Theory of Evolution and Evidence for Natural Selection - Essay Example

Theory of Evolution and evidence for natural selection The term “evolution” in biology refers to the process through which plants, animals and other living organisms changed over time. It is the foundation for modern biological theories. By examining layers of rock and soil which are also known as “strata”, researchers have found fossils which are evidence of plants and animals which lived long ago but are not found anywhere in the world today. By examining these fossils closely, it has been discovered that the greater the age of the fossil, the more is it different from the living beings found today. More recent is a fossil, more is the resemblance to present day plants or animals. This is perhaps the strongest evidence of evolution. Evolution occurs at different paces for different species. While it took a very long time for human beings to evolve from ape like primates into the modern Homo sapiens, for simpler organisms, evolution occurs over smaller time frames. For instance, quite a few bacteria have become resistant to anti-biotic drugs. Anti biotic drugs have been used only for the last eighty odd years and initially the bacteria could be killed by these drugs. But in recent times through evolution, the bacteria have become resistant to these anti-biotics. Evolution is caused by a process know an “natural selection” which was first coined By Charles Darwin in his famous book “On the Origin of Species” published in 1859. The idea behind natural selection is that certain features provides organisms with advantages that lead to easier survival in the environment. And this survival in turn leads to passing on of these features into future generations. A good example is that of the long neck of the Giraffe. Since longer necks allowed the ancestors of the Giraffe to access food located higher or more difficult places, those with longer necks survived better and thus the genes of the longer neck got passed on to future generations. Over time, the neck grew to the very tall stature that we observe today in the present day Giraffe. Taxonomy Taxonomy is the scientific classification of all living species. The classification is based upon a system of rankings. The primary unit in the process of classification in the domain of all living things is the “kingdom”. There are 5 possible kingdoms and all living things belong to any one of these with the notable exception of some symbionts like lichen which belong to two kingdoms. These are as follows: 1. Monera/Prokaryotes: simplest living organisms such as archaea and bacteria 2. Protista/Eukaryotes: unicellar organisms, i.e., living organisms with only one cell. 3. Fungi: moulds, mushrooms etc belong to this class. 4. Plantae: all plant life belongs to this kingdom, so instances are trees, grass, moss etc. 5. Animalia: is the kingdom of all animals which includes humans. The second rank in the taxonomy belongs to the Phyllum. So, the members of a certain kingdom are classified into different Phylla (plural form of Phyllum). Each Phyllum in turn is split into classes, and these classes are further divided into orders. For example, meat eating animals, known as “carnivora” are an order. These orders are further classified into families. The cat family, dog family etc are instances of families that belong to the “carnivore” order. Closely related members of each family are clubbed together under a “Genus” and the members of each genus which mate naturally are termed a “species”. There are many species in the world. For instance the crow and the raven, although similar are different species. But they belong to the same genus. These and other genus such as the magpie constitutes the crow family. The crow family along with other families such as the thrush family, swallow family are members of the order of “songbirds”. Songbirds belong to the class of “birds” and these are the members of the phylum “vertebrate”, and vertebrates belong to the kingdom “Animalia”, or the Animal Kingdom. Population Dynamics Population dynamics is the study of short term and long term variations in sizes, age compositions and other characteristics of populations over time. The factors that influence such changes are also of interest to population dynamics. Birth rates, death rates, immigration and emigration are the main natural and fundamental features of populations that determine the changes of the populations over time. While birth rates and emigration determine the addition to current population, death rates and immigration lead to outflows or reductions. Additionally, the relationship of death rates to age is also important since it determines the age composition. However, exogenous factors, i.e., factors that are external to the population also play important roles. For instance, in case of a population of fish, human predation adds to the death rates. At what age the species are considered mature enough to be fished out plays an important role in deciding the age composition of the current population. Similarly, the rate of extraction of the fish along with the factors mentioned above also determines the growth/decline of the population. A standard model of growth for a population is the exponential growth model. The idea is that the natural rate of change of a population is proportional to the already existing population. Therefore, if the numbers of a population are falling, the exponential model predicts that the rate of growth of the model will slow down and then eventually start declining if unchecked. Ecosystem An Ecosystem is made up of interacting living and non-living elements in a given area. Light, air, rocks, soil and water are the most typical non-living elements that belong to an ecosystem. The organisms living together in an ecosystem form what is known as a “Community”. Every ecosystem is characterized by the presence of its own community. Each community is populated by different species and the total numbers of each species are referred to as its population. For instance, a desert community can have cacti, scorpions and side-winder snakes as populations of the community, a forest community can be populated by a variety of trees, some plant eating animals like rabbits and some flesh eating animals like