Biosc 41 Announcements 12/1 Review: evolution (chapters 22, 23) Today s lecture: speciation and human evolution Today s lab: work on group presentations for Wed Wed s lecture: conservation biology Wed s lab: group presentations Final exam: Mon Dec 8, 5:25pm, lecture classroom
Evolution Review What is meant by paradigm shifts in science? Darwin s world- how old was the Earth thought to be? Vs. our current understanding? Darwin s term descent with modification = evolution; mechanism = natural selection (published in Origin of Species ) Fundamental tenets of evolution- (1) overproduction, (2) heritable variation among individuals. What are the sources of genetic variation? Does natural selection act on the individual or the population? What about evolution? Examples and evidence: fossil record, comparative anatomy, comparative embryology, comparative genomics, biogeography (& endemic species), artificial selection, drug-resistant bacteria Natural selection: unequal reproduction leads to evolution; natural selection does not create new traits, but selects for traits already present in the population. Traits that are selected in one environment may not be advantageous in another environment
Evolution Review Microevolution vs macroevolution; speciation Examples of geographic variation What is Darwinian Fitness? Does it act on genotypes or phenotypes? Allele frequency, gene pool, Hardy-Weinberg principle- is Hardy- Weinberg equilibrium common in nature? Five conditions of non-evolving populations: No mutations Random mating No natural selection Very large population size No gene flow
Evolution Review Frequencies of two alleles, p + q = 1 Genotype frequencies in a population: p 2 + 2pq + q 2 = 1 p 2 = homozygous dominant 2pq = heterozygous q 2 = homozygous recessive Which genotype frequency is known in a population?
Evolution Review Mechanisms of microevolution: Genetic drift: bottlenecks, founder effects- bigger influence in smaller populations Migration (gene flow)- reduces genetic variation between populations Mutations Natural selection, including nonrandom mating- be able to identify each by graph and/or situation: Balancing selection: heterozygote advantage, frequencydependent selection Directional Disruptive Stabilizing
Speciation and Human Evolution References: chapters 24 (first few slides) 34 (last few pages of chapter)
Speciation can occur rapidly or slowly, and can result from changes in few or many genes Many questions remain of how long it takes new species to form, and how many genes need to differ between species Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 million years
The Time Course of Speciation Punctuated equilibrium Species are stable for long periods of time (equilibrium) Evolution over relatively short time intervals (punctuation) Gradualism Species evolve gradually; intermediate forms persist in fossil record
Speciation Rates The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid For example, the sunflower Helianthus anomalus originated from the hybridization of two other sunflower species Laboratory studies showed that the new species could arise within a few generations
Studying the Genetics of Speciation A fundamental question of evolutionary biology persists: How many genes change when a new species forms? Depending on the species in question, speciation might require the change of only a single allele or many alleles In Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene
Studying the Genetics of Speciation In monkey flowers (Mimulus), two loci affect flower color, which influences pollinator preference Pollination dominated by either hummingbirds or bees can lead to reproductive isolation of the flowers In other species, speciation can be influenced by larger numbers of genes and gene interactions
From Speciation to Macroevolution Macroevolution is the cumulative effect of many speciation and extinction events Macroevolution often follows macro-events in earth history Asteroid impacts Major climate change
Human Speciation Monotremes (5 species) Monotremata ANCESTRAL MAMMAL Marsupials (324 species) Eutherians (5,010 species) Marsupialia Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida Macroscelidea Xenarthra Rodentia Lagomorpha Primates Dermoptera Scandentia Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphla Pholidota
Primates The mammalian order Primates includes lemurs, tarsiers, monkeys, and apes Humans are members of the ape group
Derived characters of primates A large brain and short jaws Forward-looking eyes close together on the face, providing depth perception Complex social behavior and parental care Most primates have hands and feet adapted for grasping, and flat nails A fully opposable thumb (in monkeys and apes)
Living Primates There are three main groups of living primates Lemurs, lorises, and bush babies Tarsiers Anthropoids (monkeys and apes)
The oldest known anthropoid fossils, about 45 million years old, indicate that tarsiers are more closely related to anthropoids than to lemurs
Figure 34.42 ANCESTRAL PRIMATE Lemurs, lorises, and bush babies Tarsiers New World monkeys Old World monkeys Gibbons Anthropoids Orangutans Gorillas Chimpanzees and bonobos Humans 70 60 50 40 30 20 10 0 Time (millions of years ago)
