H Human Evolution
H1. Describe key adaptations that distinguish humans from non-human primates.
Describe hypotheses for the evolution of bipedalism in humans.
Describe traits formerly attributed only to humans that are found in other species.
Upright posture and bipedal motion are key adaptations distinguishing hominids from apes.
Primates have power grip, humans have power grip and precision grip. Increase in # of
The African Emergence Hypothesis: proposes that modern humans first evolved in Africa and
then dispersed to other continents; all modern humans are descended from a fairly recent
African ancestor. They drove archaic humans to extinction.
The Multiregional Hypothesis: proposes that after archaic humans migrated from Africa to
many regions on Earth, their different populations evolved into modern humans
simultaneously. Geographically isolated, but may have experienced differentiation; gene flow
prevented reproductive isolation.
Neanderthals were culturally and technologically sophisticated. Made tools, built shelters,
hunted and buried their dead
H2. Explain why humans are more correctly described as ‘sharing common ancestry with
chimpanzees’, rather than the incorrect ‘descended from chimpanzees.’ *Comprehension,
Chimpanzees still exist and continue to evolve independently. Humans diverged from
chimpanzees; a more recent divergence
Sequence variations: contain no genes and do not go through natural selection. Result only
from random mutations and serve as molecular clock, Only 3 sequences mutations found
among 5 people of varying ethnic backgrounds. Chimps, however had 207 differences from
humans. Limited genetic diversity and recent ancestor confirms they are all from Africa.
H3. Explain and describe the evidence, from both humans and other organisms, supporting African
ancestry Of hominins, and the pattern of migration of humans over their evolutionary history,
relating evidence to founder events.
Describe evidence of the relationship between H. sapiens and Neanthertals.
African ancestry of hominins: neutral mutations accumulated in African populations much
longer = greatest variation. All human populations contains at least one mtDNA sequence of
African origin I Population Ecology
1. Identify characteristics of a population and what they tell us about a population, specifically:
why population density is more informative than population size; three methods to estimate
population size and density, providing advantages and disadvantages of each; difficulties in
accurately determining population size; the relationship between an organism’s size and its
population density, its generation time, and its rmax; and different patterns of population
Population density: number of individuals per unit area/volume of habitat
Population size: number of individuals comprising the populations at a specified time
Density > size provides more information about its relationship to the resources it uses.
3 ways to measure:
1. Simple head count: easy in small populations compared to bigger
2. Mark-release-recapture: assume mark has no effect on survival; individuals mix randomly, no
migration, and equal chance of being caught for all.
3. Random sampling?
Difficulties in accurately determining population size:
Measuring population size in organisms that are clones
The relationship between organisms’ size and population density, generation time, and rmax:
Whether the spatial distribution of a population appears to be clumped, uniform, or random
depends on size of organisms and study area. Oak seedlings may be randomly dispersed on a
spatial scale of few metres, but over an entire mixed forest, it would appear to be clumped.
Generation time: average time between birth of organism, and birth of its offspring. Usually
short in species that reach sexual maturity at small body size; population size grows rapidly
because of speedy accumulation of reproductive individuals = high population density
Rmax: maximum per capita growth rate; intrinsic rate of increase…population size increases
Different patterns of dispersion:
Clumped: individuals are grouped more closely to one another
Random: organisms are distributed independently of each other
Uniform: individuals are more widely spread separate from one other
a. Predict given a description of an organism and its environment: which method would be most
useful/feasible to determine its population size; and the type of dispersion it most likely
exhibits. [Application, Analysis] Refer above
b. Describe how age structure (and relative proportion of pre/post reproductive members) of a
population impacts population growth in a population that is: shrinking, zero-growth, or rapidly
Age structure: statistical description of the relative number of individuals in each age class
Pre-reproductive: younger than age of sexual maturity
Post-productive: older than the maximum age of reproduction
Structure reflects recent growth history, and predicts future growth potential
Those with more many pre-reproductive grew rapidly in recent past, and population will
continue to grow as young individuals mature and reproduce
Shrinking: birth rate lower than death rate
Zero-growth: birth rate equals death rate
Rapidly growing: birth rate exceeds death rate
c. Describe how an organism’s different life stages can reduce intraspecific competition.
Intraspecific competition: the dependence of two or more individuals in a population on the
same limiting resource
At different stages of life, they have different needs, this prevents entire population from vying
for same resource
2. Describe what a survivorship curve represents. Given general information about a species’
pattern of survivorship and mortality, identify or draw the type of survivorship curve (I, II, or III)
a population would exhibit. [Comprehension, Application]
Survivor ship curve: displays the rate of survival for individuals over the species average life
Type 1: high survivorship until late in life. Typical of large animals that produce few young and
provide extended care, reducing juvenile mortality.
Type 2: relatively constant rate of mortality in all age classes, pattern that produces steadily
declining survivorship. E.g., lizards. Face mortality from predation, disease, starvation…
Type 3: high juvenile mortality followed by low mortality once offspring reach a critical age and
size. E.g. 1 million seeds produced, fewer than 1000 germinate, only about 40 survive first year.
Once established, survival is higher probability. E.g. insects and fish 3. Describe how natural selection shapes life history traits, and the different trade-offs (e.g.,
parental care vs. fecundity; number of times to breed; age at first reproduction) involved in
reproductive life history traits. [Knowledge, Comprehension]
Passive parental care: amount of energy invested in each offspring before it is born: yolk in an
egg, nutrients crossing placenta
Active parental care: amount of energy invested in each offspring after it is born: nursing child
Fecundity: potential reproductive capacity of individual
Number of times to breed: some devote all stored energy to a single reproductive event,
whereas others reproduce more than once, and devote some energy to reproductive with
balance allocated to maintenance and growth. Later results in greater fecundity at a later age.
Age at first reproduction: those that first reproduce at the earliest possible age stand a good
chance of leaving surviving offspring. But energy they use in reproduction is not available for
maintenance and growth…thus early reproducers may be smaller and less healthy in
comparison to others.
Individual that delays reproduction may increase its chance of survival and future fecundity by
becoming larger and more experienced. But possibility that it will die before next breeding
season and leave no offspring. Thus, finite energy budget and the risk of mortality establish a
trade-off in the timing of first reproduction.
Delayed reproduction is favoured by natural selection if a sexually mature individual has good
chance of surviving to an old age.
Early reproduction favoured if adult survival rate are low.
4. Describe the relationship (and differentiate) between the exponential and logistic growth
models, making reference to why exponential growth cannot continue indefinitely. Provide the
exponential and logistic growth equations, identify all terms, and explain how the terms change
relative to one another.
Exponential: population size increases steadily by a constant ratio…e.g. bacteria. As population
grows, uses more resources, leads to shortening, individuals have less energy available for
maintenance and reproduction, which causes decrease in per capita births and rise in deaths.
Energy in food is not always equally available…changes cause population growth to slow
dN/dt = rmax N
population growth rate = intrinsic rate of increase x population size
Logistic: population growth slows as the population size approaches K (carrying capacity: max
number of individuals the environment can support. Populations grow slowly at low and high
population size: low – few individuals reproduce, high – per capita growth is low. Grows quickly
at intermediate when good amount of individuals breeding. Assumes vital resources ecome
increasingly limited with growth
dN/dt = rmaxN (K-N)/K population growth rate = intrinsic rate of increase x population size (carrying capacity-population
R decreases as population size approaches K
a. Explain: how r changes when b>d, bd: r has a positive value, population grows