Evidence for Evolution . Darwin's theory of evolution by natural selection . Supported by evidence gathered over a century Evidence must be gathered to support the theory of evolution- THE THEORY CANNOT BE PROVED EVIDENCE Planetology of fossils Biogeography Comparative anatomy
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Evidence for Evolution
What is Paelontology : The study of fossils – direct evidence of existence of an organism
How it supports evolution? sequence of fossils found in rock formations should reflect the order of changes observed in organisms that originated from a common ancestor
Law of superposition: sequence in which they are laid down indicates the order in which they were formed
Evolution of the modern horse from a small animal which lived 55 million years ago. This animal browsed on trees and bushes, had smaller teeth and 4 toes on the front and 3 toes on the back. The modern horse is much larger and only has one toe on each foot. These changes were probably due to a change in environment – reduction in rainfall and swampy areas becoming dry grasslands.
Prediction by Darwin :
Fossil record should yield intermediate forms – organisms that show transitions from one group to another ‘missing links’
What is Biogeography?: study of the geographical distribution of organisms both living and extinct.
How it supports Evolution ?: Supports this feature of the theory of evolution…for a new species to arise, a group of individuals must become isolated from the rest
Ancient group of flightless birds that are believed to have evolved from a common ancestor on Gondwana and different populations evolved on the isolated southern continents as they drifted apart.
South America- Rhea
PNG and Australia – cassowary
Also, there are no similar flightless birds on the northern continents . Thus flightless birds arose as a result of the isolation of the continent .
Prediction by Darwin :
The new species should resemble species with which they shared a habitat: those that lived close by or in area with similar environmental conditions OR those that lived in a common area before it split up eg. Gondwana
What is Comparative embryology ?: the comparison of the developmental stages of different species . Suggests common ancestor because embryos of closely related organisms have homologous parts
Prediction by Darwin : species that are related show similarities in their embryonic development
Evidence and Example :
Vertebrate embryos show similarities in their early devleopmetn e.g. fish, amphibian, reptiles, birds and mammals in that they all show the presence of
developed into internal gills in fish only
developed into external gills in tadpoles
developed into part of the Eustachian tube ( airway connecting middle ear with throat) in mammals
other vertebrates- no further gill formation forms
What is Comparative anatomy?: studies of similarities and differences in structure between different organisms.
Prediction by Darwin :if organisms are more closely relation ( recently separated from common ancestor) they should be more similar in structure than organisms which separated earlier.
Homologous structures – Forelimbs
Vestigial structures provide evidence of common ancestry: evolutionary remnants of body parts that no longer serve a useful function e.g. reduced tail and an appendix in humans – have evolved because they no longer carry out a useful function in that animals lifestyle.
Evidence and Examples :
involves homologous structures. Analogous structures DO NOT provide evidence for evolutionary relatedness but rather for evolution of structures to serve a common purpose in a common environment
What is DNA sequencing?:
DNA sequencing- compares variation in the order of bases in gene DNA
Evidence for Evolution :
Confirmed that humans are more closely related to other mammals than to reptiles