Evidence of Evolution p.126-133
Evidence of Evolution from Biogeography
Biogeography – The study of the geographical distribution of plants and
animals.
1876: Book by Alfred Wallace established 6 biogeographical regions.
This is still used today to describe broad distribution of organisms.
- Each region has plants and animals unique to that region.
- Regions are separated by impossible barriers.
- Millions of years: changes in positions of the continental land
masses and continental drift.
- Hypothesis of plate tectonics –
changes from a single supercontinent
called Pangaea (225 million years ago)
o Eg. Marsupials in Africa, Australia
or South America can be
explained by continental drift
- Break up if Pangaea 150 million years ago. Continents drifted and
organisms needed to adapt to their new environments
http://www.pond5.com/stock-footage/128542/pangea-earths-continents-separate.html
- Convergent evolution: development of similar forms from
unrelated species due to adaptation to similar environments.
- Differences between amphibians and reptiles can be explained by
biogeography
o Amphibians and reptiles around at the time of Pangaea, and
all distributed on other continents. They evolved after the
breakup of the continent.
http://www.youtube.com/watch?v=2NglfGlYaJo&feature=related
 Mammals did not appear until after Pangaea split, making
mammals on each continent unique
 Continents with similar or same animals can be explained by land
bridges (narrow strips of land that connects some continents)
 Remote islands are homes to unique species, many of which are
endemic (found nowhere else). This suggests that these species
have evolved in isolation. These animals do resemble animals
found on the closest continent. This suggests that animals on
islands evolved from mainland migrants, with populations
becoming adapted over time as they adjust to the environmental
conditions of their new homes.
 Evidence from biogeography suggests that different species
evolved independently in isolated parts of the world.
Evidence of Evolution from Vestigial Features
 Vestigial features provide evidence of specific changes.
 Vestigial features are rudimentary structures that serve no
useful function.
 These features once served a function in an ancient
ancestor.
 Whales and snakes have vestigial hip and leg bones –
evidence that suggests that they evolved from ancestors
that walked on four limbs.
http://www.podcast.tv/video-episodes/vestigial-organs-wings-of-the-flightless-cormorantfeaturing-richard-dawkins-8758278.html
Evidence of Evolution from Transitional Fossils
 The original fossil record gave scattered “snapshots” of
ancestral forms, and critics of the theory were concerned
about the “gaps”
 Transitional fossils link the past to the present.
 Hundreds of transitional fossils have now been found.
 Transitional fossils are the remains or impression of a
prehistoric organism that shows intermediary links
between groups of organisms and shares characteristics
common to these groups.
Evidence of Evolution from Anatomy
- Homologous Structures – body parts in different species that have the
same evolutionary origin and structural elements but may have a different
function.
o Ex. Bat wing, human arm, dolphin flipper, horse leg.
 Their limbs have similar structures, such as the number of
bones, muscles, ligaments and tendons. However, the
structural elements are arranged to be best suited for different
functions.
 Similar because they were inherited from a common ancestor.
Note: Functional similarity in anatomy, however, does not necessarily mean that
species are closely related.
- Analogous Structures – body parts in different species that have a similar
function but evolved separately.
o Bird wing (bones support wings) vs. insect wing (wings made of
chitin). These organisms evolved independently of one another and
do not share a common ancestor with wings.
Evidence from Embryology
- The embryos of different organisms exhibit similar stages of embryonic
development.
- All vertebrate embryos have paired pouches, or out-pocketings of the
throat.
o In fish and some amphibians, the pouches develop into gills.
o In humans, the pouches become part of the ears and throat.
- The similarities among embryos in related groups (such as vertebrates)
point to a common ancestral origin.
Evidence from Biochemistry & Molecular Biology
 All cells consist of membranes filled with water, genetic material, proteins,
lipids, and carbohydrates.
 Proteins called enzymes control biochemical reactions in all organisms.
 In all organisms, proteins are synthesized from amino acids.
 In all organisms, all cells that can replicate contain DNA. Since DNA carries
genetic information, scientists can determine how closely related two
organisms are by comparing their DNA. If two species have similar patterns
in portions of their DNA, this would indicate that these portions of their
DNA were most likely inherited from a recent common ancestor.
Evidence from Genetics
 Scientists now know how species pass on their traits to their
offspring, and how the blueprints (genes) for these traits could
change by mutation.
 Current evolutionary theory connects genetics with the theory of
natural selection, and how natural selection operates on
populations.
Evidence from Artificial Selection
 Humans can use artificial selection to produce dramatic
changes in species over relatively short periods of time.
 Provides
evidence that
similar and even
more dramatic
changes occur
in nature over
millions of years
and countless
generations.
Assignment:
P. 133 #’s 2-8 & 10