Natural Selection Flashcards
Evolution
Evolution is the change in frequency of a population’s inherited traits over subsequent generations.
Evolution only occurs within populations; individual organisms do not change genetically over time to adjust to their environment.
What is the difference between microevolution and macroevolution?
Microevolution relates to evolutionary changes that occur within a single population. Its scope is fairly small, since it only deals with one species at a time.
Macroevolution relates to larger-scale changes and interactions between multiple populations (and thus multiple species).
Jean-Baptiste Lamarck, a French naturalist, proposed two key ideas as part of his explanation for evolution. Name these ideas.
Use and disuse and inheritance of acquired characteristics
Use and disuse is the idea that we “build up” body parts that we use often, while those parts that we do not use tend to atrophy (weaken). This idea is still considered to be accurate today. In contrast, inheritance of acquired characteristics (or the thought that organisms pass down traits gained over their lifetimes) is now considered to be wrong.
In his famous theory, Jean-Baptiste Lamarck proposed that the “use or disuse” of a trait dictated its heritability. In a classic example, giraffes who often stretched their necks would have offspring with longer necks than average. Describe the problem with this hypothesis.
Non-genetic traits that are acquired during an organism’s lifetime cannot be passed down to its offspring.
According to the “use and disuse” concept, organisms lose traits they do not need and develop traits that are useful to them. However, genes (not acquired traits) are inherited by offspring, making Lamarck’s theory an incorrect, and now discredited, explanation for evolution.
Our modern understanding of evolution stems largely from the findings of which individual, who proposed the concept of natural selection?
Charles Darwin
Charles Darwin was a naturalist whose most famous work, On the Origin of Species, proposed the concepts that we understand to be largely true today - most notably, that natural selection drives evolutionary changes within a species as well as the development of new species.
Natural selection
Natural selection is the change in frequency of a trait within a population, based on the effect that trait has on reproductive success.
Traits that allow an organism to produce more viable offspring are more likely to be passed on to future generations.
Name five sources or fields of study that provide support for the concept of evolution.
The five fields of study typically considered to provide the most support for evolution are:
- The study of the fossil record (paleontology)
- The study of the distribution of animals and plants (biogeography)
- Comparative anatomy
- Comparative embryology
- Molecular biology
Comparative anatomy most notably includes the study of which two types of anatomical structures?
Homologous structures and analogous structures
Homologous structures
Homologous structures are anatomical features of two species that developed from the same part of a common ancestor.
Species that possess homologous structures must be related. However, the modern versions of these structures do not have to be used for the same purpose.
Analogous structures
Analogous structures are anatomical structures of two species that share a form or function, but did not develop from a common ancestor.
Species that possess analogous structures must be relatively unrelated. However, since their structures are similar in appearance or function, they may be mistaken for related species.
As mammals, both humans and whales developed from a common ancestor. What term describes the relationship between a human arm and a whale fin?
Human arms and whale fins are homologous structures.
Though used for very different purposes, the appendages are evolutionarily related; both derived from a similar structure in a common ancestor.
Birds and insects evolved independently from very different ancestors. What term describes the relationship between a bird wing and a bee wing?
Bird wings and bee wings are analogous structures.
Since both structures serve a similar purpose, it can be tempting to think that they are related. However, since they developed independently from features of different ancestors, they are analogous.
What benefit does a vestigial structure give a modern organism?
Vestigial structures provide little to no benefit to the organisms who possess them.
While these features were likely useful to ancestral organisms, they have evolved to lose most or all of their function.
Evolutionary biologists would classify the human appendix as which kind of structure?
The appendix is generally classified as vestigial.
The appendix, an outcropping of the large intestine, has long been thought to provide no function to modern humans. Though recent research has challenged this idea, for the AP Biology exam, continue to remember the appendix as a classic example of a vestigial structure.
What is the difference between ontogeny and phylogeny?
