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Evolution Unit


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Change over time The process by which modern organisms have descended from ancient organisms
Scientific Theory
A well-supported testable explanation of phenomena that have occurred in the natural world
Lamarck's Evolution Hypothesis
He proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could them be passed on to their offspring. Over time, this could led to change in a species
Artificial selection
Nature provided the variation, and humans selected those variations that they found useful Humans select from among the naturally occurring genetic variations in a species
Struggle for existence
Members of each species compete regularly to obtain food, living space, and other necessities of life
Survival of the Fittest
To survive and reproduce in its specific environment Darwin proposed that fitness is the result of adaptations
Any inherited characteristic that increases an organism's chance of survival
Natural Selection
Here only certain individuals of a population produce new individuals What Darwin referred survival of the fittest to Results in changes in the inherited characteristics of population These changes increase a species' fitness in its environment
Descent With Modification
principle that each living species has descended, with changes, from other species over time
Common Decent
All species, living and extinct, were derived from a common ancestors A single "tree of life" connects all living things
Homologous structures
Structures that have different mature forms but develop from the same embryonic tissues
Vestigial Organs
The organs of many animals are so reduced in size that they are just traces of Homologous organs in other species
Gene pool
Consists of all genes that are present in a population Including all the different alleles
Relative Frequency
The number of times that the allele occurs in a gene pool compared with the number of times other alleles for the same gene occurs Often expressed as a percentage
Any change in a sequence of DNA A result of radiation of chemicals in the environment
Gene Shuffling
Hereditable differences that occurs during the production of gametes
Single-gene trait
Controlled by a single gene that has two alleles
Phenogenic traits
Traits that are controlled by two or more genes As a result, one polygenic trait can have many possible genotypes and phenotypes
Directional Selection
Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve
Stabilizing Selection
Form of natural selection by which the center of the curve remains in its current of a distribution curve has higher fitness than individual at either end
Disruptive Selection
From of natural selection in which a gene curve splits into two occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle
Formation of new species
Reproductive isolation
When the members of two populations cannot interbreed and produce fertile offspring At this point, That populations have separate gene pools
Behavioral isolations
Occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior
Geographic Isolation
Two populations are separated by geographical barriers such as rivers, mountains, or bodies of water
Temporal Isolation
Two or more species reproduce at different times
Scientists who study fossils
Fossil Record
Provides evidence about the history of life on Earth Also shows how different groups of organisms, including species, have changed over time
Means the species died out
Steps for fossilization
Water carries small rock particles to lakes and seas Dead organisms are buried by layers of sediment, which forms new rock The preserved remains may later be discovered and studied
Relative dating
The age of a fossil is determined by comparing its placement with that of fossils in other layers of rock Allows paleontologists to estimate a fossil's age compared with that of other fossils Does not provide information about its absolute age, or age in years
Index Fossils
Used to compare the relative ages of fossils To be used as an such, a species must be easily recognized and must have existed for a short period but have a wide geographic range
Half Life
Is the length of time required for half of the radioactive atoms in a sample to decay
Radioactive Dating
Scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains Determines actual age
Geologic Time Scale
Paleontologists use division of this to represent evolutionary time
One of several subdivisions of the time between the Precambrian and the present
Unit of time into which eras are subdivided Range in length from tens of millions of years to less than two million years
Miller and Urey
This and other experiment showed how simple compounds found on the early Earth could have combined to form the organic compounds needed for life Miller and Urey's experiments showed how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth.
Microscopic fossils
The Endoplasmic Theory
Theory that eukaryotic cells formed for a symbiosis around several different prokaryotic organisms forms
Precambrian Time
90% of Earth's history occurred during this time Simple forms of life appeared and were followed by photosynthetic forms Which added oxygen to the atmosphere Aerobic forms of life evolved & eukaryotes appeared Life only existed in the sea
Paleozoic Era
Rich fossil evidence shows that early in the Paleozoic Era, there was a diversity of marine life
Cambrian Explosion
For the first time, many organisms had hard parts Including shells and outer skeletons
Mass extinction
Many types of living things became extinct at the same time 95% of the complex life in the oceans disappeared
Mesozoic Era
The increasing dominance of dinosaurs Appeared 225 million yrs ago Marketed by the appearance of flowering plants
Cenozoic Era
Mammals evolved adaptations that allowed them to life in various environments Land, water, and air

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