Watch this video on how evolution works:
Our working definition for evolution is "Genetic change over time". Darwin explained how this change occurred with Natural Selection. What are the 3 conditions that must be present in a population for natural selection to occur? What is the result of natural selection?
reply 75 words of each
Three conditions that must be present in a population for natural selection are:
Struggle to survive: Natural Selections occurs through interactions between individual organisms and the environment, individuals do not evolve. Rather, it is the population - the group of organisms - that evolves over time as adaptive traits become more common in the group and other traits change or disappear. There's several barriers that contributes to the struggle to survive, not enough food, not enough space to live, predators, and disease.
Genetic Variation: Natural Selection can amplify or diminish only heritable traits. Certainly, an organism may become modified through its own interactions with the environment during its lifetime, and those acquired characteristics may help the organism survive. But unless coded for in the genes of an organism's gametes, such acquired characteristics cannot be passed on to offspring. For example a bird with a large beak may have the advantage to get for food and then most likely would be able to produce more.
Difference in Fitness: Evolution is not goal directed; it does not lead to perfectly adapted organisms. Fitness means the ability to have offspring. If you have one child and someone else has 5 children; they have a higher "fitness" than the individual with only one child.
The result is Adaptation: Those with traits best suited to the environment survive and reproduce most successfully, passing those adaptive traits to offspring. The big beak, the little beak, whatever it is that allowed them to have higher fitness. We are going to see that trait in their offspring and that is an adaptation. Something that makes them more suited to their environment. (Lecture 11) (Biology: Concepts and Connections)
The three components required for natural selection to occur include the struggle to survive, genetic variation, and difference in fitness.
The struggle to survive, for example, might include an insubstantial amount of food to nourish all the organisms, predators, climate, etc. In Darwin's study of finches, some birds ate insects and some were able to crack nuts.
Genetic variation refers to the unique qualities of each offspring. In the finches, birds with longer, pointier beaks had easier access to insects, and birds with bigger, stronger beaks could access the nourishment inside of nut and seed shells. The ease in which they could feed themselves combined with limited food resources means that the finches better adapted to their environment had a higher chance of survival.
Finally, the difference in fitness refers to who of a species is best able to reproduce. If one bird lays two eggs and another lays six, for example, the bird with six eggs has a greater probability of offspring survival.
The result of natural selection is adaption. As referenced in the youtube video linked to this lecture, there are now four different species of finches inhabiting the Galapagos islands, all of which originated from one species. Because of the vast differences in these four types of finches, the different species cannot reproduce with one another despite their shared origins.
|Due By (Pacific Time)
||03/06/2015 10:00 pm