Ontogeny refers to the development of an individual organism throughout its life. Phylogeny describes the evolutionary history of a species or other set of organisms.
For example, human ontogeny relates to the transition from zygote to embryo to fetus, then adult. Human phylogeny deals with the descent of modern humans from early ancestors.
Is the development of a fertilized egg into an adult chicken an example of ontogeny or phylogeny?
Ontogeny refers to an organism’s development over its lifetime, while phylogeny refers to a species’s development over evolutionary time.
What qualities are exhibited by an organism with high fitness?
Organisms with high fitness are those that successfully produce a relatively large number of offspring. In general, fitness refers to the likelihood that an animal will pass down its genetic material.
On the AP Biology exam, remember that fitness is determined by reproductive success alone. A stronger, more physically capable animal that cannot reproduce is less fit than a weaker animal that can reproduce.
Which of the following is the least evolutionarily fit?
A fish with underdeveloped fins
A fish without functioning sex organs
A fish without functioning eyes
The fish that lacks functional sex organs is the least fit.
Evolutionary fitness refers only to the ability to pass on genetic material. The other two fish certainly may have difficulty surviving, but they can still reproduce.
Members of a population who possess beneficial traits survive long enough to produce offspring, while members with harmful traits often die before reaching sexual maturity. Which evolutionary term describes this tendency?
Differential reproduction describes this variation in reproductive success.
This concept is a key component of natural selection. Through this mechanism, traits that affect survival are inherited differently, regardless of whether they directly relate to reproduction.
What term refers to the set of all genes present in a population?
The gene pool
A diverse gene pool allows a species to more easily adapt to changes in its environment. This quality is referred to as genetic variation.
Genetic leakage
Leakage is the gene flow from one species to the gene pool of another.
What genetic value changes within a population as evolution occurs?
Evolution changes a population’s allele frequency.
Alleles are different forms of genes, and evolution is a change in the frequency of genetic material. Thus, evolution causes some alleles to become more prevalent while others become more rare.
What measurement determines the evolutionary success of an allele?
Evolutionary success is determined by the percent representation of an allele in the following generation.
If an allele becomes more prevalent in the gene pool, it is considered evolutionarily successful. However, factors other than natural selection can affect allele frequencies.
Which of the following must increase in future generations for an allele to be evolutionarily successful?
Its phenotypic ratio
Its genotypic ratio
Both its phenotypic ratio and its genotypic ratio
Genotypic ratio must increase.
Technically, evolutionary success of an allele refers only to an increase in its frequency in the gene pool. Allele frequencies cannot change without altering genotype frequencies. Note that phenotype frequencies are likely to change as well, but this is not a necessary measure of success.
Name three events or mechanisms that increase a population’s genetic diversity.
Many mechanisms serve to increase genetic diversity. Three of the most prevalent are:
Mutation
Migration between populations
Sexual reproduction, especially homologous recombination (crossing over)
What condition must be met for a group of individuals to be considered part of the same species?
They must be able to breed and produce viable, fertile offspring.
A species is the most specific category in which an organism can be classified.
Horses and donkeys can mate and produce healthy offspring called mules. Why are horses and donkeys considered separate species?
Mules are sterile.
Within a species, the offspring of a breeding pair must be fertile as well as viable. Since mules cannot produce offspring, this condition is not met.
Speciation
Speciation is the development of new species through evolution.
Generally, speciation occurs when groups of a single species undergo divergent evolution.
What is the difference between allopatric and sympatric speciation?
Allopatric speciation occurs when populations of the same species become physically isolated, usually by a geographical barrier. Over time, the populations evolve to become separate species.
Sympatric speciation refers to the formation of new species without a geographical barrier. This form of speciation can occur in cases of polyploidy in plants, where some members of a population develop an extra set of chromosomes and can no longer mate with the non-polyploid organisms. Gradually, the polyploid and non-polyploid plants separate into distinct species.
