Download 16.4 Evidence of Evolution - Since Darwin`s work, every scientific

16.4 Evidence of Evolution
-
Since Darwin’s work, every scientific test has supported Darwin’s basic ideas about evolution
Biogeography
- Biogeography is the study of where organisms live now, and where they and their ancestors
lived in the past
-
Patters in the distribution of living and fossil species tell us how modern organisms evolved
from their ancestors.
Closely Related but Different
- Over time, natural selection can produce variations among populations that resulted in
different, but closely related species that are separated by some structure (like islands)
Distantly Related but Similar
- Similar habitats around the world are home to distantly related animals and plants, but the
similarities among those animals and plants provide evidence that similar selection pressures
had caused distantly related species to develop similar adaptations.
The Age of Earth and Fossils
The Age of Earth
- If life has evolved, then Earth must be very old.
-
With the use of radioactive dating, scientists indicate that Earth is about 4.5 billion years old
Recent Fossil Finds
- Darwin’s study of fossils had convinced him that life evolved
-
Recently discovered fossils form series that trace the evolution of modern species from
extinct ancestors
-
Paleontologists have discovered hundreds of fossils that document intermediate stages in the
evolution of many different groups of modern species.
o Recently fossil series documents the evolution of whales from ancient land mammals.
(see figure 16.13)
Comparing Anatomy and Embryology
Homologous structures
- Structures that are shared by related species and have been inherited from a common
ancestor are called homologous structures.
o Evolutionary theory explains the existence of homologous structures adapted to different
purposes as the result of descent with modification from a common ancestor.
o Similarities and differences among homologous structures help determine how recently
species shared a common ancestor.
o Example of homologous structures: the front limbs of reptiles and birds are more similar
to each other than they are to amphibians or mammals (though they all share
homologous limb structures)
Analogous & Vestigial structures
- Body parts that share common function, but not structure, are called analogous structures
-
Vestigial structures are inherited from ancestors but have lost much or all of their original
function due to differenct selection pressures acting on the descendant.
o Example: hipbones in bottlenose dolphins (and Whales) – used by ancestors that walked
on land, but no longer needed in water.
-
Why do organisms retain structures with little or no function? The presence of the structure may not
affect an organism’s fitness, so natural selection does not act to eliminate it.
Embryology
- The early developmental stages of many animals with backbones (vertebrates) look very
similar.
o The same group of embryonic cells develop in the same order and in similar patterns to
produce homologous tissue and organs in vertebrates
-
Similar patterns of embryological development provide further evidence that organisms have
descended from a common ancestor
Genetics and Molecular Biology
- At the molecular level, the universal genetic code and homologous molecules provide
evidence of common descent
Life’s Common Genetic Code
-
All living cells use information coded in DNA and RNA to carry information from one
generation to the next and to direct protein synthesis.
o This is powerful evidence that all organisms evolved from common ancestors that shared
this code
Homologous Molecules
- Homologous proteins share extensive structural and chemical properties
-
Such profound biochemical similarities are best explained by Darwin’s conclusion: living
organisms evolved through descent with modification from a common ancestor