Human Evolution In the Origin of Species, Darwin goes out of his way to avoid mentioning human evolution

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Human Evolution

  1. In the Origin of Species, Darwin goes out of his way to avoid mentioning human evolution

  2. By this time he’d already filled two notebooks with his thoughts on human evolution

  1. He leaves us with a single cryptic sentence

  2. “Light will be thrown on the origin of man and his history”

  3. Idea that man was little more than an especially clever primate was too radical for the Victorian world to accept

  1. T.H. Huxley, Darwin’s greatest supporter, wasn’t quite so shy

  2. Huxley was always spoiling for a fight, especially if he could step on the toes of the clergy

  3. Huxley wrote his groundbreaking Man’s Place in Nature in 1863

  1. Huxley argued that man clearly belonged to the order of primates

  2. Darwin finally published his own book on human evolution in 1871, The Descent of Man

  1. Huxley had only a single fossil specimen on which to rest his case

  2. Lone Neanderthal skull was though by many to be that of a diseased person

  3. Huxley claimed otherwise…

  1. Human evolution remains one of the most challenging areas of modern biology and anthropology

  2. Many unanswered questions, large parts of our evolutionary past are dim and murky

  1. Relative scarcity of human remains

  2. End of the Pleistocene, there were only 5 million people on Earth, only a handful of those were preserved as fossils

  3. Even a fragmentary find can change established theories

  1. July 2002, a skull named Toumai, was found in Chad

  2. Unknown species, walked upright

  3. Upset the apple cart again - 1 my older than any previous find

  4. Pushes back the date when we diverged from the other apes

  1. So what can we definitely say about human evolution?

  2. Not as much as we would like…

  1. We are one of 177 species that make up the Order of Primates

  2. We are in the genus Homo, in the Class Hominoidea, with the gibbon (Hylobates), orangutan (Pongo), and the great apes (Chimpanzee - Pan, and gorilla - Gorilla)

  1. Several hypotheses proposed to explain our relationship to the other apes

  2. Recent molecular evidence suggests that the chimp is our closest relative

  1. Chimps diverged from the other great apes about 6 mya, still genetically very similar to humans

  2. Share ~ 98.4% of our DNA with chimps!

  3. Gorillas diverged ~ 8 mya

  4. We share ~ 97.7% of gorilla DNA

  1. Most primates are arboreal, they live in trees

  2. Humans are no longer arboreal, nor are baboons

  1. Arboreal lifestyle requires a larger brain, high order of intelligence

  2. Need to process a lot of information very quickly, “on the fly”

  3. An opposable thumb is another useful adaptation for an arboreal existence

  1. High intelligence, hand/eye coordination, opposable thumbs are all preadaptations

  2. Preadaptations are when evolution takes an existing structure and finds a new use for it

  3. Swim bladders of fish / human lungs, pelvic and pectoral fins on fish / our forelimbs and hind limbs…

  1. Our human lineage split from the great apes sometime during the Pliocene, ~ 6-8 mya

  2. Our immediate ancestors were a genus of intelligent ape-men called Australopithecus

  3. Upright, bipedal stance

  1. But their brains were only half the size of modern man

  2. One of these species, A. afarensis, was most probably the ancestral species of the genus Homo

  3. Most recent Australopithecus find is a relatively complete skeleton of a three year old afarensis child

  4. May revolutionize our ideas about early human anatomy and development

  5. Presence of hyoid bone ex. is critical for human speech

  6. Where do we draw the line between ape-men and men?

  7. Along with bipedal posture, one of the most characteristic human traits is tool use

  8. Tool use requires substantial intelligence

  1. We aren’t the only animal that uses tools

  2. Otters balance a flat stone on their stomach to smash open mollusks

  3. Crows have been observed using cars as nutcrackers

  4. Cactus finch uses cactus spines to probe for insects

  1. Chimps use thorns and twigs to pry into termite mounds

  2. Chimps chew leaves into a spongy mass to get water out of the cups of air plants

  3. But man outdoes them all…

  1. We use tools to a far greater extent than any other animal

  2. We even make tools whose only function is to make other tools

  1. Hallmarks of an arboreal lifestyle (hand/eye coordination, increased intellect, opposable thumbs/grasping hand) are preadaptations for tool use

