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