The division is based on a distinction between similarity due to common ancestry, or homology, and resemblance which is due solely to similarity of function, called analogy. An example is the forelimbs of humans, horses, whales and birds which are judged homologous because
‘they are all constructed on the same pattern, and include similar bones in the same relative positions because these are all derived from the same ancestral bones. The wings of birds and insects, on the other hand, are analogous: they serve the same purpose, but do not constitute modified versions of a structure present in a common ancestor. The wings of birds and bats are homologous in skeletal structure because of descent from the forelimb of a common reptilian ancestor; but they are analogous in terms of their modification for flight—feathers in birds, skin membranes in bats.’
In other words, if a design similarity supports evolutionary assumptions, it is listed as an homology and is accepted as evidence for evolution. Conversely, if a design similarity does not support evolution, it is called analogy, and the conclusion is drawn that the similarity exists because a certain design is highly functional for a specific body part, and not because of a common ancestor. Many analogous structures are assumed to exist due to convergent evolution, which is defined as the separate evolution of similar structures because of similar environmental demands. Convergent evolution also is used to explain similar structures that have formed from different embryo structures or precursors.
Many examples of Homology are actually better explained by Analogy, and the resemblance that exists is often due to similarity of function and/or design constraints. The forelimbs of humans, whales and birds are similar because they serve similar functions and have similar design constraints. The conclusion that two homologous bones are similar because they are putatively ‘derived from the same ancestral bones’ (as Barr claims) is not based on direct evidence but instead on a priori conclusions demanded by macroevolution. Jones concluded that
“ … the evolutionist argument from homology lacks scientific content. This particular lack has very serious implications; it strikes at the root of all attempts by evolutionists to give homology an objective basis and distinguish homology (similarities due to descent) from analogy (similarities not due to descent). The only way they can recognize analogous variation, especially when due to convergent evolution is by criteria (e.g. genetic or embryological) which we now know do not hold for organs of "unquestionable" homology. The evolutionist concept of homology is now shown to be entirely subjective.”
Stephen J. Gould suggested that ‘the central task of evolutionary biology is … the separation of homologous from analogous likeness’, and then emphasized that ‘homology is similarity due to descent from a common ancestor, period’. The problem with this definition is that without direct knowledge we cannot know ancestry. In answer to the question ‘Can we identify fossil ancestors of species alive today?’, University of Michigan Professor Mark Siddall contends that this is impossible and that the use of stratigraphic data when assembling phylogenies must be based on speculation.
Huxley understood as far back as 1870 that when dealing with fossils, which are the only evidence we have of past life, one cannot distinguish uncles and nephews from fathers and sons. Among the many reasons ancestors cannot be distinguished from sister taxa, as noted by Siddall and others, is that there can be no positive evidence of ancestry, only inferences. Lack of evidence can only allow it as a possibility or an ad hoc postulate.
Although many similarities exist in almost all animal structures, structural variations are the norm. Often the variations found in the animal world seem to exist solely to produce variety, and not for the purpose of conferring a survival advantage. Some examples in humans are Attached earlobes, Tongue rolling, Hitchhiker’ thumb, Bent little finger, Interlacing fingers, Widow’ peak.
No biological or logical requirement exists to vary the design of bones, muscles and nerves needlessly in every living form beyond what is necessary to adapt the animal to its environment. Although variety is universal in the natural world, variety that interferes with the life process or an animal’ survival usually is avoided in animal design. Design constraints severely limit the possible variations in an animal’ anatomy, and excess deviation from the ideal can interfere with the animal’ ability to survive.
The many similarities that exist among members of the animal kingdom is the result of the fact that a single designer created the basic kinds of living ‘systems’, then specially modified each type of life to enable it to survive in its unique environmental niche. Examples of major environments for which organisms must be designed include the air, ground and water. Structures that serve similar purposes under similar conditions and that are nourished by similar foods ought to possess similarity in both design and function. This is illustrated in a critique of Berra’ Corvette analogy cited previously:
“ … Berra’ primary purpose is to show that living organisms are the result of naturalistic evolution rather than intelligent design. Structural similarities among automobiles, however, even similarities between older and newer models (which Berra calls "descent with modification") are due to construction according to pre-existing patterns, i.e., to design. Ironically, therefore, Berra’ analogy shows that even striking similarities are not sufficient to exclude design-based explanations. In order to demonstrate naturalistic evolution, it is necessary to show that the mechanism by which organisms are constructed (unlike the mechanism by which automobiles are constructed) does not involve design.”
Homology and Analogy
Dating Fossils : Relative Dating and Absolute Dating
DATING FOSSILS
Knowing the age of a fossil can help a scientist establish its position in the geologic time scale and find its relationship with the other fossils.
Fossils, Fossil Types and Fosilization
There are two ways to measure the age of a fossil: relative dating and absolute dating.
1. RELATIVE DATING
I. Based upon the study of layer of rocks
II. Does not tell the exact age: only compare fossils as older or younger, depends on position in rock layer
III. Fossils in the uppermost rock layer/ strata are younger while those in lowermost deposition are oldest
How Relative Age is Determined
I. Law of Superposition: if a layer of rock is undisturbed, the fossils found on upper layers are younger than those found in lower layers of rocks
II. However, because the Earth is active, rocks move and may disturb the layer making this process not highly accurate
Rules of Relative Dating
A. LAW OF SUPERPOSITION:
Sedimentary layers are deposited in a specific time- youngest rocks on top, oldest rocks at the bottom
B. LAW OF ORIGINAL HORIZONTALITY: Deposition of rocks happen horizontally- tilting, folding or breaking happened recently
C. LAW OF CROSS-CUTTING RELATIONSHIPS: If an igneous intrusion or a fault cuts through existing rocks, the intrusion/fault is YOUNGER than the rock it cuts through
INDEX FOSSILS (guide fossils/ indicator fossils/ zone fossils): fossils from short-lived organisms that lived in many places; used to define and identify geologic periods
2. ABSOLUTE DATING
• Determines the actual age of the fossil
• Through radiometric dating, using radioactive isotopes carbon-14 and potassium-40
• Considers the half-life or the time it takes for half of the atoms of the radioactive element to decay
• The decay products of radioactive isotopes are stable atoms.
