Section 5.3 Evidence of Evolution from Biology 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