Chapter 22: An Introduction to Evolution Flashcards
Define evolution
A heritable change in characteristics of a population that from one generation to the next.
Define species
We will look more at the defining features of a species in chapter 24, but for now we can think of a species as a group of related organisms that share distinctive characteristics. In species that reproduce sexually, members of the same species can interbreed to produce viable and fertile offspring. Members of different species usually cannot interbreed to produce viable and fertile offspring, but there are exceptions.
Define population
All members of the same species that occupy the same geographical location at the same time.
A founder population of finches migrates to a new area where seeds are small. Individuals with small beaks are better able to obtain food, and therefore more likely to survive and reproduce. Assuming beak size is a heritable trait, what would happen to the mean beak size in the population of finches over time? How does this change come about?
The mean beak size would decrease. Natural selection favors a small beak size in this example. Individuals with small beaks are more likely to survive, and therefore reproduce and pass on their beneficial small beak alleles to the next generation. Individuals with large beaks are less likely to survive and reproduce and pass on the large beak alleles.
What does biogeography study? How can it provide evidence of evolutionary change? What is an example we discussed?
Biogeography is the study of geographic distributions of species (including extinct and living species). Comparing the distributions of species highlights how one species may have evolved from an existing species to become better adapted to a different environment (for example, island species often have a closely related relative on the mainland), or how two or more species may have evolved in isolation from a common ancestor.
Example: The channel island fox likely evolved from the mainland gray fox to become smaller in size. During the last ice age, the Channel Islands were connected to the mainland US, so the fox population could move freely between the Channel Islands and mainland US. That connection was severed when the ice age ended. Resources on the Channel Islands are more limited than on the mainland US, so smaller foxes that were left on the Channel Islands were more likely to survive on the limited resources. Therefore, a smaller body size was naturally selected on the Channel Islands.
Example: Australia has many endemic marsupial species (i.e., not found anywhere else). Marsupials arrived in Australia before Australia separated from the continent to become an island. The early marsupials that were present in Australia when it separated then evolved in isolation from the marsupial species on the continent, resulting in many unique, endemic species in Australia.
Define homology
Similarity due to descent from a common ancestor.
What is anatomical homology? What is an example?
Different organisms have similar anatomical structures due to descent from a common ancestor.
For example, humans, bats, turtles, and whales all have the same arrangement of bones in the forearm, but the bones have evolved over time to serve different purposes in the different organisms.
What is developmental homology? What is an example?
Species show similarities during embryonic development indicating that they have evolved from a common ancestor. For example, early human embryos have gill slits even though adult humans don’t have gills, which indicates that humans share a common ancestor with fish.
What is genetic and molecular homology? What is an example?
Many diverse organisms have similar gene sequences (genetic homology) and metabolic pathways (molecular homology) indicating that the genes and metabolic pathways arose early in evolutionary time in a common ancestor.
For example, in class, we compared the amino acid sequence of the p53 protein between 8 different organisms. The more recently two organisms shared a common ancestor, the more similar their gene sequences are expected to be. For example, if we compare human gene sequences to gene sequences of chimpanzees and dogs, we see more similarities between human and chimp sequences than between human and dog sequences; we shared a common ancestor more recently with chimps than with dogs, so there has been less evolutionary time for change to occur between humans and chimps compared to humans and dogs.
What are fossils? How can fossils provide evidence of evolutionary change?
Fossils are the preserved remains of deceased organisms. Comparing fossils from different ages may enable us to physically see successive changes that have taken place over evolutionary time.
Define endemic species. What are examples of endemic species we discussed?
Endemic species are only found in one location.
Example: the Channel Island fox is only found on the Channel Islands and nowhere else. The Koala is found only in Australia and nowhere else. Islands often have many endemic species that have evolved in isolation.
Define convergent evolution. What is an example of convergent evolution?
Two organisms have independently evolved to have a similar characteristic/trait because they live in a similar habitat.
Example: The giant anteater and echidna are different species that live on different continents, but they have both independently evolved to have long snouts and tongues because they both occupy a similar habitat and feed on ants
Define selective breeding. What is an example?
Humans modify/develop desirable traits in domesticated animals or plants by choosing which parents to breed together. The underlying mechanism is like natural selection, so it enables us to appreciate the process of natural selection. However, instead of nature choosing which traits are most beneficial in natural selection, humans choose which traits are most desirable in selective breeding.
For example, the many different dog breeds have come about by selective breeding.
Define vestigial structures. What is an example?
Vestigial structures are structures that have no apparent function, but resemble structures that were present in an ancestor where they served a useful purpose.
For example, humans have a tailbone even though they do not have a tail. An ancestor that humans evolved from had a tail that served a purpose. In humans, the tailbone is now a relic from our evolutionary past.