Carbon-14 Dating:
A living organism has carbon-14.
For the amount of Carbon in the organism’s body to become half, it will take about 5,700 years; which is the half-life of carbon-14.
Take a look at the table below. Then answer the exercise below.
Exercise Questions :
A.) Fill up the remaining data in the table.
4 , Mass Remaining : _____________ , Number of Years : __________
5 , Mass Remaining : _____________ , Number of Years : __________
6 , Mass Remaining : _____________ , Number of Years : __________
B.) What is the limit in using carbon-14 as a measure to determine a fossil’s age?
C.) Do you think Carbon Dating is an accurate method of determining the correct age of dead organisms? Please state your reason. Read More......
FOSSILS, FOSSIL TYPES and FOSSILIZATION
FOSSILS are evidences of organisms that lived in the past. They can be actual remains like bones, teeth, shells, leaves, seeds, spores or traces of past activities such as animal burrows, nests and dinosaur footprints or even the ripples created on a prehistoric shore.
Molds - Impression made in a substrate = negative image of an organism e.g. Shells
Casts - When a mold is filled in e.g. Bones and teeth
Petrified - Organic material is converted into stone e.g Petrified trees; Coal balls (fossilized plants and their tissues, in round ball shape)
Original Remains - Preserved wholly (frozen in ice, trapped in tar pits, dried/dessicated inside caves in arid regions or encased in amber/fossilized resin) Woolly mammoth; Amber from the Baltic Sea region
Carbon - Film Carbon impression in sedimentary rocks e.g. Leaf impression on the rock
Trace / Ichnofossils - Record the movements and behaviors of the organism e.g. Trackways, toothmarks, gizzard rocks, coprolites (fossilized dungs), burrows and nests
THE SIX WAYS OF FOSSILIZATION
1. Unaltered preservation - Small organism or part trapped in amber, hardened plant sap
2. Permineralization/ Petrification - The organic contents of bone and wood are replaced with silica, calcite or pyrite, forming a rock-like fossil
3. Replacement - hard parts are dissolved and replaced by other minerals, like calcite, silica, pyrite, or iron
4. Carbonization or Coalification - The other elements are removed and only the carbon remained
5. Recrystalization - Hard parts are converted to more stable minerals or small crystals turn into larger crystals
6. Authigenic preservation - Molds and casts are formed after most of the organism have been destroyed or dissolved
More than 90 percent of all organisms that have ever lived on Earth are extinct. This is due to mass extinctions events that wiped out organisms in the past.
Geologic Time Scale - History of Life on Earth
Dating Fossils : Relative Dating and Absolute Dating
Goelogic Time Scale - History of Life on Earth
The Geologic Time Scale is a tabular representation of the major divisions of the Earth’s history. The time intervals are divided and described from the longest to the shortest as EONS, ERAS, PERIODS and EPOCHS. Each period has an approximated time frame and characterized by distinctive features (events and organisms).
The Geologic Time Scale (GTS)
A. Four eras - Precambrian; Paleozoic; Mesozoic; Cenozoic
B. Periods under the Paleozoic era - Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian
C. Periods under the Mesozoic era - Triassic, Jurassic, Cretaceous
D. Periods under the Cenozoic era - Tertiary and Quaternary
The Geologic time is divided into four large segments called Eons:
Hadean, Archean, Proterozoic and Phanerozoic.
The Phanerozoic is divided into Eras: Paleozoic, Mesozoic, and Cenozoic.
Extinction events and appearance of new life forms characterized the divisions among Eras.
Smaller divisions, called Periods, characterized by a single type of rock system, make up each Era.
Some Periods are further divided into smaller time frame called Epochs.
CAMBRIAN EXPLOSION is the belief that there was a sudden, apparent explosion of diversity in life forms about 545 million years ago. The explosion created the complexity of multi-celled organisms in a relatively short time frame of 5 to 10 million years. This explosion also created most of the major extant animal groups today.
The start of the Cambrian was characterized by the breaking up of supercontinent Gondwana into smaller land masses opening up new environmental niches where organisms can colonize and specialize.
Memory Aid / Mneumonic Technique to memorize GTS :
Eras: Precambrian, Paleozoic, Mesozoic, Cenozoic:
* Please Pay My Children!
Periods: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary:
* Cold Oysters Seldom Develop Many Precious Pearls, Their Juices Congeal Too Quickly.
* Cows Often Sit Down Carefully. Perhaps, Their Joints Creak
Epochs of Cenozoic Era: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene (or Recent):
* Put Eggs On My Plate Please Honey.
Precambrian Archean, Proterozoic
What are the evidences that suggest that we are entering / have entered a new epoch?
A new proposed Epoch, the Anthropocene.
- derived from the Greek and means the “ recent age of man ”
- interval of geologic time, (2.6 million years ago to the present), characterized as the time in which the collective activities of human beings (Homo sapiens) began to substantially alter Earth's surface, atmosphere, oceans, and systems of nutrient cycling.
- denote the present time interval, in which many geologically significant conditions and processes are profoundly altered by human activities.
These include changes in:
erosion and sediment transport ,
the chemical composition of the atmosphere, oceans and soils,
environmental conditions.
Fossils , Fossil Type and Fosilization
Dating Fossils : Relative Dating and Absolute Dating