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Assoc Prof. Rebecca AckermannDepartment of ArchaeologyBeattie Bldg, Rm 3.19becky.ackermann@uct.ac.za

7 billion people

Anthropology Socio CulturalLinguistics

Archaeology

Anthropology Socio-Cultural

Biology

Linguistics

Biogeography & Adaptation Overview of Humans/Primates Vision

Bi d li Bipedalism Brains Skin Agriculture Domestication World Population Growth

All readings are on Vula

Practicals and supplemental materials for the practicals are also on Vula

Remain at the ENGEO Building venue for the first practical

/ Practical 1 will run Th/F (May 3 & 4) in first week and M/Tu (May 7 & 8) in second week

Bring a calculator

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Practical 2 will run Th/F of the second week (May 10 & 11) and M/Tu of the third week (May 14 & 15)

Meet at the Pick-up / drop off area at the end of University Avenue SouthAvenue South

13h00 – 18h00

Wear good shoes!!! Bring appropriate clothes (e.g. rain gear)!!!

Bring something (e.g. clipboard) to write on

Be sure to read background material AHEAD of time

Introduction Adaptation through natural selection What is a species?p How does one species split into two? Extinction

Biogeography = the study of the pattern of distribution of organisms (individuals, species, ecosystems) across space and through geological time

Patterns of distribution of organisms across geographical areas can usually be explained through historical factors (e.g.

i i i i i l d if l i i i i ispeciation; extinction; continental drift; glaciation, variations in sea level, river routes, habitat) in combination with geographic constraints (landmass areas and isolation) and the available energy supplies in the ecosystem

Evolution (adaptation through natural selection) provides the key explanation for the pattern of distribution of organisms (i.e. the link between organismal variation and the climate/environment)

Evolution = descent with modification (i.e. change through time)

(mutation, selection, gene flow, genetic drift)

fast slow

Adaptation of plants and animals to their environment occurs through the process of natural selection

Adaptation = a change of structure, form, or habits to fit different conditions, which increases fitness

Adaptive traits = a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection

Natural selection = preservation of favorable individual differences and variations and the destruction of those that are injurious

Ship Naturalist

1831-1836: Voyage of the1831 1836: Voyage of the Beagle

1859: On the Origin of Species by Means of Natural Selection

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Parallel between species morphology, behaviour, geography and adaptation (‘fit’) to environments (the foundation of biogeography!!)

Demonstrated FACT of evolution (and defined it as descent with modification)

Offered explanatory mechanism (i.e. natural selection… survival and mortality KEY to this definition)

Malay Archipelago: 1848-1862

1857: “On the Tendency of Variation to Depart Indefinitely from the Original Type”

Heredity of most features Heritable variation in the population Variation leads to differential rates in survival &

reproductive success among variations Differential survival and reproduction leads to change

in frequency of characters (e.g. populations will diverge from one another)

If process goes on long enough, parent & daughter species can no longer interbreed (e.g. they have become too different)

ENVIRONMENTAL CONTEXT IS ESSENTIAL!!!

The peppered moth, Bistonbetularia, occurs in two varieties, melanic and non-melanic

Non-melanic form is virtually invisible against pale-colouredinvisible against pale coloured backgrounds, vice versa for melanicform.

Differential survival rates under environments of different colour.

Prior to industrial revolution, lighter form dominant - a survival advantage against lichen-covered trees.

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After the industrial revolution, more offspring of melanic form survive to reproduce.

Relative frequency shift: beforel i 5% f 98%melanic = 5%, after = 98%.

Process occurred in just 40 generations.

Note that in this case natural selection does not create the forms, but rather edits the populations.

Natural selection is ‘fine-tuning’ populations to their physical environments.

Angraecum sesquipedaleXanthopan morganii praedicta

Daubentoniamadagascariensis

Bergmann’s Rule Allen’s Rule

Correlates between latitude (climate) and body mass / limb length

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Natural selection can act to create (or delete) forms (species) when viewed over deep (geological/evolutionary) time

Other evolutionary forces (mutation, drift, gene flow) also play a role in creating new forms

Species are uniform ‘types’ of organisms: biogeographers classify organisms as belonging to one or other species.

There are many different ways of defining species

In practice, species are generally recognised not solely (or even necessarily) by reproductive isolation, but by some combination of factors such as morphology, genetics, geographic proximity, and ecology, that together make a species distinct even in the face of gene flow.

Western Meadowlark Eastern Meadowlark

Modes of species change

anagenesiscladogenesis

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Tempo (pace/rate)

Phyletic gradualism Punctuated equilibrium

Tempo + Mode

time

gradual gradual punctuated punctuated stasisanagenesis cladogenesis anagenesis cladogenesis

phenotype

Adaptive radiation

Speciation – e.g. diversification of lineages (lineage splitting)

Most important type of speciation is allopatric speciation (although you may also encounter the terms sympatric and parapatric speciation).

Species becomes geographically divided by a barrier (continental drift, rifting, change in course of river, fire etc).

Separate populations are reproductively isolated from each other.

N l l i i d d tl i h l i d h Natural selection operates independently in each population and the populations gradually become adapted to their own unique environments (divergence also occurs through genetic drift).

Reproductive isolation is initially imposed by the geographical constraints, but eventually populations diverge too much resulting in permanent barrier (different genomes, behaviours, etc).

Speciation is complete; one species has become two (or more).

Time 4Differentiation (speciation)

Time 3Reproductive isolation

Time 2Physical barrier

Time 1Original population

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If speciation occurs all the time, there should be more species today than 10,000 years ago, and more then than there were 10 million years ago, right?

No because extinction is ubiquitous No, because extinction is ubiquitous.

99% or all species that have ever existed on Earth have gone extinct.

Some geological periods are characterised, or dominated, by extinction (e.g. end-Permian, end-Cretaceous).

These are so-called mass extinction events

Causes varied and sometimes controversial

End-Permian event resulted in loss of 90% of all marine species - global warming may have been the culprit (a lesson?).

End-Cretaceous (K-T) likely caused by asteroid impact. Loss of large proportion of reptiles (especially the dinosaurs).

Causal factors may have been climate change induced by impact: global cooling.

Chicxulub crater

Sudden disappearance ~50Ka

Human-induced environmental change caused by burning practicesp

Drought-adapted flora with palatable nutritious grasslands became fire-adapted desert scrub with low-nutrition grasses

Stress and extinction of megafauna

Climate? 14 genera disappear

before the first Clovis point is found

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In the American South-West the dates for Clovis sites (~13Ka) coincide closely with the dates for the last appearance of the Shasta Ground Sloth.

Climate change (severe droughts).

Arrival of humans (including overhunting, introduction of alien species, the use of agricultural fires).

Hypervirulent/hyperlethaldisease

Human-induced climate change, habitat change, and hunting are continuing to threaten megafaunaworldwide