History of Life on Earth-II Lectures 18-24: From Early Primates to Homo Sapiens

1. History of Life on Earth-IILectures 18-24: From Early Primates toHomo Sapiens Instructor: Steve Greenhouse

2. Course Outline(From the Great Courses) Lecture 18 – Moving on Up: The First Primates Lecture 19 – Apes: Swinging Down from the Trees Lecture 20 – From 4 Legs to 2: The Hominin Radiation Lecture 21 – First Humans: Toolmakers and Hunter-Gatherers Lecture 22 – From Homo to sapiens: Talking and Thinking Lecture 23 – Our Accelerating Evolution Lecture 24 – Reflections on Major Transitions

3. References

4. Evolution (from Part I) • Evolution is the process by which all living things have developed from primitive organisms through changes occurring over billions of years. • Charles Darwin used the term “descent with modification” to describe evolution: • Darwin’s idea is elegant in its simplicity but, in a sense, obvious. • At the time, there was little information available to him about genetics and plate tectonics. • Natural selection is the underlying mechanism of evolution.

5. Evolution (cont’d) • Evolution is a scientific fact. There are competing theories as to the exact explanatory mechanisms for certain aspects of evolution. • The theory of gravity may be a good analogy – there is no question in anyone’s mind that gravity is a fact, but there may be various theories as to its cause or mechanism. • Evolution is not mathematically provable like the Pythagorean theorem, but is provable by the overwhelming weight of evidence for it, the fossil record and molecular biology. • And I would add: it is self-evident from a common sense point-of-view, i.e., how could it be otherwise? • I take issue with the term “believing” (or not believing) in evolution; the better term is “accepting” (or not accepting). • Science is not a belief system. • It is a methodology for arriving at facts about nature.

6. Evolution (cont’d) • Evolution has no foreordained purpose or desired goal. Humans (Homo sapiens) are not the goal or culmination of evolution. In terms of evolutionary success: • Humans are (arguably) the most intelligent species yet evolved. Dolphins may be a close second. • Insects are the most diverse class of animals. • Fish are the most speciose group of vertebrates. • Birds are the most speciose class of tetrapod vertebrates. • Bacteria have the greatest biomass. • Humans are, however, the end result – the last session - of these two courses!

7. Evolution (cont’d) *Better-designed in the sense of better adapted to its environment, more likely to survive and reproduce. • It is remarkable that humans have evolved at all: • We are apes, a group that almost went extinct 15 mya in competition with the better-designed* monkeys. • We are primates, a group of placental mammals that almost went extinct 45 mya in competition with the better-designed* rodents. • We are synapsid tetrapods, a group of mammal-like reptiles that almost went extinct 200 mya in competition with the better-designed* dinosaurs. • We are vertebrates, descended from a group of lobe-finned fish that almost went extinct 360 mya in competition with the better-designed* ray-finned fish. • We are chordates, a phylum that almost went extinct 500 mya during the Cambrian era in competition with the incredibly successful arthropods.

8. The Geologic Time Scale

9. Important Transitional Events (some dates are approx or ranges – sources vary)

10. Part I Course Summary • Background: • Life, Evolution, Decent with Modification, Natural Selection Example • Myths about Evolution • Selection and Adaptation, Species Data, Sexual and Artificial Selection, Homologous Features and Camouflage, The Selfish Gene Theory, • Macro- and Microevolution, Continental Drift, Ranking Systems, Geologic Time, Mass Extinctions, Fossils and Fossil Dating • Evolutionary Transitions: • Original Life, Early Life, Prokaryotes, Eukaryotes • Metazoans, Skeletons, The Cambrian Explosion

11. Part I Course Summary (cont’d) • Vertebrates, Arthropods, Powered Flight, Seed Plants and Forests • Fish, Tetrapods, Amniotes, Dinosaurs, Flying and Marine Reptiles • Birds, Flowers and Pollinators, Mammals, Whales

12. From the Fall Term: Part I After the end-Cretaceous mass extinction, 65 mya, mammals began to fill ecological niches left by dinosaurs and other large animals. Perhaps the most surprising example was the radiation of mammals back to the oceans and the evolution of whales. Now, we begin Part II. It is December 26…

13. Primates • Kingdom- Animalia • Phylum- Chordata • Subphylum-Vertebrata • Class- Mammalia • Order- Primates • Prosimians: • Lemurs, Lorises, Tarsiers • Anthropoids (or Simians): • New World Monkeys • Old World Monkeys • Hominoids: • Apes (e.g., Gibbons) • Hominids: • Great Apes (e.g., Orangutans) • Hominins: • Gorillas • Chimps, Bonobos, Humans (Hominini?) • Extinct Australopithecus and Homo genera

14. Lecture 18 – Moving on Up: The First Primates • The end-Cretaceous period mass extinction opened up niches for surviving species including mammals: • About 60 mya (Cenozoic era, Paleocene epoch) many kinds of animals took to the trees developing adaptations to newly evolved fruits, flowers and leaves. • This resulted in the first primate-like mammals about 58-55 mya which included ancestors of today’s tarsiers, lemurs and lorises (prosimians). • Living prosimians are nocturnal, insectivorous and solitary.

