Comparative Anatomy

EVIDENCE FOR EVOLUTION: COMPARATIVE ANATOMY By comparing the anatomy of different animals much can be learned about their evolution. HOMOLOGOUS STRUCTURES: Bones in the forelimb of the human, whale, cat, bat, bird, alligator are used for vastly different movement, they all have remarkably similar structure and organization (bones, nerves, blood vessels This indicated common ancestry (DNA) Organs with similar structure but different functions are called HOMOLOGOUS STRUCTURES

COMPARATIVE ANATOMY: Homologous Structures

COMPARATIVE ANATOMY: Vestigial Structures Many animals have structures in their bodies which seem to be of no use to them These parts are called VESTIGIAL STRUTURES In other species the same structures exist and they have a definite function

COMPARATIVE ANATOMY: Vestigial Structures Human Wisdom Teeth ARE Vestigial

COMPARATIVE ANATOMY: Vestigial Structures Dogs & humans have a similar set of muscles attached to their ears. The dog can use these to “point” its ears in the direction of a sound, humans cannot In humans the appendix, coccyx and hair are all vestigial structures

COMPARATIVE ANATOMY: Vestigial Structures TOP 10 VESTIGIAL SRUCTURES OF ALL TIME !

#10 The Wings on Flightless Birds In general, wings of a bird are considered complex structures that are specifically adapted for flight and those belonging to these flightless birds are no different. They are, anatomically, rudimentary wings, but they could never give these bulky birds flight. The wings are not completely useless, as they are used for balance during running and in flagging down the honeys during courtship displays

# 9 Hind Leg Bones in Whales Biologists believe that for 100 million years the only vertebrates on Earth were water-dwelling creatures, with no arms or legs. At some point these ?fish? began to develop hips and legs and eventually were able to walk out of the water, giving the earth its first land lovers. Once the land-dwelling creatures evolved, there were some mammals that moved back into the water. Biologists estimate that this happened about 50 million years ago, and that this mammal was the ancestor of the modern whale. Despite the apparent uselessness, evolution left traces of hind legs behind, and these vestigial limbs can still be seen in the modern whale. There are many cases where whales have been found with rudimentary hind limbs in the wild, and have been found in baleen whales, humpback whales, and in many specimens of sperm whales. Most of these examples are of whales that had only leg bones, but there were some that included feet with complete digits. It was reported recently that whales and hippos were distantly related.

# 8 Erector Pili and Body Hair The erector pili are smooth muscle fibers that give humans’ goose bumps. If the erector pili are activated, the hairs that come out of the nearby follicles stand up and give an animal a larger appearance that might scare off potential enemies and a coat that is thicker and warmer. Humans, though, don’t have thick furs like their ancestors did, and our strategy for several thousand years has been to take the fur off other warm looking animals to stay warm. It,s ironic actually that an animal, sensing danger is near, would puff up its coat to look scarier, but the human hunter would see the puffier coat as a warm prize, leaving the thinner haired weaker looking animals alone. Of course, some body hair is helpful to humans; eye brows can keep sweat out of the eyes and facial hair might influence a woman’s choice of sexual partner. All the rest of that hair, though, is essentially useless.

# 7 The Human Tailbone (Coccyx) These fused vertebrae are the only vestiges that are left of the tail that other mammals still use for balance, communication, and in some primates, as a prehensile limb. As our ancestors were learning to walk upright, their tail became useless, and it slowly disappeared. It has been suggested that the coccyx helps to anchor minor muscles and may support pelvic organs. However, there have been many well documented medical cases where the tailbone has been surgically removed with little or no adverse effects. There have been documented cases of infants born with tails, an extended version of the tailbone that is composed of extra vertebrae. There are no adverse health effects of such a tail, unless perhaps the child was born in the Dark Ages. In that case, the child and the mother, now considered witches, would’ve been killed instantly.

