Biology
Chapter 19: 11-17 Hominid Evolution
Lecture
Primates and Hominids
Web Lecture
The Evolution of Primates
Perhaps most fascinating to us is our own place in the theory of evolution, a topic which raises debates within and without scientific circles. Whatever scheme scientists come up with challenges our perception of ourselves, our relationship to God, our role as stewards and consumers of the universe, and we are forced to determine to what extent we will allow our understanding of theology to guide and enform us as we analyze our scientific observations.
The Evidence cited for Human Evolution
Different kinds of evidence are used to establish the relationship between species. Modern theories rest primarily on DNA similarities. Based on the idea that DNA replicates precisely unless there is a heritable mutation, and that random mutations happen at a statistically steady rate, species with few differences in DNA sequences are considered more closely related than species with many sequence differences.
Biologists use DNA similarities and mutation rates to determine the relationships between primates, animals that share a certain body plan and often share behaviors as well, whether or not we find the evolutionary explanation for the similarities compelling.. For most of the rest of the year, we will be discussing human anatomy. Understanding the close relationship between humans and other primate species will help you determine to what degree you can compare or assume structures, functions, and behavior in primates is similar human physiological and anatomical characteristics.
It is important also to realize the assumptions and limitations that underly DNA comparisons, especially in controversial areas with bearing on the debate between evolution and creationism. Studies may claim a "98% similarity" between DNA in chimpanzees and humans, meaning that for certain genes, the DNA sequences are the same. But reports from these studies often gloss over the fact that there are significant differences in the organization of the genes on chromosomes. Chimpanzees have 24 chromosomes, humans have only 23. The protein complexes in histones vary significantly, and we are only now beginning to realize that histone support in the DNA sequence may influence gene expression. When looking at the DNA evidence (as, indeed, with any scientific survey reported by secondary sources), we need to understand both the methods and assumptions made in collecting the data, and the methods and assumptions of those conducting the analysis, as well as our own assumptions in interpreting what we read.
Primates
Primates are divided into two main groups. The "lower primates" (prosimii) are generally small and best adapted to dwell in trees. Lemurs are now found only in Madagascar, lorises in Africa and Southeast Asia, tarsiers in Indonesia and the Philippines -- all tropical areas. Most are endangered as their forests are cleared for farms.
The "higher primates" (anthropoids) are monkeys, apes and humans. Old World monkeys found in Asia and Africa are often arboreal, al though baboons and macaques are ground dwellers. Most are large, have short tails or lack them completely, but have opposable thumbs. New World monkeys are arboreal, have prehensile tails that are long enough to wrap around branches to aid in balance and movement, and they have smaller thumbs (and in some species, no thumbs).
The apes are most similar to humans; this group includes gibbons, orangutans, gorilla, and chimpanzees. Similarities exist not only in structure and anatomy but also in behavior: apes form communities. The main differences between apes and humans lie in the skeletal structures of the backbone, hips, and feet. Human bone structure is designed to support upright movement; most ape structure supports crawling movement.
A number of different systems have been developed to try to explain relationships between fossils that appear most similar to modern humans.
Ten years ago, the "human evolution" chart looked like this:
| Period | Name | Area Found | Characteristics of skeletons | Characteristics of culture |
| 4.4 MYA | Australopithecus ramidus | Africa | Skull only | No evidence |
| 3-4 MYA | Australopithecus afarensis | Africa | "Lucy" small (3'), small brain, but leg structure indicating upright posture | No evidence of tools or fire |
| 3 MYA | Australopithecus africans | Africa | Small stature and brain, with hands and feet similar to modern man | |
| 2.5 MYA | Homo habilis | Africa | Larger brain | Evidence of tools used for cutting and scraping |
| 2 MYA | Homo erectus | Africa, Asia | Taller, progressively larger brain sizes as time passes | Stone tools, hand axes |
| 200 000 YA | Homo sapiens | All | Neanderthals: short sturdy build, heavy brow ridge
Cro-Magnon: Larger brain sizes |
Spears, burial
Weapons, tools of bone, ivory, wood, stone; cave painting. |
Compare this with the more recent chart in your text (p. 403). Additional information about already known fossils, plus new fossil discoveries, has caused evolutionists to redefine their classification of skull shapes and relations. This still remains a controversial area, partly because there are few samples for some of the species now identified, partly because groups apparently overlap in time and territory, and we don't know how to explain any interaction that may have occurred.
Biologists are constantly reorganizing the classification of the Primate order. Review the animation Old and New Primate Order Organization.
The first page of the animation shows how the primate order was organized from around 1945 to 2000, using physical characteristics and similar structures. The second screen shows how a current popular has rearranged groupings to reflect the evolutionary phylogenetic trees, based on DNA and protein similarities between species. Even modern classification is an area of controversy, with different biologists favoring different characteristics as "primary" for determining relationships and evolutionary descent.
There is also, of course, great debate about what actually would make someone human. The cultural aspects we use to mark "men" include the use of language, and a sense of moral right and wrong. There is no physical evidence for these characteristics.
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