Patterns of Evolution

Ever wondered why birds and mosquitoes both have wings, even if they aren’t related? The answer lies in today’s lesson. Today we’re going to learn about convergent and divergent evolution.

Convergent evolution occurs when two or more unrelated species evolve to develop similar adaptations as a result of being subject to similar selection pressures (factors which may reduce reproductive success).

Selection pressures are environmental factors which may reduce reproductive success in a population. Examples of selection pressures include: Disease Parasitism Pollutants Competition predation

Convergent evolution results in analogous structures with different origins but have evolved to appear similar or have similar functions.

Examples of convergent evolution are the wings of birds, dolphins and sharks, and many species of alpine plants.

Divergent evolution, however, occurs when two or more species arises from a common ancestor due to different ecological niches, usually by allopatric speciation. RECAP: Allopatric speciation is the process where new species are formed from one common ancestor while in different geographical areas.

Different selection pressures in the different environments results in the two populations diverging. Different phenotypes get selected for to meet the demands of the different environments, resulting in the production of two new species. RECAP: Phenotype is an organism’s observable traits.

Divergent evolution Take notes

Divergent evolution produces homologous structure Divergent evolution produces homologous structure. These are anatomical structures that have the same origins but have evolved different functions. For example, the forelimb bones of crocodiles, birds, humans, whales, bats and all other vertebrates are the same and are arranged in a similar pattern, but the limbs perform different functions in each animal.

Homologous structures show us that evolution works primarily by modifying pre-existing structures.

Adaptive radiation is a type of divergent evolution Adaptive radiation is a type of divergent evolution. It is a process in which organisms change rapidly from an ancestral species into an abundance of new forms.

Using examples, discuss the selection pressures that result in divergent and convergent evolution. Include in your discussion definitions for, and examples of, homologous and analogous structures.

Parallel evolution and Co-Evolution There are two more patterns of evolution that you need to know about. Along with divergent and convergent evolution, you need to know about parallel evolution and co-evolution.

Co-evolution is where two species influence each others evolution Co-evolution is where two species influence each others evolution. This is because each species exerts a selective pressure on the other species. Both of these species has a close ecological relationship. Some examples of this include predator-prey relationships, as well as plant and pollinator relationships.

In other words, when organisms that are ecologically intimate, influence each other’s evolution, we say that co-evolution is occurring. Predators and prey, hosts and parasites are examples of ecologically intimate organisms.

So for example, an evolutionary change in the biology of a plant, might affect the biology of a herbivore that eats the plant, which in turn might affect the evolution of the plant, which might affect the evolution of the herbivore…and so on.

Us humans are an excellent example of co-evolution Us humans are an excellent example of co-evolution. We often selfishly benefit ourselves, while changing other species. For example, the giant panda bears found in Asia, are becoming more and more endangered. This is largely due to the immense population China has. Losing that species then affects many other species.

In situations such as predator/prey, host/parasite, the fitness of one organism directly impacts the fitness of the other. For example, the increase in the speed of the gazelle will make it more difficult for the lion to feed itself (a decrease in fitness), while the same increase in speed provides an obvious increase in fitness for the prey.

The organisms are therefore exerting a selection pressure on one another: faster gazelles create a selection pressure for a faster or smarter lions, which in turn selects for even greater prey speed.

Watch Co-evolution Take notes

Parallel evolution occurs when species share a common ancestor (but not related) and evolve in similar ways independent of other species.

Parallel evolution happens because the two different species, though they don’t necessarily share a common ancestor, experience similar kinds of environmental pressures and survive only by undergoing similar adaptations.

There is no clear-cut distinction between parallel and convergent evolution, since the degree of relatedness between evolutionary starting points may vary from very close, to very distant. The closer the evolutionary starting points, the more convergent evolution merges with parallel evolution.

A good example of parallel evolution is elephants and extinct mammoths A good example of parallel evolution is elephants and extinct mammoths. Both animals are closely related but their similarities evolved independently.

Tasks Draw the table comparing the different types of evolution (off the board). Explain the difference between parallel evolution and convergent evolution. Use your textbook to use NZ plants and animals as an example. Work through Patterns of evolution worksheet. Continue for homework.