15. Extant Prosimians Tarsiers live on southeast Asian islands Lemurs are endemic to Madagascar Lorises live in south and southeast Asia

16. Lecture 18 – Moving on Up: The First Primates(cont’d) • Plesiadapis is one of the oldest known primate-like mammal (rodent) genera which existed about 58-55 mya in North America and Europe. This genus probably arose in North America and colonized Europe on a landbridge via Greenland. • Molecular clock studies suggest the primate branch may be even older, originating in the mid-Cretaceous period around 85 mya. This is disputed. • The authors of the paper describing Darwinius (47 mya), an adapid, classified it as a member of the primate family suggesting that it has the status of a significant transitional form between the prosimian and anthropoid primate lineages. Others have disagreed with this placement.

17. Lecture 18 – Moving on Up: The First Primates (cont’d) • Adapids are a family of extinct prosimians that primarily radiated during the Eocene epoch (55 to 34 mya). However, one specialized endemic Asian group (sivaladapines) survived into the Miocene (24-5 mya). Features that characterize many adapids include: • Small orbits (eye sockets). • Elongate rostra. • Cheek teeth adapted for folivorous (leaves) or frugivorous (fruits) diets • Relatively large body mass (greater than 1 kg), but • Some genera were very small (about 250 g or less) and partly insectivorous. • Small orbits in some genera indicate that they were probably diurnal, but • At least one adapid genus had large orbits and was probably nocturnal. • Like living primates, adapids had grasping hands and feet with digits tipped by nails instead of claws. • Their skeletons strongly indicate that they lived in trees. • Adapids had skulls similar to those of living lemurs.

18. Lecture 18 – Moving on Up: The First Primates (cont’d) • Omomyids were prosimians that were ancestral to anthropoids: • They also lived in the Eocene (55-34 mya). • Features that characterize many omomyids include: • Large orbits indicating they were probably nocturnal, but • One genus from the late Eocene had small eye orbits and was probably diurnal. • Shortened snout and dental arcades. • Loss of anterior premolars. • Cheek teeth adapted for insectivorous or frugivorous diets. • Relatively small body mass (less than 500 g), but by the late middle Eocene (about 40 mya), some North American omomyids evolved body masses in excess of 1 kg and frugivorous or folivorous diets. • Grasping hands and feet with digits tipped by nails instead of claws. • Their skeletons strongly indicate that they also lived in trees. • Omomyids had skulls similar to those of living tarsiers.

19. Plesiadapis (1st Primate-like Mammal Fossil Found) Restoration Nearly complete skeleton

20. Extinct Prosimians Adapid Omomyid Skulls and renditions

21. Lecture 18 – Moving on Up: The First Primates (cont’d) • A suborder of early primates, anthropoids or simians, evolved from tarsier-like ancestors during the Middle and Late Eocene (49-34 mya) probably in Asia and rather quickly migrated to Africa. The suborder, anthropoidea, includes: • All (Old and New World) monkeys. • Hominoids which include living apes and humans and their fossil ancestors. • Anthropoid characteristics include: • Larger brains • An accentuated visual sense • Color vision • Social behavior, unlike prosimians which are solitary • They are mostly diurnal, unlike prosimians which are nocturnal • They eat a mixed diet while prosimians are insectivores

22. Lecture 18 – Moving on Up: The First Primates(cont’d) • An important true-anthropoid fossil, Eosimias, was found in Southeast Asia and dated to 43 mya. • Anthropoids migrated to Africa from Asia soon after 43 mya: • Landbridges existed in the Eocene. • They may have floated on natural “rafts” made of vegetation. • The two infraorders of anthropoids, which diverged from each other 30 mya, are: • Platyrrhini, the New World Monkeys: • The five families of primates that are found in Central and South America and portions of Mexico. • and Catarrhini, the Old World monkeys, apes and humans: • OW monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous terrain, and are also known from Europe in the fossil record.

23. New World Monkeys Cotton-top tamarin Pygmy marmoset Capuchin monkey Spider monkeys with prehensile tails

24. Old World Monkeys Olive baboon Black-footed gray langur

25. Eosimias (1st Anthropoid Fossil Found) Artist’s rendition of Eosimias Drawings of skeletons of Darwinius, an adapid and Eosimias, an anthropoid

26. Divergence of Primates

28. Primates • Kingdom- Animalia • Phylum- Chordata • Subphylum-Vertebrata • Class- Mammalia • Order- Primates • Prosimians: • Lemurs, Lorises, Tarsiers • Anthropoids (or Simians): • New World Monkeys • Old World Monkeys • Hominoids: • Apes (e.g., Gibbons) • Hominids: • Great Apes (e.g., Orangutans) • Hominins: • Gorillas • Chimps, Bonobos, Humans (Hominini?) • Extinct Australopithecus and Homo genera

29. Lecture 19 – Apes: Swinging Down from the Trees • Old World monkeys diverged from the human lineage 22-26 mya; gibbons diverged from our lineage 16-20 mya; orangutans, 10-13 mya; gorillas, 6-9 mya, and chimpanzees, 4-7 mya: • So, humans and all the living great apes shared a most recent common ancestor (MRCA) about 10-13 mya. • Humans and chimpanzees shared a MRCA 4-7 mya. • Gibbons, which live in southeast Asia, are considered lesser apes. • The earliest apes appeared about 20 mya [This was mid-morning on 30 December]. • All the great apes live in Africa except orangutans which live in southeast Asia. • Apes are the largest primates and the orangutan is the largest living arboreal animal. • Hominoids are traditionally forest dwellers, although chimpanzees may range into savanna.

30. Lecture 19 – Apes: Swinging Down from the Trees (cont’d) • Living apes have the following features that Old World monkeys, their closest relatives, don’t share: • Those related to locomotion: • anatomical adaptations to vertical hanging and swinging locomotion (brachiation), as well as better balance in a bipedal pose • Those related to their teeth: • Low crowns adapted for grinding rather than tearing as in monkeys • the number of cusps on their molars (hominoids have five; Old World monkeys have only four) • Long lifespan • Late maturation • Long birth intervals (often longer than humans) • They are tailless, most monkeys have tails • They are considerably larger (except gibbons which are smaller than some monkeys) • They are considered more intelligent; monkeys have more primitive brains

31. Extant Apes Gibbon, a lesser ape Chimpanzees are social animals A gorilla using a stick possibly to gauge the depth of water Female bonobo The critically endangered Sumatran orangutan Human

32. Lecture 19 – Apes: Swinging Down from the Trees (cont’d) • The environment and land masses of the Miocene epoch (24-5 mya) allowed primates to disperse to east and central Africa, Asia and Europe and to diversify: • Some apes became specialized for quadrupedal movement, • Others toward climbing and hanging from branches. • Proconsul, the earliest ape (22-16 mya) for which we have good fossil evidence: • Was a quadruped and walked with its back horizontal. • Had thick-enameled teeth for grinding. • Species varied in size from that of a cat to a large dog. • Other fossil primates/apes of the Miocene were quite diversified regarding habitat, locomotion and eating habits, having some features resembling hominids:

33. Lecture 19 – Apes: Swinging Down from the Trees (cont’d) • Gigantopithecus survived in south China from 9 mya until about 100-300 kya, while it is believed most of the other Miocene apes became extinct prior to 5 mya. • Morotopithecus (20.6 mya in east Africa) had a stiff and vertical lumbar spine suggesting it was more of a climber than a runner. • Kenyapithecus (14 mya) had a dental pattern similar to living apes suggesting it may have been the first ape to disperse out of Africa: • One theory states that Kenyapithecus may be the common ancestor of all the great apes; however, recent investigations suggest it is more primitive than that. • Dryopithecus (13 mya), a European ape, probably ate many diverse food types such as leaves, fruits and seeds as living apes do: • Dryopithecus was about 4 feet tall, and more closely resembled a monkey than a modern ape. Its limbs and wrists show that it walked in a similar way to modern chimpanzees, but that it used the flat of its hands, like a monkey, rather than knuckle-walking, like modern apes. • The fossil, Ardipithecus, (5.8-4.4 mya): • Was not a knuckle-walker and carried its spine more vertically than today’s great apes. • My have been a close relative of the ancestor of hominins and, later, humans.

34. Proconsul, The First Ape Restoration Proconsul skeleton reconstruction

35. Gigantopithecus Gigantopithecus is an extinct genus of ape that existed from roughly nine million years to as recently as three hundred thousand years ago, in what is now China, India, and Vietnam.

36. Morotopithecus Morotopithecus seems to be a sister taxon to extant great apes while Hylobates (gibbons) seem to have branched off before this clade appeared.

37. Kenyapithecus Kenyapithecus wickeri was a fossil ape discovered by Louis Leakey in 1961 in Kenya. The upper jaw and teeth (right) were dated to 14 million years ago.

38. Dryopithecus Jaw of Dryopithecus fontani Dryopithecus likely spent most of its life in trees, and was probably a brachiator, similar to modern orangutans and gibbons. Its molars had relatively little enamel, suggesting that it ate soft leaves and fruit, an ideal food for a tree-dwelling animal.

39. Ardipithecus Ardi’s skull Artists rendition Skeletal fragments Ardipithecus ramidus is a fossil hominine. It is still a matter of debate what the relation of this genus to human ancestors was, and whether it is a hominin or not.

40. Hominids and Hominins >The most commonly used recent definitions are: Hominid – the group consisting of all modern and extinct Great Apes (that is, modern humans, chimpanzees, gorillas and orangutans plus all their immediate ancestors). Hominin – the group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus). >Note: hominid and hominin are sometimes used interchangeably. >Two other (confusing) terms: Hominini – Humans, Chimpanzees and Bonobos (a tribe of hominins) Hominine – Ardipithecus, Homo Denisovan and Homo Floresiensis (human-like or possibly human)

41. Extant Hominoids, Hominids, Hominins and Homo Q3

42. Taxa of Chimps and Humans

43. Skeletons of Hominoids (Hominoid) (Hominini) (Hominini) (Hominin) (Hominid)

44. Genetic Differences between Humans and Other Primates [1] Measurement of only substitutions in the base building blocks of those genes that chimpanzees and humans share. Comparison of the entire genome indicates that segments of DNA have been deleted, duplicated over and over, or inserted from one part of the genome into another. When these differences are counted, there is an additional 4 to 5% distinction between the human and chimpanzee genomes.

45. Humans are African Apes • Based on the small genetic distance between humans and the great apes, it is evident that not only are humans closely related to the great apes – we are one. • Based on the genetic distance between humans, chimps and gorillas (African great apes) and orangutans (Asian great apes) and the lesser primates, Africa is the likely place where the human lineage branched off from other animals: • Africa is the place where the common ancestor of humans, chimps and gorillas once lived. • Remarkably, Darwin predicted this in 1871 without the benefit of DNA evidence. • The fossil evidence confirms that the first 4 my or so of human evolutionary history took place exclusively in Africa. • A definitive fossil at or near the branching point from our last common ancestor has not yet been found – the search continues in Africa. Ardipithecus may be a close relative. • Chimpanzees are actually closer genetically to humans than they are to gorillas.

46. Humans are African Apes (cont’d) • All the living great apes except humans have 24 pairs of chromosomes: • Humans have 23 pairs; 2 medium-sized ape chromosomes have fused together to form human chromosome #2, the second largest human chromosome. • We know this from observing the pattern of black bands on the respective chromosomes. • Of course, it is the genes on all the chromosomes that make the vast difference between humans and the other great apes, both anatomical and behavioral, despite the relatively small genetic differences measured (1-3%).

48. Primates • Kingdom- Animalia • Phylum- Chordata • Subphylum-Vertebrata • Class- Mammalia • Order- Primates • Prosimians: • Lemurs, Lorises, Tarsiers • Anthropoids (or Simians): • New World Monkeys • Old World Monkeys • Hominoids: • Apes (e.g., Gibbons) • Hominids: • Great Apes (e.g., Orangutans) • Hominins: • Gorillas • Chimps, Bonobos, Humans (Hominini?) • Extinct Australopithecus and Homo genera

49. Next: Dr. Briana Pobiner of the SI NMNH’s Human Origins Program presents: The Human Family Tree

50. Lecture 20 – From 4 Legs to 2: The Hominin Radiation NOTE: Data in my material for Lectures 20-22 may differ somewhat from Dr. Pobiner’ presentation – sources vary. • Hominids are the branch of primates closely related to humans and more distantly related to the living apes: • Our branch originated 7-4 mya and lived only in Africa until 2 mya. • Ardipithecus (5.8-4.4 mya) was a possible ancestor of the hominids or a close relative of our common ancestor with chimps and gorillas: • Its small canine teeth enabled it to eat meat but, not display threatening gestures indicating it may have communicated more like humans than great apes and may have had a social organization.