  2. We use tools to mimic the adaptations of other animals (sharp teeth, claws/knives, airplanes to fly etc…)

  1. It is tempting to conclude that tool use selected for increased intelligence

  2. Increased intellect in turn led to more and better tools etc…evolutionary spiral

  3. Human brain size has more than doubled in the four million years of human evolution

  1. Tool use is not the only hypothesis that could explain large brain size

  2. Could also result from upright posture

  3. Lengthens lower trunk, more space for uterus to expand during pregnancy

  4. Could have made room for bigger heads...

  1. Upright posture (bipedalism) is an important step in the transition to tool use

  2. It’s hard to swing a hammer when you’re walking on your hands…

  1. What could cause an arboreal quadruped to evolve into a cursorial (running) biped?

  2. No one knows for sure…

  3. Ultimate cause may have been changing global climate

  1. Remember that 4-7 mya, when the climate cooled, the African jungles gave way to a savanna, an open grassy plain dotted with trees

  2. In this open habitat, our ancestors would have needed to both live in trees and cross the open grasslands between

  1. Australopithecus lived in this mosaic of forest and plain

  2. It’s skeletal structure shows a mixture of arboreal and cursorial adaptations

  1. Another reason bipedalism may have evolved was to free the hands to carry food, during extensive foraging trips across the savanna

  2. Or perhaps bipedal posture is an adaptation to shed heat…

  1. Pete Wheeler, British anthropologist, says “stand tall and stay cool”

  2. Wheeler maintains that an animal walking upright across an open plain absorbs less heat than an animal on all fours, and also sheds heat more rapidly

  1. Problems with Wheeler’s theory:

  2. Would only have been advantageous at/around high noon (unlikely time to forage)

  3. Muscular exertion of standing upright would generate more body heat – cancel advantage

  4. If it was such a great idea, why are we the only species that thought of it?

  1. Loss of dense bodily hair, high density of sweat glands in the skin, may also be adaptations to cope with a hotter and more open environment

