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Chapter 5
Section 5.3
Evidence of Evolution from
Biology
Evidence from Anatomy
• Homologous vs. Analogous Features:
Homologous – features with similar structures but
different functions, and are similar because they
share evolutionary origin.
Analogous – features that are similar in
appearance and function, but do not appear to
have the same evolutionary origin.
Homologous Features
Analogous Features
Evidence from Embryology
• Embryology is the study of embryos or
the study of organisms before they are
fully developed.
• In the early weeks of development, human
embryos possess a tail and gill slits,
similar to those in chicken and fish
embryos.
• The embryonic tail serves no function in
humans and later becomes the tailbone.
• The gill slits become modified in both
humans and birds to form various internal
ear structures.
• But these pre-development relationships
show that there may have been a shared
ancestor along the evolutionary line.
Evolutionary Embryology
Vestigial Features
• Vestigial features – are structures found
in an organism that have no useful
function.
• One explanation for vestigial organs is that
they once served some function in an
ancient ancestor, but due to changes in
environmental conditions they were no
longer needed.
• Examples of vestigial features:
- Appendix
- Tonsils
- Whale leg and hip bones
- Snake leg and hip bones
- Blind cave salamanders have empty eye
sockets, suggesting they evolved from
salamanders with fully functioning eyes.
Vestigial Features
Evidence from Biochemistry
• Evidence for evolution has also been found by
comparing biochemical characteristics of
different species.
• Proteins are molecules that are used to make
structures in our bodies such as muscle cells
and skin cells.
• They are made of long chains of compounds
called amino acids
Amino Acids
• In many species the sequence of amino acids is
very similar.
• Ex. Hemoglobin is an oxygen carrying protein
found in the blood of all mammals, but each
species has a slightly different amino acid
sequence.
• Suggesting that each species evolved to suit
their own conditions. Such as animals that have
adapted to low oxygen environments.
• Scientists have also found evidence for
evolution in DNA sequences.
• DNA – deoxyribose nucleic acid is the
hereditary material that determines which
characteristics are passed on to the next
generation.
• Each DNA molecule contains many
different genes that provide the
instructions for traits such as eye colour or
hair colour.
• Gene – a segment of DNA that performs a
specific function, such as coding for a
particular trait (hair color, eye color,
proteins).
• DNA is composed of four chemicals called
nucleotide bases that arranged in different
sequences.
• The four bases are adenine (A), thymine
(T), cytosine (C) and guanine (G).
• DNA sequences from different species
that code for a particular trait vary in the
number and order of the nucleotides.
AGTCCCAAAGTGAAGGAGA
AGTCC AAAGTGAAGGAGA
• Geneticists have found homologous and
vestigial genes in DNA sequences.
• Ex. Humans possess a set of defective genes
that would allow us to make our own Vitamin C.
• We have lost the ability but still possess the
genes.
• Suggesting once again that we have evolved
due to our environmental conditions.
Evidence from Artificial Selection
• Artificial selection – the process of
humans selecting and breeding individuals
that have desired characteristics.
• The fact that we are able to change
organisms artificially provides evidence
that the same process is possible in
nature.
Artificial Selection
Assignment
• Lab Exercise 5.A
• Pg. 147