You are here
Classification systems help us to understand where humans fit into the history of life on earth Organizing the great diversity of life into categories (groups based on shared characteristics) Showing the evolutionary relationships of past and present species
whale catfish shark Whale, catfish, and shark are all aquatic and have similar body types. bat bird Bats and birds have wings and fly Horse looks very different from these other species
Mammals Fish Birds Looks can be deceiving. Groupings based on scientific classification are very different from groups based on looks
Classification must reflect evolutionary patterns; similar traits inherited from a common ancestor E.g. bat, horse, and whale have mammary glands = mammals We analyze both living and extinct life forms to determine evolutionary relationships
Humans are classified as: Animals (kingdom) Chordata (phylum) Vertebrate (subphylum) Mammalia (class) Eutheria (subclass) Primates (order) Haplorhini (suborder) Anthropoidea (infraorder) Catarrhini (parvorder) Hominoidea (superfamily) Homindae (family) Homininae (subfamily) Hominini (tribe)
Constructing a classification based on homology First, classify on the basis of physical similarities (like having spinal cord) Make sure the basic physical similarities reflect evolutionary descent = must have been inherited from a common ancestor Similarities based on shared traits inherited from a common distant ancestor are called homologies
Example of homology Basic structure is the same two lower limb bones - radius and ulna; five digit hand with carpal and metacarpal bones single upper limb bone humerus Homology These similarities are based on shared traits inherited from a common distant ancestor
How could major evolutionary modifications like the development of the forelimb occur? They could be the result of relatively minor genetic changes over time Forelimb development in all vertebrates is directed by a few regulatory genes A few mutations in certain genes in early vertebrates could then lead to further changes in the structure of the wing of a chicken, flipper of a porpoise, or arm of a human remember hox genes?
Not all similarities reflect evolutionary relationship or descent from a common ancestor. Consider these two situations: Analogies Similarities are based on common function, with no assumed common evolutionary descent Homoplasy Independent development of similar characteristics due to function rather than evolutionary descent; traits were not inherited from a common distant ancestor
Example of Homoplasy The wings of birds and flies look similar on the outside and serve the same function flight But the wings of birds and insects are due to independent evolution, and not descent from a common ancestor Analogous structures
Are the similarities in the structure of a shark s fin and a dolphin s flipper an example of homology or homoplasy?
Even though the flippers look similar and have the same function, dolphins are mammals and sharks are fish They evolved independently, so the trait was not inherited from a common ancestor
Homology Structures shared by related species Inherited from common ancestor Example common forelimb bone structure of humans and bat wings is inherited from common ancestor Homoplasy Similar traits (analogies) in unrelated species Traits result of independent evolution (adaptation), not inherited from common ancestor Example wings of birds and flies have same function but not same structure and not inherited
Evolutionary Systematics traditional approach ancestors and descendants are traced in time by analysis of homologous traits (shared traits inherited from common ancestor) Cladistics rigorous evolutionary interpretations based solely on analysis of certain types of homologous characters must be based on derived traits (traits that changed away from ancestral condition)
Clade - Lineage, or a group of organisms sharing a common ancestor Includes the common ancestor and all descendants Cladistic = the field that identifies these groups Uses derived or modified traits (that have changed from ancestral condition) to identify clades
Ancestral Characters/traits inherited from a remote ancestor Not diagnostic of groups that diverged after the character appeared; also called primitive traits, but this reflects negatively on the value of the trait and may assume inferiority Derived (Modified) Traits that are modified (changed) from the ancestral condition & are diagnostic of particular evolutionary lineages
Clades and Derived Characteristics All these species have four limbs = shared inherited ancestral trait (here amphibians appeared earliest in the history of life on earth) Mammals have hair = a derived trait that has changed relative to amphibians. Mammals appeared later in the history of life than amphibians
Five digit hand is an ancestral trait inherited from a common distant ancestor Can we use this to establish a cladistic relationship between humans and apes? Why/why not?
No, both apes and humans still have the 5 digit hand. It has been retained from a very ancient common ancestor This trait has not changed or been modified; it is not a derived trait
Both humans and apes share certain features of shoulder anatomy that are not shared with monkeys or other primates This is a derived, modified trait
Traditional view, no close relationship
Revised view, common ancestry of birds and dinosaurs
The presence of feathers in the proposed relationship between some (theropod) dinosaurs and birds is an example of derived traits These are specific character traits shared in common between two life-forms and considered the most useful for making evolutionary interpretations
A chart showing evolutionary relationships as determined by evolutionary systematics It contains a time component and implies ancestor descendant relationships
A simple phylogenetic tree
A chart showing evolutionary relationships as determined by cladistic analysis It s based solely on interpretation of shared derived characters It contains no time component and does not imply ancestor-descendant relationships
This cladogram shows relationships of birds, dinosaurs, and other terrestrial vertebrates There s no time scale and ancestor-descendant relationships are not indicated
Intraspecific Variation Variation within a species; such as age and sex differences Interspecific variation Variation representing differences between species
A genus is a group of species composed of members more closely related to each other than to species from any other genus Species that are members of the same genus share the same broad adaptive zone Members of the same genus should all share derived characters not seen in members of other genera
Remains of animals and plants are found in sedimentary rock Shows the tremendous variety of living things Some species are now extinct Some species had traits that were transitional between major groups of organisms Confirms that species are not fixed but can evolve into other species over time
Traces of ancient organisms are formed in several ways Mineralization occurs very slowly as water carrying minerals, such as silica or iron, seeps into the tiny spaces within a bone. In some cases, the original minerals within the bone or tooth can be completely replaced. Traces of life forms that include insects trapped in tree sap, leaf imprints, footprints, skeletal remains and remains of digestive tracts Taphonomy (from Greek taphos grave ) is the study of how bones and other materials come to be buried in the earth and preserved as fossils
Illustration of layers of sedimentary rock
Containing an evolutionary sequence of fossils
An example of Stratigraphy
Taxa above the level of genus are referred to as the higher taxa There are five major higher taxa: kingdom, phylum, class, order and family. However, this can be expanded by the use of prefixes and other terms, such as: suborder, superfamily, and tribe.
