Darwin and Mendel | Ask A Biologist
Start studying Darwin Quiz. What can scientists use to help understand relationships that D didn't have? . What happened when D read Wallace's work ?. Charles Darwin quiz that tests what you know. Perfect prep for Charles Darwin quizzes and tests you might have in school. Alfred Russell Wallace . With whom did Darwin have a flirtatious relationship before leaving on the Beagle?. It's years since Charles Darwin first published On the Origin of Species. But can your evolutionary knowledge survive our quiz? of Darwin's 'tree of life', a metaphor to explain the evolutionary relationships between different species.
A little refinement there. I truly believe that "the most complex and perfect instinctive actions, wondrous though they be, have been slowly acquired and perfected" Prete. But here I am letting ideas carry me off again.
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You asked for honey and it shall be yours. The spring wildflower blend is truly delightful this year. Darwin passes a small pot of honey to Mendel, who dribbles a small amount of the golden liquid into his cup and also onto the remainder of his shortbread cookie.
I can understand your frustration with the social insects. Just as they have vexed you, I have been confounded by simple pea plants. Perhaps that is why my hairline is receding. But do go on. Black and white sheep - Wikimedia Mendel: Those pea plants had me mystified. But I have finally cracked the nut, so to say, or better yet, I have split the pea pod! Yet these lovely white, wooly creatures will on occasion throw a black baby, to the annoyance of the shepherd, for their fleece has no value at all.
Gesturing at the landscape surrounding them, Darwin replies: Yes, as a country gentleman here in Kent I am well aware of the difficulties such throwbacks cause. Well, I have come across something most surprising in my humble garden plot. You see, I have been crossing true breeding pea plants that bloom in white or vibrant purple. I simply take on the role of honey bee or butterfly and deliberately spread the pollen from the anthers of a purple pea plant onto the stigma of a white pea plant.
I see, you cross pollinate. I then gather the pea pods produced to harvest the seeds and plant these again. What I have found is if I cross pollen from a purple plant onto a white plant, the peas will all grow into purple plants. And the same is true if I cross the pollen from a white flower with a purple flower. Again, all the peas produced from such a conjunction will grow into purple plants.
By Jove, that is most interesting. I would have expected blending to occur. When a tall man marries a short woman, their children are most often of intermediate size. What you describe would be as if all the children would grow to be tall.
You do surprise me! Please go on and tell me more. You have raised my curiosity. Remember those black lambs. Well the same occurred with my pea plants. I took those offspring from the purple and white cross, the pea plants that all bloomed purple. Yes, do go on. Well I self-pollinated that first generation of offspring.
And the peas I harvested and planted too. The second generation of offspring were a motley bunch. Pea flowers - Wikimedia Darwin: Let me be sure I am following your line of action. You took the pollen from the offspring of the first cross, which were all purple, and used that pollen to fertilize the flowers of those same plants? Exactly, my dear Charles.
I crossed those purple flowers with themselves. Can you guess what I found? But you gave that answer away with the story of the lambs.
But what was most interesting was that I repeated this experiment many, many times. I crossed white flowered pea plants with purple flowered pea plants. I crossed peas that produced yellow peas with peas that produced green peas. I even crossed smooth skinned peas with wrinkly ones! And each and every time the same thing happened.
Salivation, Anticipation and Simple Addition Darwin: Well do tell me, Gregor! You have me salivating with anticipation. Well I counted and I counted and I counted. When I went to university in Vienna, I had a most excellent physics professor. He insisted that experiments aimed at understanding nature must rest on mathematical models.
What an unusual position. Common developmental patterns reflect evolutionary kinship. Lizards and humans share a developmental pattern inherited from their remote common ancestor; the inherited pattern of each was modified only as the separate descendant lineages evolved in different directions. The common embryonic stages of the two creatures reflect the constraints imposed by this common inheritance, which prevents changes that have not been necessitated by their diverging environments and ways of life.
The embryos of humans and other nonaquatic vertebrates exhibit gill slits even though they never breathe through gills. These slits are found in the embryos of all vertebrates because they share as common ancestors the fish in which these structures first evolved. Human embryos also exhibit by the fourth week of development a well-defined tailwhich reaches maximum length at six weeks. Similar embryonic tails are found in other mammals, such as dogs, horses, and monkeys; in humans, however, the tail eventually shortens, persisting only as a rudiment in the adult coccyx.
A close evolutionary relationship between organisms that appear drastically different as adults can sometimes be recognized by their embryonic homologies. Barnacle s, for example, are sedentary crustaceans with little apparent likeness to such free-swimming crustaceans as lobsters, shrimps, or copepods. Yet barnacles pass through a free-swimming larval stage, the nauplius, which is unmistakably similar to that of other crustacean larvae. Embryonic rudiments that never fully develop, such as the gill slits in humans, are common in all sorts of animals.
