Evolution and Genetics

Evolution and Genetics Darwin Double-Helix of DNA Carl Sagan’s Universe Calendar  24 days = 1 billion years  1 second = 475 years  “Big Bang”  Milky Way  Solar System  Life on Earth  Humanlike Primates January 1 May 1 September 9 September 25 December 31, 10:30pm Chain of Being and Beyond Animals and plants could not become extinct under this theory  Apes were created with less perfection by God   Linnaeus (1707-1778) - classification system Lamarck (1744-1829) - acquired characteristics could be inherited and passed on (species could evolve)  Creationism and Catastrophism  Creationism accounts for biological diversity by referring to the divine act of Creation as described in Genesis. The discovery of fossil remains of creatures clearly unknown to modern humans was not accountable within the terms of simple Creationism.   Catastrophism (Georges Cuvier) is a modified version of Creationism, which accounts for the fossil record by positing divinely authored worldwide disasters that wiped out the creatures represented in the fossil record, who were then supplanted by newer, created species. Both versions of creationism describe the different species of plants and animals as essentially different, having distinct, separate moments of creation.  Evolution An alternative term for early evolutionism was “transformism.”  Darwin was influenced by the geological concept of uniformitarianism.    Uniformitarianism (Lyell and Hutton) states that past geological events can be best explained by observing the ongoing events of the present and generalizing backward through time. It further asserts that current geological structures are the result of long-term natural forces.  Transformism had posited the primordial relatedness of all life forms. Evolution  Darwin posited natural selection as the mechanism through which speciation takes shape (reaching this conclusion at the same time as Alfred Russell Wallace). “Natural selection is the gradual process by which nature selects the forms most fit to survive and reproduce in a given environment.” For natural selection to work on a given population, there must be variety within that population and competition for strategic resources.    The concept of natural selection argues that organisms which have a better fit within their environmental niche will reproduce more frequently than those organisms that fit less well. Genetics and Mendel  The science of genetics explains the origin of the variety upon which natural selection operates. The study of hereditary traits was begun in 1856 by Gregor Mendel, an Austrian monk. By experimenting with successive generations of pea plants, Mendel came to the conclusion that heredity is determined by discrete particles, the effects of which may disappear in one generation, and reappear in the next.   Genetics and Mendel Mendel’s second set of experiments with pea plants. Dominant colors are shown unless otherwise indicated. Genetics and Mendel  Mendel determined that the traits he observed occurred in two basic forms: dominant and recessive.   Dominant forms manifest themselves in each generation. Recessive forms are masked whenever they are paired with a dominant form of the same trait in a hybrid individual. It has since been demonstrated that some traits have more than these two forms—human blood type, for example, has several forms, some of which are codominant.  Genetics and Mendel Punnett square of a homozygous cross and a heterozygous cross. These squares show how phenotypic ratios of the F1 and F2 generations are generated. Colors show genotypes. Genetics and Mendel       The traits Mendel identified occur on chromosomes. Humans have twenty three matched pairs of chromosomes, with each parent contributing one chromosome to each pair. Chromosomes contain several genes, or genetic loci, which determine the nature of a particular trait. A trait may be determined by more than one gene. Alleles are the biochemically different forms which may occur at any given genetic locus. Chromosome pairs’ loci may be homozygous (identical alleles) or heterozygous (mixed). Genetics and Mendel       Mendel also determined that traits are inherited independently of one another. The fact that traits are transmitted independently of one another, and hence may occur in new combinations with other traits, is responsible for much of the variety upon which natural selection operates. Mitosis is ordinary cell division, wherein one cell splits to form two identical cells. Meiosis is the type of division particular to sex cells, wherein four cells are produced from one, each with half the genetic material of the original cell (i.e., twenty three chromosomes instead of forty six). Fertilization allows the products of meiosis from one parent to recombine with those from the other parent. Because genes sort independently during recombination, the number of possible combinations is exponentially high (223): a major source of variety. Mitosis A fertilized human egg (zygote) undergoes mitosis, or ordinary cell division. Shown here, two cells have split to form four identical cells. DNA and RNA  DNA - deoxyribonucleic acid    Watson and Crick - double helix adenine/thymine and cytosine/guanine Human Genome Project - July 2000, initial mapping complete  RNA - ribonucleic acid    messenger RNA (mRNA) adenine/uracil and cytosine/guanine single-stranged  Protein Synthesis Population Genetics  Population genetics looks at changes in gene frequencies at the level of the community or breeding population.  