selection Theory)

1.) All species of the potential to increase in numbers.

2.) There is a finite amount of resources for any species. Species tend to make too many

organisms for these resources.

3.) Species will show genetic variability due to mutation, crossing over, and

genetic recombination (during fertilization) of genes.

4.) The scarce finite resources of the environment will select those offspring better able to survive and leave offspring.

Variation within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.

** Traits which are beneficial to the survival of an organism in a particular environment tend to be retained and passed on, and therefore, increase in frequency within a population.

** Traits which have a low survival value to organisms tend to diminish in

frequency from generation to generation.

** If environmental conditions change, traits that were formerly associated with a

low survival value may, in a changed environment, have greater survival value and

increase accordingly.

(Examples of Evolution in Modern Times)

1. Peppered moth -- light colored vs. dark colored (industrialization influence) Manchester, England

2. Insect resistance to insecticides. (Resistance is not in response to the insecticide. The insecticide acts as a selecting agent.)

3. Bacterial resistance to antibiotics.

** Evolutionary factors operate on population -- but not on individual organisms.

speciation: formation of two or more different species from one original population

Evolution does not necessarily mean long term progress is going to go in a certain direction. Evolutionary changes often appear to be like the growth of a bush: Some branches survive from the beginning with little or no change, many die out altogether, and others branch out repeatedly, sometimes giving rise to more complex organisms.

Note the divergence of the various groups from a common ancestor and the fact that some branches became extinct.

Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of a species is common; most of the species that have lived on earth no longer exist.

The SPECIES is the most fundamental unit of classification.

The purpose of biological classification is to show how organisms are related. Organisms are branched into hierarchies or groups based on structural similarities and evolutionary relationships.

Small differences between parents and offspring can accumulate in successive generations so that descendants become very different from their ancestors.

** The degree of kinship between organisms or species can be estimated from the similarity of their

DNA sequences; this similarity often closely matches organisms' or species' classification based on anatomical similarities.

Origin of Life

1.) 3 to 4 billion years ago -- it is thought the first primitive single-celled life appeared on earth

2.) These original unicellular organisms added of carbon dioxide to the environment.

3.) Some autotrophs evolved a means of using the carbon dioxide added to do photosynthesis

4.) Autotrophic activity added free oxygen to the atmosphere. Some autotrophs

and heterotrophs evolved mechanisms by which they used this oxygen to

derive their energy. (aerobic respiration)

5.) About a billion years ago, increasingly complex multicellular organisms began to evolve.

** The great diversity of organisms is the result of billions of years of evolution that has filled available niches with life-forms.