Some, however, like the tail rudiment in humans, persist as adult vestiges, reflecting evolutionary ancestry. The most familiar rudimentary organ in humans is the vermiform appendix.
This wormlike structure attaches to a short section of intestine called the cecumwhich is located at the point where the large and small intestines join. The human vermiform appendix is a functionless vestige of a fully developed organ present in other mammals, such as the rabbit and other herbivores, where a large cecum and appendix store vegetable cellulose to enable its digestion with the help of bacteria.
Vestiges are instances of imperfections—like the imperfections seen in anatomical structures—that argue against creation by design but are fully understandable as a result of evolution. Biogeography Darwin also saw a confirmation of evolution in the geographic distribution of plants and animals, and later knowledge has reinforced his observations.
For example, there are about 1, known species of Drosophila vinegar flies in the world; nearly one-third of them live in Hawaii and nowhere else, although the total area of the archipelago is less than one-twentieth the area of California or Germany. Also in Hawaii are more than 1, species of snails and other land mollusks that exist nowhere else. This unusual diversity is easily explained by evolution.
The islands of Hawaii are extremely isolated and have had few colonizers—i. Those species that did colonize the islands found many unoccupied ecological nicheslocal environments suited to sustaining them and lacking predators that would prevent them from multiplying. In response, these species rapidly diversified; this process of diversifying in order to fill ecological niches is called adaptive radiation. In Africa are rhinoceroses, hippopotamuses, lions, hyenas, giraffes, zebras, lemurs, monkeys with narrow noses and nonprehensile tails, chimpanzees, and gorillas.
South Americawhich extends over much the same latitudes as Africa, has none of these animals; it instead has pumas, jaguars, tapir, llamas, raccoons, opossums, armadillos, and monkeys with broad noses and large prehensile tails.
These vagaries of biogeography are not due solely to the suitability of the different environments. There is no reason to believe that South American animals are not well suited to living in Africa or those of Africa to living in South America. The islands of Hawaii are no better suited than other Pacific islands for vinegar flies, nor are they less hospitable than other parts of the world for many absent organisms.
In fact, although no large mammals are native to the Hawaiian islands, pigs and goats have multiplied there as wild animals since being introduced by humans. This absence of many species from a hospitable environment in which an extraordinary variety of other species flourish can be explained by the theory of evolution, which holds that species can exist and evolve only in geographic areas that were colonized by their ancestors.
Molecular biology The field of molecular biology provides the most detailed and convincing evidence available for biological evolution.
This has made it possible to reconstruct evolutionary events that were previously unknown and to confirm and adjust the view of events already known. The precision with which these events can be reconstructed is one reason the evidence from molecular biology is so compelling. Another reason is that molecular evolution has shown all living organisms, from bacteria to humans, to be related by descent from common ancestors.
A remarkable uniformity exists in the molecular components of organisms—in the nature of the components as well as in the ways in which they are assembled and used. In all bacteria, plants, animals, and humans, the DNA comprises a different sequence of the same four component nucleotide s, and all the various protein s are synthesized from different combinations and sequences of the same 20 amino acid s, although several hundred other amino acids do exist.
The genetic code by which the information contained in the DNA of the cell nucleus is passed on to proteins is virtually everywhere the same. Similar metabolic pathways—sequences of biochemical reactions see metabolism —are used by the most diverse organisms to produce energy and to make up the cell components. This unity reveals the genetic continuity and common ancestry of all organisms. There is no other rational way to account for their molecular uniformity when numerous alternative structures are equally likely.
The genetic code serves as an example.
- Evolution: Constructing a Fundamental Scientific Theory
- Evolution: Constructing a Fundamental Scientific Theory
- Origin of Species quiz
Each particular sequence of three nucleotides in the nuclear DNA acts as a pattern for the production of exactly the same amino acid in all organisms. This is no more necessary than it is for a language to use a particular combination of letters to represent a particular object. If it is found that certain sequences of letters—planet, tree, woman—are used with identical meanings in a number of different books, one can be sure that the languages used in those books are of common origin.
Gene s and proteins are long molecules that contain information in the sequence of their components in much the same way as sentences of the English language contain information in the sequence of their letters and words. The sequences that make up the genes are passed on from parents to offspring and are identical except for occasional changes introduced by mutations.
As an illustration, one may assume that two books are being compared. Both books are pages long and contain the same number of chapters. Closer examination reveals that the two books are identical page for page and word for word, except that an occasional word—say, one in —is different.
The two books cannot have been written independently; either one has been copied from the other, or both have been copied, directly or indirectly, from the same original book. Similarly, if each component nucleotide of DNA is represented by one letter, the complete sequence of nucleotides in the DNA of a higher organism would require several hundred books of hundreds of pages, with several thousand letters on each page. The two arguments presented above are based on different grounds, although both attest to evolution.
