Human Evolution/Evolution of Sexual Reproduction

Paleoanthropology

Study of human evolution through fossil records

3 Shared characteristics(Synapomorphies) of great apes

Very flexible elbows and shoulders

Similar postures/positioning

Heel is first to touch ground when walking

Chimpanzees and gorillas have what unique form of locomotion

Knuckle walking

Chimps and gorillas have thin enamel, humans have

Thick enamel

5 unique human characteristics

Relatively hairless

Reduced canines

Bipedal locomotion

Extremely large brains

Hands with very fine muscle control

Hominim

Modern humans and extinct human ancestor species

Lucy

Famous early bipedal hominim(3.3 million years old)

Homo erectus

First well established hominin

Java man

Homo erectus fossil that had larger brains Hands and made tools

Homo heidelbergensis

A transitional species between Homo erectus and Homo sapiens

Homo florensis

Very small hominin species(ancient)

Two main models of human migration

Multi regional hypothesis

Out of Africa hypothesis

Multi-regional hypothesis

Homo erectus evolved in Africa and migrated to Eurasia 2, Homo sapiens then evolved independently from these

Multi regional hypothesis is believed to have occurred when

2 million years ago

Out of Africa Hypothesis

Modern humans originated in Africa 200,000 years ago and spread across the globe 100000 years ago

Sexual reproduction is a near universal feature of what

Eukaryotic organisms

2 stages of sexual reproduction

Meiosis

Fusion of haploid gametes to form zygote(fertilization)

Meiosis

Production of haploid gametes

Life originated without what

Sex

Sexual reproduction is something that

Evolved

Sexual reproduction in not what

A biological requirement

parthenogenesis

Offspring developed from unfertilized eggs

Parthenogenesis allows what

Asexual reproduction to occur in females

4 main costs of sexual reproduction

Cost of meiosis

Cost of males(2 fold cost of sex)

Cost of breaking adapted genetic combinations

Costs associated with mating

Cost of meiosis

Each parent only contributes 50 percent of genetic material(opposed to 100 in asexual)

Const of males(2 fold cost of sex)

Cost of having less number of offspring due to production of males

Cost of breaking adapted genetic combinations

Reproducing sexually may disrupt beneficial genetic combinations

The disruption of beneficial genetic combinations lowers what

The mean fitness of offspring

4 Costs associated with mating

Finding a mate

Energy spent in courtship

Increase risks of predation

Risk of disease transmission/parasitism

First fossilized evidence of sexual reproduction was documented in eukaryotes when

1 to 2 billion years ago

paradox of sex

Sex is widespread in eukaryotes despite overwhelming costs

3 hypotheses for advantage of sex

Lottery hypothesis

Mullets ratchet hypothesis

Red queen hypothesis

Lottery hypothesis

Sexual reproduction allows organisms to produce genetically diverse offspring

Some offspring may survive better due to what

Chance

In sexual organisms, offspring are genetically different from parents due to what 2 reasons

Recombination during meiosis

Fusion of gametes from different parents

Prediction of lottery hypothesis

Organisms with sexual reproduction survive better in changing environments

Why is lottery hypothesis not supported by data

Sexual reproduction is most common in stable environments, asexual reproduction is common in unstable environment

Mullets ratchet hypothesis

Sexual reproduction decreases deleterious mutations through recombination

Did empirical data support the ratchet hypothesis

Yes

Red Queen Hypothesis

Sexual reproduction allows Coevolving species to maintain dynamic equilibrium

Red queen hypothesis is used to explain how sexual reproduction does what

Increases host resistance to parasites

Sexual reproduction can provide offspring with what

Genetic potential to break equilibrium

Is there a general explanation for the maintenance of sex in all eukaryotes

No