foxes and wolves. The members of the community of the ecosystem share what is known as a “symbiotic” relationship. Each depends upon the other member for survival. There are primarily three types of members in a community: producers, consumers and decomposers. The producers are typically plant like forms that produce their own food. Consumers are the members that either survives by eating producers, or other consumers, or both. Finally, decomposers are typically the organisms that decompose the dead bodies of the consumers so that these then become the source of the elements required for production of food for the producers. This cyclical pattern of food sources is known as the food-chain. The members of the community or ecosystem by performing their own duties ensure the survival of the other members. There is a required balance or stability of each population and this is maintained through the food chain. Biomes and biological communities Biomes are essentially major ecosystems spread over a moderately large geographical area. Similar climatic and geographic conditions are present and as a result, similar plant and animal communities as well as similar soil organisms are present over the large area. Typically, differences in plant structures or type of leafs spacing of plants and the climate are the features that set one Biome apart from another. One important classification of Biome is in accordance to whether the Biomes are based on a land mass (these are known as Terrestrial Biomes) or whether the Biomes are aquatic (Freshwater or Marine Biome). Some commonly known Biomes are temperate grassland biomes which are present in Central Asia, North America as well as South America. These are referred to as steppe, praire and pampas in the local dialects. Similarly, a tropical grassland biome is called veld in Southern Africa and Savanna in Australia. Climate plays a critical role in deciding the geographical distribution of land based biomes. Latitude, humidity, Elevation etc are all important factors in the development of the features of Biomes. As a result, one most typical classification of biomes is according to latitude or humidity. Greater diversity is found away from the poles towards the equator. Biological communities are essentially akin to the communities discussed in the context of ecologies. These are communities that populate the biomes. However, these can be different in terms of size and one large biological community may contain smaller biological communities. Interactions among species within such communities are best observed in terms of food-source relationships. Thus, a convenient way of distinguishing between such communities is to track the food-chain or network. There will be evident boundaries between these communities where least amount of consumption links will be found relative to number of species within the networks. Photosynthesis The process of making food by plants and some other organisms is known as photosynthesis. In this process energy of light is used to transform carbon dioxide into glucose and some other organic compounds. Oxygen is the bi-product of the process. Apart from plants, certain types of bacteria and protists also use this process and make their own food. The total transformation has two distinct parts – one is the reaction that is dependent upon light, and the other is the reaction that does not use light. The light dependent part of the process primarily uses energy of light to split water into hydrogen, oxygen and electrons. The hydrogen then becomes NADPH and ATP is extracted from ADP and inorganic Phosphate which are then utilized in the light independent reaction. The plants diffuse oxygen during this process. The light dependent reaction occurs in the “grana” of chloroplasts. During the light independent reaction the NADPH and ATP are used along with Carbon dioxide to synthesize glucose. This occurs in the stroma of the chloroplasts. The glucose is then spread across all cells in the plant as food. Thus in the process of photosynthesis, carbon dioxide and water in the presence of light energy and chlorophyll is transformed into glucose and oxygen. The oxygen is then diffused out of the plant. Intensity of light, concentration of carbon dioxide and not too less or too much of heat are essential for the process of photosynthesis. If there is not enough light or if the concentration of carbon dioxide is not adequate, then enough glucose will not be produced. Thus these are critical for the process. Cellular Respiration The process which all life forms use to transform glucose into energy is known as cellular respiration. Essentially, food is transformed into ATP, which is what cells derive energy from. Although respiration in most life forms happens in the presence of oxygen (known as aerobic respiration) there are some simpler organisms which do not use oxygen (anaerobic). In aerobic respiration, glucose and oxygen are transformed into carbon dioxide, water and ATP. The process involves four distinct stages. The first stage is known as Glycolysis. In this stage glucose is broken into two pyruvate molecules. The energy required for the process is derived from two ATP. In the second stage, which is known as the “link reaction”, the pyruvate from the first stage is transferred into mitochondria from which then an enzyme known as acetyl CoA is formed. The third stage is called the “Krebs cycle” a continuously repeating process which uses the acetyl CoA and generates ATP and carbon dioxide at each turn of the cycle. Apart from the main functions, some hydrogen molecules are removed from the compounds in stages two and three and these are put to use in the fourth stage known as the electron transport chain (ETC). The majority of the ATP generated in respiration is synthesized in this stage. All molecules of hydrogen removed before are pumped into mitochondria using electron released energy. This continues until the electrons that power this process mingle with some of the hydrogen and oxygen and transforms into water thereby stopping the hydrogen pumping process. The residual hydrogen then flows back to the cytoplasm section of mitochondria using protein channels. This process of hydrogen flows leads to creation of ATP from ADP and ions of phosphate. Read More