Gene pool refers to all of the alleles and genotypes within a breeding population. Genetic evolution is defined as change in the frequency of alleles in breeding population from generation to generation.   There are four basic mechanisms which produce changes in gene frequency in a population (i.e., genetic evolution): natural selection, mutation, genetic drift, and gene flow. Natural Selection  Genotype refers to the genetic makeup of an organism.  Phenotype is the expression of the genotype as it has been influenced through development by interacting with its environment (outward appearance). Environmental influence in this interaction is extremely important, and lends great plasticity to human biology.   Natural selection acts upon phenotypes. Directional/Balancing/Normalizing Selection      Natural selection affects gene frequencies within a population. Adaptive genes are selected for (organisms containing them reproduce more frequently) and maladaptive genes are selected against (organisms containing them reproduce less frequently). Directional Selection - When specific adaptive genes are selected for over a long time period, causing a major shift in gene frequency.  Continues until equilibrium is reached and can reduce variation in a gene pool Normalizing Selection - Average does not change, but natural selection removes the extremes (e.g. birth weight of babies) Balancing Selection - Heterozygous combination of alleles is favored even though a homozygous combination is disfavored (e.g. sickle cell anemia) Mutation  Mutation introduces genetic variation into a breeding population. Chemical alterations in genes may provide a population with entirely new phenotypes, with possible concomitant selective advantages. Cultural factors come into play in allowing mutations to be passed on instead of selected out of a population   Random Genetic Drift  Random genetic drift is the loss of alleles from a population's gene pool through chance. There is no set form for this chance; it may simply occur through a statistical fluke in sexual reproduction patterns, or through the effects of a catastrophe on the population as a whole.   Founder Principle - Occurs when a small group recently derived from a larger population migrates to a relatively isolated location Gene Flow    Gene flow occurs through interbreeding: the transmission of genetic material from one population to another. Gene flow decreases differences Gene flow inhibits speciation, the formation of new species.  A species is an internally interbreeding population whose offspring can survive and are capable of reproduction.  Speciation occurs when populations of the same species become isolated from each other (thus stopping gene flow) allowing natural selection and genetic drift gradually to produce gene pools that are different, to the extent that successful interbreeding is no longer impossible.  Cline - variation in gene frequency from one end of the region to another Natural Selection at Work: Bergmann and Allen’s Rules Different climates have selected for different body shapes.  Bergmann's rule states that because of the respective ratios between mass and surface area, smaller bodies dissipate heat faster, and larger bodies retain heat better; thus more larger animals are found in colder habitats, while smaller animals have been selected for in hotter habitats.   Allen's Rule states that slender bodies with long limbs dissipate heat more efficiently, and are selected for in tropical climates: heavy, short-limbed bodies retain heat better, and are selected for in colder climates. Allen’s Rule This Nilotic man, a Nuer herder from Sudan, has a tall linear body with elongated extremities (note his fingers). Such proportioning increases the surface area relative to mass and thus dissipates heat according to Allen’s Rule. Allen’s Rule Cold weather populations tend to have relatively larger chests and shorter arms then do people from warm areas. Among the cold-adapted Inuit, such as this Alaskan woman, short limbs and stocky bodies help conserve heat. Hardy-Weinberg Formulæ  To get:    allele (gene) frequencies: solve for p and q genotype frequencies: AA = p2; Aa = 2pq; aa = q2 phenotype frequencies: AA + Aa = A phenotype; aa = a phenotype # of people with genes: AA x population; Aa x population; aa x population # of people with traits: AA + Aa x population; aa x population   Rates of Evolution  Punctuated equilibrium  Niles Eldredge and Stephen Jay Gould - 1972 Dobzhansky, Huxley, Mayr, Simpson - 1930s and 1940s  Phyletic gradualism (aka “modern synthesis”)  Sociobiology  Sociobiology is the study of the evolutionary basis for behavior.  