15-3 Darwin Presents His Case

Variation and Artificial Selection Variation – an appearance of an inherited trait that makes them different from others. He than learned about heredity and a little about how it is passed from parents to offspring. Darwin idea about variation began to matter more so and introduced the process of Artificial Selection. Artificial selection is where nature provides the variation and humans select those variation that they found useful. It has produced many diverse domestic animals and crop plants.

Evolution by natural selection Struggle for existence: members of each species compete regularly for food, living space and other necessities. In this struggle those organisms that are faster, fitter or have a particular characteristically advantage tend to catch more prey, survive and reproduce. Fitness: the ability of an individual to survive and reproduce in its specific environment. Adaptation: any inherited characteristic that increases an organisms chance in survival.

Survival of the fittest Individuals that are best suited to their environment, with adaptations that enable fitness, survive and reproduce most successfully. Adaptive Advantage – is a favorable trait gives the organism an advantage in survival.

Decent with modifications Every living species has descended, with changes, from other species over time. It also means that all living organisms are related to one another. During long periods of time, natural selection produces organisms that have different structures, establish different niches, and as a result animals look different today than their ancestors

Homologous Body Structures A. Homologous – structures that have different mature forms but develop from the same clumps of cells in embryos. This shows that all 4 limbed vertebrates have descended, with modifications, from common ancestors. B. Example – forelimbs The forelimbs look strikingly different and vary greatly in function, they are very similar in skeletal structure and they derive from the same structures in the embryo.

D. Example – wings on birds and insects C. Analogous – features have similar appearance and function, but different embryological origin. D. Example – wings on birds and insects Same purpose = flight, but are different in structure and embryo development. 2. Vestigial Structures A. Many organisms have features that serve no useful function B. Examples: 1. Humans have a tailbone 2. Human appendix 3. Nictictating eye membrane 4.

C. Vestigial features were useful to ancestors, but not to modern organism. D. An organism with a vestigial feature probably shares common ancestry with an organism that has a functional version of the same feature.

3. Similarities in Embryology A. Similarities in early embryonic stages of vertebrates are evidence that vertebrates share a common ancestry. B. In no stage of development does a gorilla look like an adult fish. But in early stages all vertebrates are similar, fading as development continues.

Who’s who? Choices: human chicken tortoise dog

Did you get any correct?

4. Similarities in Macromolecules A 4. Similarities in Macromolecules A. Darwin hypothesized that more-similar forms of organisms have a more recent common ancestor than do less-similar forms B. Amino acid sequence in human and gorilla hemoglobin differ by one amino acid 1. Human and frogs differ by 67 amino acids 5. Patterns of evolution A. Coevolution – change of two or more species in close association with each other 1. Predators and prey sometimes co--evolve. 2. Plants and animals can co-evolve.

Hawk moth feeding on the orchid

Analogous structures are associated with convergent evolution B. Convergent evolution – sometimes organisms that appear to be very similar, such as a shark and a porpoise( similar to a dolphin) are not closely related. This occurs when 2 organisms independently evolve similar traits as a result of having to adapt to similar environments. Analogous structures are associated with convergent evolution

Shark, porpoise and dolphin all show convergent evolution

The wings of three vertebrates (bats, birds, pterodactyl) show convergent evolution. Their outer forms are similar, even though they are based on different bone arrangements and use different surface structures.

1. It’s a response to differing habitats and can result in new species C. Divergent evolution – two or more related populations or species become more and more dissimilar 1. It’s a response to differing habitats and can result in new species 1a. Adaptive radiation – Organisms diverged in response to what is available to them in their habitats. 1b. Artificial Selection – Selective characteristics are sped up by artificial methods performed by humans. Dog breeding. This speeds up the process of Divergent.