Human Evolution

Could the Ape Family Be Man’s Ancestor?

There are two ways to approach this question. One is to investigate the DNA. The other is to investigate the fossil evidence.

The textbook presents the fossil evidence so let us investigate the DNA evidence. There is general agreement that the human probably descended from the chimpanzee. It is usually maintained that the DNA order is only 1.4% different.

The 1.4% number was obtained by comparing only substitution type mutations in a fraction of the total DNA’s. If insertions, deletions and substitutions are considered in only 1% of the DNA the number rises to 5%. In 2004, numbers were reported to be 7.7% and 20% as more of the DNA was compared.

Think Critically When it is recognized that chimps have 10% more DNA and two more chromosomes than humans, is the 1.4% difference reasonable? Of the numbers 5%, 7.7% and 20%, which is the most reasonable?

Assume that the chimp and human genomes have the same number of base pairs. Using the 7.7% figure and 3,200,000,000 as the total number of base pairs there is a 246,000,000 base pair difference.

This difference is the same number of letters contained in approximately 43 textbooks like yours if there were nothing but letters on each page – no pictures, charts or tables.

Think Critically How could this have come about when mutations are random chance happenings and the following constraints are considered? 1. Under the best of conditions, only one in one thousand mutations is considered favorable. The rest are unfavorable and possibly fatal or neutral at best.

2. Unless the mutation occurs in THE particular egg or sperm that is to be used in reproduction then the mutation has no effect on future generations. In other words it has to occur in one particular cell out of about 30 trillion cells.

3. Not only do the mutations have to occur in that particular cell but the same mutations have to occur in a member of the opposite sex at the same time and place to make the change dominant. 4. These two chimps have to mate and have a successful pregnancy.

Think Critically Explain any conflicts that exist between the fossil and DNA approaches.

Click to Return to PPT List Click to Return to PPT List