Evolution

How did charles darwin explain evolution

natural selection

what did darwin study

finches on the galapagos islands and observed that different beak shapes were adapted to the food sources found on different islands

Darwins theory of natural selection

-variation; different traits exist in a population

-enviornmental pressure

-organisms with beneficial traits are more likely to survive and reproduce

-populations evolve over time

conditions for natural selection

-variation exists within a population (random mutations introduce new genetic variations)

-variations must be heritable (traits can be passed to offspring)

-selection pressure is present (some traits provide an advantage)

-organisms with beneficial traits have higher fitness and are more likely to survive and reproduce successfully (survival of the fittest)

what are adaptations?

inherited traits that increase an organisms ability to survive and reproduce in an enviornment

evidence for evolution: comparative embryology

-how do embryos compare in early development

-ex: human embryos briefly develop pharyngeal arches, structures similar to those that develop into gills in fish

evidence for evolution: homologous structures

-structures with similar anatomy inherited from a common ancestor, even if they serve different functions

-ex: (cat, bat, human, and whale) organisms share a similar bone structure, but the appendadges different functions

-divergent evolution

evidence for evolution: analogous structures

-structures with similar functions, but different underlying anatomy

-ex: shark fins and dolphin flippers analogous appendages that evolved independently in different ancestors

similar enviornmental pressures favored streamlined bodies and efficient swimming in both organisms

-shark fins are supported by cartilage, while dolphin flippers contain bones similar to other mammals

-convergent evolution

evidence for evolution: vestigial structures

-structures that have reduced or no function, but were inherited from ancestors

-provides evidence of change over time

-ex: whales contain small pelvic/leg bones inherited from land dwelling ancestors

these structures are remnants of hind limbs that are no longer used for walking

evidence for evolution: fossils

-ex: a archaeopteryx is a traditional fossil between dinosaurs and birds

it had both reptile-like and bird-like traits

-provides evidence that species evolve over time

fossil record over geological time

-fossils appear in a predictable order within rock layers

-order fossils are generally found in deeper rock layers, while newer fossils are found closer to the surface

-the fossil record shows that organisms have evolved over time

-new species appear while other become extinct throughout earth’s history

evidence for evolution: molecular biology

-molecular evidence is among the strongest evidence for evolution

-organisms with more similar DNA and protein sequences are more closely related

-differences in DNA and amino acid sequences accumulate over evolutionary time

-species with fewer molecular differences likely share a more recent common ancestor

what are selection patterns?

describe how natural selection acts on traits within a population, leading to different evolutionary outcomes

what is directional selection?

one extreme phenotype is favored, causing the population to shift over time

ex: peppered moths

what is stabilizing selection?

intermediate phenotypes are favored, while extreme phenotypes are selected against

ex: human infant birth weight

what is disruptive selection?

extreme phenotypes are favored, while intermediate phenotypes are selected against

ex: light- and dark-colored beach mice

what is divergent evolution?

related organisms become increasingly different as they adapt to different enviornments

what is convergent evolution?

unrelated organisms independtly evolve similar adaptaions in response to similar enviornmental pressures