UNIT 2 DAY 5 - EVOLUTION IN THE GALAPAGOS Flashcards
Selective argument
- if in each generation only a few organisms survive, and if organisms vary, and if survival is not random, but instead if influenced by the traits that vary, then a trait that makes survival more likely will be more common among the survivors than it was before mortality ensued
Evolution argument
- if such an advantageous trait is more common among survivors, and if the trait is heritable, then it will also be more common among the offspring of the survivors, who then too will have a better chance of surviving
- each generation, the trait will increase in frequency in the species, and the species will change over time in ways that keeps it closely fitted to its environment
Selection in Evolution arguments are
- both arguments are deductive
- flaw in deductive arguments –> lead to correct conclusions only if the premises are correct, scientists use deductions not to prove an argument but to make testable predictions
Darwin’s finches
denied a starring role in the origin because he didn’t label them by island
Daphne Major
small volcanic island in the galapagos about the size and shape of large sports arena
Species Grants chose
medium group finches (geospiza fortis)
- chosen because it varied in traits (beak/body size)
Medium Ground Finches (1975-1978)
- 1500 birds were colour-banded and measured for 7 external morphological characters
-continuous records were kept of the banded birds and rainfall
Rainfall levels in 1976, 1977,1978
- 1976 and 1978: 127 and 137 mm
- sufficient for production of plants, insects and finches
- 1977: 24 mm –> medium ground finches did not breed at all
- suffered 85% decline population
- seeds were scarce
3 ways mortality of Medium Ground Finches was non-random
- small seeds decline in abundance than large ones, resulting in a sharp increase in average size and hardness of available seeds
- feeding behaviour changed
- 1976 only 17% of feeding was on medium or large seeds
- 1977 49% of feeding was on medium or large seeds
- small birds had no food source because plant that produced small seeds died in the drought - Small seeds declined in abundance faster than large ones resulting in a sharp increase in average size and hardness of available seeds
Geospiza fulginiosa
small ground finces
Geospiza fortis
medium ground finches
Geospiza magnirostris
large ground finches
small beak
small seeds
large beak
large seeds
1977
- severe drought destroyed plant life, reducing the production of seeds on which medium ground finches feed
- mortality was no longer the result of hatching to many chicks, that they could not reproduce
Did the finches evolve from the 1977 drought?
- yes, far few birds were alive in 1978 but those that were alive had deeper beaks
- natural selection occured increasing beak size from 8.8mm in 1976 to 9.8mm in 1978
-parents with deep beaks will have offspring with deep beaks
Grants tested Darwin’s Selection and Evolution Argument
- 2 step process
- mortality leads to selection on a trait
- the trait, if heritable, becomes more common in the next generation
Darwin’s theory and Lamarck theory
- both involved both evolution of traits that adapted an organisms to its environment and heritability of those traits
Lamarck theory of evolution
- individuals themselves evolve by developing adaptive traits during their lifetime, which then pass on offspring
Darwin’s theory of evolution
- individuals are stuck with traits they inherit from parents
- individuals are selected, they either live or due based on whatever traits they possess
- populations evolve, they change overtime as traits favoured by selection becomes more common
