Download Topic 5 - Fillingham

TOPIC 5
Evolution and Biodiversity
DARWIN AND WALLACE

Charles Darwin, in 1858, traveled on board the HMS Beagle for
scientific exploration lasted for 5 years.

He saw nature in a new way which became the most important,
controversial, and misinterpreted ideas in biology: Evolution by
natural selection.

Alfred Russell Wallace had independently developed a nearly
identical theory.

Together in 1858, they presented their ideas to the Linnaean
Society.
WHAT IS EVOLUTION?

Evolution is defined as the process of cumulative change in the
heritable characteristics of a population.

Cumulative-one change is typically does not have a major
impact on a species.

Heritable- it must be passed down

Population- the change does not affect a single individual.

*If enough change occurs in a population, a new species can
arise. (This process is call speciation)
SPECIATION

The new members will be different enough from the pre-existing
population that they came from, they can no longer interbreed.

*Such a process is rarely observable during a human lifetime.
EVIDENCE FOR EVOLUTION BY
NATURAL SELECTION.

1) The fossil record

2) Animal breeding

3) Homologous Structures
THE FOSSIL RECORD AND EVOLUTION

Fossils are the petrified remains or traces of animals and plants.

It is the accumulation of evidence from these remains and
traces, such as skeletons and footprints.
AGEING FOSSILS

The age of a rock can be determined by examining
differences in the ratios of isotopes.
 14C
(carbon-14) has a half life of 5730 years.

When an animal dies, 5730 years later its bones will have lost half
their 14C life. 11,460 will have lost 75%.

Important: looking at the ratio of radioactive 14C to 14N, it is
possible to determine the age of a fossil.

After so many half-lives it is hard to tell how much 14C is left.
AGEING FOSSILS
 40K
(potassium-40) is another radioactive isotope, that has much
longer half-live.

Formed when minerals in rocks crystallize from magma.

Once hardened no more 40K can be added.

Used to measure the age of rocks between 100,000 years and 4.6
billion years ago.
ARTIFICIAL SELECTION AND EVOLUTION

Breeding domesticated animals, for example cattle, horses, dogs,
sheep, and pigeons.

Breeders can see which characteristics an offspring will have by
watching which male mates with which female.

Producing more milk, better beef. Over the years breeders have
learned how to choose which pair mates, getting the desired
genetic characteristics. (Selective breeding)

Artificial selection is evidence that evolution is happening, but it is
certainly not the driving force of evolution in natural ecosystems.
ARTIFICIAL SELECTION
EVOLUTION OF HOMOLOGOUS
STRUCTURES BY ADAPTIVE RADIATION

Homologous anatomical structures which are similar in form but
which are found in seemingly dissimilar species.

Ex. Five-fingered limb found in animals: humans, whales, and bats.

Pentadactyl limbs: “penta” means five; “dactyl” means fingers

The shape and number of bones may vary, despite the fact that
the specific functions of the limbs may be very different.

Darwin explained that homologous structures were not just a
coincidence but evidence that the organism in question have a
common ancestor.
SPECIES DIVERGENCE

The process of an evolving population changing significantly
enough so that the production of offspring with the original
population becomes impossible.

*two populations of a species have diverged, and a new species
have evolved from an old one.

*Both species will then continue on their separate ways.
ADAPTIVE RADIATION

Similar but distinct species evolve relatively rapidly from a
single species or from a small number of species.

This happens as variation within a population allow certain
members to exploit a slightly different niche in a more
successful way.

Niche-is a position or role within a community of an ecosystem.
ADAPTIVE RADIATION

Example: Primates found in Madagascar and the
Comoro Islands.

Without competition from monkeys or apes, lemurs on these
islands were able to proliferate.

Large numbers of offspring meant a greater change for diversity.

Adaptions: living on land, living in trees, living in lush rainforests,
and some survive in the desert.

Example: Galapagos finches and Hawaiian honeycreepers

Both have a variety of beak shape/size.

It is possible, within a species that has a wide geographical
distribution, to have measurable differences in DNA.

Soil/climate so different that populations adapt to those conditions
that are available to them.

Genes will be selected for some and against others. (Selective
Pressure)

Over a long enough period of time the populations are so great that
they are no longer the same species.
TRANSIENT POLYMORPHISMMELANISTIC INSECTS

Different versions of a species within a population.


Can be from a result of a mutation.
Biston betularia, a moth found in temperate climate.

This species can have peppered (grey) color or melanic (black)
color. Melanic moths (carbonaria)

Melanic is rare <1% of population.

Around the 1860s the melanic (carbonaria) form was
increasing in numbers.


What was happening around the 1860s?
The lichen was very sensitive to the air pollutants, killing it.

The air was also filled with black soot.

The light colored moths were now more easily visible in the
lichen free, darken tree branch.

Since the significant air quality, the carbonaria population
went from 95-100% down to 30% and often at 0%.

This changing of colors is an example of transient
polymorphism, temporary changes in the form of a
species.