34 lecture presentationstreaming.missioncollege.org/jtaylor/media/biosc_041... · 2015-07-20 ·...

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© 2014 Pearson Education, Inc.

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: p2 + 2pq + q2 = 1

§  p2 = homozygous dominant

§  2pq = heterozygous

§  q2 = 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, frequency-

dependent selection §  Directional §  Disruptive §  Stabilizing


Speciation and Human Evolution

References: chapters 24 (first few slides) 34 (last few pages of chapter)

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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 © 2014 Pearson Education, Inc.

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

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ANCESTRAL MAMMAL

Monotremata

Marsupialia

Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida Macroscelidea

Xenarthra

Rodentia Lagomorpha Primates Dermoptera Scandentia

Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphla Pholidota

Monotrem

es (5 species)

Marsupials

(324 species) Eutherians (5,010 species)

Human Speciation


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

Orangutans

Gorillas

Humans

Chimpanzees and bonobos

Anthropoids

70 60 50 40 30 20 10 0 Time (millions of years ago)

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§  The first monkeys evolved in the Old World (Africa and Asia)

§  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

New World monkey: spider monkey

Old World monkey: macaque

(b)

(a)


§  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

(e) Bonobos (d) Chimpanzees

(c) Gorilla


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

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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

Paranthropus boisei

Australopithecus africanus

Australopithecus garhi

Kenyanthropus platyops

Australo- pithecus anamensis

Australopithecus afarensis

Ardipithecus ramidus

Sahelanthropus tchadensis

Orrorin tugenensis

Homo habilis

Homo rudolfensis

Homo erectus

Homo ergaster

Homo neanderthalensis

Paranthropus robustus

Homo sapiens

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§  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

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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 © 2014 Pearson Education, Inc.

§  “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, large-brained 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

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§  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

These relatively high bars indicate that the Neanderthal genome was more similar to genomes of non-Africans than of Africans.

Africans to Africans

Non-Africans to Africans Non-Africans to Non-Africans

Populations being compared in relation to Neanderthals

Gen

etic

sim

ilarit

y in

dex

(D)

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Results


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

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§  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

Ardipithecus ramidus

Australopithecus afarensis

Homo habilis

Homo ergaster

Homo erectus

Homo heidelbergensis

Homo neanderthalensis

Homo sapiens 0.0

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Mean age (millions of

years; x)

Mean Brain Volume (cm3; y) xi x yi y

xi x)(

yi y)(

34 lecture presentationstreaming.missioncollege.org/jtaylor/media/biosc_041... · 2015-07-20 ·...

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