Genetic diversity and Population genetics An individual organism's phenotype results from both its genotype and the influence from the environment it has lived in. A substantial part of the phenotypic variation in a population is caused by genotypic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene. Variation disappears when a new allele reaches the point of fixation —when it either disappears from the population or replaces the ancestral allele entirely.
Fossil record[ edit ] Research in the field of paleontologythe study of fossils, supports the idea that all living organisms are related. Fossils provide evidence that accumulated changes in organisms over long periods of time have led to the diverse forms of life we see today.
Cuvier noted that, in sedimentary rockeach layer contained a specific group of fossils. The deeper layers, which he proposed to be older, contained simpler life forms. He noted that many forms of life from the past are no longer present today. As a result, the general idea of catastrophism has re-emerged as a valid hypothesis for at least some of the rapid changes in life forms that appear in the fossil records.
A very large number of fossils have now been discovered and identified.
These fossils serve as a chronological record of evolution. The fossil record provides examples of transitional species that demonstrate ancestral links between past and present life forms. The implication from such a find is that modern reptiles and birds arose from a common ancestor.
Convergent evolution and Divergent evolution The comparison of similarities between organisms of their form or appearance of parts, called their morphologyhas long been a way to classify life into closely related groups. Taxonomy[ edit ] Taxonomy is the branch of biology that names and classifies all living things.
Scientists use morphological and genetic similarities to assist them in categorising life forms based on ancestral relationships. For example, orangutansgorillaschimpanzeesand humans all belong to the same taxonomic grouping referred to as a family—in this case the family called Hominidae.
These animals are grouped together because of similarities in morphology that come from common ancestry called homology. Strong evidence for evolution comes from the analysis of homologous structures: The forelimbs of a human, catwhaleand bat all have strikingly similar bone structures.
Such a "design" makes little sense if they are unrelated and uniquely constructed for their particular tasks. The theory of evolution explains these homologous structures: These changes in structure have produced forelimbs adapted for different tasks. However, anatomical comparisons can be misleading, as not all anatomical similarities indicate a close relationship.
Organisms that share similar environments will often develop similar physical features, a process known as convergent evolution.
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Both sharks and dolphins have similar body forms, yet are only distantly related—sharks are fish and dolphins are mammals.About.
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Invertebrate Relationships: Patterns in Animal Evolution 1st Edition. Phylogenetic study is an important corner-stone of biology, for the evolutionary relationships between groups of animals bear heavily upon the analysis of their physiology, behavior and ecology. Until now, there have been few books which analyse the diversity of animal Author: Pat Willmer.
A laboratory course recommended for nonscience majors, relating reproduction, heredity, evolution, ecology, and behavior to human life and the problems of society. This general education course does not count toward a major or minor in biology.
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