Lions hunt in packs, but cats are solitary  Large human brain came about because of tool-making  Longer educational period came about because of long maturation period of human adolescents The Living Primates COMMON PRIMATE TRAITS      Dense hair or fur covering Warm-blooded Give birth to live young Suckle Long period of infant dependence Physical Traits of Primates   Arboreal existence (grasping feet, suspensory upper limbs) Omnivorous diet   specific chewing teeth molars and premolars / canines and incisors   Prehensile hands with opposable thumbs Larger portion of brain for stereoscopic vision rather than smell (smaller rhinencephalon, larger cerebellum)  Specific reproductive systems    pendulous penis two nipples on chest uterus holds one fetus Physical Traits of Primates Common physical traits of primates include similarities in: • hands and feet • eye position • rotation of the forearm • brain size and function THE SOCIAL PRIMATE  Social life, especially for diurnal primates, is very important for survival  Most primates have an extended length of dependency (secondary altriciality) during which time the young can observe and learn from adult members   Play is an important part of the learning process for primates Some research has noted that chimpanzees learn from observation and imitation  Pecking order among primates is governed by rules of conduct  Subordinates show respect Classifying Primates Phylogenetic Classification The principle classificatory units of zoological taxonomy. Humans in Zoological Taxonomy Taxon Kingdom Phylum Subphylum Class Infraclass Order Suborder Infraorder Superfamily Family Genus Species Subspecies Scientific (Latin) Name Animalia Chordata Vertebrata Mammalia Eutheria Primates Anthropodea Catarrhini Hominoidea Hominidae Homo Homo sapiens Homo sapiens sapiens Common (English) Name Animals Chordates Vertebrates Mammals Eutherians Primates Anthropoids Catarrhines Hominoids Hominids Humans Recent humans Modern humans Prosimians Prosimian = “Pre-monkey”  Unlike anthropoids in ears, whiskers, snouts, and faces  Like anthropoids in hands, vision, and brain  Lemurlike Forms  Lorislike Forms  Tarsierlike Forms  Quadrupeds - Move on all fours  Vertical clinging and leaping  Active during the evening (nocturnal)  Lemurs and Tarsiers Most of the remaining prosimians, by far, are lemurs.  These live only in Madagascar, which separated from Africa prior to the development of anthropoids.  Tarsiers survived in Asia, where there are monkeys, by adapting to night conditions (monkeys are not nocturnal).  A crown lemur. Anthropoids     Anthropoids - Include the monkeys, apes, and humans  Two main groups  Platyrrhines = “flat nose” (New World monkeys)  Catarrhines = “hanging nose” (Old World monkeys) Vision  Evolutionary changes in vision probably occurred in response to a the pressures of an arboreal habitat.  Binocular, stereoscopic vision and color vision may have been selected due to the improved depth perception it endows (locomotion, catching insects, identifying edible fruits). The arboreal habitat (climbing, feeding) and the increasingly social environment (mutual grooming, tool making) were likely factors in selecting for increased manual tactility. Proportionately larger (than prosimians) brain mass and emphasis on memory and cognition were likely selected for by the social environment. Platyrrhines and Catarrhines Nose structure of catarrhines and platyrrhines. Above is the narrow septum and “sharp nose” of a guernon, a catarrhine (Old World monkey). Below is the broad septum and “flat nose” of Humbolt’s woolly monkey, a platyrrhine. NEW WORLD MONKEYS  New World Monkeys (Platyrrhines)  Marmosets and tamarins  Small, have claws, give birth to twins, and call for two or more adults for care for two years  universally arboreal, some brachiate, some have prehensile tails (among primates, a trait exclusive to the New World)  Adults may practice monogamy or polyandry  poly- = many ; mono- = one  -andry = males ; -gyny = females  -gamy = mates OLD WORLD MONKEYS  Two major subfamilies  Colobine Monkeys - Mostly tree monkeys with diet consisting mainly of tree leaves  Cercopithecine Monkeys - Many show a great deal of sexual dimorphism; calloused bottoms for sitting comfortably in trees or on the ground for long periods of time  di = dividing into two  -morph = body  (meta- = change) Old World Monkeys  Many are terrestrial but can be arboreal  Significant distinctions existing between arboreal and terrestrial Old World monkeys include size (arboreal monkeys are smaller than terrestrial monkeys) and sexual dimorphism (terrestrial males are significantly larger and fiercer than terrestrial females, while little or no such differentiation exists among arboreal monkeys. Old World Monkeys Yellow baboons, an Old World monkey. Primate Family Tree The Hominoids Old World Monkeys comprise the superfamily Cercopithecoidea, while humans and apes are in the superfamily Hominoidea.  