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Theory of Evolution (Gradually, Species Change (It is the gradual…
Theory of Evolution
Gradually, Species Change
It is the gradual accumulation of many adaptations that, over many generations within one lineage of organisms, results in a new species. These adaptations occur through genetic change.
Through chance variation, overproduction of offspring, and differential survival and reproduction, the proportion of individuals with a favorable trait (or favorable phenotype) will increase.
Changes accumulate and a new species is formed.
Darwin's Theory of Evolution
From his observations of animal breeding, he recognized that, even within species, individuals showed variation in traits and that the variations could be passed to offspring.
Darwin defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved,"
Everyone is Different
Scientists learned that mutations in DNA can change genes and produce variations in traits.
He expressed considerable concern that his own health problems might be heritable, especially when his beloved daughter Annie grew ill and died.
Survival of the Fittest
Darwin reasoned that death was not random. Offspring which, by chance, had variations which “fit” or adapted them to their environment would have a greater chance to survive to maturity and a greater chance to reproduce.
"Differential survival and reproduction" is a cornerstone of natural selection.
Adaptations
Adaptations are logical because the environment imposes limits on organisms, selecting against those who are not “fit.” Adaptations arise through gradual accumulation of chance variations, so they cannot be predicted, despite the fact that they appear to be goal-directed or intentional.
Adaptations relate to every aspect of life: food, water, oxygen, nutrients, shelter, growth, response, reproduction, movement, behavior, and ability to learn. Adaptations connect organisms to the resources in their environments.
Overproduction of Offspring
Malthus argued that human populations grow exponentially if unchecked, but that disease, starvation, or war will limit population growth eventually.
Natural Selection vs. Inheritance of Acquired Characteristics
Heritable variation: The change in the size of giraffe's necks.
Overproduction of offspring: Giraffes had a lot of babies that they could not support.
Differential survival and reproduction: Giraffes with long necks were more likely to survive than those with short necks.
Species change: The next generation of giraffes had long necks because they were more likely to survive.
The Present Arises From The Past
Darwin studied the life found across continents and saw, in addition to tremendous variation, that species had changed in response to the changes in their environment, over that vast amount of time.
Descent with Modification
Darwin delighted in the great diversity of life, but also saw unity within that diversity. He saw striking patterns in the similarities and differences.