Ch.16 Flashcards
Natural selection
in which individuals with certain heritable traits are more likely to survive and reproduce than other individuals, leading to population level changes.
Conditions for evolution by natural selection to occur
1. There must be variation for the trade within a population.
2. That variation must be inheritable (that is, capable of being passed from parents to offspring.)
3. Individuals with one version of the trait must produce more offspring than those with a different version of the trait.
A wide variety of environmental factors can also act as agents of selection. Limited food and habitat, predation, competition, disease, and other threats reduce the ability of individual organisms to survive and/or reproduce.
In addition, individuals within a population are not identical but differ in certain traits- result from differences in their DNA and thus can be inherited.
Individuals in the population that lacked such traits are less likely to reproduce, leaving fewer, if any, offspring. Thus, advantageous heritable traits will become more common in the next generation.
•Many offspring are produced, not all survive.
•Traits vary among individuals within a population and may be inheritable.
•Some inheritable traits give individuals in advantage.
•Advantageous traits, conferring higher Fitness, become more common.
Important questions to ask about natural selection
try to identify the key factors driving evolutionary change: What was the genotypic makeup of the starting population? What was the selection pressure and what impact did it have on the populations? Did the selection pressure change over time? And, what caused it to change?
Population
Individual organisms do not evolve over their life-time. The unit upon which evolution acts is the population—a group of interbreeding individuals of a species that live together in a specific place.
Evolution depends on differential survival and reproduction that comes from (1) variation among individuals in a population and (2) the heritability of that variation. It is the population that has the capacity to change from one generation to the next.
Endemic species
Species found in a restricted single geographic area, such as an island. And don’t occur naturally anywhere else in the world.
For example, the Galápagos Islands are home to four unique species of mockingbird (genus Neso-mimus,) Each of these four species is found on only one island. Although similar in appearance, each mockingbird species is morphologically distinct, with notably different traits (e.g., beak size and shape, coloration).The under-lying similarity of the mockingbirds, however, indicates that the four species all diverged from a common ancestral population.
The simplest scenario to explain this is that a population of one species of mockingbird came and colonized most of the islands at or around the same time.populations that devel-oped on different isolated islands responded to different selective pressures (e.g., climate, food sources, predators) that favoured different traits.becoming less and less similar to one another as their respective, favoured, heritable traits became more common.This example offers evidence for multiple species that share a common ancestor diverging with time through descent with modification.
Adaptations
The inherited aspects of an individual that make it well suited to thrive in a particular environment. From generation to generation, a species becomes better adapted to a specific environment as a consequence of natural selection.
Artificial selection
The process of causing evolutionary change by human choice. choosing organisms with desired traits to breed could produce, for example, bigger beets, plumper pigs, and prize-winning pigeons. When humans selectively breed for the traits they desire in crop plants or domestic animals, they are the agents of evolutionary change, or the agents of selection. Selective breeding causes artificial selection.
Fitness
Individuals with the set of traits that lead to greater survivorship and reproductive success are said to be more fit compared to others.
In the context of evolution, the term fitness describes an individual’s reproductive success—an organism has higher fitness than another if it leaves more offspring that, in turn, survive to reproduce.
Three aspects of fitness that are important to an understanding of how evolution works: (1) Fitness is a relative concept. It doesn’t matter in absolute terms how many offspring an individual leaves, only that it leaves more than others in the population.
(2) A trait is only adaptive if it increases fitness. We tend to think of traits such as being faster, stronger, or bigger as valuable; how-ever, they are only valuable, and thus selected for, if they increase reproductive success. In some situations, being slower, weaker, or smaller may confer an advantage.
(3) The traits that increase fitness may change. If the envi-ronment changes (e.g., climate change, the introduction of a new predator), those traits that previously increased fitness may no longer be advantageous.
Mutantion
a random and heritable change in the DNA sequence. Mutations arise as an inevitable consequence of the imperfect nature of DNA replication, as well as from the effects of certain physical, chemical, and biological agents. It is critical to understand, however, that while mutations are the source of variation, they do not determine the path of evolution. Because mutations are undirected, they can occur anywhere in the genome: in essential genes required for life, or in a DNA sequence that has no function. Beneficial, neutral, or harmful.
transposable element
a biological agent that can cause mutations. Transposable elements are pieces of DNA that can move from one position to another in the genome, sometimes inserting themselves in ways that affect expression of genes
Convergent evolution
is the independent evolution of comparable traits in unrelated species, such as the wings of insects, birds, and bats. The convergent evo-lution of solutions to threats to survival is a recurring theme among organisms.
biogeography
Studies of the worldwide distribution of plants and animals, now called biogeography
Good questions to ask
Where did all these species fit in the Scale of Nature? Why did some species have limited geographical distributions, whereas others were widespread? Why were some species found in Africa or Asia so different from those found in Europe, while others had a similar appearance
vestigial structures
Buffon proposed that some animals must have changed since their creation. He suggested that vestigial structures, these useless parts he observed, must have functioned in ancestral organisms, although he offered no explanation of how functional structures became vestigial.
Homology
The similarity present in a group of organisms because of shared ancestry is called homology. Similar structures suggest common ancestry. Traits that are similar due to common ancestry today are referred to as homologous. What set Darwin apart from his predecessors is that he arrived at how evolution occurs, its mechanism.
modern synthesis
Movement that married Darwinian evolution and natural selection with genetics, systematics, and paleontology.
• Term coined by Julian Huxley call my grandson of Thomas Huxley.
Population geneticists constructed mathematical models, which applied equally well to simple and complex traits, to predict how natural selection and other processes influence a population’s genetic structure.
modern synthesis integrated data from biogeography, comparative morphology, comparative embryology, genetics, palaeontology, and taxonomy within an evolutionary framework.
Focused on evolutionary change within populations. Although they considered natural selection the primary mechanism of evolution, they acknowledged the importance of other processes such as genetic drift.
Also embraced Darwin’s idea of gradual change and deemphasized the significance of mutations that changed traits suddenly and dramatically.
Tried to link the two levels of evolutionary change that Darwin had identified: microevolution and macroevolution.
Microevolution
Microevolution describes the small-scale genetic changes that populations undergo, often in response to shifting environmental circumstances; a small evolutionary shift in the size of the bill of a Galápagos finch is an example of microevolution.
