Evidence for Evolution Flashcards
Where has evidence for evolution come from?
- lines of investigation from direct observation, experimentation (eg. fossil evidence, continental drift) to indirect investigations
Evidence examined are
1) fossil records (radiometric dating)
2) Biogeography (continental drift/theory of pangea)
3) anatomy (comparative embryology)
4) biochemistry
5) genetics
6) artificial selection: selective breeding is evolution in practice
Fossil Formation
- fossils form when an organism dies and is quickly buried by layers of sediment
- over time the soft tissue decomposes but the hard bones, teeth, and shells remain and get replaced by minerals, the replacement is called petrification
- molds and impressions can also form after and organism makes a print, it is filled with sediment hardens, and erodes over time and the print is revealed
What do fossil records tell us?
- the fossil record shows the existence of organisms that inhabited the earth but don’t exist now; some bear resemblance to those who exist now
- recent fossils resemble present day species; older fossils are more primitive
- rocks are dated using radio-carbon dating, indicating the approximate time the organisms inhabited the Earth
- fossil records are not complete, there are missing links (which is expected since the process of fossilization requires specific events) - in complete fossil records are accounted for
Found missing links
Archaepteryx
- link between reptiles and birds
- dinosaur like skeleton
- reptilian features including jaws with teeth and long jointed tail but also had feathers and wings
- Evolutionary ancestor that bridges the evolutionary split between higher primates and monkeys was recently discovered
Findings from Fossil Evidence
1) different species lived on Earth at various times in past
- very few species of today were alive 1 million years ago
- almost all are now extinct
2) complexity of living organisms generally increases from most distant past to present
- progression from very simple organisms to species of increased complexity
3) living species and their closely related matching fossils live in same geographic region
Location of fossils
- mostly found in sedimentary rock = layered rock that is the oldest at the bottom
- petrified fossils are organisms that have skeletal matter replaced with calcite
- dated using a relative timescale; the geological time scale has major and minor corresponding with major evolutionary events
- separated into:
Eon
Era
Period
Epoch
Dating the Past - Lyell 1830s
Observed geological stratification and fossils and suggested that most geological change was show and gradual and constant
Based on
- fossil deposits
- geological processes of erosion and sedimentation
Processes have been going on over vast expanses of time suggesting that the Earth is hundred of millions of years old
Lord Kelvin
- prominent physicist that disagreed with Lyell
- believed that Earth was gradually cooling from a molten state
- used mathematical calculations for rates of cooling to estimate the age of Earth at 15-20 million years old
- did not realize that the Earth’s core is a viscous fluid that acts as a source of heat
- disproved by discovery of radioactive decay
Absolute dating
The process of determining a specific date for an archaeological or paleontological or artifact
Uses radioactive isotopes which decay at a constant rate, giving off radiation (radioactive decay)
Because this rate is constant and unaffected by temperature, moisture, or other environmental conditions, it can be used to determine the age
- radioactive=unstable
Dating is based upon the half-life of an isotope
The half-life is the time it takes for half of the atoms in the original element (parent isotope) to decay (daughter isotope)
Only half of the atoms decay in one half-life; this can take between a few seconds or a million years depending on the element
If parent isotopes of different radioactive elements are used, the dating becomes more reliable
Radioactive Calculations
- if we know the ratio of parent to daughter material, we can calculate the number of half-lives elapsed
- from this info, the age of the sample can be calculated from the known length of the half-life of the radioisotope
1 - 50% 50%
2 - 25% 75%
3 - 12.5% 87.5%
4 - 6.25% 93.75%
Biogeography
- Biogeography: the study of the geographic distribution of life on Earth
- patterns of distribution suggest that Earth’s continents were part of a single land mass 225 million years ago - broke apart resulting in continental drift
- fossils dating back 150 million years ago and older were in the same geographic region but are now found at different continents
- fossils younger than 150 million years are restricted to certain continents (endemic)
Continental Drift Theory
- pangea: 1 super continent existed 180 million years ago: broke off into two parts (Australia and Antarctica first)
- similar organisms should evolve by natural selection if environment stressed are similar
- marsupials in Australia resemble those from the rest of the world, also found marsupials in Antarctica
- after Pangea broke up, the common ancestor evolved into mammals in the northern parts and into marsupials in the southern parts, yet similarities exist due to a similar environment
- mammals: offspring developed in womb
- marsupials: offspring developed in pouch
Islands
- islands are often products of volcanic activity but eventually get populated by unique species
- islands have fewer species than their mainland counterparts
- animals get to islands by flying, hitch a ride, swim, cross ice and land bridges, or raft on vegetation and ice floats
- species native to remote islands are invariably and exclusively birds, insects, and potentially xobile - evidence for relationships between organisms on islands on other land masses is from genetic testing
Evidence from Anatomy
Embryological similarities
Embryology: the study of organisms in the early stage of development
- embryos of many vertebrates are remarkably similar in the early stages
- embryologists suggest this is because vertebrates evolve from a common ancestor
- many embryonic structures are similar to those found in ancestors
Vestigial Structures
- muscles/appendages that are considered useless
- includes: tails, ear muscles, appendix, and limb bone of whale
- thought to have once served a useful function but now are just remenants of a no-longer existing use
- products of divergent evolution
