Student Expectation
The student is expected to analyze and evaluate how evidence of common ancestry among groups is provided by the fossil record, biogeography, and homologies, including anatomical, molecular, and developmental; AND analyze and evaluate scientific explanations concerning any data of sudden appearance, stasis, and sequential nature of groups in the fossil record; AND analyze and evaluate scientific explanations concerning the complexity of the cell.
Key Concepts
- The study of the similarities between species in the fossil record shows that organisms have a common ancestry. Variations in the physical features, such as shell shape or bone structure, of specific species reflect changes over time. The fossil record has also revealed links between large groups of organisms such as fish and reptiles, and reptiles and birds.
- Some species evolution is explained by the study of biogeography (geographic isolation and continental drift). Geographic isolation occurs when members of a single species are split into separate populations and can no longer mate because of geographic barriers; the result is two isolated gene pools that diverge over time, eventually becoming two separate species. Continental drift caused the ancient supercontinent Pangaea to split into separate continents; when this happened, some members of the same species were separated by water and became separate species over time.
- Homologies are seen in anatomical structures, genetics, and the developmental stages of different organisms. Species with common origins (e.g., birds, reptiles, and mammals) all show similar patterns of anatomy, such as those in the bones of the forelimbs. Genetic studies of the similarities between DNA sequences are revealing additional information about the similarities between species. Embryological studies also show that different species have similar developmental stages, suggesting evolution from a common ancestor.
- The fossil record reflects that the rates and patterns of evolution are not constant over geologic time. Species can change very little for long periods of time (evolutionary stasis); they can change very little for a long time, then undergo dramatic change over a relatively short period of time, followed by another long period of little change (punctuated equilibrium); or they can change gradually and sequentially (gradualism).
- The Endosymbiotic Theory states that mitochondria and chloroplasts were once free-living prokaryotes that adapted to living inside other cells and eventually formed a symbiotic relationship with their host cells.
Fundamental Questions
- How do scientific observations and evidence of common ancestry help to answer questions about the history of life?
- How does the fossil record reflect changes in groups of organisms over time?
- What are the different types of evolution?
- What are some factors that influence evolution?
Student Expectation
The student is expected to analyze and evaluate the effects of other evolutionary mechanisms, including genetic drift, gene flow, mutation and recombination.
Key Concepts
- There are five mechanisms of biological evolution: natural selection, genetic drift, gene flow, mutation, and recombination. Each of the mechanisms of evolution either increases or decreases the genetic diversity within and among populations.
- Genetic drift is the change in gene frequencies due to chance. Genetic drift is much stronger in smaller populations than in larger ones. Genetic drift can increase or decrease diversity; but it cannot create genetic variation, it can only destroy it.
- Gene flow is the movement of alleles between populations. It reduces the genetic diversity between populations, but increases the genetic diversity within populations by introducing new genes.
- Mutations are changes in genes that occur within a single individual. They are the raw materials for evolutionary change because natural selection favors beneficial mutations, increasing their frequencies, and eliminates harmful ones. The vast majority of mutations are either neutral, with no effect on fitness, or deleterious (harmful).
- Recombination occurs during sexual reproduction and via other mechanisms in asexual organisms. It results in new combinations of alleles and vastly increases the diversity of genotypes in each generation. Because most alleles segregate independently and randomly during meiosis, sexual organisms are able to generate millions of new allele combinations in their gametes.
Fundamental Questions
- What are the five mechanisms of biological evolution and how do these mechanisms change diversity of populations?
- Why are mutations the raw materials for natural selection?
- How does recombination increase genetic variation?
Student Expectation
The student is expected to analyze and evaluate how natural selection produces change in populations, not individuals AND analyze and evaluate how the elements of natural selection, including inherited variation, the potential of a population to produce more offspring than can survive, and a finite supply of environmental resources, result in differential reproductive success AND analyze and evaluate the relationship of natural selection to adaptation and to the development of diversity in and among species.
Key Concepts
- Natural selection is a process by which the gene frequencies in a population change over time because of the differential survival and reproductive success of various genotypes. An organism’s survival depends on its inherited traits, which influence its ability to compete for resources, procure mates, and avoid danger to itself and its offspring. The overall ability to survive and pass its genes on to the next generation is called fitness. In each generation, the individuals with the highest fitness are more likely to reproduce and pass on their traits to their offspring.
- Changes in the gene pool of a population due to natural selection take many generations. Natural selection does not occur within individuals; it occurs within and among populations. Within a diverse population, different individuals of the same species have unequal fitness; this is called within-population diversity. In addition, different species may have unequal fitness in a particular environment; this is called among-species diversity.
- The frequencies of alleles within a population change due to different levels of reproductive success among individuals, as some produces more successful offspring than others. Allelic frequencies can also change when more individuals are produced than the environment can support and strong competition for resources results.
- Species are usually defined as groups of organisms that can interbreed and produce viable, fertile offspring (species are defined differently for asexual organisms). Speciation occurs when the gene pools of populations diverge to the point where individuals from different populations can no longer produce viable, fertile offspring together; their gene pools then become permanently isolated. Speciation can be allopatric (with geographic isolation between populations) or sympatric (without geographic isolation between populations). Over many generations following speciation, each newly diverged species accumulates its own adaptations, and the species slowly become more and more different from one another. In this way, natural selection and adaptation create species diversity.
Fundamental Questions
- What is the relationship between overpopulation and natural selection?
- Why does natural selection take place within populations and not within individuals?
- How do differing degrees of reproductive success result in natural selection?
- How do natural selection and adaptation relate to diversity of species?
- What factors might influence the rate of natural selection?