Hominoidea is subdivided into three families.      Hominids (humans and their fossil ancestors). Pongids (“great apes”: gorillas, chimpanzees, and orangutan). Hylobatids (gibbons and siamangs). Recent biochemical evidence suggests that gorillas and chimpanzees are almost as closely related to humans as they to each other. The Hominoids      Gibbons and Siamangs  Spectacular brachiators  Long arms and fingers allow hand-over-hand swinging through tree cover Orangutans  Most live solitary lives; unusual among higher primates, but good for selfpreservation (hide from humans) Gorillas  Knuckle-walking is their common/”all fours” form of locomotion Chimpanzees  Move best on the ground with knuckle-walking form  Group life ebbs and flows, depending on environmental conditions; e.g. availability of food, defense, etc. Hominids  Modern humans who share over 90% of their DNA with chimpanzees and gorillas Gibbons and Siamangs  Above: Gibbon  Right: Siamang Orangutans Orangutans relatively large (up to 200 pounds), solitary, and markedly sexually dimorphic.  Orangutans move between arboreal and terrestrial habitats.  Gorillas   Gorillas are large (up to 400 pounds), the most sexually dimorphic of all primates, and are primarily terrestrial. They live in relatively stable social groups, typically led by a mature silver-back male. Members of a mountain gorilla troop sit with primatologist Dian Fossey. Chimpanzees Bonobos (left) Chimp (right) African Apes Map of the ranges of the three species of African apes. VARIABILITY IN PRIMATE ADAPTATIONS    Body Size  What accounts for such difference?  Time of day the species is active (diurnal, nocturnal)  Where the species is active (trees, plains, savanna)  Kinds of food eaten (carnivorous, omnivorous, frugiferous) Relative Brain Size  Ratio of brain size to body size  Leaf eaters tend to have smaller brains because amount of nutrients needed for larger brains (glucose) is missing Group Size  Nocturnal monkeys have smaller bodies and group size, feeding alone or in pairs  Terrestrial groups may be larger due to the need for more eyes and ears for protection; more teeth and strength to defend against predators Human-Primate Similarities   Adaptive Flexibility Through Learning  Neotony and life in cooperative social groups allows primates to learn behavior from their fellows, rather than relying only on genetically encoded behaviors.  Learned behavior has been observed in monkeys as well as apes. Predation and Hunting  Hunting is a regular and normal component of wild chimpanzee behavior.  Hunting by chimps is both opportunistic and planned.  Wild chimpanzees have been observed hunting consistently, using cooperative techniques, with some sex specialization (males hunt more than females). Human-Primate Similarities  Tools   Tool use allows primates to adapt to a wider range of niches more quickly than physiological adaptation alone (although primates are not the only animals that use tools). Wild chimps have been observed constructing tools. At Tanzania’s Gombe Stream National Park, chimps use specially prepared twigs to “fish” for termites Human-Primate Similarities  Aggression and Resources   The capacity for hunting exists among many different primates, but expression of this capacity can depend upon environmental pressure and opportunity. Observations of chimps and orangutans indicate that aggressive behavior (“warfare,” in some chimp cases) may increase when territorial encroachment occurs. Washoe (common chimp) - ASL Kanzi (bonobo) - Graphic symbols  Language   Human-Primate Differences   Sharing, Cooperation, and Division of Labor  Sharing and cooperation is common to most primates, however humans do it much more complexly.  Human foraging bands tend to have a sexual division of labor (e.g., men hunt, women gather), other primates do not.  Homo sapiens is the only primate species that engages in food sharing consistently on a large scale. Mating and Kinship  Human females do not experience estrus.  Marriage and kinship are two exclusively, universally human systems that give identity and stability to certain types of human relationships in a way that is absent from other primate social systems. Distinctive Human Characteristics  Physical Traits    Bipedalism Cerebral cortex - Center for speech and other higher mental activities Continuous female sexuality (loss of estrus) Toolmaking - Humans are unique for using one tool to make another one Only humans have spoken, symbolic language To what degree do other primates use language (or are capable of using it)? Only humans have hunted very large animals Humans are completely terrestrial Humans have the longest dependency period (secondary altriciality) of all primates  Behavioral Abilities   Language    Other Human Traits     Humans have complex division of labor, often divided by sex