Descent With Modification: A Darwinian View of Life

Warm-Up 8/24/2016 Explain the process of natural selection. Identify one example of evolution that you are familiar with.

What Evolution Is Descent with modification Change in genetic frequencies over time Change with inheritance “descent with modification”: phrase coined by Charles Darwin to describe evolution of life forms Change in gene frequences is key—if genes don’t change, traits don’t change and species don’t evolve Changes must be inherited From http://evolution.berkeley.edu/evosite/evo101/IIntro.shtml

What’s a theory? In your own words, describe the concept of a theory. Give another example of a theory in science?

History of Evolution Aristotle (384-322 BC) Scala naturae- life forms can be arranged on a scale of increasing complexity. Life was fixed, perfect, and permanent   Natural theology (1700s) Perfect species were individually designed by God. Linnaeus (1707-1778) Taxonomy: grouping and naming of organisms that are similar; binomial nomenclature Nested, not linear

What Lamarck proposed 1744-1829 The environment gives rise to changes in animals Use and Disuse theory: animals could adapt to their environment Jean Baptiste-Lamarck, early evolutionary biologist was one of the first scientists to propose that evolution was an organic process He proposed two major concepts about evolution: “The first was that the environment gives rise to changes in animals. He cited examples of blindness in moles, the presence of teeth in mammals and the absence of teeth in birds as evidence of this principle. The second principle was that life was structured in an orderly manner and that many different parts of all bodies make it possible for the organic movements of animals” (from wikipedia) He also thought organisms could adapt to their environments. --Use and Disuse theory of characteristics --inheritance of acquired characteristics

Inheritance of Acquired Characteristics Modifications acquired during an organism’s lifetime could be passed on to their offspring. Lamarck proposed that organisms could pass along traits they had acquired during their lifetimes Not so, said many scientists, since these traits were not inherited Now with the field of epigenetics, researchers are revisiting Lamarck’s ideas See: http://hpathy.com/homeopathy-scientific-research/miasms-a-new-look-through-epigenetics-i/ People exposed to famine during WWII passed along characteristics they acquired as a result of poor nutrition…you are what your ancestors ate!

Charles Darwin Darwin grew up in a wealthy family Was the son of a doctor Went to medical school at 16; withdrew after viewing his first surgery Had varied interests—liked to hunt, fish, be outside; also active in church life Went to divinity school when med school plans failed; earned a degree in divinity Was offered ship naturalist position on the Beagle by the British government Father did not want Charles to go on the Beagle, thought it would be a disgrace

Where Darwin Went He was gone for 5 years! Darwin traveled for 5 years around the world, surveying all the flora and fauna of the areas he visited Collected thousands of specimens, took hundreds of notebooks’ worth of data back to England for further examination He was gone for 5 years!

What Darwin saw Noticed that there were unique animals found nowhere else Also noticed finches had different beaks, lived on different islands, different parts of same islands Noted this correlated to food availability

Development of Theory of Natural Selection Darwin noticed that the beaks were different Food availability on the islands varied He surmised there must be different variants in the population Those with the favorable trait were able to eat the food their beak was best suited for They then became more numerous Those birds whose beaks were not suited to available food sources must have migrated to other parts of the islands Darwin observed 12 different species of finches collected from Galapagos islands Beaks were different...why?

“An Essay on the Principle Thomas Malthus “An Essay on the Principle of Population” Malthus was a minister, social scientist who wrote an essay called “An Essay on the Principle of Population” Wrote about checks on the population: famine, war, disease “Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will shew the immensity of the first power in comparison of the second.” Basically says, population size outpaces abundance of resources—there are not enough resources to sustain the population so all must struggle Also stated that humans overproduce offspring and then cannot support them Darwin borrowed these ideas and applied them to other living things, since nature presented a struggle for survival as well.

Descent with Modification Darwin’s famous “Tree of Life” sketch from his notebooks Proposed that there were common ancestors for living things Current forms were descended from ancient forms, and that ancient forms had to have experienced extinction Proposed that this change that occurred took place over long periods of time; gradual changes added up to more significant ones Darwin’s famous “Tree of Life” sketch from his notebooks Proposed that there were common ancestors for living things Current forms were descended from ancient forms, and that ancient forms had to have experienced extinction Proposed that this change that occurred took place over long periods of time; gradual changes added up to more significant ones All life has a common ancestor

Observation #1 Variation exists among members of a species. Genetic variety exists within a species Members of a species exhibit continuous variation in traits: eye color, skin color, hair color, etc., etc. so many variants exist in the same population Variation exists among members of a species.

Observation #2 This variation is inherited. Offspring inherit the characteristics their parents have Genetic variety is passed on by sexually reproducing organisms This variation is inherited.

Observation #3 Because there are limited resources in the environment organisms must struggle for survival Competition is key—competition for food, mates, space. There are limited resources in the environment. There is a struggle for survival.

Observation #4 Those organisms with traits that are favorable/suitable for the environment where they live will reproduce more frequently than those whose traits are unfavorable/unsuitable Overall fitness of population increases It doesn’t matter if YOU can reproduce; it matters if your OFFSPRING reproduce Organisms with favorable traits are more fit, thus they leave behind more offspring than those who are less fit.

Observation #5 Favorable traits increase in the population as a whole because organisms possessing those traits are suited to the environment This increases the frequency of favorable traits in the population; this does not mean that unfavorable traits get completely bred out, however These favorable traits persist in the population and will become more frequent.

Result: Differential reproductive success leads to change in favorable traits among generations Differential reproductive success = each organism’s capacity to reproduce varies based on traits it possesses that make it suited/not suited to its environment This then leads to changes in trait frequency --> changes in gene frequency --> evolution of the population

+ In sum… Genetic Variety Environmental factors Natural Selection It is the interaction of genetic variation and environmental factors that drives the process of natural selection! This change is gradual and takes place over many, many generations Natural Selection