# 6 The Blind Fish: Astyanax Mexicanus In an experiment designed by nature, the species of fish known as Astyanax mexicanus, dwelling in caves deep underground off the coast of Mexico, cannot see. The pale fish has eyes, but as it is developing in the egg, the eyes begin to degenerate, and the fish is born with a collapsed remnant of an eye covered by flap of skin. These vestigial eyes probably formed after hundreds or even thousands of years of living in total darkness. As for the experiment, a control is needed; and luckily for us, fish of the same species live right above, near the surface, where there is plenty of light, and these fish have fully functioning eyes. To test if the eyes of the blind mexicanus could function if given the right environment, scientists removed the lens from the eye of the surface-dwelling fish and implanted it into the eye of the blind fish. It was observed that within eight days an eye started to develop beneath the skin, and after two months the fish had developed a large functioning eye with a pupil, cornea, and iris. The fish were blind, but now they see.

# 5 Wisdom Teeth in Humans With all of the pain, time, and money that are put into dealing with wisdom teeth, humans have become just a little more than tired of these remnants from their large jawed ancestors. But regardless of how much they are despised, the wisdom teeth remain, and force their way into mouths regardless of the pain inflicted. There are two possible reasons why the wisdom teeth have become vestigial. The first is that the human jaw has become smaller than its ancestors? and the wisdom teeth are trying to grow into a jaw that is much too small. The second reason may have to do with dental hygiene. A few thousand years ago, it might be common for an 18 year old man to have lost several, probably most, of his teeth, and the incoming wisdom teeth would prove useful. Now that humans brush their teeth twice a day, it’s possible to keep one’s teeth for a lifetime. The drawback is that the wisdom teeth still want to come in, and when they do, they usually need to be extracted to prevent any serious pain.

# 4 The Sexual Organs of Dandelions Dandelions, like all flowers, have the proper organs (stamen and pistil) necessary for sexual reproduction, but do not use them. Dandelions reproduce without fertilization; they basically clone themselves, and they are quite successful at it. Look at any lawn for the proof. If dandelions were to revert to sexual reproduction, they might not retain whatever traits they have that allow them to be pests to gardeners everywhere. If flowers can begin reproducing in this manner, does that mean animals, even humans could too? Asexual reproduction can be a good strategy in an environment that is constant if a species is well suited to those conditions. It doesn’t take a scientist to figure out that humans wouldn’t last long if the condition set forth was no sexual contact with others. Therefore, the human sexual organs are probably in no danger of becoming vestigial.

# 3 Fake Sex in Lizards (Vestigial Behavior) Only females exist in several species of the lizards of the genus Cnemidophorus, which might seem like a problem when it comes time to propagate the species. The females don’t need the males though, they reproduce by parthenogenesis, a form of reproduction in which an unfertilized egg develops into a new individual. So basically, the females don’t need the males; they just produce clones of themselves as a form of reproduction. Despite the fact that it is unnecessary and futile to attempt copulation with each other, the lizards still like to try, and occasionally one of the females will start to ?act like a male? by attempting to copulate with another female. The lizards evolved from a sexual species and the behavior to copulate like a male -- to engage in fake sex -- is a vestigial behavior; that is, a behavior present in a species, but is expressed in an imperfect form, which in this case, is useless.

# 2 Male Breast Tissue and Nipples The subject of male nipples is a sensitive, and maybe confusing, topic to many. Those who wish to invalidate evolutionary theory might pose the question, ?Was man descended from woman?? The answer, of course, is no. Both men and women have nipples because in early stages of fetal development, an unborn child is effectively sexless. Nipples are present in both males and females; it is only in a later stage of fetal development that testosterone causes sex differentiation in a fetus. All mammals, male and female, have mammary glands. Male nipples are vestigial; they may perform a small role in sexual stimulation and a small number of men have been able to lactate. However, they are not fully functional and, because cancer can grow in male or female breast tissue, the tissue can be dangerous.

# 1 The Human Appendix In plant-eating vertebrates, the appendix is much larger and its main function is to help digest a largely herbivorous diet. The human appendix is a small pouch attached to the large intestine where it joins the small intestine and does not directly assist digestion. Biologists believe it is a vestigial organ left behind from a plant-eating ancestor. Interestingly, it has been noted by paleontologist Alfred Sherwood Romer in his text The Vertebrate Body (1949) that the major importance of the appendix ?would appear to be financial support of the surgical profession,? referring to, of course, the large number of appendectomies performed annually. In 2000, in fact, there were nearly 300,000 appendectomies performed in the United States, and 371 deaths from appendicitis. Any secondary function that the appendix might perform certainly is not missed in those who had it removed before it might have ruptured.

