Discuss the proofs of evolution. Be complete in your answer by including informa

Question

Discuss the proofs of evolution. Be complete in your answer by including information about laboratory results, the fossil record, signs of evolution in the body, genetic proof for evolution and homology examples.

2.       How do scientists know how old a set of rocks are? What techniques can be used to show the age of the rocks compared to those around it? What techniques can be used to definitively place an age-date on a set of rocks?

3.       Discuss the similarities AND differences between forming a new species by gradualism and/or punctuated equilibria. What role does natural selection play in both? What evidence would you look for in a species to determine whether it evolved by either process?

Explanation / Answer

1) The most direct evidence of evolution is provided by fossils. Unfortunately, fossil records are and will always be fragmentary. Inspite of this, study of fossilshas been highly significant in reconstructing the different events of evolution. Analysis of fossil records show general features. Firstly, none of the past forms of life is exactly like any of those now living. Secondly, fossils of most primitive and simple forms are first recorded in the oldest rocks. Moving up through the rock succession from the oldest to the most recent, there ocurs a succession of organisms in the form of fossils from more simple to complex types. Thirdly, a group of organisms when arose in one period, at first remained scarce but within the next few geological periods the became dominant after undergoing great adaptive radiation. Fourthly, fossil record also indicates extinction of many large and small organic groups although organisms related to such groups may be found persisting down to the present. Fossil record also indicates that different forms of life dominated the different geological periods for example Lower Palaeozoic were dominated by invertebrates and algae. The middle Palaeozoic is called the age of fishes. The Upper Palaeozoic saw the rise of ferns and land dwelling amphibias i.e. age of ferns and amphibias. Mesozoic which is called the age of reptiles and gymnosperms. Cenozoic is called the age of mammals and angiosperms.

The anatomical observation on vertebrates reveals many similarities though externally and functionally they are dissimilar in many cases. For example, there appears little external resemblance between a whale's flippers, a bat's wing, a horse's front legs and arms of human being. The first one is used for swimming, the second for flying, the third for running and the fourth for grasping. This phenomenonof similarity of structures based on inheritence from common ancestor is known as HOMOLOGY and the related structures so derived are called homologous. In fact a comparision of forelimbs of vertebrates reveals that a common basic plan is utilized for all. In many instances it has been found that some organs of the ancestor have been significantly modified in its descendants to perform functionswhich are different from their ancestor. Gill structure of fish is modified in other vertebrates to upper and lower jaw, and bones of middle ear. Thus evolution tends to be a conservative process. Instead of forming new structures it tends to remodel the existing one.

In signs of evolution in the body:

Small Eocene Horses :

Small Eocene Horses Hyracotherium Orohippus Epihippus

Hyracotherium :

Hyracotherium It had a "doggish" look with an arched back. short neck, short snout, short legs, and long tail. It browsed on fruit and fairly soft foliage probably scampered from thicket to thicket like a modern muntjac deer, only stupider, slower, and not as agile. Legs were flexible and rotatable with all major bones present and unfused. 4 toes on each front foot, 3 on hind feet Small brain with especially small frontal lobes

Medium-Sized Browsing Horses (Oligocene) :

Medium-Sized Browsing Horses (Oligocene) The climate of North America was becoming drier The vast forests were starting to shrink. The late Eocene horses responded by developing tougher teeth and becoming a bit larger and leggier Mesohippus Miohippus

Mesohippus :

Mesohippus It didn't look as doggish, either. The back was less arched, the legs a bit longer, the neck a bit longer, and the snout and face distinctively longer. It had a shallow facial fossa, a depression on the skull Mesohippus had three toes on its hind feet and on its front feet -- the 4th front toe was reduced to a vestigial nubbin

Miohippus :

Miohippus A typical Miohippus was distinctly larger than a typical Mesohippus, with a slightly longer skull. The facial fossa was deeper and more expanded. Miohippus also began to show a variable extra crest on its upper cheek teeth.

The Miohippus Radiation :

The Miohippus Radiation The horse family began to split into at least 2 main lines of evolution and one small side branch 3-toed browsers called "anchitheres". They were very successful, spread into the Old World, and thrived for tens of millions of years. A line of small "pygmy horses", e.g. Archeohippus. These horses did not survive long. A line that underwent a transformation from browsing to grazing, taking advantage of the new grasses.

