Unit 7: Evolution and Natural Selection-Science Study Guide
How does natural selection determine fitness?
-Certain traits may be an advantage for survival. Alleles for these traits increase in frequency -Certain traits may be an advantage for survival. Alleles for these traits increase in frequency
Evolution
-Change in a species overtime -the process of biological change by which descendants come to differ from their ancestors
Is evolution random?
-The process of mutation, which generates genetic variation is, is RANDOM, but selection is non-random. -Selection favored variants that were better able to survive and reproduce (e.g., to be pollinated, to fend off pathogens, or to navigate in the dark). -Over many generations of random mutation and non-random selection, complex adaptations evolved. To say that evolution happens "by chance" ignores half of the picture. -Individuals with traits that are better adapted for their environment have a better chance of surviving and reproducing than do individuals without these traits.
What are the two main mechanisms that cause evolution?
1.) Variation 2.) Natural selection
Fossil Record
A term used by paleontologists to refer to the total number of fossils that have been discovered, as well as to the information derived from them
Analogous Stuctures (Define, be able to identify each, provide examples)
Analogous structures are structures that perform a similar function but are not similar in origin. Ex. Suppose two organisms have similar needs caused by the environment. For example, two different organisms need to be able to fly. Both can develop similar adaptations using different body parts. Think about the wings of bats and the wings of flying insects. Clearly, these organisms differ in more ways than they are similar. Insects are arthropods, while bats are mammals. The wings of bats and insects are called analogous structures, as shown in FIGURE 4.5. Analogous structures are structures that perform a similar function—in this case, flight—but are not similar in origin. Bat wings have bones. In contrast, insect wings do not have bones, only membranes. The similar function of wings in bats and flying insects evolved separately. Their ancestors faced similar environmental challenges and came upon similar solutions.
Behavioral Isolation
Chemical scents, courtship dances of birds, and courtship songs of frogs are sexual signals used to attract mates. Changes in these signals can prevent mating between populations. Behavioral isolation is isolation caused by differences in courtship or mating behaviors.
Types of Evolution
Convergent: Evolution toward similar characteristics in unrelated species is called convergent evolution. Analogous structures, such as wings on birds and insects, are common examples of convergent evolution. Divergent: When closely related species evolve in different directions, they become increasingly different through divergent evolution. The evolution of the red fox and the kit fox is an example of this trend. Though closely related, the two species have different appearances that are the result of adapting to different environments. The red fox lives in temperate regions, usually in forests. Its dark reddish coat helps it to hide from predators. The sandy- colored coat of the kit fox allows it to blend in with its desert surroundings. Kit foxes also have large ears relative to their body size. This adaptation helps them to keep cool in the desert heat. Coevolution: Coevolution is the process in which two or more species evolve in response to changes in each other
How does a changing environment impact natural selection?
Darwin's theory predicted exactly what the Grants observed. A trait that was already in the population became favorable for survival because of a change in the environment, and thus was passed on to future generations. As an environment changes, different traits will become beneficial. The numbers of large-beaked finches on this Galápagos Island kept rising until 1984, when the supply of large seeds went down after an unusually wet period. These conditions favored production of small, soft seeds and small-beaked birds. With evolution, a trait that is an advantage today may be a disadvantage in the future.
Why is evolution important biologically?
Evolution is the process by all living creatures change to meet the expectations of their environments so all living creatures don't go extinct.
Evidence of Evolution
Fossil: DNA: As with homologous traits, very different species have similar molecular and genetic mechanisms. Because all living things have DNA, they share the same genetic code and make most of the same proteins from the same 20 amino acids. DNA or protein sequence comparisons can be used to show probable evolutionary relationships between species. DNA sequence analysis Recall that the sequences of nucleotides in a gene change over time due to mutations. DNA sequence analysis depends on the fact that the more related two organisms are, the more similar their DNA will be. Because there are thousands of genes in even simple organisms, DNA contains a huge amount of information on evolutionary history. Pseudogenes Sequences of DNA nucleotides known as pseudogenes also provide evidence of evolution. Pseudogenes are like vestigial structures. They no longer function but are still carried along with functional DNA. They can also change as they are passed on through generations, so they provide another way to figure out evolutionary relationships. Functioning genes may be similar in organisms with similar lifestyles, such as a wolf and a coyote, due to natural selection. Similarities between pseudogenes, however, must reflect a common ancestor. Homeobox genes As you will learn, homeobox genes control the development of specific struc- tures. These sequences of genes are found in many organisms, from fruit flies to humans. They also indicate a very distant common ancestor. Evidence of homeobox gene clusters are found in organisms that lived as far back as 600 million years ago. Protein comparisons Similarities among cell types across organisms can be revealed by comparing their proteins, a technique called molecular fingerprinting. A unique set of proteins are found in specific types of cells, such as liver or muscle cells. Cells from different species that have the same proteins most likely come from a common ancestor. For example, the proteins of light-sensitive cells in the brain of an ancient marine worm, as shown in FIGURE 5.2, were found to closely resemble those of cells found in the vertebrate eye. This resemblance shows a shared ancestry between worms and vertebrates. It also shows that the cells of the vertebrate eye originally came from cells in the brain.
