Human Evolution

Evolved human features from Africa

(1) Good vision: As the jungle disappeared and grasslands emerges, the emphasis shifted away from a keen sense of small towards a keen vision. (2) Bipedal movement: The earliest primates were able to live most of their lives in the trees; as a result, bipedal movement was unnecessary. • However, as the trees disappeared, primates had to develop bipedal movement in order tog et from place to place as it is more energetically efficient than quadruple pedal movement. • This allowed homo sapiens to develop larger and larger brains. (3) Hands that could make fine movements: Modifications to early arboreal primates eventually gave them the ability to make fine movements, such as grasping a tool. (4) Small teeth, and jaws with chins: The earliest primates had robust skills, with thick jaws and large teeth. • Over time, primates developed smaller teeth and more well defined chins. • It is believed that this may be due to primates changing diets. (5) A longer life span: Humans live in excess of 70 years, whereas chimps, our closest relative, live only 40. (6) Longer period of dependency: Humans do not reach their adult stages until their late teens, whereas chimps are adults at age 10.

Reasons for changed in dentition and mouth structures

(1) cooking food: with the discovery of fire, we began cooking food, making it softer and no longer needed hard, strong teeth. (2) Use of tools: when hominids developed tools to cut their food, they no longer needed to use their teeth for that purpose. (3) Language: As hominids began to use language to communicated with one another, their mouths and jaws had to change structurally in order to produce sounds. (4) Development of agriculture: Agriculture developed about 10,000 to 12,000 years ago in the Fertile Crescent, impacting human diets and thus structures relating to eating.

Homo sapiens

(Modern man) Emerged approximately 200,000 years ago. • Hunter gatherers until 10,000 years ago with the invention of farming. • Most "modern" forms of man emerged between 2000 and 3000 years ago.

Steps of human evolution

1. the craniates (animals with skulls) diverged. 2. the vertebrates (animals with backbones or spinal columns) diverged. 3. jawed vertebrates (vertebrates with jaws) diverged. 4. tetrapods (animals with four legs) diverged. 5. amniotes (animals with terrestrially adapted egg) diverged. The group of amniotes includes reptiles, birds and mammals.

The earliest primates shared characteristics:

(1) Dexterous hands and feet: Early primates had specialize hands with opposable thumbs for gripping tree trunks (2) Nails: These animals had fingernails instead of claws (3) Eyes in front: Animals with eyes on the sides of their head tend to lack depth perceptions.When two eyes share the same field of view, they acquire the depth perception that in characteristic of primates. (Humans who have lost vision in just one eye typically have trouble with depth perception) (4) Large brains: The brains of primates are much larger, as compared to those of earlier, more primitive organisms.

Changes in dentition and mouth structures in humans

Compared to our primate ancestors, human have a rounder mouth with reduced molars and thicker, more mineralized teeth. • Our jaw muscles are much smaller than our primate ancestors, reflecting the smaller size of our jaws and dental structures.

Evolution of primates

Evidence shows that there was a huge adaptive radiation of primates beginning approximately 65 million years ago, after the mass extinction during the Cretaceous Period (when the dinosaurs went extinct). • During this period, a number of new primate species emerged; one of these species gave rise to modern humans. • Scientists believed that primates' most ancient ancestor, which lived about 65 million years ago, was an arboreal insectivore.

Human beings

Homo sapiens • Relatively new "branch" in the tree of life belonging to the chordate brand which is most closely related to the echinoderms (sand dollars, sea urchin and sea starts).

Human evolution

Homo spaiens did not evolve from chimps, our direct ancestors were not chimps or any other apes; they were other humans. • The evolution of primates has not been linear, as we have not gradually evolved from our earliest ancestor, rather, there have been a mini adaptive radiation of primates over the past five million years • As a result, a number of primate species have evolves, some of them, were evolutionary dead ends and died off. • Different species of humans coexisted with one another at different points in time.

