Human Origins

Four Forces of Evolution
Mutation
When an allele changes into something new or is lost
Creation of a new allele (a new variant) is more common
Very rare and very random, although certain environmental influences can have a strong impact on mutation, such as radiation
Mutation is the only source of new genes/alleles in a species
It must occur in the gametes in order to pass it on
Allele Definition: An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. These DNA codings determine distinct traits that can be passed on from parents to offspring.
Genetic Drift
Random change in the frequency of an allele
Occurs in every generation
Has strongest effect in smaller populations
Founder’s Effect
When a small group contributes exclusively to the gene pool of the next generation, it creates a genetic bottleneck where the chances of variation decrease
Can lead to allele fixation, in which everyone in a population has the same trait and it is unchanging
Gene Flow
Movement of alleles from one population to another
The exchange of genes when populations interbreed
The closer populations are, the more likely they are to interbreed, and vice versa – geographical distance
When populations start to interbreed, they become more similar, in that they have the same range of variation
Natural Selection
Some alleles will be passed on more frequently if they aid the chances of survival
The gene pool changes over time when an allele is advantageous, or the opposite
Three Premises of Natural Selection
More offspring are produced than can possibly survive
Offspring vary in ability to survive and reproduce
Partly based in genetics
Fitness – the ability to survive and reproduce
Genotypes that have greater fitness will show up more frequently and produce more offspring

Modern Evolutionary Theory
Natural selection + genetics – Darwin + Mendel
Comprehensive theory of evolution
Production and redistribution of variation
Process of natural selection
Mutation creates variation, natural selection spreads it around
Evolution, as defined in a biological context, is a change in an allele frequency from one generation to the next
Occurs within a population
Micro-evolution – short term changes
Macro-evolution – long term changes, such as extinction and creation

Human Variation
Race
“Race” is an arbitrary classification of different skin colors
Races are discrete units of biological variation within certain conditions
Most variation is between groups – very specific differences among races
10% of variation is within a groups
90% is between groups
Human groups have almost all variation
Some traits are more common in certain groups

Human Adaptation
Skin color is based on latitude – distance from the equator
Melanin provides protection from UV rays
UV rays affect folic acid, a building block for the brain and spine – also affect intake of vitamin D
Race is a social description – a poor attempt to group people together
Adaptation – a response to a stress
Stress – interferes with homeostasis, which maintains body limits
Plasticity – ability to respond or adapt to stress

Climate & Morphology
Temperature and humidity affect the shape and size of your body
In colder climates, body size (volume) is larger, in heat it’s smaller
Bigger bodies burn more energy, which creates more heat
Bergmann’s Rule – the amount of heat the body loses is related to body size
Heat loss = ratio of surface area to volume
Smaller volume = more heat loss, bigger = more
The biggest surface area and the smallest volume creates the most heat loss
The smallest surface area and the biggest volume creates less heat loss
Long narrow body shapes are better for hot climates and vice versa
Allen’s rule
In cold climates you tend to have shorter, bulkier limbs to retain heat – high volume, low surface area
In hot climates you tend to have longer, narrower limbs to lose heat faster – low volume, large surface area
Nasal shape has to do with filtering air – moistens and warms air in cold climates, and vice versa for dry climates
High and narrow nose = cold and dry air
Low and wide nose = warm and humid air

Cenozoic Era
Epochs (Ma- millions of years ago) (ka- Thousands of years ago)
Paleocene – 55-65 Ma
Eocene – 35-55 Ma
Oligocene – 23-35 Ma
Miocene – 5-23 Ma
Pilocene – 1.8-5 Ma
Pleistocene – 10,000 ka – 1.8 Ma
Holocene – present to 10,000 ka

Transition to Modern Humans
Out of Africa
Modern humans originated in Africa and only in Africa
Once they developed, they migrated and replaced archaic groups
They defeated the Neandertals in Asia and Europe – no gene flow
Multi-Regional Continuity
Modern humans developed throughout the Old World at different locations – Asia, Africa, Europe
Lots of interbreeding and gene flow
Assimilation
Modern humans evolved in Africa
Moved out and interbred with Neandertals – lots of gene flow
Modern Humans in the New World
Migration from Russia into Alaska – used the Bering Strait – multiple migrations – 50,000 ka to 13,000 ka
Went by land and by boat

Smithsonian: http://humanorigins.si.edu/evidence/human-fossils/species NYU Center for the Study of Human Origins (CSHO): http://www.nyu.edu/gsas/dept/anthro/programs/csho/pmwiki.php/Home/HumanEvolutionExplorer Y-chromosomal Adam: http://en.wikipedia.org/wiki/Y-chromosomal_Adam Mitochondrial Eve: http://en.wikipedia.org/wiki/Mitochondrial_Eve