deep time lecture 3

our ancestors were

multicellular eukaryotes

• but prokaryotes and single celled eukaryotes are major clades with living descendants (that we depend on)

animals

• (one clade of multi-celluar eukaryotes)

• but fungi and plants are other MAJOR clades of multicellular eukaryotes with living descendants

mammals

• (one clade of animals)

• but older clades of other types of animals are also very important and have many living descendants

primates

• (one clade of mammals)

• but many primate lineages with which we share ancestry have living descendants

primates (order)

two homologous traits that were favored by natural selection in an arboreal (tree environment)

1. grasping fingers and toes

2. Binocular Vision

• eyes shifted toward the front of the face

• lets brain judge distances precisely (depth perception)

Hominidae (family)

humans and our close relatives

• genus PONGO (living: orangutans)

• genus GORILLA (living: gorillas)

• genus PAN (living: chimpanzees, bonobos)

• genus HOMO (H. Spaiens are they only living species)

• genus AUSTRALOPITHECUS (extinct but also our close relatives)

Bipedalism

walking upright (2 feet)

evolved as homo ancestors left forests for grasslands and open woodland

emerged at least 4 MYA. Why bipedalism evolved is still a matter of controversy (tool use emerged 2.5 MYA)

Substantial brain expansion on the other hand did not emerge until 2MYA

genus homo

early humans were called homo habilis and were able to use tools

had a larger brain

interbreeding among homo species

Denisovans and neanderthals all interbred with each other on multiple occasions in the past 100,000 years

lots of interbreeding among homo species

homo sapiens

progressive increase in brain size

• use of tools

• conceptual thought

• language

extensive cultural experience

• change and mold the world rather than evolving in response to the environment

• pass on knowledge across generations

human genetic diversity is higher in Sub-Saharan Africa

two main reasons for the reduction in diversity:

• successive bottleneck and founder effect (genetic drift)

• local adaptation to new environments (strong directional selection)

lactase gene

allows mammals to digest lactose, a sugar found in dairy products

lactase persistence

tells the lactase gene to turn off shortly after weaning

favored by natural selection: enhanced survival of people in populations relying on milk for nutrition

human populations living in high altitude have adapted to

the low oxygen environment

ways humans have evolved and continue to evolve

disease resistance

selection related to head size

• stabilizing selection- medium head size

• c-section has stopped selection

race

A. the idea that the human species is divided into distinct groups on the basis of inherited physical and behavioral differences and

B. These differences are indicative of deeper biological connections

it is a “social construct” because A is flexible/ depends, and B is not correct

Human Populations and Race

constant gene flow has prevented subspecies of humans from forming

humans rely on visual cues

can objectively test the hypothesis of human races using molecular genetic data

find local adaptations to environment but no subspecies or races

race is used to test bias and human society

individuals

acclimate- respond physiologically to a change in an environmental factor (“getting used to” hot temps)

populations

adapt- individuals in a population have a mutation that make them more likely to survive and reproduce; over time more individuals in the population have that new characteristic

evolution of skin color

wavelengths of light are either absorbed by pigment or reflected from objects to our eyes

melanin

pigment for skin, hair, and eye color

• eumelanin

• phenoelanin

eumelanin

brown and black

pheomelanin

reddish-yellow

melanosomes

organelles that synthesize and store melanin

melanocytes

cells that produce melanosomes

equatorial Africa

about 1.2 MYA alleles for dark skin in human ancestor were fixed

ancestral alleles=dark skin

MC1R- africa

africa: extremely high proportions of darker skin

demonstrates natural selection selected AGAINST light skin mutations in africa

mutates for light skin occur but this characteristic does not survive well (is out competed by dark skin)

MC1R- western asia and europe

some proportion of light skin alleles

• demonstrates NO natural selection AGAINST light skin mutations

• implies genetic drift allowed light-skinned people to survive

MC1R- east asia

high proportion of light skin alleles

• implies natural selection FOR light skin and AGAINST dark skin

SLC24A5- africa

extremly high proportions of darker skin

• demonstrates natural selection selected against light mutations in Africa

SLC24A5- asia

some proportion of light skin alleles

• demonstates NO selection AGAINST light skin muatations

SLC24A5- Europe

high proportion of light skin alleles

• implies natural selection FOR light skin and AGAINST dark skin

evolution is about ___

fitness

old age has no impact on evolution (already produced)

evolution is affected by what happens to you

• before you reproduce or

• during pregnancy/ giving birth

folate

B vitamin

nessecary for reproductive success:

• DNA synthesis and repair

• normal embryonic development (deficiency causes birth defects such as spina bifida)

• healthy sperm production

low UVR in high latitudes (light skin)

melanin interferes with vitamin D synthesis, so lighter skin would enhance Vitamin D3 photoproduction

• Vit D3 is essential for proper bone growth and developemnt

without the strong selective pressures for dark skin, random accumulation of mutations (dark skin) can occur

deficiency in Vit D

impairs bone mineralization = leads to bone softening diseases

vitamin D

essential for absorbing calcium from diet

make this when exposed to sunlight

high UVR at low latitudes (dark skin)

melanin protection from

• sunburn DNA damage

• photodestruction of circulating folate

• folate is nessecary for DNA synthesis and repair

UVR destorys

folate