The first monkeys evolved in the Old World (Africa and Asia) (a) New World monkey: spider monkey In the New World (South America), monkeys first appeared roughly 25 million years ago New World and Old World monkeys underwent separate adaptive radiations during their many millions of years of separation (b) Old World monkey: macaque
The other group of anthropoids consists of primates informally called apes This group includes gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans Apes diverged from Old World monkeys about 25 30 million years ago (a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees (e) Bonobos
Video: Gibbons Brachiating
Video: Chimp Agonistic Behavior
Video: Chimp Cracking Nut
Concept 34.7: Humans are mammals that have a large brain and bipedal locomotion The species Homo sapiens is about 200,000 years old, which is very young, considering that life has existed on Earth for at least 3.5 billion years
Derived Characters of Humans A number of characters distinguish humans from other apes Upright posture and bipedal locomotion Larger brains capable of language, symbolic thought, artistic expression, creation and use of complex tools Reduced jawbones and jaw muscles Shorter digestive tract
The human and chimpanzee genomes are 99% identical Changes in regulatory genes can have large effects
The Earliest Hominins The study of human origins is known as paleoanthropology Hominins (formerly called hominids) are more closely related to humans than to chimpanzees Paleoanthropologists have discovered fossils of about 20 species of extinct hominins
Figure 34.45 0 0.5 Paranthropus boisei Paranthropus robustus Homo ergaster Homo neanderthalensis? Homo sapiens 1.0 1.5 Australopithecus africanus Millions of years ago 2.0 2.5 3.0 3.5 4.0 Australopithecus anamensis Kenyanthropus platyops Australopithecus garhi Homo habilis Homo rudolfensis Homo erectus 4.5 5.0 Australopithecus afarensis 5.5 6.0 6.5 7.0 Orrorin tugenensis Ardipithecus ramidus Sahelanthropus tchadensis
The oldest fossil evidence of hominins dates back to 6.5 million years ago Early hominins show evidence of small brains and increasing bipedalism
Misconception: Early hominins were chimpanzees Correction: Hominins and chimpanzees shared a common ancestor Misconception: Human evolution is like a ladder leading directly to Homo sapiens Correction: Hominin evolution included many branches or coexisting species, though only humans survive today
Australopiths Australopiths are a paraphyletic assemblage of hominins living between 4 and 2 million years ago Some species, such as Australopithecus afarensis walked fully erect (a) The Laetoli footprints (b) An artist s reconstruction of A. afarensis
Robust australopiths had sturdy skulls and powerful jaws Gracile australopiths were more slender and had lighter jaws
Bipedalism Hominins began to walk long distances on two legs about 1.9 million years ago Bipedal walking was energy efficient in the arid environments inhabited by hominins at the time
Tool Use The oldest evidence of tool use, cut marks on animal bones, is 2.5 million years old Fossil evidence indicates tool use may have originated prior to the evolution of large brains
Early Homo The earliest fossils placed in our genus Homo are those of Homo habilis, ranging in age from about 2.4 to 1.6 million years Stone tools have been found with H. habilis, giving this species its name, which means handy man
Homo ergaster was the first fully bipedal, largebrained hominid The species existed 1.9-1.5 million years ago Homo ergaster shows a significant decrease in sexual dimorphism (a size difference between sexes) compared with its ancestors
Homo ergaster fossils were previously assigned to Homo erectus; most paleoanthropologists now recognize these as separate species
Homo erectus originated in Africa by 1.8 MYA It was the first hominin to leave Africa
Neanderthals Neanderthals, Homo neanderthalensis, lived in Europe and the Near East from 350,000-28,000 years ago They were thick-boned with a larger brain, buried their dead, and made hunting tools Recent genetic analysis indicates that gene flow occurred between Neanderthals and Homo sapiens
Figure 34.49 Results Genetic similarity index (D) 7 6 5 4 3 2 1 These relatively high bars indicate that the Neanderthal genome was more similar to genomes of non-africans than of Africans. 0 Africans to Africans Non-Africans to Africans Non-Africans to Non-Africans Populations being compared in relation to Neanderthals
Homo Sapiens Homo sapiens appeared in Africa by 195,000 years ago All living humans are descended from these African ancestors A 160,000-year-old fossil of Homo sapiens
The oldest fossils of Homo sapiens outside Africa date back about 115,000 years and are from the Middle East Humans first arrived in the New World sometime before 15,000 years ago In 2004, 18,000-year-old fossils were found in Indonesia, and a new small hominin was named: Homo floresiensis
Homo sapiens were the first group to show evidence of symbolic and sophisticated thought In 2002, a 77,000-year-old artistic carving was found in South Africa
Figure 34.UN09a Hominin Species Mean age (millions of years; x) Mean Brain Volume x i x (cm 3 ; y) y i y (x i x) (y i y) Ardipithecus ramidus 4.4 325 Australopithecus afarensis Homo habilis Homo ergaster Homo erectus Homo heidelbergensis Homo neanderthalensis 3.4 1.9 1.6 1.2 0.5 0.1 Homo sapiens 0.0 375 550 850 1,000 1,200 1,400 1,350