Homologous Structures and Adaptive Radiation
Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.
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Populations of a species can gradually diverge into separate species by evolution.
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Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
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We share so many detailed structures with so many other organisms, showing us how we are all so closely related. For example, limbs. We share a similar structure of a long bone, connected to two thin bones which are connected to carpals (cluster of small bones) followed by fingers or digits. Bats, dogs, humans, tigers, etc all share this similar structure. Even if we all use these limbs for completely different purposes such as flying, driving, eating, walking, we all know that we come from the same organism, and hence the same prokaryotic microorganism around 3.8 billion years ago.
So, we have a similar structure of limbs to a number of organisms but the limbs have different functions. However, a bird's wing and a bat's wing are not the same or similar homogeneously. They both do have the same function - to fly - but not the same anatomically. Another thing to notice is the number of digits - 5. We have five fingers and the number five is quite common between various species. Why is that so? Is it because the organism that had five digits ended up being the fittest and there was naturally selected to survive? This question is yet to be answered. Also, we all, living things, have DNA and RNA so our molecules are also the same. |
Darwin's finches:
He found a group of similar birds (very obviously related) across different islands and found that the difference between these birds were their beaks. Some birds preferred worms, because they came from one island, and therefore they would have a beak specialized to eat worms and pick them out. Another bird would eat bugs and therefore their beaks would be formed in order to best suit this meal. The radiation is therefore from a common ancestor from which they have each derived from. the birds migrated or were blown over to a different island and the best fit birds for that island would live whereas the others would die. Other birds would have traveled to a different island and hence adapt to that island. This created variation from one specific species - leading to adaptive radiation. |
A species is when a group of organisms can mate and produce a fertile offspring. For example, ligers. Ligers, as the name suggests, are an offspring of a male lion and a female tiger mate. However, these ligers are sterile and so they cannot make babies (so there cannot be any more generations of ligers produced by ligers themselves). This means that lions and tigers are two different species. Ligers are therefore hybrids.
As species adapt and evolve according to their environment there are examples of species which appear to be similar and may be thought be genetically linked but are in fact from very different classes. An example of this is the whale or dolphin which both appear to be similar to the shark, a large species of fish. Yet they are in fact mammals which are believed to derive from land mammals which then returned to the ocean, where they were then required to adapt to their environment, which caused them to develop similar characteristics to other sea-based animals who used these characteristics (fins, tail, long smooth body shape) to navigate and survive in their environment when they are in constant competition with other organisms, adapted for this environment. This process of adaptation that mimics characteristics of species from a different class in called convergent evolution. |
Through the process of evolution, a variety of species emerged, giving us the billions of organisms that we can see today. As all organisms derive from the same 'origin of life', as the theory of evolution states, we all share similar DNA. However, some species are genetically closer depending on their closest common ancestor.
Due to the biodiversity that exists today, there is a multi-level categorisation process for each species, which maps out its various families and origins, grouping species at different levels to other species that share similar characteristic and so are thought to be genetically linked at that point. It is a common assumption that humans are evolved from the apes or chimpanzees that exist today but this not true as the genetically similar species that exist today are in fact our cousins and are evolved from a common ancestor. This means that they are not any less evolved, rather they are simply evolved differently. There are species like old world monkeys that are genetically similar to us but are less similar than apes or chimpanzees as our common ancestor can be tracked back further than that between us and apes, illustrating that we branched off and diverged further back.
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