  1. Another controversial theory on bipedalism is Elaine Morgan’s “aquatic ape”

  2. Proboscis monkeys live in a flooded environment, and often have to walk upright to cross water

  3. Buoyancy of water cancels out some of the disadvantages of walking upright

  1. By ~ 2.8 mya, glaciers had claimed a large part of the northern hemisphere, further fragmenting the African forests

  2. About ~ 2 mya ago, we see the emergence of a new genus of primate, the fully bipedal genus Homo

  3. The genus Homo includes

  4. Homo habilis ~ 2 mya

  5. Homo erectus ~ 1 mya

  6. Homo heidelbergensis ~ 600,000 ya

  7. Homo sapiens ~ 130,000 ya

  8. Homo sapiens neanderthalis ~ 130,000 ya

  1. Studies of DNA in cell’s mitochondria show that modern human came from Africa

  2. Mitochondria in our cells are the cell’s “power packs”

  3. Used to be independent organisms!

  4. Still have their own DNA, divide independently of the cell

  1. DNA of mitochondria is very prone to a particular type of mutation, a nucleotide substitution

  2. We know roughly how often such mutations occur

  1. Gives us a molecular clock for evolutionary dating, compare mitochondrial DNA of different species

  2. See roughly how long ago they must have diverged from a common ancestor

  1. Incidentally, it is Eve’s DNA we test, not Adam’s…

  2. Egg cell is mostly cytoplasm with lots of mitochondria, sperm is mostly DNA

  3. Mitochondria in our cells come down to us through a female lineage!

  1. Recent studies of DNA in the nucleus of cells reached the same general conclusion about human origins

  2. The human species evolved in Africa

  3. At various times, several species of Australopithecus and other hominids coexisted on the African plains

  1. After the late Pliocene cold snap (2-3 mya), climate grew warmer again for a while, with temperatures much like today

  2. Deep freeze returned about 1.6 mya, during the Pleistocene

  3. Series of Ice Ages, spaced about 100,000 years apart

  1. In the harsher climate of the Ice Ages, tool use and intelligence would have been extremely valuable traits

  2. Ability to set snares, hunt for food with sharp spears, build strong shelters, wrap yourself in the cured skins of other animals to keep warm…

  1. Coinciding with this harsh climate we find the emergence of modern man

  2. The earliest modern man is Homo heidelbergensis, ~ 600,000 years ago

  3. Coexisted with H. erectus, more advanced skull, larger brain

  1. One of the biggest enigmas during this period of our evolution is the nature and fate of the Neanderthals

  2. Neanderthal man was a modern descendant of the initial migration of Homo from Africa

  3. Settled in Europe

  1. Neanderthals used to be considered a vastly inferior species, easily run into extinction by the more modern H. sapiens

  2. Recently these misconceptions have been greatly altered (and not just by Jean Auel)

  1. They were an advanced race, with a well-developed culture, buried their dead

  2. Neanderthals are now considered by many to be a subspecies of Homo sapiens, not a separate species

  1. They died out in modern times, probably did not interbreed with H. sapiens

  2. Were they victims of competition??

  1. Did neanderthals contribute to the human bloodline?

  2. Recent discoveries in Ethiopia of the oldest known human skulls refute this idea

  1. 3 skulls dated at ~160,000 years ago, 30-60,000 years older than previous discoveries

  2. Supports African origin of Homo sapiens

  3. No trace of Neanderthal features in the skulls

  1. Homo sapiens idaltu (Afar word for “elder”)

  2. Found with over 640 tools, including hand axes and blades

  1. First humans (H. habilis or H. erectus) migrated out of Africa ~1.5 mya to Europe and Asia

  2. Gave rise to all the modern races of man

  1. Multiregional theory of human evolution holds that separate human races evolved in parallel from this original migration

  2. Peking Man

  3. Java Man

  4. Neanderthals

  5. Monogenesis theory holds that these populations were later swept away by a second, and more successful African migration, about 200,000 years ago

  6. Monogenesis theory holds that all modern races are direct descendants of this second invasion

  1. However modern man became established, with the emergence of the genus Homo came the advent of a new phase in human evolution - cultural evolution

  1. Cultural evolution is the growth of the human record of art, science, technology, philosophy, our hopes and dreams…

  1. Cultural evolution is affected by organic evolution, but exists outside of it, following its own path

  2. With the evolution of human intelligence, the universe has finally become aware of itself…

Directory: ~bfleury -> darwinmed -> darwinmedlectures
darwinmedlectures -> Although our evolutionary heritage has saddled us with some significant health problems, in the long run it has served us well…
darwinmedlectures -> The 1918 Flu 1 – a conspiracy of Silence
darwinmedlectures -> Germ Theory
darwinmedlectures -> Although our evolutionary heritage has saddled us with some significant health problems, in the long run it has served us well…
darwinmedlectures -> In our last lecture, we looked at the ways that trade, travel, technology and agriculture can provide new habitats and new dispersal routes for microbes
darwinmedlectures -> The Evolutionary Arms Race Remember the Red Queen in Alice in Wonderland?
darwinmedlectures -> The 1918 Flu 2 The Philadelphia Story
darwinmedlectures -> The 1918 Flu 1 – a conspiracy of Silence
darwinmedlectures -> So say the Laws of Manu, an ancient Brahmin text on moral conduct Man is a moral animal…
darwinmedlectures -> Pandora's Box Remember the legend of Pandora's Box?

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