18: Evolution and the Origin of Species Flashcards
Understanding Evolution, Formation of New Species, Reconnection and Rates of Speciation
What is adaptation?
A heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment.
What is convergent evolution?
The process by which groups of organisms independently evolve to similar forms.
What is divergent evolution?
The process by which groups of organisms evolve in diverse directions from a common point.
What are homologous structures?
Parallel structures in diverse organisms that have a common ancestor.
What is natural selection?
The reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change.
What is variation?
Genetic differences among individuals in a population.
What is a vestigial structure?
A physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor.
Who were involved in the discovery of evolution by natural selection?
In the mid-nineteenth century, the mechanism for evolution was independently conceived of and described by two naturalists: Charles Darwin and Alfred Russel Wallace.
Where did Darwin and Wallace travel?
Each naturalist spent time exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world on the H.M.S. Beagle, including stops in South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, like Wallace’s later journeys to the Malay Archipelago, included stops at several island chains, the last being the Galapagos Islands west of Ecuador.
What adaptations did Darwin discover in finches?
On the Galapagos Islands, Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galapagos Islands comprised several species with a unique beak shape. The species on the islands had a graded series of beak sizes and shapes with very small differences between the most similar. He observed that these finches closely resembled another finch species on the mainland of South America. Darwin imagined that the island species might be species modified from one of the original mainland species. Upon further study, he realized that the varied beaks of each finch helped the birds acquire a specific type of food. For example, seed-eating finches had stronger, thicker beaks for breaking seeds, and insect-eating finches had spear-like beaks for stabbing their prey.
When was the theory of evolution by natural selection proposed?
Papers by Darwin and Wallace presenting the idea of natural selection were read together in 1858 before the Linnean Society in London.
What was the result of Darwin’s research?
Darwin’s book, published On the Origin of Species in 1859, outlining in considerable detail his arguments for evolution by natural selection.
Which scientists have presented observable evidence for the process of natural selection?
Peter and Rosemary Grant were evolutionary biologists who studied Galapagos finch populations every year since 1976, and have demonstrated the process of natural selection. They found changes from one generation to the next in the distribution of beak shapes with the medium ground finch on the Galapagos island of Daphne Major. The birds have inherited variation in the bill shape with some birds having wide deep bills and others having thinner bills. During a period in which rainfall was higher than normal because of an El Niño, the large hard seeds that large-billed birds ate were reduced in number; however there was an abundance of small soft seeds which the small-billed birds ate. Therefore, the survival and reproduction were much better in the following years for the small-billed birds. In the years following this El Niño, the Grants measured beak sizes in the population and found that the average bill size was smaller. Since bill size is an inherited trait, parents with smaller bills had more offspring and the size of bills had evolved to be smaller. As conditions improved in 1987 and larger seeds became more available, the trend toward smaller average bill size ceased.
What is the fossil evidence of evolution?
Fossils of organisms in the past show a progression of evolution. Scientists determine the age of the fossils and categorize them from all over the world to determine when the organisms lived relative to each other. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years.
What are some examples of fossil records being used to map evolutionary history?
Scientists have recovered highly detailed records showing the evolution of humans and horses. The whale flipper shares a similar morphology to appendages of birds and mammals, indicating that these species share a common ancestor.
What is the anatomical evidence of evolution?
For example, the appendages of a human, dog, bird, and whale all share the same overall construction. Though the shapes and sizes have changed over time, the overall layout has been maintained. These are called homologous structures. Some appendages have no apparent function whatsoever (vestigial structures), and can be explained as residual parts from a common ancestor.
What are some examples of vestigial structures?
Examples of vestigial structures are wings on flightless birds, leaves on some cacti, and hind leg bones in whales.
What is an example of convergent evolution?
Both the arctic fox and ptarmigan, living in arctic regions have been selected for seasonal white phenotypes during winter. This occurs because of common selection pressures.
What is the embryological evidence of evolution?
Embryo formation tends to be conserved because mutational tweaking in the embryo can have magnified consequences in the adult. As a result, structures that are absent in some groups often appear in their embryonic forms and disappear by the time the adult or juvenile form is reached. For example, all vertebrate embryos, including humans, exhibit gill slits and tails at some point in their early development. These disappear in the adults of terrestrial groups but are maintained in adult forms of aquatic groups such as fish and some amphibians. Great ape embryos, including humans, have a tail structure during their development that is lost by the time of birth.
What is the biogeographical evidence of evolution?
The geographic distribution of organisms on the planet follows patterns that are best explained by evolution in conjunction with the movement of tectonic plates over geological time. Broad groups that evolved before the breakup of the supercontinent Pangaea (about 200 million years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, such as the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of members of the plant family Proteaceae in Australia, southern Africa, and South America is best explained by their presence prior to the southern supercontinent Gondwana breaking up. The great diversification of marsupials in Australia and the absence of other mammals reflect Australia’s long isolation. Australia has an abundance of endemic species which is typical of islands whose isolation by expanses of water prevents species from migrating. The marsupials of Australia, the finches on the Galapagos, and many species on the Hawaiian Islands are all unique to their one point of origin, yet display distant relationships to ancestral species on mainlands.
What is the molecular biological evidence of evolution?
Like anatomical structures, the structures of the molecules of life reflect descent with modification. Evidence of a common ancestor for all life is reflected in the universality of DNA as the genetic material and in the near universality of the genetic code and the machinery of DNA replication and expression. Fundamental divisions in life between the three domains are reflected in major structural differences in otherwise conservative structures such as the components of ribosomes and the structures of membranes. In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences - exactly the pattern that would be expected from descent and diversification from a common ancestor. DNA sequences have also shed light on some of the mechanisms of evolution. For example, it is clear that the evolution of new functions for proteins commonly occurs after gene duplication events that allow the free modification of one copy by mutation, selection, or drift (changes in a population’s gene pool resulting from chance), while the second copy continues to produce a functional protein.
What is adaptive radiation?
Speciation when one species radiates out to form several other species.
What is allopatric speciation?
Speciation that occurs via geographic separation.
What is an allopolyploid?
Polyploidy formed between two related, but separate species. It results when two species mate to produce viable offspring. For example, a normal gamete from one species fuses with a polyploid gamete from another. Two matings are necessary to produce viable offspring.
