Evolution Midterm Review
1.1 Whales: Mammals Gone to Sea
- Cetacean’s posses many traits only found in mammals. In The Origin of Species, Darwin
proposed an explanation for these similarities and differences. Cetaceans descended from
mammals that lived on land, and their lineage evolved into marine mammals through
natural selection. In a process of convergent evolution the ancestors of whales lost their
hindlimbs and front legs became flippers.
- Whales still have some similar traits from mammalian ancestors. Mammary glands of
whales and land mammals are examples of homology.
- Numerous cetacean fossils were found and they knew this due to synapomorphies.
- Dorudon Atrox is a 40 million year old fossil that had the same synapomorphies as
cetaceans. It also has some features that aren’t seen today in cetaceans. Such as, different
teeth shapes that were more like land mammals. This proved that the evolution of peg-
like teeth and baleen occurred after cetaceans had become aquatic.
- In 1979 Gingerich traveled to Pakistan to investigate geological formation from the
Eocene period (rocks that formed from 56 million to 34 million years ago). They found
one interesting fossil that was similar to cetaceans. Gingerich and colleagues named it
Pakicetus, which means “whale of Pakistan” in Latin.
- Pakicetus was a big discovery since it was the oldest fossil of a cetacean found (50
million years) up to that point. Second reason was due to where it lived, on land.
- Gingerich’s student, Thewissen traveled to Pakistan later and found a large mammalian
fossil. It had cetacean synapomorphies too and thus concluded that it was a whale that
could walk. So he named it Ambulocetus “walking whale”.
- Research in the future concluded those cetaceans are most closely related to a group of
mammals called artiodactyls, more specifically hippos.
- Darwin argued that life evolved like a branching tree with new lineages from old ones.
To reconstruct this phylogeny scientists can analyze morphology and genes. I.e. you
could tell if ancestors were terrestrial or aquatic by looking at whether they drank
freshwater or salt water since both contain oxygen atoms but the oxygen atoms are
slightly different. Sea water has more oxygen atoms with 10 neutrons. Therefore whales
and dolphins have larger percent of oxygen in bones.
- When dolphin embryos are growing they have the same leg-building genes as humans
however, it stops growing and dies back.
- Natural selection favoured dolphins with large brains for processing social inforamtion
Lineage A chain of ancestors and their descendants
Natural Selection A mechanism that can lead to evolution, whereby differential survival or
reproduction of individuals causes some genetic types to replace others Convergent Evolution The independent origin of similar traits in separate lineages
Homology Characteristics are similar in two or more species because they inherited them from
a common ancestor.
Synapomorphies A derived form of a trait that is shared by a group of related species.
1.2 Viruses: The Deadly Escape Artists
Mutations Any change to the genomic sequence of an organism
- Some mutations affect the ability of organisms to replicate. For viruses a mutation may
leave a virus unable to invade a host cell. However, other viruses can enable the virus to
- These viruses allow their descendents to dominate the virus population. Flu viruses are
evolving extraordinarily fast.
- Scientists ran an experiment in which the vaccinated mice against flu and them exposed
them to the virus. These mice were then exposed to other mice allowing them to infect
other mice. The vaccinated mice’s hemagglutinin proteins were altered at the tip, which
allowed the virus to be unrecognized by the immune system. While the hemagglutinin in
non-vaccinated mice didn’t change.
- All human flu’s descend from strains that infected other animals.
- The number of different mutations in two lineages provides clue to how long ago these
viruses diverged from a common ancestor.
Reassortment When genetic material from different strains gets mixed into new
combinations within a single individual.
Triple Reassortment When the genes of three viral strains exchange genes (H1N1
involves strains from swine, birds and human.
2.1 Nature before Darwin:
- Carl Linnaeus (father of modern taxonomy) organized all living things at the time into a single
hierarchy of groups (taxa). He could assign every species to a particular genus, family, or order
according the traits it shared with other species. He believed that the overall patterns of life’s
diversity had not changed since the biblical creation of the world. - Nicolaus Steno studied a shark’s teeth and it occurred that they looked like triangular rocks
which were known as tongue stones. He proposed that tongue stones had started out as teeth in
living sharks. After sharks died their teeth turned to stone. However, how could animals that
lived in the ocean end up so far away on mountains? He argued that originally a sea must have
covered the mountains. Shelled animals then died and were covered over in sediment and turned
to rock. He was known as the father of geology and stratigraphy since he studied the layering in
Taxon A group of organisms that a taxonomist judges to be a taxonomic unit, such as a
species or order.
Taxonomy The science of describing, naming, and classifying species of living or fossil
2.2 Evolution before Darwin:
- Georges-Louis Buffon proposed that new varieties of a species could arise in response to new
habitats. However, he did not believe that species could arise this way. A comet struck the sun,
he argued, breaking off debris that formed a planet. Earth cooled and hardened and oceans
formed this process he said took 70,000 years. He argued that each species had a supply of
organic particles that somehow transferred an egg or seed into its adult form. These animals first
came to exist in hot ocean of early earth then migrated to warm tropics, overall argued that life
had changed over time.
- Georges Cuvier compared elephant fossils to skeletons of living elephants and documented that
these species had become extinct.
- James Hutton realized rocks formed through slow changes, such as rain, molten etc. Eroded
sediments form and erode away again like a cycle. The world has deep history shaped by gradual
transformations of landscapes.
- William Smith noticed that the same kinds of fossils tended to appear in older rocks, but
different ones appeared in younger rocks. He could find the same set of fossils in rocks separated
by hundreds of miles. Created first geological map .
- Jean-Baptiste de Lamarck proposed that life was driven inexorably from simplicity to
complexity and that human and other large species descended from microbes. He argued that
primitive life was being spontaneously generated all the time. He believed that organisms could
adapt to their environment and did not accept extinction. For example if a giraffe stretched its
neck for leaves a nervous fluid would flow to its neck and make it longer.
Paleontology The study of prehistoric life Extinction The permanent loss of a population or species, arising with failure or death to
breed last individual
2.3 The Unofficial Naturalist:
- Darwin was sent to school in Edinburgh to become a Doctor when he realized he would much
rather be studying nature. In 1831, Darwin went on a voyage on the HMS beagle from England
to South America. He recognized layers of rocks that had gradually formed and experienced an
earthquake in Chile observing the shoreline being lifted.
- Darwin read Charles Lyell’s book, “ The Principles of Geology”, which made the argument
that the Earth’s landscapes had been created not by gigantic catastrophes but by a series of many
small changes (uniformitarianism). Viewing the earthquake it made him a passionate “Lyellian”.
- Darwin observed the dramatically different beak sizes of finches in Galapagos and concluded
that they adapted to their environment. In 858 Darwin received a letter from Alfred Russell
Wallace presenting his own ideas this made Darwin publish his work before Wallace had a