Ch22: Human Evolution

Evolution Vs. Intelligent Design

Evolution

Change in heritable traits within a population over successive generations

Supported by scientific evidence

Intelligent Design

Concept that “certain features of the universe and of living things are best explained by an intelligent cause”

Can not be supported or rejected by research

Geological Time

Chemical Evolution

Atmospheric gases reacted and produces small organic molecules Stanley Miller performed an experiment to support this hypothesis

Small organic molecules joined to produce organic macromolecules

Organic macromolecules formed the first Protocell. Lipid-protein membrane Heterotroph – takes in preformed food Fermenter- created energy without oxygen

Protocells incorporated RNA (& then DNA) to create a True cell. Cell was able to reproduce & pass on its genetic information.

Biological Evolution

Biological evolution is a change in life forms between generations.

Two aspects of biological evolution: Common descent – all living descended from a common ancestor

Explains unity of all living things (i.e. all living things are made up of cells and have the same biochemistry)

Adaptation – modification in structure, function, or behavior to better suit the environment Explains the diversity of life

Charles Darwin

A naturalist that formulated the theory of evolution based on the following evidence: Biogeographical – even though there were suitable environments for

certain plants & animals they were not distributed everywhere.

Anatomical Homologous structures – anatomical parts that are similar, but have

different functions; these anatomical similarities indicate common descent. Analogous structures – have the same function, but are anatomically

different; thus, there is no common descent

Fossils – remains or traces of past life that has been preserved in the earth’s crust.

Homologous Structures

Additional Evidence

Biochemical Evidence – almost all living organisms use the same basic biochemical molecules. DNA – genetic information

Organisms that are closely related have a higher percentage of similar DNA

Proteins – same 20 amino acids ATP – molecule for energy

Evolutionary Mechanisms

Natural Selection - the process by which a species becomes adapted to its environment.

Sexual Selection – the process by which certain individuals are chosen to mate.

Genetic Drift – random changes in gene frequency in a population

Evolutionary Mechanisms

Evolutionary Mechanisms are dependent on:

Mutations – changes in chromosome structure

Genetic Recombination – changes in alleles combinations often due to crossing-over

Gene flow – movement of alleles of genes into or out of a population by migration and interbreeding.

Natural Selection

Variation - physical variations can be passed from generation to generation

Competition - the environment “selects” these better adapted members to have offspring and to pass on this characteristic

Adaptation - subsequent generation include more individuals that are adapted in the same way to the environment.

Sexual Selection

Intrasexual competition – same sex individual fight to mate with females

Intersexual competition – females (or males) choose certain mates based on certain characteristics.

Human Evolution: Humans are Primates

Characteristics of Primates:• Grasping fingers and toes, some

with opposable thumbs• Well-developed brain• Nails• Single birth• Extended period of parental care• Emphasis on learned behavior

Two Suborders:• Prosimians—lemurs, tarsiers, and

lorises.• Anthropoids—monkeys, apes,

and humans

Evolution of Hominids

Hominid – humans Family branch Bipedal posture (walking on two

feet) Flat face Brain size

Australopithecines - a group of individuals that evolved and diversified in Africa. Hominids lived about 3 MYA Walked erect Small brain compared to us, but

large brain compared to other primates

Limb proportions are ape-like

Australopithecus africanus with its large brain is the best ancestral candidate for early Homo

Evolution of Homo

Homo habilis - may be the ancestor to modern humans (2.0-1.9 MYA)• Made tools• Large brain• Dentition• Omnivores (plant gatherers and hunters)• May have had the rudiments of a culture

Homo erectus – may have evolved from Homo habilis (1.9 -.3 MYA)• Large brain• Striding gait• Made well-fashioned tools• Control of fire• Migrated into Europe and Asia

Evolution of Modern Humans Multiregional Continuity Hypothesis – evolution of modern

humans was essentially similar in many different places. Out-of-Africa Hypothesis – evolution of H.sapiens evolved

from H.erectus only in Africa and then H.sapiens migrated to Europe & Asia

We are one Species

Biological definition of a species – Any group of organisms able to interbreed and bear fertile offspring.