Evolution - This Old Earththisoldearth.net/ESC102_lectures/ch07.pdfhumans evolved from monkeys so...
Transcript of Evolution - This Old Earththisoldearth.net/ESC102_lectures/ch07.pdfhumans evolved from monkeys so...
Evolution
What is Evolution?
Evolution involves inheritable changes in a population of organisms through time
Fundamental to biology and paleontology
Paleontology is the study of life history as revealed by fossils
Explains the development of life as seen in the fossil record
Misconceptions regarding Evolution
Evolution proceeds strictly by chance
Nothing less than fully developed structures, such as eyes, are of any use
There are no transitional fossils (the so-called missing links connecting ancestors and descendants)
humans evolved from monkeys so monkeys should no longer exist
Historical Perspective
Evolution is usually attributed solely to Charles Darwin, but actually considered long before he was born.
ancient Greeks, philosophers, theologians, and all others who tried to explain fossils during the Middle Ages
Nevertheless, the prevailing belief in the 1700s was that Genesis explained the origin of all life.
Lamark (1744-1829)
Theory of Inheritance of Acquired Characteristics.
new traits arise in organisms because of their needs
Once acquired new traits are somehow passed on to their descendants
Lamarck’s theory seemed logical at the time and was widely accepted
Example
The fossil record shows that giraffe necks got longer over time. This also coincides with the development of taller trees
Darwin (1809-1882)
On the Origin of Species, published in 1889
details his ideas on evolution formulated 20 years earlier
proposes a mechanism for evolution called natural selection
What Darwin notices
By selecting desirable traits and then breeding plants and animals with those traits we produce more useful species
dogs, cats, vegetables, flowers
What if natural processes could do the same thing?
Thomas Malthus’s essay on population suggested that competition for resources and high infant mortality limited population size
What was different about the animals that survived?
Natural SelectionOrganisms in all populations posses heritable variations.
size, speed, agility, visual acuity, digestive enzymes, color, and so forth
Some variations are more favorable than others and give an organism a competitive edge in acquiring resources and/or avoiding predators (i.e. baby birds and rabbits)
Not all young survive to reproductive maturity, however, Those with favorable variations are more likely to survive and pass on their favorable variations.
Back to the giraffesIn any population there is bound to be numerous variation in all inherited traits
For example giraffe with all different neck lengths (some long some a bit shorter)
As environments changed and trees grew taller and taller those giraffe with longer necks had distinct advantage over those with shorter necks. These giraffe were more likely to survive and therefore pass on there characteristics
Survival of the fittestIn colloquial usage, natural selection is sometimes expressed as “survival of the fittest”
This is misleading because natural selection is not simply a matter of being the strongest; it involves differential rates of survival and reproduction
One characteristic might provide an advantage to the individual in a specific circumstance but nature may favor the something else
the smallest if resources are limited
the most easily concealed
those that adapt most readily to a new food source
those having the ability to detoxify some substance
and so on...
Apparent limits to darwin’s theory
Darwin’s theory of Natural selection works on existing variation in a population.
It could not account for the origin of new variations within a population
Some critics also reasoned that traits would blend with other traits and be lost
Red hair+blonde hair = strawberry blondeLong neck+ Short neck= medium neck
The answer to these criticisms existed but remained hidden until 1900
Gregor Mendel
During the 1860s, performed a series of controlled experiments with true-breeding strains of garden peas
strains that when self-fertilized always display the same trait, such as flower color
Labs, pugs, boxers, shepherds are examples of true breeding strains of dog
Mendel’s workMedel first cross pollinated to different strains of garden peas; one strain that produced red flowers and one strain that produced white flowers
The resulting seeds produced plants that only produced red flowers
Mendel’s experimentMendel then allows the second generation to self fertilize and produced a third generation. The third generation seed produces the following result.
From his experiments Gregor determined that traits are controlled by a pair of factors now called genes
Genes occur in alternate forms, called alleles
One allele may be dominant over another
Offspring receive one allele of each pair from each parent
Why this is important
His work showed that genes controlling traits do not blend during inheritance
Although traits may not be expressed in each generation or each individual they are not lost
Therefore, some variation in populations results from alternate expressions of genes (alleles) based on inheritance
Modern GeneticsComplex, double-stranded helical molecules of deoxyribonucleic acid (DNA) called chromosomes are found in cells of all organisms
Specific segments of DNA are the basic units of heredity (genes)
The number of chromosomes varies from one species to another
fruit flies 8; humans 46; horses 64
Modern Genetics
Modern evolution incorporates chromosome theory of inheritance into Darwin’s theory of natural selection
along with alternate expression of variation described by Mendel and the environmental forces described by Darwin genes may also mutate.
mutation occurs constantly in all animals
Most mutations have no visible effect
only mutations that occur in sex cells (sperm and egg) can be passed on.
Politics and ScienceLamarck’s idea of inheritance of acquired characteristics no longeraccepted as a valid scientific theory
Russian agronomist Lisenko believed Lamarcks ideas fit much more closely with communist ideology (no gene could be better than another).
Eventually put in charge of Russian Science and purges all evolutionary scientist
Responsible for massive wheat famine
The SpeciesSpecies is a biological term for a population of similar individuals that in nature interbreed and produce fertile offspring
Species are reproductively isolated from one another
Goats and sheep do not interbreed in nature, so they are separate species
Genetic DriftThe randomness with which alleles are transferred through a population as a result of sexual reproduction
Recipe for a speciesSpeciation is the process by which a new species arises from an ancestral species
It involves change in the genetic makeup of a population, which also may bring about changes in form and structure
Allopatric speciation
species arise when a small part of a population becomes isolated from its parent population
The peripheral isolates evolve as a result of genetic constriction and new environmental factors
Process of changePhyletic gradualism
the gradual accumulation of minor changes eventually bring about new species
process of change
Punctuated Equilibrium
Holds that little or no change takes place in a species during most of its existence then evolution occurs rapidly
styles of evolution
Divergent evolution occurs when an ancestral species giving rise to diverse descendants adapts to various aspects of the environment
Divergent evolution leads to descendants that differ markedly from their ancestors
Convergent evolution involves the development of similar characteristics in distantly related organisms
Parallel evolution involves the development of similar characteristics in closely related organisms
divergent evolution
convergent evolution
Icthyosaur-reptile
Parallel evolution
Death the driving force of evolution
Perhaps as many as 99% of all species that ever existed are now extinct
•Organisms do not always evolve toward some kind of higher order of perfection or greater complexity
•Vertebrates are more complex but not necessarily superior to bacteria after all, bacteria have persisted for at least 3.5 billion years
Natural selection yields organisms adapted to a specific set of circumstances at a particular time
Extinction
The continual extinction of species is referred to as background extinction
It is clearly different from mass extinction during which accelerated extinction rates sharply reduce Earth’s biotic diversity
Extinction is a continual occurrence
As species go extinct new species usually quickly exploit the opportunities the other species’ extinction creates
Mammals began a remarkable diversification when they began occupying niches the extinction of dinosaurs and their relatives left vacant