22.2 Descent with 22.2 Descent with modificationmodification

Evolution through natural Evolution through natural selection selection

It was Darwin’s It was Darwin’s research that was the research that was the catalyst that would catalyst that would change the way in change the way in which we understand which we understand evolution. evolution. All life is interconnected All life is interconnected in some way. It is in some way. It is through observing both through observing both the unity and diversity the unity and diversity of life that we begin to of life that we begin to understand how Darwin understand how Darwin arrived at his arrived at his conclusions.conclusions.

Unity and Diversity of Unity and Diversity of life?life?

The HMS BeagleThe HMS Beagleand Darwin’s Voyageand Darwin’s Voyage

Darwin considered much Darwin considered much about geology in his travels. about geology in his travels. He was well read on Lyell’s He was well read on Lyell’s works on geology and works on geology and understood the mechanics understood the mechanics by which geologic by which geologic processes worked.processes worked.

He noticed that along his He noticed that along his travels around Chile, he travels around Chile, he noticed that after a violent noticed that after a violent earthquake, several small earthquake, several small crags were jetting out of the crags were jetting out of the water a few feet in the air. water a few feet in the air. The crags contained fossils The crags contained fossils of sea life in them.of sea life in them.

He also made this same He also made this same observation in the Andes observation in the Andes mountains, where he found mountains, where he found the same phenomena of sea the same phenomena of sea shells on tops of mountains. shells on tops of mountains. He concluded that these He concluded that these mountains were created by mountains were created by the same types of the same types of earthquakes, which earthquakes, which reinforced the idea that the reinforced the idea that the Earth was more than just a Earth was more than just a couple thousand years old.couple thousand years old.

continued...continued...Another important Another important thing Darwin noticed thing Darwin noticed was in the Galapagos was in the Galapagos islands. islands.

A large and diverse A large and diverse population of population of organisms that had organisms that had some similar features some similar features of a mainland South of a mainland South American bird were American bird were unique and only found unique and only found on those islands.on those islands.

Darwin’s Focus on Darwin’s Focus on AdaptationsAdaptations

Adaptations are Adaptations are inherited inherited characteristics that characteristics that helps an organism helps an organism enhance its chances enhance its chances of survival and of survival and reproduction.reproduction.

Natural Selection in the Natural Selection in the finch populationsfinch populations

Natural selection is a Natural selection is a process by which process by which individual that have a individual that have a certain trait tend to certain trait tend to survive and survive and reproduce at higher reproduce at higher rates than other rates than other individuals individuals because because ofof those traits. those traits.

Darwin still felt he did Darwin still felt he did not have enough not have enough evidence and did not evidence and did not publish his work right publish his work right away.away.

Wallace and his theory on Wallace and his theory on natural selectionnatural selection

Alfred Russel Wallace, a Alfred Russel Wallace, a British naturalist sent a British naturalist sent a paper to Darwin in 1858 paper to Darwin in 1858 that outlined, nearly that outlined, nearly identically, all of the identically, all of the points and conclusions points and conclusions drawn by Darwin, asking drawn by Darwin, asking him if it were worthy of him if it were worthy of being published.being published.Soon after, Darwin quickly Soon after, Darwin quickly finished his book, finished his book, On the On the Origin of Species By Origin of Species By Means of Natural Means of Natural Selection.Selection.

Although Wallace Although Wallace published first the credit published first the credit still remains Darwin’s.still remains Darwin’s.

On the Origin of SpeciesOn the Origin of Species

Evolution was not used Evolution was not used in the book’s first in the book’s first edition. The words edition. The words “Descent with “Descent with modification” were modification” were used instead.used instead.

It was explained that all It was explained that all organisms that share organisms that share common traits must have common traits must have some form of common some form of common ancestor that through ancestor that through migration to various migration to various places, accumulated places, accumulated modifications, or modifications, or adaptations that fit them adaptations that fit them to a certain way of life.to a certain way of life.

Darwin the concluded Darwin the concluded that descent with that descent with modification led to a rich modification led to a rich diversity of life.diversity of life.

Artificial Selection, Natural Artificial Selection, Natural Selection, and AdaptationSelection, and Adaptation

Artificial SelectionArtificial SelectionAlso called selective Also called selective breeding, this has breeding, this has allowed for desirable allowed for desirable (chosen) characteristics (chosen) characteristics and even animals to and even animals to survive over long survive over long periods of time.periods of time.Processes like artificial Processes like artificial selection often lead to selection often lead to organisms that are next organisms that are next to nothing like their to nothing like their ancestors.ancestors.

Natural SelectionNatural SelectionIndividual that have a Individual that have a certain trait tend to certain trait tend to survive and reproduce at survive and reproduce at higher rates than other higher rates than other individuals individuals because ofbecause of those traits.those traits.

Darwin concluded that Darwin concluded that processes like artificial processes like artificial selection mirror those of selection mirror those of natural selection, only by natural selection, only by different means of different means of selection.selection.

Darwin’s Observations and Darwin’s Observations and Inferences about Natural Inferences about Natural

selectionselectionObservationsObservations

Members of Members of populations often vary populations often vary in inherited traits.in inherited traits.

All species can produce All species can produce more offspring than more offspring than their environment can their environment can support, and many of support, and many of these offspring fail to these offspring fail to survive and reproduce.survive and reproduce.

InferencesInferencesIndividuals whose Individuals whose inherited traits give them inherited traits give them a higher probability of a higher probability of surviving and reproducing surviving and reproducing tend to leave more tend to leave more offspring.offspring.

The unequal ability of The unequal ability of individuals to survive and individuals to survive and reproduce will lead to the reproduce will lead to the accumulation of favorable accumulation of favorable traits in the population traits in the population over generations.over generations.