ANTB14- LECTURE 1
Charles Darwin, who is credited with the “discovery” of the principal of natural selection in 1838, was
born in England in 1809. He died in 1882. Darwin was part of an expedition to map the coast of South
America between 1831 and 1834-35 aboard the HMS Beagle. As the Naturalist for the expedition, Darwin
was in charge of collecting and describing plant and animal specimens encountered on this expedition.
During his long journey, after observing incredible plant and animal diversity, as well as fossils, he
became interested in the question of how species come about. He was convinced that species came about
by slow change. Just HOW species changed was still a mystery. In 1838, shortly after returning home from
his journey, Darwin read Thomas Malthus’ essay titled “An Essay on the Principal of Population”. In this
essay Malthus, among other things, presents the notion that populations can increase in size exponentially
while food supplies remain relatively stable. This means that eventually a population will increase to the
point that there is not enough food or resources. This notion would become the cornerstone of Darwin’s
theory of evolution.
1. The ability of a population to expand is infinite, but the environment's ability to sustain that population
2. Organisms within the population vary, and this variation affects the ability of individuals to survive and
3. This variation is transmitted from parents to offspring.
Darwin’s theory is based on three postulates or concepts. The book summarizes these as:
1) A struggle for existence
2) Variation in fitness
3) Inheritance of variation
When resources are in demand (i.e. when the environment can’t support the existing population), a
struggle for existence occurs within the population.
Some individuals will possess physical or behavioral traits that allow them to better compete for resources
allowing those individuals to survive and reproduce.
These individuals pass these traits along to their offspring. Traits that are advantageous within the
environment are therefore retained within the population, while disadvantageous traits eventually
This process is termed NATURAL SELECTION. These advantageous traits are termed
Example: The Finches of Daphne Major (Galapagos Islands)
Studied by two Princeton biologists.
The finches (approximately 1500) on this island are trapped every year and measured, their behavior was
observed, and environmental factors such as rainfall and temperature were monitored.
The finches subsisted primarily on seeds.
Shortly after their study began there was a severe drought, at which time the plants began producing fewer
Soon the finches had eaten all of the softer easy-to-process seeds leaving only the larger, more difficult-
The shallow-beaked birds were forced to process larger seeds.
During this nearly 2-year drought the population of finches dropped from 1200 to 180.
A schematic diagram of how directional selection increased mean beak depth among medium ground
finches on Daphne Major.
Birds with deeper beaks were able to process the larger seeds and were more likely to survive and
reproduce. It is important to note that even birds with deeper beaks died during the drought.
The drought can be termed a selection event. This event selected for larger beaks, which was an adaptation
to the new condition. Because a greater proportion of those birds with deeper beaks survived and
reproduced, the average beak depth in the population increased. When the average of the population
increases or decreases this is termed DIRECTIONAL SELECTION.
The average beak depth in the population of medium ground finches on Daphne Major increased during
the drought of 1975-1978.
Because having a larger/deeper beak requires more calories when developing there are disadvantages to
having a deep beak. The Daphne Major finches with deeper beaks experience greater juvenile mortality.
This disadvantage is offset by the reduced mortality and greater probability of reproduction after the
juvenile period. Beak size increases until the disadvantages outweigh the advantages. At this point the
average beak size in the population is selected for and the birds with an average size beak are the most
likely to survive and reproduce.
Parents with deeper-than-average beaks tend to have offspring with deeper-than-average beaks.
This is consistent with Darwin’s postulate that variation is passed down from parent to offspring.
Diverse Order: diversity in diet among taxa, diversity in social organization, diversity in daily activity
Why are ANTHROpologists interested in nonhuman primates? Primates are of interest to anthropologists
because they can help us to study human evolution through the principal of homology, because we share a
common ancestor, and through analogy, because human and nonhuman primates are similar
morphologically, physiologically, and even behaviorally.
Primates is a diverse order. This diversity includes diet: some primates eat primarily leaves, while others
rely on fruit, or insects, or even sap.
Diversity in social organization: some primate taxa live in multimale groups, while others live in single
Diversity in activity patterns: some are active during the day (diurnal), others are active at nigh
What makes a primate: opposable big toe or thumb, flat nail on at least one digit, reduced olfactory
apparatus, stereoscopic vision, large brain, postorbital bar
Prosimians (or lesser primates) have wet noses (strepsirhine), an open orbit, and a higher level of
olfaction. Anthropoids (higher primates), have dry noses (haplorhine), and closed orbits.
Charles darwin, who is credited with the discovery of the principal of natural selection in 1838, was born in england in 1809. Darwin was part of an expedition to map the coast of south. America between 1831 and 1834-35 aboard the hms beagle. As the naturalist for the expedition, darwin was in charge of collecting and describing plant and animal specimens encountered on this expedition. During his long journey, after observing incredible plant and animal diversity, as well as fossils, he became interested in the question of how species come about. He was convinced that species came about by slow change. Just how species changed was still a mystery. In 1838, shortly after returning home from his journey, darwin read thomas malthus" essay titled an essay on the principal of population . In this essay malthus, among other things, presents the notion that populations can increase in size exponentially while food supplies remain relatively stable.