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Evidence for
• This is the study of the geographical
distribution of species, both presentday and extinct.
• Geologically separate areas tend to
be inhabited by organisms that are
ecologically similar: on islands, the
organisms tend to be unique.
– E.g. the development of marsupials in
Australia but not elsewhere.
The Fossil Record
• Any non-living object obtained from
the ground that indicates the former
presence of a living thing is a fossil.
• Fossils are the remains of living
things – bones, shells, or other parts
resistant to decay – or their traces
such as footprints or burrows that
have been preserved in the rock.
The Fossil Record
• Where rock strata can be aged, the
succession of fossils in the layers
show that the most primitive forms of
life are the oldest strata.
• The progression of the fossils follows
the evolution of life as we know it
from other sources.
Formation of Fossils
• Most fossils occur in sedimentary
• Sediments in the sea gradually cover
the dead body on the sea floor and
petrify it.
The Process
• A dead animal falls to the sea floor.
• Sediment covers the skeleton; other
bodies fall to the new sea floor.
• Time passes; layers of different rocks
• Movement of the Earth’s crust folds
the rock layers.
• Erosion of the rock means that fossils
can be seen.
Comparative Anatomy
• Homologous Structures – these
show similar characteristics resulting
from common ancestry.
– E.g. pentadactyl limbs
Comparative Anatomy
• Analogous Structures - these have
the same function but different
– E.g. birds and insects have wings.
Comparative Anatomy
• Vestigial Organs – these are organs
that have become reduced or have
lost their function.
– E.g. the tail bones in humans and the
wing bones in a kiwi.
Comparative Embryology
• The early embryonic stages of all
vertebrates are very similar, even
though the adults are all very
Molecular Biology
• Species which are close in
evolutionary terms have only small
differences in their DNA and proteins.
• Even organisms from different
taxonomic groups have some
common proteins.
– All living things have DNA so they must
have had a common ancestor.