Homo erectus

Humans closest ancestor • Homo erectus was a primate that evolved in Africa about 2 million years ago and survived until about 53,000 years ago. • Homo erectus was taller than a more distantly related species called Homo habilis, which existed 2.3 to 1.3 million years ago and was a creative tool maker. • This species began to use fire, and it made more sophisticated use of tools than did Homo habilis.

Changes in brain size

Humans have larger brains than other similar mammals, and the brain size of hominids has increased by more than threefold in species that arose over the course of the past several million years. •

Ardi

In 2009, scientists discovered the remains of Ardipithecus ramidus in Ethiopia. • Naming him Ardi, he was older than Lucy, dating back 4.5 million years. • He clearly walked upright and had long arms and weird feet. • He walked on two legs but could still climb trees.

Lucy

In the 1970s, scientists found the retains of a species in North Africa they names Lucy. She lived about 3.2 million years ago, had hands and feet like ours, and walked upright. • Only, she was just three or four feet tall. • Approx. 150 other individuals of this species have been found since Lucy.

Cultural evolution

Out ability to extract and use energy may also have evolutionary consequences. • Fertility rates tend to be lower for organisms that use more energy. • Culture has an affect on phenotypes as much as other inventions, use of fire, tools, etc. do.

Changes in sexual size dimorphism

Sexual size dimorphism exists when males and females are different sizes. • There has been a reduction in sexual size dimorphism throughout the course of human evolution • Males were once much larger than females, twice the size, while now human males are only about 1.2 times heavier than females on average. • Scientists don't know what caused this reduction in sexual size dimorphism but there is a theory that the trend towards monogamy and change in family structure is one as sexual size dimorphism is more common when males or females tend to have multiple mates and is uncommon in monogamous species.

Groups of early ancestors that came before craniates...

The cephalochordates and the urochordates. • These are small, fishlike marine invertebrates that have a hollow, dorsal nerve cord that was the precursor to our backbones and nervous system. • Like all chordates they have a notochord, nerve cord, gill slits and a postanal tail at some stage in their lives. • Cephalochordates appeared in the fossil record for the first time about 500 to 550 million years.

Changes relating to dipedal movement

The evolution of bipedal movement provided a number of important benefits to early hominids, including efficient locomotion, predator avoidance, food gathering, freeing the hands, tracking migrating herds, and provisioning of offspring. • The evolution of bipedalism has corresponded with a number of important structural changes to the human phenotype: (1) The point of entry of the spring into the skull: The human spine enters through the bottom of the skull, while the spines of apes enter at the back (2) Size and shape of the pelvis: The human pelvis is smaller and more bowl shaped than the pelvises of apes. This allows the human pelvis to hold critical organs when the human walks upright, and it also lowers the center of gravity for better balance. (3) Knee: The human knees have thicker musculature and a different kind of attachment to support the body's weight when walking upright. (4) Feet: Human feet feature larger ankle bones and arches that make walking more efficient. They also typically do not have opposable big toes, whereas the big toes of apes are opposable.

Origin of humans

The evolution of primates occurred due to the impact of selective forces on primate phenotypes. • It is believed that, approximately 23 million years ago, a change in climate turned the African continent from a warm, wet forest to a cool, dry grassland during the Miocene Epoch. • As a result, the arboreal animals that live in the African forests had to adapt to the changing conditions. • Without these climate changes, the human species would probably never have evolved.

Arboreal insectivore

• A species that lives in trees and eats insects. • Scientists believe that primates most ancient ancestor is an arboreal insectivore.

Mammals

• Arose 175 million years ago and are characterized my mammary glands, sweat glands, hair and four-chambered hearts. • Animals other than mammals, such as birds and alligators, have four-chambered heats as well. • Mammals generally use internal fertilization for reproduction and generally give birth to live young. • They are warm blooded thermoregulators, meaning they control their body temperatures.

How Homo sapiens differed from Homo erectus:

• Its teeth and jaws were smaller • Its facial bones were smaller • Its skull was able to hold a larger brain and could engage in symbolic thought.