Hominid Evolution

• Hominids family of organism that includes humans

• First appeared between 6 and 7 million ears ago

• Has evolved several times..we can tell by looking at fossil evidence…Skulls in particular

Hominid Evolution

• Today researchers believe Hominid evolution proceed by

• Adaptive radiation is a process by which a several species evolve from single ancestral species.

Hominid Evolution

Hominid Evolution• Adaptations in hominid

evolution include …• Bipedal locomotion-walking

upright on 2 legs• Large brains- specially cerebrum;

Increase in cranial capacity• Changes in skull shape, including

decrease in size of brow ridge (section of bone above eye)

• Decrease in jaw size and angle at which jaw protrudes from face

• Decrease in the number of teeth • Opposable thumbs- adapted for

grasping• Development of the ability to

make and use tools• Development of the ability to

communicate using language

• Homo habilis-– Oldest…existed 2 million years ago– handy man.” fossils found with tools

• Homo erectus means upright human– Existed 1.6 million years ago to about 200,000 years ago– Taller and larger brain than Homo habilis– Smaller teeth than Homo habilis– Lived in groups (suggest language use) and used fire

• Homo sapiens- means wise human– Existed about 100,000 to 200,000 years ago– Some believe they arose directly from Homo erectus while other believe they

arose from Homo Neanderthals (who descended from Homo erectus)– By about 40,000 years ago, H. sapiens were physically identical to modern

humans

• Homo neanderthalensis - Neanderthals – Emerged in Germany 300,000 years ago– Lived till about 30,000 years ago– made stone tools and lived in organized social groups and had

organized societies– Brain was similar in size to modern humans– DNA evidence now supports this theory…modern human DNA is

99.7 % identical to that of the Neanderthals• Cro-Magnons appeared in Europe (shortly after, Neanderthals

disappeared) • Modern Humans –Last 10,000 years, Earth’s only hominid.

Embryology

• Zygote– When male gamete fertilizes female gamete– Gametes fuse, making one new cell with chromosomes

from both parents– Zygote will divide into 2 new cells…each of those into 4

and so on…– Cleavage division of embryonic cells to form two new

cells• Genetic material is copied before each cleavage

• Blastula– Hollow ball of cells

• Gastrula – When blastula implants itself on the uterine wall (to get

nourishment from mother)– Ball of cells composed of three layers “GERM LAYERS”

(undifferentiated)– Differentiation begins…

Zygote formation

Cleavage

4 cells

Morula

Blastocyst

Gastrula • Germ layers– Differentiation the

process by which a cell develops in different ways to perform different functions…begins with the forming of three germ layers

– Ectoderm• Outer layer• Forms skin, nerves and sense

organs

– Mesoderm• Middle layer• Forms bones, muscles and

connective tissue

– Endoderm• Inner layer• Forms digestive system and

lungs

Fetus

• When the structures of the developing embryo have become distinguished

• Cells have differentiated into their permanent role in that organism