Biology, 9th ed,Sylvia Mader Chapter 17 Chapter 17 Darwin and Evolution Darwin and Evolution

Outline History of Evolutionary Thought Darwin’s Theory of Evolution Earth very old Descend with change from a common ancestor Adaptation to a changing environment The Evidence of Evolution Fossil Biogeographical Anatomical Biochemical

Voyage of the HMS Beagle

Charles Darwin at 31

History of Evolutionary Thought Prior to Darwin View of nature determined by deep-seated beliefs Held to be intractable truths Biology thought had slowly begun to accept Various ideas of evolution Similarities between living things reflect recent common ancestry Dissimilarities between living things reflect ancient common ancestry

Mid-Eighteenth Century Taxonomy matured during mid-eighteenth century Linnaeus believed in: The fixity of species That each species had: An ideal structure and function, and A place in the scala naturae (scale of complexity) Count Buffon: Wrote 44-volume catalog of all known plants and animals Suggested descent with modification

Late Eighteenth Century Cuvier: First to use comparative anatomy to develop a system of classification Founded Paleontology Proposed Catastrophism Local catastrophes in past had caused later strata to have a new mix of fossils After each catastrophe, the region was repopulated by species from surrounding areas

Late Eighteenth Century Lamarck: First biologist to: Propose evolution Link diversity with environmental adaptation Concluded more complex organisms are descended from less complex organisms Proposed inheritance of acquired characteristics – Lamarckianism Charles Lyell: Earth is subject to slow but continuous cycles of erosion and uplift Proposed uniformitarianism, rates and processes of change are constant

Evolutionary Thought before Darwin Lamarck: First biologist to: Propose evolution Link diversity with environmental adaptation Concluded more complex organisms are descended from less complex organisms Proposed inheritance of acquired characteristics – Lamarckianism

Formation of Sedimentary Rock Charles Lyell: Earth is subject to slow but continuous cycles of erosion and uplift Proposed uniformitarianism, rates and processes of change are constant

Darwin’s Theory of Evolution Geological observations consistent with those of Hutton & Lyell Biogeographical observations: The study of the geographic distribution of life forms on earth Darwin saw similar species in similar habitats; Reasoned related species could be modified according to the environment

A Glyptodont and a Giant Sloth

The Patagonian Hare, Dolichotis patagonium Did the Patagonian Hare resemble a rabbit because the two types of animals were adapted to the same type of Environment? Did the Patagonian hare have the face of a guinea pig because of common descent with guinea pigs?

Galápagos Islands Tortoises Finches Darwin observed tortoise neck length varied from island to island Proposed that speciation on islands correlated with a difference in vegetation Finches Darwin observed many different species of finches on various islands Speculated they could have descended from a single pair of mainland finch

Galápagos Tortoises, Geochelone Darwin observed tortoise neck length varied from island to island Proposed that speciation on islands correlated with a difference in vegetation

Galápagos Finches Finches Darwin observed many different species of finches on various islands Speculated they could have descended from a single pair of mainland finch

Geology and Fossils Darwin began to accept the idea that the earth is very old. And that there would be enough time for “descent with modification” to occur. Darwin decided adaptations develop over time; he sought a mechanism by which adaptations might arise.

Natural Selection & Adaptation Natural selection was proposed by both Alfred Russel Wallace and Darwin as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation. Because the environment is always changing, there is no perfectly-adapted organism

Natural Selection & Adaptation Individuals have heritable variations More individuals produced each generation than environment can support Some individuals have adaptive characteristics Enables increased survival and reproduction Increasing proportion of succeeding generations will have these characteristics Populations become adapted to their local environment through change in individuals

Natural Selection Preconditions for Natural Selection The members of a population have random but heritable variations. In a population, more individuals are produced than will survive. Some individuals have adaptive characteristics that enable them to survive and reproduce better. (Fitness) Consequences of Natural Selection An increasing proportion of individuals in succeeding generations have the adaptive characteristics. (Adaptation) The result of natural selection is a population adapted to its local environment.

