Themes in Biology – Evolution

2008/05/07
By Lauren

Evolution is arguably the most central theme in biology because it ties all other major themes together. Evolution is defined as a change in alleles in a population over time. In each level of life, there is evidence of evolution on a population through natural selection on individuals. Darwin, credited as the founder of modern evolutionary theory, made four main points in his book that described how natural selection works:

1.Each species produces more offspring than can survive.
2.These offspring must compete with each other for limited resources required to survive.
3.Organisms in all populations vary in alleles and are different.
4.The individuals with the most favorable traits or variations are the most likely to survive and therefore produce more offspring.

Molecular

Genes are the units that help code for proteins within an organism. Evolution has seen the selection of specific genes that code for specific proteins over less desirable genes. For instance, the gene that codes for blindness in the blind cavefish is chosen over the gene for eyesight. The reason for this is that one of the two genes involved in senses of the fish must be traded for the others. In easier terms, the eyesight of the fish must be sacrificed so that the jaw and taste buds can develop. In this case, the pleitrophy gene that controls this development is slightly inhibited by another gene. The only reason the inhibiting gene is selected is because while it inhibits eyesight, the fish can rely on its other sensory organs, which proves to be successful.

Cellular

Photo by Akay

On a cellular level, eukaryotic cells are complex in comparison to prokaryotic cells. According to the endosymbiotic theory, the evolution of organelles originated from a prokaryotic cell that joined with separate prokaryotic cells. The organelles in the cell proved to be exceptionally helpful, such as the mitochondria, which supplied it with energy. The earliest mitochondrion is believed to have begun as a very primitive bacterium. With a source of internal energy, the eukaryotic cell was more favorable and through natural selection, became more frequent.

Organismal

Photo by Kaptain Kobold

The kidneys are responsible for filtering the wastes of the blood and reabsorbing nutrients during the process. Some animals have evolved to have excretory systems to compliment the environment that they live in. For instance, in dry and arid environments, many animals have an extra complex collecting duct, where the most water is reabsorbed during excretion, to maximize the amount of water conserved. Those organisms that have the systems to do this can survive longer and are favorable to the environment because of their success in retaining water, which is a necessity in their environment.

Population

Photo by Kaibara

One of the easiest examples to observe since it reproduces so quickly, bacteria helps explain genetic drift in populations. If you were to put a culture of bacteria in a nutrient rich environment, they would reproduce. But if you added an antibiotic into the environment that killed most of the bacteria, only the bacteria that had alleles that made them resistant to the antibiotic would survive. Since the bacteria that died did not have a high fitness, they were not able to continue contributing their genes to the pool. Only the surviving bacteria will be able to pass on their genes, which include resistance. This, in time, will lead to a whole generation of antibiotic resistant bacteria that has evolved from the original population to one made of resistant genes.

Community

Photo by Thomas Hawk

The predators and prey evolve together, the prey trying to stay one step ahead of the predator, and the predator trying to catch up. In the case of wolves and rabbits, wolves evolve mechanisms to help them survive by obtaining food such as speed, stealth, camouflage, and excellent sensory senses. Likewise, the prey, rabbits, develop similar mechanisms to aid in avoidance and escape of a predator. Any trait such as long legs to run or hop faster will enable the prey to escape its predator, and pass its genes to its offspring. Those that are eaten obviously were not fit to their environment and their genes, which did not help them, will not be passed on.

Biosphere

Photo by Brent Danley

The globe is made up of many different climates and geographic features, each factors of a specific biome. With in a biome, an ecosystem of organisms exists which specifically suit that particular biome. Producers within the biome have evolved features that give them high evolutionary fitness. The consumers that feed off of these producers are also well suited to their biome, as discussed in population. With the combination of all of the organisms well suited to their environment in one biome, there is an ecosystem that is specifically designed to survive there. If you were to take a kangaroo and place it in the arctic, the kangaroo would not be able to find the resources it needs to survive. The food that it lives off of, the habitat it is used to and the mates it needs to reproduce are not there. That is why each biome is made up of biotic and abiotic factors that specially suit the surrounding ecosystem.

  • http://WildlifeConservationSociety Jeri Hallberg

    I will be posting your site as most favorable for online research and interaction regarding biology and predators. Thank You!!

  • Lek2k

    Awesome post Lauren. In addition to the text, I really like your pictures. Just quick comment regarding your section on population. The example of using antibiotic resistance on bacterial populations is a case of “selection” rather than “genetic drift”. The process of genetic drift is random, while selection is not. It is not “random” that only antibiotic resistant bacteria survives after a certain amount of time. What is due to chance (i.e. genetic drift) and what has happened for a reason (i.e. selection) is the biggest challenge in studying human genetic diversity (see HapMap project).
    Anyways great post, keep up the good work !

    http://en.wikipedia.org/wiki/Genetic_drift

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