NATURAL SELECTION AND TYPES OF EVOLUTION

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This week we will work on Natural selection concepts and types of Evolution.

So please, print the following worksheet.

Types of Evlolution worksheet

Watch the video and take notes or write questions about what you didn´t understand

And read this nformation, take note in your notebook to get extrapoints

Types of Evolution

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Evolution over time can follow several different patterns. Factors such as environment and predation pressures can have different effects on the ways in which species exposed to them evolve. shows the three main types of evolution: divergent, convergent, and parallel evolution.

Figure%: Types of evolution; a)divergent, b)convergent, and c)parallel.

Divergent Evolution

When people hear the word "evolution," they most commonly think of divergent evolution, the evolutionary pattern in which two species gradually become increasingly different. This type of evolution often occurs when closely related species diversify to new habitats. On a large scale, divergent evolution is responsible for the creation of the current diversity of life on earth from the first living cells. On a smaller scale, it is responsible for the evolution of humans and apes from a common primate ancestor.

Convergent Evolution

Convergent evolution causes difficulties in fields of study such as comparative anatomy. Convergent evolution takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure. For example, whales and fish have some similar characteristics since both had to evolve methods of moving through the same medium: water.

Parallel Evolution

Parallel evolution occurs when two species evolve independently of each other, maintaining the same level of similarity. Parallel evolution usually occurs between unrelated species that do not occupy the same or similar niches in a given habitat.

Problems >> 

Problem : On his voyage with the Beagle, Charles Darwin carefully studied several species of finches. He found that many had come from a single species, but they had adapted to their environment by choosing different food sources and developing radically different beak designs to match their choice of food. What pattern of evolution did the finches show?

The finches showed divergent evolution. As time passed, the different species adapted to their own lifestyles and became more and more different from the other closely related species.

Problem : Many species of owls hunt only at night. These winged predators have evolved extremely sensitive hearing to help track insects and other prey. Another night hunting winged predator, the bat also has extremely sensitive hearing to track prey in the dark. What pattern of evolution does this show?

This is an example of convergent evolution. Owls (birds) and bats (mammals) are not closely related, but both have evolved similar traits (flight and good hearing) to help them fill the same role as night hunters.

Problem : Imagine two types of ancient forest animals: a goat-like grazing animal and a small ground-dwelling rodent that lives on insect prey. At the same time, these two animals leave the forest and begin living in grassy plains. The rodent evolves large powerful claws for digging burrows to hide in, while the grazer develops long legs for running from predators. What type of evolution does this show?

This is an example of parallel evolution. The two animals were fairly dissimilar to begin with. They filled different roles in the forest environment. When they moved to the plains, both animals evolved to adapt to the new environment, but they did not become any more or less similar to each other.

Problem : What difficulty does convergent evolution pose for evolutionary biologists?

The major difficulty involved with convergent evolution is the formation of analogous structures. These structures may appear similar and perform similar functions, making it seem that two species are closely related. However, analogous structures develop from different ancestral structures and do not indicate close relationships.

Coevolution 

Just as no man is an island, neither is any bird, insect, plant, or mammal. Many species live in close relationships with others, affecting each others ways of life. It seems logical to think that species that live closely with each other might evolve in adaptation to each other. This logic is extremely difficult to prove, since it requires direct proof of evolution in not one but two species. However, there is ample evidence to suggest that coevolution does take place.

Coadaptation

In order to live in symbiotic or parasitic relationship, species must be adapted to each other. For example, cattle harbor bacteria in their stomachs that help them break down plant material. To live like this, the immune system of the cattle must be adapted to not kill these useful bacteria and the bacteria themselves must be adapted to live in the harsh environment of the cow's stomach. If a population of cattle moved to a new location where radically new plant material was available, they might adapt to eating this new food source. The bacteria, in turn, might then undergo adaption of their own digestive mechanisms to the new plant material. This would be an example of coadaptation. Most biologists accept coevolution on the basis of coadaptation if there is no overwhelming evidence to the contrary.

Coevolutionary Arms Races

In parasitic relationships, the prey species often evolves mechanisms to defend itself against the parasite. However, the parasite may also evolve to evade these new mechanisms. This back-and-forth evolution of defense and offense, often called a coevolutionary arms race, can often result in a rapid burst of evolutionary change in both species.

Problems

Problem : Describe a coevolutionary arms race.

A coevolutionary arms race takes place in a predator-prey relationship when the prey evolves a new defense or the predator evolves a new offense. Each species will evolve a new trait to give them an advantage over the other. When this process occurs with several new adaptations over a short period of time, it is known as a coevolutionary arms race.

Problem : Why is coevolution difficult to prove?

Coevolution is difficult to prove because it requires direct evidence of not one but two species evolving together.

Problem : What do most biologists accept as evidence for coevolution?

Most biologists will accept coadaptation as proof of coevolution in the absence of evidence to the contrary.

Problem : What might be another explanation of coadaptation?

Coadaptation may arise from coevolution, the development of traits in two species in direct relation to each other. However, coadaptation may also occur as a result of two species developing traits independently of each other that then happen to make the species well adapted to each other.

Taken from:

SparkNotes Editors. (n.d.). SparkNote on Patterns of Evolution. Retrieved August 5, 2018, from http://www.sparknotes.com/biology/evolution/patternsofevolution/

Punctuated equilibrium Punctuated equilibrium is an important but often-misinterpreted model of how evolutionary change happens. Punctuated equilibrium does not: Suggest that Darwin's theory of evolution by natural selection is wrong. Mean that the central conclusion of evolutionary theory, that life is old and organisms share a common ancestor, no longer holds. Negate previous work on how evolution by natural selection works. Imply that evolution only happens in rapid bursts. Punctuated equilibrium predicts that a lot of evolutionary change takes place in short periods of time tied to speciation events. Here's an example of how the model works: Stasis: A population of mollusks is experiencing stasis, living, dying, and getting fossilized every few hundred thousand years. Little observable evolution seems to be occurring judging from these fossils. Isolation: A drop in sea level forms a lake and isolates a small number of mollusks from the rest of the population. Strong selection and rapid change: The small, isolated population experiences strong selection and rapid change because of the novel environment and small population size: The environment in the newly formed lake exerts new selection pressures on the isolated mollusks. Also, their small population size means that genetic drift influences their evolution. The isolated population undergoes rapid evolutionary change. This is based on the model of peripatric speciation. No preservation: No fossils representing transitional forms are preserved because of their relatively small population size, the rapid pace of change, and their isolated location. Reintroduction: Sea levels rise, reuniting the isolated mollusks with their sister lineage. Expansion and stasis: The isolated population expands into its past range. Larger population size and a stable environment make evolutionary change less likely. The formerly isolated branch of the mollusk lineage may out-compete their ancestral population, causing it to go extinct. Preservation: Larger population size and a larger range move us back to step 1: stasis with occasional fossil preservation. This process would produce the following pattern in the fossil record: Evolution appears to happen in sharp jumps associated with speciation events. We observe similar patterns in the fossil records of many organisms. For example, the fossil records of certain foraminiferans (single-celled protists with shells) are consistent with a punctuated pattern. Scanning electron micrograph of a foraminiferan Howev