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Transcript
History of an Idea
“that species change over time”
• Greek philosopher Anaximander, 2,500 yrs ago
– promoted the idea that life arose in water and that simpler forms of
life preceded more complex ones.
• Greek philosopher Aristotle
– Generally held that species are fixed and do not evolve.
• Judeo-Christian culture fortified this idea with the
common interpretation of the biblical book of Genesis.
– All species were individually designed by a divine creator.
– The ideas that the Earth and all living species are static and perfect,
and that planet Earth is about 6,000 to 10,000 years old, have
dominated the intellectual climate of the Western world for
centuries.
History of an Idea
“that species change over time”
• George Buffon in the mid-1700’s
– Study of fossils
– Suggested that the Earth might be much older than
6,000 years.
• Scientists observed some similarities between
fossils and living animals.
• In 1766, Buffon raised the possibility that different
species had arisen from common ancestors.
– Buffon later argued against the idea.
History of an Idea
“that species change over time”
• Jean Baptiste de Lamarck (1744-1829)
– In the early 1800’s, Lamarch was the first to propose a
hypothesis of species modification.
• Proposed that similar species descended from a common
(the same) ancestor.
– Living species were descended from similar extinct species
evident in the fossil record.
– Mechanism (erroneous)
• Inheritance of acquired characteristics
• Hypothesized that acquired traits were passed on to offspring.
– Acquired trait is one that is not determined by genes.
» Shore birds’ webbed feet.
History of an Idea
“that species change over time”
• Charles Darwin (1809-1882)
• Alfred Wallace (1823-1913)
• Both proposed the hypothesis that species were
modified by natural selection.
– Organisms best suited to their environment reproduce
more successfully than other organisms.
– Therefore, over generations, the proportion of
organisms with favorable traits increases in a
population.
• Darwin’s book published in 1859
– The Origin of Species by Means of Natural Selection
History of an Idea
“that species change over time”
• Charles Darwin
– Voyage of the Beagle
• Started December of 1831
• Ended in 1836 (27yrs old)
– Acted as the ship’s
naturalist.
• collected specimens and
keep careful records of
his observations.
– Charles Lyell- Principles of
Geology
• Led Darwin to realize that
natural forces of the past
are still operating in
modern times.
– Marine snails in the
Andes Mountians
History of an Idea
“that species change over time”
• After the Beagle
– Darwin believed the Earth very old and doubted the
Earth and living organisms were unchanged
– In the early 1840’s, Darwin composed a long essay
describing the major features of his theory of evolution.
– In the mid-1850’s, Wallace conceived a theory identical
to Darwin’s.
– In 1858, Wallace’s and Darwin’s finding were
presented to the scientific community.
– In 1859, the publication of Darwin’s text, On the
Origins of Species by Means of Natural Selection
Theories of Evolution
• Descent with Modification
– The newer forms appearing in the fossil record are
actually the modified descendants of older species.
– Galapagos finches
• All species of finches on the Galapagos Islands, had descended
from a recent common ancestor.
– Reasoned that all living things probably had descended
from one, or a few, remote common ancestors.
– Accounted for the fact that similar organisms arise in
the same geographic location.
Theories of Evolution
• Modification by Natural Selection
– The environment may affect individual organisms in a
population in different ways because individuals of a
species are not identical.
– Some organisms have traits that make them better able
to cop with their environment.
– Organisms that have a greater number of these
favorable traits tend to leave more offspring than
organisms with fewer beneficial traits.
– Darwin called the different degrees of successful
reproduction among organisms in a population natural
selection.
Theories of Evolution
• Modification by Natural Selection
– Species with the best fitness in the environment are
likely to survive and reproduce.
• Survival of the Fittest
– Individuals whose characteristics are well-suited to the
environment survive.
– Individuals whose characteristics are not well-suited to their
environment either die or leave fewer offspring.
– Variations in species
– High birthrates and a shortage of life’s necessities.
– Constant struggle to survive
The Fossil Record
• Fossil- a trace of a dead organism
– Found in:
• Layers of sedimentary rock
– Usually develop from hard body parts
– Over long periods of time, hard minerals replace the
tissues, leaving rocklike structures
– Types
•
•
•
•
Shells, bones, teeth
Mold
Cast
Amber
Distribution of Fossils
• Law of superposition by Nicolaus Steno
– States that successive layers of rock or soil were
deposited on top of one another by wind or water.
– The lowest stratum, or layer is the oldest
– The top stratum is the most recent
– Fossils within a single stratum are of the same
approximate age.
– Relative age vs Absolute age (estimated from
radiological evidence)
Distribution of Fossils
• Succession of Forms
– Extinctions and Mass extinctions
• Biogeography
– Study of the geographical distribution of fossils
and of living organisms
– Shows that new organisms arise in areas where
similar forms already lived
Evolution in Process
Evidence of Evolution
• Homologous and Analogous structures
– Homologous structure
• Feature with similar structure, but different function
• Example: forelimbs of penguin, alligator, bat, and
human.
– Analogous structure
• Feature with similar function, but different structure
• Vestigial structures
– Features that serve no useful function.
Evolution in Process
Evidence of Evolution
• Similarities in Embryology
– Embryos are similar at certain stages.
– This pattern would be expected if organisms were
descended from a common ancestor.
– Similar genes functioning.
• Similarities in macromolecules
– Similarity in the subunit sequences of biological
molecules such as RNA, DNA, and proteins indicates a
common evolutionary history.
Patterns of Evolution
• Coevolution
– Change of two or more species in close association with
each other
• Predators and their prey
• Parasites and their host
• Plants and animals
– Plants and the animals that pollinate them
• Convergent evolution
• Divergent evolution
– Adaptive radiation