Darwinian Evolution

Evolution ► Evolution is the accumulated change in the frequencies of alleles within isolated gene pools due to the selective pressure of the environment such the population becomes unable to reproduce with any other and can be said to be a new species.

“On the Origin of Species” ► Title of Charles Darwin’s book ► Published December, 1859 ► Sold out in one day “A century and a half later, it still argues the case for evolution better than any other book. “ Edward J. Larson, Evolution

Darwin’s Case for Evolution - Artificial Selection ► An idea with which people were comfortable ► Farmers select for breeding only the animals or plants that have the traits they like  Fast horses, plants with the biggest fruit ► Named this process “artificial selection”

Darwin’s Case for Evolution Artificial Selection

Artificial Selection of Wild Mustard (Brassica oleracea)

Darwin’s Case for Evolution – Variety also exists in nature – among species

Darwin’s Case for Evolution variety -and (more importantly) variety also exists within species -Genetic Diversity

Darwin’s Case for Evolution Overproduction of Offspring In nature, many more individuals are born than can possibly survive. Thomas Malthus

Darwin’s Case for Evolution Why can’t they all survive? Limiting Factors ( factors that limit pop. size )  Predation  Food supply Competition  Shelter  Mates

Darwin’s Case for Evolution A high rate of reproduction combined with competition for food, shelter, and mates creates a struggle for existence. The fiercest struggle is among individuals of the same species, for they share the same niche, habitat, and dangers.

Darwin’s Case for Evolution “Can we doubt that individuals having an advantage, however slight, over others, would have the best chance of surviving and procreating their kind?...This preservation of favorable conditions… I call Natural Selection.” Natural Selection.”

What was Darwin Proposing? 1. Competition among species for limited resources leads to differential survival and reproduction (natural selection). 2. Organisms of different kinds descended from a common ancestor. 3. The number of different kinds of species multiplied over time. 4. Evolution occurs through gradual changes in a population.

Darwin’s Evidence Fossil Record ► Over millions of years, deposits compress older sediments below into layers More recent Older

Darwin’s Evidence Fossil Record ► embryology in extinct organisms similar to that in living organisms

Darwin’s Evidence Embryology Similarities in patterns of development among different species today suggest common ancestor: Similarities in patterns of development among different species today suggest common ancestor: Chick Chick Pig Pig Human Human

Darwin’s Evidence Morphology (the form and structure of an organism) ► Homologous structures  Similarities in morphology of different organisms suggest common (same) ancestor

Darwin’s Evidence Vestigial Structures - morphologies which no longer function

Darwin’s Evidence Morphology – Imperfect Structures: structure not perfect for function, but serves purpose Geese have up to 20 vertebrae – very flexible! Giraffe has only 7 vertebrae – NOT very flexible!

Darwin’s Evidence Geographic proximity of similar species – species on different Galapagos Islands were more similar to one another than they were to those on mainland

Remaining 19 th Century Questions Natural Selection Special Creation The complexity and perfection of structures such as the human eye indicates the work of a supernatural Designer. William Paley William Paley Natural selection results in better-adapted organs and organisms, not perfect ones. Charles Darwin Charles Darwin

► Darwin did not attempt to scientifically answer the question of life’s origin

Remaining 19 th Century Questions ► What about gaps in the fossil record?  What about “great leaps” forward? ► Is the Earth old enough for the slow process of natural selection? ► How does inheritance work? ► What causes individuals with new variations to appear?