COMPARATIVE ANATOMY: Analogous Structures Features of different species that are similar in function but are structurally different Do not have a common ancestry Evolved due to a similar environmental challenge Ex) Birds & insects have wings to fly although their wing structure is different Ex) Fat insulated, streamlined shapes of seals & penguins

COMPARATIVE ANATOMY: Analogous Structures

COMPARATIVE ANATOMY: Embryology Embryological development of all vertebrates (fish to mammals) is remarkably similar especially in the early stages The more closely the related organisms, the longer their embryonic development proceeds in a parallel fashion

COMPARATIVE ANATOMY: Embryology

COMPARATIVE ANATOMY: Embryology Humans have gill pouches in early development In fish these pouches develop into gill slits In humans they form the eustachian tube and auditory canal, which except for the eardrum, are a direct connection between the outside of the body and the pharynx Human embryo has a tail and body hair like embryos of all other mammals but in the human embryo these features disappear before birth The presence of these features provides evidence that humans & other mammals developed from common ancestors

COMPARATIVE BIOCHEMISTRY In studying the complex molecules making up the bodies if living things, we find incredible similarities in the structures of these molecules in various organisms. Closely related species are very similar at the molecular level Distantly related species are more dissimilar at the molecular level but similarities still exits

COMPARATIVE BIOCHEMISTRY 1. All cells are made up of the same basic types of organic compounds: nucleic acids, lipids, carbohydrates

COMPARATIVE BIOCHEMISTRY 2.In all organisms, reactions involving these organic compounds are controlled by proteins known as enzymes

COMPARATIVE BIOCHEMISTRY 3. In all cells, proteins are synthesized from about 20 known amino acids

COMPARATIVE BIOCHEMISTRY 4.Carbohydrate molecules of cells consist of 6 carbon sugars (glucose) and polymers of these (cellulose, starch, glycogen)

COMPARATIVE BIOCHEMISTRY 5.All cells obtain energy from processing glucose in glycolysis In most organisms, oxygen can be used as an electron acceptor in the breakdown of pyruvic acid to CO 2 and water

COMPARATIVE BIOCHEMISTRY 6.All cells contain DNA, a molecule that carries coded information controlling the metabolism of the cell. DNA also transmits the coded information to new cells

COMARATIVE BIOCHEMISTRY 7. DNA in organisms determines the specificity of proteins through intermediate compounds such as mRNA

COMPARATIVE BIOCHEMISTRY 8. Structures of important lipids, proteins, & specialized molecules such as DNA, RNA, ATP and some co-enzymes are similar

COMPARATIVE BIOCHEMISTRY The Genetic Code is Universal

AGE OF THE EARTH Lord William Thomson Kelvin was the 1 st to try to determine the age of the Earth In 1866 he assigned it an absolute age of 400 million years (later revised his estimate to 15-20 millions yrs. Pierre Currie (1903) discovers radioactive decay. Its use provided geologists with the means to estimate the absolute age of the Earth Radiometric dating has been used to date meteorite samples. All that have struck Earth have been about 4.6 billion yrs Moon rocks from the Apollo missions have been dated at 4.53 billion yrs Oldest rock on Earth (from Canadian Shield) is 3.9 billion yrs old. This is the age where the Earth began to cool & did not undergo further melting. The Earth is likely 4.6 billion years old.

GEOGRAPHIC DISTRIBUTION Inhabitants of ocean islands resemble forms of the nearest mainland but show some differences, which suggests that they have evolved from mainland migrants Green Iguana from Panama Galapagos Land Iguana

PROTECTIVE RESEMBLENCE: Industrial Melanism Shows the effects of an environmental change on selection patterns of birds that eat peppered moths Industrial melanism is a phrase to describe the evolutionary process in which light colored moths become dark as a result of natural selection

DOMESTICATION & ARTIFICIAL SELECTION We can easily breed animals/plants to achieve desirable characteristics If we can achieve these changes over a a short period of time, the environment could cause changes in a long period of time

Comparative Anatomy

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