Unit 6 Lesson 6: Evolution Versus Natural Selection Flashcards
natural selection
the process that results in an organism having favorable adaptations to its environment, which are passed on through reproduction, thus changing the genetic makeup of future generations
What is the relationsip betwwen natural selection and evolution
Natural selection is one of the mechanisms that can cause evolution in a species. It is possible for evolution to occur without natural selection—or for artificial selection to be the driving force behind changes in organisms. It is even possible for evolution to occur without any selection.
There are five factors that can cause evolution in a species over time: gene flow
Gene flow, or the movement of alleles into and out of a population due to migration patterns,
evolution
change in the genetic makeup of a population over time
There are five factors that can cause evolution in a species over time: genetic drift
Genetic drift, or changes in the genetic makeup of a population due to random events, such as natural disasters or diseases or pure luck,
There are five factors that can cause evolution in a species over time: Selection
Selection, such as natural selection or artificial selection,
There are five factors that can cause evolution in a species over time: Mutation
Mutation, or changes in the sequence of DNA, can lead to new alleles and, therefore, new traits,
There are five factors that can cause evolution in a species over time: selective mating
Selective mating, when individuals choose mates based on certain characteristics.
Natural selection is a process that involves the following steps:
- An organism, as a result of genetic drift or mutation, develops an unusual trait. The trait can be anything from longer legs to darker coloration to a larger or smaller brain.
- The trait provides the organism with an advantage that makes it better adapted to its environment than other, similar organisms. The advantage allows it to survive and reproduce. For example, the organism with the advantageous trait may be able to outrun predators or digest food more efficiently. Meanwhile, similar organisms without the trait may not survive and reproduce.
- The organism with the advantageous trait passes along the trait to its offspring.
Evolution that leads to individuals that are better suited to the environment requires
Evolution that leads to individuals that are better suited to the environment requires natural selection on traits that are determined by genetics. In other words, the advantageous traits must be inheritable for natural selection to produce evolution to be better adapted to the environment.
It is also possible to influence evolution through artificial selection, or breeding.
Human beings artificially select traits to produce desired outcomes in both plants and animals. Hybrid crops, for example, are new plant strains created by the crossbreeding of crops with desirable traits.
Genetic modification is a newer way of impacting traits.
Because those traits are genetic, they can be passed along to offspring. So far, genetic modification is mainly used with crops in order to make plants more resilient, nutritious, or pest resistant. Some researchers are starting to modify animal genes as well in order to produce a variety of desirable traits.
Evolutionary change can and does occur without natural selection.
This is usually a result of gene flow or genetic drift. This change may be beneficial, detrimental, or neutral.
Gene flow
Gene flow occurs when alleles from one population are introduced to another. This happens when migrating animals, such as birds or insects, interact with a different population and reproduce. New alleles are infused into the population and are passed on.
vector
an organism that transmits a substance from one organism or source to another
Example of a vector
Sometimes animals can act as vector, carrying seeds and pollen from one locale to another, introducing new plant alleles to the environment. Even bacteria can transfer genetic material between organisms.
Genetic drift
Genetic drift is another mechanism that can affect the gene pool of a population. In small populations, some alleles may be less common than others. Over time, this results in the probability of that gene being passed from one generation to another being lowered. There is no evolutionary benefit to the organisms with one or the other gene, it is a matter of chance.
Do humans experinece gene flow
Humans experience gene flow as well, due to our modern ability to travel around the world quickly and easily. Many people have moved away from their homeland to settle in another far away, introducing new genes as a result. Mitochondrial and Y-Chromosome studies in humans have provided a lot of information about human migration and the gene pool.
Scientists have identified two causes of genetic drift:
the bottleneck effect and the founder effect.
bottleneck effect
a dramatic reduction in the size of a population that results in a decrease in genetic variation
Example of bottleneck effect
For example, the Australian wildfires of 2023 reportedly killed as many as 3 billion animals. This will severely impact the gene pool of the surviving plant and animal species, potentially removing some alleles from the gene pool entirely.
founder effect
the effect on the resulting gene pool that occurs when a new isolated population is founded by a small number of individuals possessing limited genetic variation relative to the larger population from which they have migrated
Example fo founder effect
Isolation can occur in many ways, one of which is geography. Plants, animals, and humans on the Pitcairn islands in the South Pacific have been isolated from the rest of the world and have a limited gene pool as a result. In the human population, cultural isolation can result in the founder effect. An example of this is the Amish community, which tends to be confine itself to its own society.
Can evolution occur without natural selection? Explain your answer.
Yes. Evolution can occur as a result of genetic drift or by luck or accident.
Many zoos participate in efforts to help endangered species, such as the red-ruffled lemur, survive and not go extinct. Selective breeding of these animals involves very small numbers of individuals. Analyze the impact on the evolution of these endangered species.
Having such a small population of breeding animals will cause the founders effect, a form of genetic drift. The number of different alleles will be limited in the surviving population.
Bees travel from flower to flower collecting nectar. Their range is generally about two miles but can be even farther. Analyze how their action impacts the evolution of some plants.
Because bees transfer pollen from plants that are far apart from each other, they contribute to gene flow in those populations. The alleles of plants miles away are shared with a different population.
The giraffe’s long neck is a(n) _____ which makes it easier for giraffes to feed on the higher branches of trees.
adaptation
The video describes four requirements for natural selection, which is one important reason why evolution occurs. What are these four requirements?
Over production, genetic variation, competition, differential survivorship and reproduction
Artificial selection can be the result of intentional breeding and crossbreeding of organisms.
For example, some tomatoes are intentionally bred to be larger, juicier, or more disease resistant. Artificial selection of crops has been practiced for thousands of years, as farmers chose to collect the seeds of only the hardiest plants to replant for the following year.
What are some of the pros and cons of hybridization and genetic modification?
The pros are that it is possible to create crops that have the traits humans prefer. This saves time and money and makes it easier to produce healthy, nutritious crops. The cons are that we don’t know what the long-term outcome of genetic modification might be. Will it lead to evolutionary change?
Genetic modification allows an entirely new gene to be added to an existing genome. What does this mean
This allows a gene with a known function to be introduced to a species. Genes from certain bacteria, for instance, might be introduced to corn to give it better virus resistance. The trait can be introduced in a single generation, rather than being selected over time.