Variation in a Population

Organisms Have Variations Darwin emphasized that individuals from a population vary in their: Functional characteristics Physical characteristics Behavioral characteristics Proposed that these VARIATIONS: Are essential Allow adaptation to the environment over time

Artificial Selection of Animals

Artificial Selection of Plants

Organisms Struggle to Exist Malthus Each generation has the same reproductive potential as the previous generation Reproductive potential is greater than environment can support Death, disease, and famine were inevitable if population were to have stability Individuals experience a constant struggle for survival

Organisms Differ in Fitness Fitness is the relative reproductive success of an individual The most-fit individuals in a population capture a disproportionate share of goodies Interactions with the environment determine which individuals reproduce the most Adaptation Changes that help a species become more suited to its environment Product of natural selection

Transitional Fossils

Evidence for Evolution Common Descent “Descent with Modification” The hypothesis of common descent is supported by many lines of evidence. The more varied the evidence, the more certain it becomes. Darwin synthesized much of the current data but biochemical research was yet to come.

Evidence for Evolution Fossils Evidence Biogeographical Evidence Anatomical Evidence Embryological development Biochemical Evidence

The Evidence of Evolution: Fossil Fossil Evidence Fossils record the history of life from the past Document a succession of life forms from the simple to the more complex Sometimes the fossil record is complete enough to show descent from an ancestor

Evidence for Evolution Fossils Evidence The fossil record is the history of life recorded by remains from the past. Fossils are at least 10,000 years old and include skeletons, shells, seeds, insects trapped in amber, and imprints of leaves. The fossil record traces history of life and allows us to study history of particular organisms. Fossil evidence supports the common descent hypothesis; fossils can be linked over time because they reveal a similarity in form, despite observed changes.

Evidence for Evolution Fossils Evidence Transitional forms reveal links between groups. Caudipteryx is between dinosaurs and birds This Chinese fossil shows some dinosaurs had feathers on arms, tail and probably body. Advantages during running and escape gave rise to birds once lift-off occurred. Eustheopteron is an amphibious-like fish Seymouria is a reptile-like amphibian Therapsids were mammal-like reptiles

Fraud!

Intermediate & Transitional Links Charles Darwin acknowledged that the fossil record was a serious problem for his theory: “By the theory of natural selection, all living species have been connected with the parent-species of each genus, by differences not greater that we see between the natural and domestic varieties of the same species at the present day… the number of intermediate and transitional links, between all the living and extinct species, must have been inconceivably great.”

Evidence for Evolution Fossils Evidence According to Darwin’s theory of evolution, all animals are descended from a common ancestor in the distant past. Supposedly, a single primitive species gradually diverged into two species, then those diverged over millions of generations to the point where we now see the major differences in body plans

Evidence for Evolution Fossils Evidence When we look at the fossil record we see that most of these major differences were present at the earliest appearance of animal life. Darwin himself knew this, and in The Origin of Species he called it a “serious” problem for his theory.

Evidence for Evolution Fossils Evidence Paleontologists James Valentine and Douglas Erwin wrote in 1987 that the Cambrian explosion “is real; it is too big to be masked by flaws in the fossil record.” And in 1991, Valentine and his colleagues wrote that the Cambrian explosion “was even more abrupt and extensive than previously envisioned.”

The Evidence of Evolution: Biogeographical Distributions of plants and animals across earth Consistent with origin in one locale and then spread to accessible regions

All of the marsupials in Australia presumably evolved from a common ancestor

Evidence for Evolution Biogeographical Evidence Physical factors, such as the location of continents, determine where a population can spread. Marsupials arose when South America, Antarctica, and Australia were joined; Australia separated before placental mammals arose, so only marsupials diversified in Australia. The distribution of organism on the earth is explainable by ASSUMING that related forms evolved in one locale. They then diversified as they spread out.