Using the alphabet analogythe first argument says that languages that use the same dictionary—the same genetic code and the same 20 amino acids—cannot be of independent origin. The second argument, concerning similarity in the sequence of nucleotides in the DNA and thus the sequence of amino acids in the proteinssays that books with very similar texts cannot be of independent origin. The evidence of evolution revealed by molecular biology goes even farther.
The degree of similarity in the sequence of nucleotides or of amino acids can be precisely quantified. For example, in humans and chimpanzees, the protein molecule called cytochrome c, which serves a vital function in respiration within cellsconsists of the same amino acids in exactly the same order. It differs, however, from the cytochrome c of rhesus monkeys by 1 amino acid, from that of horses by 11 additional amino acids, and from that of tuna by 21 additional amino acids.
The degree of similarity reflects the recency of common ancestry. Thus, the inferences from comparative anatomy and other disciplines concerning evolutionary history can be tested in molecular studies of DNA and proteins by examining their sequences of nucleotides and amino acids.
See below DNA and protein as informational macromolecules. Not all possible tests have been performed, but many hundreds have been done, and not one has given evidence contrary to evolution. There is probably no other notion in any field of science that has been as extensively tested and as thoroughly corroborated as the evolutionary origin of living organisms. History of evolutionary theory Early ideas All human cultures have developed their own explanations for the origin of the world and of human beings and other creatures.
Traditional Judaism and Christianity explain the origin of living beings and their adaptations to their environments —wings, gills, hands, flowers—as the handiwork of an omniscient God.
Early Evolutionary Thinkers
The philosophers of ancient Greece had their own creation myths. Anaximander proposed that animals could be transformed from one kind into another, and Empedocles speculated that they were made up of various combinations of preexisting parts. The notion that organisms may change by natural processes was not investigated as a biological subject by Christian theologians of the Middle Ages, but it was, usually incidentally, considered as a possibility by many, including Albertus Magnus and his student Thomas Aquinas.
Aquinas concluded, after detailed discussion, that the development of living creatures such as maggots and flies from nonliving matter such as decaying meat was not incompatible with Christian faith or philosophy.
But he left it to others to determine whether this actually happened. The idea of progress, particularly the belief in unbounded human progress, was central to the Enlightenment of the 18th century, particularly in France among such philosophers as the marquis de Condorcet and Denis Diderot and such scientists as Georges-Louis Leclerc, comte de Buffon.
But belief in progress did not necessarily lead to the development of a theory of evolution. Pierre-Louis Moreau de Maupertuis proposed the spontaneous generation and extinction of organisms as part of his theory of origins, but he advanced no theory of evolution—i. Buffon, one of the greatest naturalists of the time, explicitly considered—and rejected—the possible descent of several species from a common ancestor.
He postulated that organisms arise from organic molecules by spontaneous generation, so that there could be as many kinds of animals and plants as there are viable combinations of organic molecules.
The English physician Erasmus Darwingrandfather of Charles Darwin, offered in his Zoonomia; or, The Laws of Organic Life —96 some evolutionary speculations, but they were not further developed and had no real influence on subsequent theories. The Swedish botanist Carolus Linnaeus devised the hierarchical system of plant and animal classification that is still in use in a modernized form. Although he insisted on the fixity of species, his classification system eventually contributed much to the acceptance of the concept of common descent.
The great French naturalist Jean-Baptiste de Monet, chevalier de Lamarckheld the enlightened view of his age that living organisms represent a progression, with humans as the highest form. From this idea he proposed, in the early years of the 19th century, the first broad theory of evolution. Organisms evolve through eons of time from lower to higher forms, a process still going on, always culminating in human beings.
As organisms become adapted to their environments through their habits, modifications occur.
Early Evolutionary Thinkers
Instructional Procedures Make copies of the student handouts 12 copies of each for a class of 36also make a copy of the student question sheet 1 per student. Make overhead of quizzes. Pass out readings with all students at a table receiving the same author. Have students read the papers aloud at their table. You may want to warn the students that they must read carefully for comprehension. The readings are difficult because the language is "old fashioned.
Explain to the students they must become an expert on the ideas of their author, they will be joining a different group with 2 representatives from each of the authors and explaining the view point of their author and helping other group members answer the questions.
Divide students into groups of 6 with 2 students representing each author. Allow students time to discuss and share answers in their groups. Alert students that they will be taking a quiz on one of the authors that they were not the expert on. They will be graded on their score on the quiz as well as the scores of the other students in their group on their author. Put quiz paper on the overhead.
Allow students to answer the question to the quiz of their choice as long as it was not the author they were an expert on. Answers to Analysis Questions: