Lecture 25 Evolution

1. Lecture 25Evolution

2. What is Evolution? • Change over time, building on past & current features • Products evolve • Knowledge evolves • Beliefs evolve

3. What is Evolution? • In other cultures and religions, for example Taoism, evolution plays a central role • Evolutionary patterns in biology have been noted as far back as Aristotle • Darwin initially used the phrase “descent with modification” to explain the concept of evolution • Patterns of biological evolution have been observed in three major areas: • Fossil records • Anatomical features • Molecular distances

4. Macroevolution • Evolutionary change on a grand scale • Encompasses the origins of new species and major episodes of extinction • Microevolution • Evolutionary change on a small scale • Encompasses the genetic changes that occur within populations over time • These changes are the result of changes in gene frequencies Evolution: Getting from There to Here

5. Prior to Darwin and Wallace it was widely thought that biological evolution occurred by inheritance of acquired characteristics • Individuals passed on to offspring body and behavior changes acquired during their lives • In contrast, Darwin and Wallace proposed that: variation is an inherent characteristic of all biological populations • It is not created by experience • This is readily observable in all populations – just look around this room Evolution: Getting from there to Here

6. The Pace of Evolution • The standard view since Darwin was that evolutionary change occurred extremely slowly • Imperceptible changes accumulate such that, over thousands or millions of years, major changes could occur • This is termed gradualism • In 1972, Niles Eldredge and Stephen Jay Gould proposed thePunctuated Equilibriumhypothesis • Evolutionary change occurs in bursts separated by long periods of little or no evolutionary change (termed stasis) • Examples of both gradualism and punctuated equilibrium exist • So speciation clearly occurs in different ways • However, the idea that speciation is necessarily linked to phenotypic change has not been supported • Speciation can occur without phenotypic change • Phenotypic change can occur within a species in the absence of speciation

7. The Rate of Evolution • Different kinds of organisms do evolve at different rates • Bacteria evolve much faster than eukaryotes • The rate of evolution also differs within the same group of species • In punctuated equilibrium, evolution occurs in spurts • In gradualism, evolution occurs in a gradual, uniform way

8. The Evidence For Evolution • Evidence for evolution comes from the following • Fossil record • Anatomical record • Molecular record

9. Provides the most direct evidence for macroevolution Fossils are the preserved remains, tracks, or traces of once-living organisms They form when organisms become buried in sediment and calcium in hard surfaces mineralizes Arraying fossils according to age often provides evidence of successive evolutionary change Fossil Record Large blunt horns Small bony protuberance Hoofed mammals Evolution in the titanotheres

10. Fossils have been found linking all the major groups The forms linking mammals to reptiles are particularly well known Fossil Record

11. Anatomical Record: Ontogeny • Ontogeny Recapitulates Phylogeny • All vertebrates share a basic set of developmental instructions

12. Anatomical Record: Homology • Homologous structures • Have different structure and function but are all derived from the same part of a common ancestor • A common ancestor possessed this 1-2-5 structure • Adaptations to different environments modified this structure in different ways

13. Anatomical Record: Analogy • Analogous structures • Resemble each other as a result of parallel evolutionary adaptations to similar environments

14. Convergent evolution: many paths to one goal • Analogous structures are the result of convergent evolution • Different animals often adapt in similar fashion when challenged by similar adversities or opportunities

15. Anatomical Record • Vestigial organs • Structures that are no longer in use such as the human appendix • Apes have a much larger appendix that is involved in digestion

16. Molecular Record: Evolutionary Distance • New alleles arise by mutations and they come to predominance through favorable selection • Thus, evolutionary changes involve a continual accumulation of genetic changes • Distantly-related organisms accumulate a greater number of evolutionary differences than closely-related ones • This divergence is seen among vertebrates in the 146-amino acid hemoglobin b chain

17. This same pattern of divergence is seen with DNA sequences, such as that of the cytochrome c gene The changes appear to accumulate at a constant rate This phenomenon is referred to as a molecular clock Molecular Record: Molecular Clock Note: Different proteins evolve at different rates

18. The eyes of these organisms are NOT homologous The genes controlling eye development ARE homologous 500 million years ago an ancestor evolved the “switch” for eye development Probably simplest type of eye structure 1 pigment cell & 1 photoreceptor The gene was passed on to all its descendents These descendents evolved different types of complex eyes Each switched on by a descendent of the original gene Molecular Record: Homology

19. Evolution’s Critics • Critics of evolution raise seven principal objections • 1. Evolution is not solidly demonstrated • 2. There are no fossil intermediates • 3. The intelligent design (irreducible complexity) argument • 4. Evolution violates the 2nd law of thermodynamics • 5. Proteins are too improbable • 6. Natural selection does not imply evolution None of these objections has held up to scientific scrutiny

20. Evolution & Religion • “Today, almost half a century after the publication of the Encyclical, new knowledge has led to the recognition of more than a hypothesis in the theory of evolution. • It is indeed remarkable that this theory has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge. • The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favor of the theory.” Pope John Paul II November 19, 1996 Address to the Pontifical Academy of Sciences

21. The Evolutionary Path to Apes • The Earliest Primates had two distinct featuresthat allowed them to succeed in the arboreal insect-eating environment • Grasping fingers and toes • Allow them to grip limbs, hang from branches & use tools • Overlapping binocular vision • Lets the brain judge distance precisely • ~ 40 mya, the earliest primates split into two groups: Prosimians and Anthropoids • Prosimians (“before monkeys”) • Primarily nocturnal and herbivorous • Only a few survive today • The story of human evolution begins around 65 mya with the Archonta • A group of small, arboreal mammals that were primarily insectivorous • They underwent an explosive radiation that gave rise to different types of mammals including bats and primates

22. Origin of the Anthropoids • Higher primates include monkeys, apes and humans • Anthropoids are almost all diurnal and herbivorous • Evolved a bigger brain and improved senses to adapt to daytime foraging • Live in groups with complex social interactions • Tend to care for their young for prolonged periods of time • Early anthropoids, now extinct, evolved in Africa • Their direct descendants are: • New World Monkeys • Migrated to South America • Developed in isolation • All are arboreal • Most have prehensile tails • Old World Monkeys • Stayed in Africa • Split into two lineages • i. Old world monkeys • ii. Hominoids • Many are ground dwellers • None have prehensile tails

23. Comparing Apes to Hominids • Hominoids evolved from anthropoids • Apes • Hominids (humans and their direct ancestors) • Chimpanzees are the closest living human relatives • Chimpanzees and humans share 98.4% of their nuclear DNA • Gorillas and humans share about 97.7% • The common ancestor of apes and hominids is thought to have been an arboreal climber • Hominids became bipedal (walking upright) • Apes evolved knuckle-walking • Anatomical differences between the two are related to bipedal locomotion • Considerable controversy exists about the identity of the first hominoid • Attention is now focused on an early Miocene ape,Proconsul • Has many of the characteristics of Old World Monkeys • It lacks a tail and has apelike hands, feet and pelvis

24. Bipedalism seems to have evolved as our ancestors left dense forests for grasslands and open woodland Did bipedalism precede or succeed brain enlargement? Fossils unearthed in Africa demonstrate that bipedalism extended back 4 mya Substantial brain expansion, on the other hand, did not appear until about 2 mya A Hominid Evolutionary Tree • There are two major groups of hominids • The genus Homo • 3-7 species depending on how you count them • The genus Australopithecus • 7 species • Older • Smaller-brained • Australopithecine characteristics • Bipedal • ~ 1 m tall and ~ 18 kg in weight • Hominid dentition • Brains not any larger than those of apes • Fossils only found in Africa

25. Out of Africa: Homo erectus • In 1976, a 1.5 million year old H. erectus skull was found in East Africa • This suggests that H. erectus originated there and migrated into Asia and Europe • H. erectus survived for over a million years - longer than any other species of humans • The first humans evolved from australopithecine ancestors about 2 mya • The exact ancestor is thought to be A. afarensis • In the 1960s, hominid bones were found near stone tools in Africa • This early human was called Homo habilis (Latin for “handy man”) • It closely resembled Australopithecus but had a larger brain • In 1891, in Java, a Dutch anatomist named Eugene Dubois found a 500,000 year old skull cap and thighbone which he calledJava man, • The thigh bone indicated that he was bipedal • The skull indicated a brain twice the size of that of Australopithecus • Now recognized as Homo erectus: Taller than H. habilis with a larger brain

26. Modern humans first appeared in Africa about 600,000 years ago Three human species are thought to have evolved Homo heidelbergensis Evolved in Africa about 600,000 years ago Migrated to Europe and Western Asia Homo neanderthalensis Appeared in Europe about 130,000 years ago as H. heidelbergensis was becoming rarer Likely branched off of the ancestral line leading to modern humans Homo sapiens (“wise man”) Evolved in Africa about 130,000 years ago then migrated to Europe and Asia This is called theRecently-Out-of-Africa model This model is supported by a variety of gene studies Human mitochondrial DNA Y and X chromosomes Autosomes The Last Stage of Hominid Evolution

27. Neanderthals(H. neanderthalensis) Named after the Neander Valley of Germany where their fossils were first discovered in 1856 Evolved in Europe, then migrated to Asia Abruptly disappeared about 34,000 years ago Cro-Magnons(H. sapiens) Named after the Valley in France where their fossils were first discovered Evolved in Africa, then migrated to Asia Eventually spread to N. America and Australia We humans are unique animals and the product of evolution Our evolution has been marked by a progressive increase in brain size Refined and extended conceptual thought Symbolic language Cultural evolution Our Own Species: Homo sapiens