The Evidence of Evolution: Anatomical Vertebrate forelimbs: Homologous - All contain the same sets of bones in similar ways Yet they are modified extensively to meet various adaptive needs Darwin interpreted this as support for a hypothesis of common descent

Significance of Homologous Structures

The Evidence of Evolution: Anatomical Homologous Structures: Anatomically similar because they are inherited from a common ancestor May be functionally similar or not Analogous Structures: Serve the same function Not constructed similarly Do not share a common ancestor Vestigal Structures: Fully-developed anatomical structures Reduced or obsolete function

Vestigial Limbs in Whales

Arguments against Homology 1. If homology is defined as similarity due to common descent, then it is circular reasoning to use it as evidence for common descent. Common Descent Homology

Arguments against Homology 2. Biologist have known for decades that homologous features are NOT due to similar genes, so the mechanism that produces them remains unknown. “Because homology implies community of descent from… a common ancestor it might be thought that genetics would provide the key to the problem of homology. This is were the worst shock of all is encountered…[because] characters controlled by identical genes are not necessarily homologous… [and] homologous structures need not be controlled by identical genes” Gavin de Beers

Arguments against Homology Homologous Structures can arise from different genes In fruit flies “even-skipped” gene – development of body segments. Not found in all other insects “Sex-lethal” gene – sex determination in fruit flies but not other insects

Arguments against Homology Non-homologous structures can arise from identical genes. “Distal-less” gene – an appendage developmental gene found in: Mice, spiny worms, Butterfly, sea urchins, velvet worm Yet the appendages are not homologous either by similar structure or by common ancestry (descent)

The Evidence of Evolution: Anatomical Embryological development All vertebrate embryos have: A postanal tail and Paired pharyngeal (gill) pouches

Significance of Developmental Similarities Embryological development All vertebrate embryos have: A postanal tail & Paired pharyngeal (gill) pouches

Evidence for Evolution Anatomical Evidence Embryological development reveals a unity of plan. During development, all vertebrates have a post-anal tail and paired pharyngeal pouches. In fishes and amphibian larvae, the pouches become gills. In humans, first pair of pouches becomes a cavity of middle ear and auditory tube; second pair becomes tonsils, while third and fourth pairs become thymus and parathyroid glands. Above features are explained if fishes are ancestral to other vertebrate groups.

Haeckel’s Embryos – similarities in early embryos not only demonstrate that they are descended from a common ancestor, but also reveal what that ancestor looked like. “The [human] embryo itself at a very early period can hardly be distinguished from that of other members of the vertebrate kingdom.” Since humans and other vertebrates “pass through the same early stages of development, … we ought frankly to admit their community of descent” Charles Darwin, The Descent of Man

Contrary Evidence Embryological Development Pharyngeal pouches (or folds) are never rudimentary gills in reptiles, birds or mammals. British embryologist Lewis Wolpert: “A higher animal, like the mammal, passes through an embryonic stage when there are structures that resemble the gill clefts of fish. But this resemblance is ILLUSORY and the structures in mammalian embryos only resemble the structures in the embryonic fish that will give rise to gills.” The only way to see “gill-like” structures in human embryos is to read evolution into development.

Contrary Evidence Concerning Haeckel’s Embryos Include ONLY those classes and orders closest to fitting Haeckel’s theory. They distort the embryos they purport to show (Most Seriously) they entirely omit earlier stages in which vertebrate embryos look very different.

Contrary Evidence Concerning Haeckel’s Embryos Stephen Jay Gould, Natural History magazine March 2000 Gould acknowledged that Haeckel faked his drawings. “To cut to the quick of this drama, Haeckel had exaggerated the similarities by idealizations and omissions. He also, in some cases – in a procedure that can only be called fraudulent – simply copied the same figure over and over again.”

Contrary Evidence Concerning Haeckel’s Embryos Stephen Jay Gould, (Natural History magazine, March 2000, pg. 45) Gould acknowledged that Haeckel faked his drawings. “We do, I think, have the right to be both astonished and ashamed by the century of mindless recycling that has led to the persistence of these drawings in a large number, if not a majority, of modern textbooks. Atrocious!”

Biochemical Evidence Almost all living organisms: Use the same basic biochemical molecules Utilize same DNA triplet code Utilize same 20 amino acids in their proteins DNA base-sequence differences: When very similar, suggest recent common descent When more different, suggest more ancient common descent

Significance of Biochemical Differences

Review History of Evolutionary Thought Darwin’s Theory of Evolution Earth very old Descend with change from a common ancestor Adaptation to a changing environment The Evidence of Evolution Fossil Biogeographical Anatomical Biochemical

Biology, 9th ed,Sylvia Mader Chapter 17 Ending Slide Chapter 17 Darwin and Evolution Darwin and Evolution