Evolution of Living Things
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.
Limiting Factor: A factor present in an environment that controls a process, particularly
the growth, abundance or distribution of a population of organisms in an ecosystem.
** 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
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.