5 factors that lead to evolution
Genetic drift Allele frequencies can change due to chance alone. • Gene flow The movement of alleles from one population to another changes the allele frequencies in each population. • Mutation New alleles can form through mutation. Mutations create the genetic variation needed for evolution. • Sexual selection Certain traits may improve mating success. Alleles for these traits increase in frequency. • Natural selection Certain traits may be an advantage for survival. Alleles for these traits increase in frequency
Geographic Isolation
Geographic isolation involves physical barriers that divide a population into two or more groups. These barriers can include rivers, mountains, and dried lakebeds.
Homologous Structures (Define, be able to identify each, provide examples)
Homologous structures are features that are similar in structure but appear in different organisms and have different functions. Ex. The most common examples of homologous structures are the forelimbs of tetrapod vertebrates. The forelimbs of humans, bats, and moles are compared in FIGURE 4.4. In all of these animals, the forelimbs have several bones that are very similar to each other despite their different functions. Notice also how the same bones vary in different animals. Homologous structures are different in detail but similar in structure and relation to each other. -Look in book for picture pg. 294
The fossil species known as Archaeopteryx is a wonderful transition species. (it show traits of more than one type of organism) What transition does it show?
It shows the transition from reptile to bird
Reproductive isolation
Reproductive isolation occurs when members of different populations can no longer mate successfully. Sometimes members of the two populations are not physically able to mate with each other. In other cases, they cannot produce offspring that survive and reproduce. Reproductive isolation between populations is the final step of becoming separate species.
Temporal Isolation
Temporal isolation exists when timing prevents reproduction between populations. Some members of a population may show signs of courtship at different times if there is a lot of competition for mates. Reproductive periods may change to a different time of the year or a different part of the day. These differences in timing can lead to speciation.
Speciation
The rise of two or more species from one existing species is called speciation
What are the four main principle of natural selection? Explain each principle.
There are four main principles to the theory of natural selection: variation, overproduction, adaptation, and descent with modification. • Variation The heritable differences, or variations, that exist in every population are the basis for natural selection. The differences among individuals result from differences in the genetic material of the organisms, whether inherited from a parent or resulting from a genetic mutation. • Overproduction While having many offspring raises the chance that some will survive, it also results in competition between offspring for resources. • Adaptation Sometimes a certain variation allows an individual to survive better than other individuals it competes against in its environment. More successful individuals are "naturally selected" to live longer and to produce more offspring that share those adaptations for their environment. • Descent with modification Over time, natural selection will result in species with adaptations that are well suited for survival and reproduction in an environment. More individuals will have the trait in every following generation, as long as the environmental conditions continue to remain beneficial for that trait.
Atavisms
Traits from an ancestor that have randomly reappeared in a modern organism -Atavus(Latin for ancestor) -Only in very few individuals (under-developed traits) -Vestigial structures are in all or most of a species Ex. -Hind flippers on a dolphin -Extra nipples on humans -a human tail "coccygeal projection"
Vestigial Structures (Define, be able to identify each, provide examples)
Vestigial structures are remnants of organs or structures that had a function in an early ancestor. Ex. For example, snakes have tiny pelvic bones and stumplike limbs, even though snakes don't walk. Underdeveloped or unused features are called vestigial structures -The wings of ostriches are another example of vestigial structures. Ostriches have wings that they use for balance but not to fly, as shown in FIGURE 4.6. Over generations, their increasingly large bodies and powerful long legs may have been enough to avoid predators. If ostriches that lived long ago could escape by running or by kicking viciously, their large wings would no longer have been useful. Thus, the genes coding for large wings were not preserved over generations. -Examples of vestigial structures are found in many organisms. In humans, the appendix is an example of a vestigial structure. The appendix is a remnant of the cecum, which makes up a large part of the large intestine in plant-eating mammals. It helps to digest the cellulose in plants. As omnivores, humans do not eat much cellulose. The human appendix does not have the ability to digest cellulose. In fact, it performs no known function at all.
Population
all of the individuals of a species that live in the same area
Genetic Drift
change in allele frequencies due to chance alone, occurring most commonly in small populations
Gene Pool
collection of alleles found in all of the individuals of a population
Hardy-Weinberg Equilibrium
condition in which a population's allele frequencies for a given trait do not change from generation to generation
Cladogram
diagram that displays proposed evolutionary relationships among a group of species.
Founder Effect
genetic drift that occurs after a small number of individuals colonize a new area
Bottleneck Effect
genetic drift that results from an event that drastically reduces the size of a population
Adaptation
inherited trait that is selected for over time because it allows organisms to better survive in their environment
Biological Fitness(fitness)
measure of an organism's ability to survive and produce offspring relative to other members of a population
Gene Flow
physical movement of alleles from one population to another
Artificial Selection
process by which humans modify a species by breeding it for certain traits
Adaptive Radiation
process by which one species evolves and gives rise to many descendant species that occupy different ecological niches
Sexual Selection
selection in which certain traits enhance mating success; traits are, therefore, passed on to offspring
Biogeography
study of the distribution of organisms around the world
Radiometric Dating
technique that uses the natural decay rate of isotopes to calculate the age of material
Punctuated Equilibrium
theory that states that speciation occurs suddenly and rapidly followed by long periods of little evolutionary change
