Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks. [2]
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Darwin believed that the desires of animals have nothing to do with how they evolve, and that changes in an organism during its life do not affect the evolution of the species. He said that organisms, even of the same species, are all different and that those which happen to have variations that help them to survive in their environments survive and have more offspring. The offspring are born with their parents' helpful traits, and as they reproduce, individuals with that trait make up more of the population. Other indeviduals, that are not so well adapted, die off. Most elephants used to have short trunks, but some had longer trunks. When there was no food or water that they could reach with their short trunks, the ones with short trunks died off, and the ones with long trunks survived and reproduced. Eventually, all of the elephants had long trunks. Darwin also believed that evolution does not happen according to any sort of plan.
Darwin's theory has been supported by a lot of evidence. Lamarck's Theory of Inheritance of Acquired Characteristics has been disproved. This was done in two major ways. The first is by experiment. We have seen through many real examples and observations that changes that occur in an animal during life are not passed on to the animal's offspring. If a dog's ears are cropped short, its puppies are still born with long ears. If someone exercises every day, runs marathons, eats well, and is generally very healthy, the fitness is not passed on and the person's children still have to work just as hard to get that fit and healthy. These and other examples show that Lamarck's theory does not explain how life formed and became the way it is.
The other way that Lamarck's theory has been proven wrong is the study of genetics. Darwin knew that traits are passed on, but he never understood how they are passed on. During the time when Darwin's first book first came out, Gregor Mendel, who discovered genetics, was just starting his experiments. However, now we know a lot more about genetics, and we know that the only way for traits to be passed on is through genes, and that genes can not be affected by the outside world. The only thing that can be affected is which gene sets there are in a population, and this is determined by which individuals die and which ones live. This is the other way that we have learned that the fruits of an animal's efforts can not be inherited by its offspring.
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| | Jean Baptiste de Lamarck | Charles Darwin |
| Conception of species: |
Population of individuals all of the same kind (identical characteristics in all members). Individuals capable of transformation.
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Population of interbreeding individuals with similar characteristics, though variation is common among all of them at all times. Individuals fixed and unchanging. Population capable of transformation.
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| Mechanism of new species production: |
Internal drive toward greater complexity modified by the inheritance of acquired characteristics. Change directed to meet organism needs.
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Natural selection. Variation exists regardless of organism's needs not directed toward any purpose.
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| Example of this type of explanation: |
The giraffe's neck: “At some point in the past, giraffes must have found themselves in an environment where they had difficulty reaching food present on the tops of trees. In order to eat, they must have had to stretch their necks and in doing so physically elongated them some. This longer neck was passed on to the offspring in the next generation, who in turn stretched their necks even further, thus resulting in the giraffe species having very long necks."
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Keen eyesight of the hawk: “In a population of hawks, individual variation existed in the power of their vision, just as variation exists in the color of their feathers. In their competition for food, the individuals with keener eyesight could more easily spot their prey (small voles and mice) and thus were successful in securing food to eat. The hawks with poor eyesight had difficulty spotting prey and died for lack of food. The hawks with the keen eyesight passed on this trait to their offspring. The hawks that died were not able to produce any offspring. Over a number of generations, the population of hawks all came to possess extremely powerful vision."
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| Phenomena the model can account for: | • Adaptation
• Fossil record | • Adaptation
• Fossil record
• Homologous structures
• Biogeographical diversity patterns |
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