Spring-Foot & High-Crowned Teeth (Miocene, 18 My) :

Spring-Foot & High-Crowned Teeth (Miocene, 18 My) the teeth changed to be better suited for chewing harsh, abrasive grass these horses started to become specialized runners. There was a simultaneous increase in body size, leg length, and length of the face the horses began to stand permanently on tiptoe (another adaptation for speed); instead of walking on doglike pads

Miocene horses, 18 My :

Miocene horses, 18 My Kalobatippus Parahippus Merychippus

Merychippus :

Merychippus The muzzle became elongated, the jaw became deeper and the eye moved farther back Merychippus was still 3-toed, but was fully spring-footed The radius and ulna of the forearm fused so that leg rotation was eliminated All these changes made Merychippus' legs specialized for just one function: rapid running over hard ground.

The Merychippine Radiation (Miocene, 15 My) :

The Merychippine Radiation (Miocene, 15 My) hipparions: Three-toed grazers protohippines: Protohippus and Calippus true equines Throughout the evolution of all these related merychippine descendents, the facial fossae got deeper and more elaborate

One-Toed Horses (Pliocene) :

One-Toed Horses (Pliocene) Pliohippus Astrohippus Dinohippus

Pliohippus :

Pliohippus Pliohippus's skull has deep facial fossae, whereas Equus has no facial fossae at all Pliohippus's teeth are strongly curved, and Equus's teeth are very straight.

Dinohippus :

Dinohippus Finally, a third one-toed horse called Dinohippus (recently discovered) arose about 12 My. They look smashingly like Equus in foot morphology, teeth, and skull. Throughout the end of the Pliocene, Dinohippus showed a gradual decrease in the facial fossae, straightening of the teeth, and other gradual changes

Equus :

Equus The first Equus were 13.2 hands tall (pony size) rigid spine, long neck, long legs fused leg bones with no rotation long nose, flexible muzzle, deep jaw straight grazing teeth with strong crests lined with cement.

Modern Equines (Recent) :

Modern Equines (Recent) one-toed Equus was very successful. Until about 1 million years ago, there were Equus species all over Africa, Asia, Europe, North America, and South America In the late Pleistocene there was a set of devastating extinctions that killed off most of the large mammals in North and South America. For the first time in tens of millions of years, there were no equids in the Americas..

2) To know the age of a rock a scientist first have to see the origin of the rock body. If the rock is basalt it age would not be more that 200 M.a. because the the oceanic crust gets destructed in the subduction zone after an span of 200 M.a. If the rock is a komatiite or charnokite or tonalite gneiss the scientist can predict that the age is of Proterozoic time because only at that period these rocks were formed. So these are the field knowledge through which a scientist can predict the rock's age.

There are certain techniques that can be used to show the age of the rocks are either older or younger compared to those around it. They are:

Principle of superposition: Younger sedimentary rocks are deposited on top of older sedimentary rocks.
Principle of cross-cutting relations: Any geologic feature is younger than anything else that it cuts across.

Dating techniques:

Uranium-lead dating method: Uranium-lead radiometric dating involves using uranium-235 or uranium-238 to date a substance's absolute age. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. An error margin of 2–5% has been achieved on younger Mesozoic rocks. One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of the age of the sample even if some of the lead has been lost.

Samarium-neodymium dating method: This involves the alpha-decay of 147Sm to 143Nd with a half-life of 1.06 x 1011 years. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable.

Potassium-argon dating method: This involves electron capture or positron decay of potassium-40 to argon-40. Potassium-40 has a half-life of 1.3 billion years, and so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in micas, feldspars, and hornblendes, though the closure temperature is fairly low in these materials, about 350 °C (mica) to 500 °C (hornblende).

Rubidium-strontium dating method: This is based on the beta decay of rubidium-87 to strontium-87, with a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocks, and has also been used to date lunar samples. Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample.

3) Species with a shorter evolution evolved mostly by punctuated equilibrium, and those with a longer evolution evolved mostly by gradualism. Gradualism is selection and variation that happens more gradually. Over a short period of time it is hard to notice. Change is slow, constant, and consistent.

In punctuated equilibrium, change comes in spurts. There is a period of very little change, and then one or a few huge changes occur, often through mutations in the genes of a few individuals.

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