The development of classifications depends on knowledge of evolutionary relationships among taxa A comparison between two animals may reveal many anatomical correspondences Structural correspondences that are the result of inheritance from a common ancestor are known as homologies or homologous features
Structures that are similar in two species, without being due to inheritance from a common ancestor, are said to be homoplastic Homoplasy can develop in four different ways: - Parallelism - Convergence - Analogy - Chance
In cladistics, homologies that appeared recently and are shared by a relatively small group of closely related taxa are called shared derived features Homologies that first appeared long ago and are shared by a larger group of species are called shared ancestral features Uniquely derived features are particular to a specific species within a group of species
The animal kingdom is divided into several units known as phyla, with each phylum representing a basic body plan Humans belong to the phylum Chordata A distinctive feature of the chordates is the presence of an internal skeleton and a notochord and nerve cord that runs along the back of the animal All chordates also have gill slits at some time in their development
The phylum Chordata includes the subphylum Vertebrata, which is comprised of most animals in the phylum In place of a notochord, a true vertebral column, or spine, has developed A major event in vertebrate evolution was the evolution of jaws The ancestors of land vertebrates were freshwater bony fish capable of coping with drought conditions These early vertebrates had lungs for supplementing their oxygen supply. The origin of land vertebrates also depended on the evolution of limbs
Mammals are homeothermic and can control their body temperature through physiological means Hair or fur provides a layer of insulation Mammals are characterized by heterodont dentition and have two sets of teeth, deciduous and permanent The reptilian jaw is composed of six bones, while the mammalian lower jaw is composed of only two bones, often fused into a single structure Other anatomical features aid mammals in dealing with terrestrial habitats - these characteristics include the diaphragm, hard palate, and the fourchambered heart
Offspring develop inside the mother Newborn mammals are nourished by taking milk from their mother s mammary glands Care is given to the young by the mother and often by the father and other adults Much of mammalian behavior is learned Mammals are characterized by improvements in the nervous system and elaboration of the brain Mammals are divided into three groups Prototherian - monotremes Metatherian - marsupials Eutherian - placental mammals
Monotremes Most primitive mammals Egg-laying mammal Only 3 species; duck-billed platypus and two Echidnas Marsupials Born incompletely developed and are typically carried and suckled in a pouch on the mother's belly Placental Characterized by the presence of a placenta, which facilitates exchange of nutrients and wastes between the blood of the mother and that of the fetus
Marsupials from Australia Koala Tasmanian Devil Kangaroo Australian marsupials inhabit Australia and New Guinea and include animal groups such as the kangaroos, wallabies, koalas, quolls, wombats, numbats, possums, marsupial moles, bandicoots and many others. Good example of reproductive isolation and speciation no placental mammals in Australia until they were introduced in the 1700 s All marsupials in Australia today evolved from one common ancestor Over time and via natural selection in different environments, the many marsupial species have occupied their own ecological niche, adapted and evolved
Placental mammals are a rather diverse group, with nearly 4000 described species, mostly rodents and bats. The placental mammals include everything from whales to primates, bears to bats, rabbits to seals, wolves to cows, and dogs to cats. Most of the mammals we are familiar with fall under this category.
The Cenozoic era - Age of Mammals The enlargement of the cerebrum, especially the neocortex, which controls higher brain functions, resulting in more nerve cells A longer, more intense period of growth in utero Distinctive dentition, termed a heterodont dentition, with 3 incisors, 1 canine, 4 premolars, and 3 molars in each quarter of mouth Maintenance of constant internal body temperature, warm-bloodedness, and endothermic
Able to maintain internal body temperature by producing energy through metabolic processes within cells; characteristic of mammals, birds, and perhaps some dinosaurs In contrast to Ectothermic - regulation of body temperature dependent on external sources, such as sunlight or a heated surfaces
Lateral view of the brain in fishes, reptiles, and primates Note the increased size of the cerebral cortex of the primate brain
Reptilian teeth (top) are homodont Mammals are heterodont, they have different kinds of teeth; incisors, canines, premolars, and molars
The organization of earth history into eras, periods, and epochs; commonly used by geologists and paleoanthropologists
Cenozoic - Age of Mammals All modern mammals evolved Primates Mesozoic - Age of Reptiles - Reptiles were dominant land vertebrate until around 65 mya Dinosaurs Monotremes egg-laying mammals Placental mammals, appeared 70 mya Birdlike reptiles Paleozoic Vertebrates appeared 500 mya first vertebrates- jawless fish first primitive amphibian first primitive reptiles fungi, plants, insects Multi-celled animals
Categories of the geological time scale In the Cenozoic, epochs include: Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Holocene I won t be using this
The movement of continents on sliding plates of the earth s surface As a result, the positions of large landmasses have shifted drastically during the earth s history Consider the possibilities for reproductive isolation and speciation as land masses separate and came together
The positions of the continents during the Mesozoic (c. 125 mya.) Pangea is breaking up into a northern landmass (Laurasia) and a southern landmass (Gondwanaland)
Map of earth 65,000,000 years ago Earth today Adaptive radiation Land mass of Earth once consisted of one single continent, Pangaea Continent drifted apart, mammals became separated Unable to breed and reproduce with one another, the gene pool of these groups of mammals became increasingly different Eventually they could no longer reproduce with one another
The positions of the continents at the beginning of the Cenozoic (c. 65 mya)