Chapter 22- Darwin and Natural Selection

Where did Darwin journey to and what did he observe?

• adaptation to the environment related to the origin of new species

• though many species have difference to each other and the fossil record, there is also striking relatedness

• all organisms must somehow be related by a common ancestor; he drew something like a family tree or the first phylogeny

For evolution to happen there must be a hereditary component 

Darwin (with Alfred Russell Wallace) proposed that natural selection is the mechanism behind the evolution of species in nature (versus artificial selection caused by humans or other types of evolution).

The traits of some organisms (derived from alleles) make them better suited to their environment, more able to survive and reproduce than other organisms and pass on their genetic material to the next generation.

Understand the findings of Peter and Rosemary Grant’s research on Galapagos finches and how they support the occurrence of natural selection. 

13 different species with different beak characteristics

What occurred on the island from 1976-1978 and what resulted in the finch populations?  

year 1 (1976) 

• measured beak depth 

• 137 mm of rain fell ()

• 1 m2 of lava on the islands has over 10 grams of seeds. 

year 2 (1977)

• rain at the beginning of the year 

• the entire year was 24 mm of rain fell (drought)

• 6 grams of seeds per m2 

  • in the drought plants reserved energy and stopped creating seeds

• no new finches hatched

year 3 (1978)

• 3 grams of seed per m2 

• birds affected because they are feeding on seeds and if seeds are not produced because plants don't have water they don't create seeds

• one day of rain in january (50 mm of rain fell)

• only finch born in year 1 survived until year 3 

• the average beak depth increased to 10mm 

• beak shape: structure fits function

years later: 

• 1359 mm of resin fell 

• finch population increase by 400% 

• el niño year 1986 (brings rain)

• la niña year (brings little to no rain)

finch food: seeds 

• they choose the less difficult seed to eat. 

• birds are able to recognize that they can not eat all of the seeds because of the size of their beaks

What was the natural pressure, what happened to their physiological traits, the number of offspring they produced, and their gene frequencies in the population?

Evolution by natural selection can be observed within a short period of time and is reversible. Natural selection may happen to individuals, but evolution by natural selection only occur within populations; Individual organisms do not themselves change to adapt or evolve during their lifetimes; some organism’s genes have already provided them with certain phenotypes that make them more adaptable to their environment, which allows them to leave more offspring than less adapted individuals. 

Populations evolve, and this is because the heritable nature of natural selection means the traits have to be passed on to progeny. Evolution by natural selection cannot occur without heritability; evolution is genetic change through time. 

Nature can refer to lots of different things fluctuating environmental phenomena (weather, climate, storms, earthquakes, food shortages, habitat destruction), but also predator/prey changes, sexual selection, pests or pathogens, etc

video: 

• we all come from a common ancestor

artificial inheritance

sexual selection: attraction and need to inherit (help to survive and evolve)

darwin probably had mitochondrial disease inherited from mom

animals in the island are probably similar to each other than having similarities from animals 

Limited gene flow means

A: Birds rarely move between the mainland and the islands.

darwin perceived adaptation to the environment and the origin of new species as closely related processes

biological evolution: change in species over time 

natural selection is just a mechanism

natural selection predates our understanding of genetics. 

galapagos endemics

is like a natural lab where evolution can be observed

animals live there that are found nowhere else in the world: endemic

biodiversity is huge in the galapagos island 

Endemic means:  The species isn’t found anywhere else. 

evolution: a change in the frequency of an allele over a period of time. 

2 surprises: 

1. evolution could occur quickly enough to observe within a few field seasons (natural selection)

2. evolution can occur at very small scale (microevolution)

natural selection can occur without heritability but evolution by natural selection cannot

• mechanism of evolution 

• requires heritable variation 

• requires differential survival and or reproduction

heritability: passing valuable traits to offspring