Evolution and the Nervous System

Evolution
• Evolution works by trial and error.
• It has no goal, but it functions to keep life adapting to a constantly-changing environment.
• Organisms that are able to survive and pass on genes influence the development of future organisms.
• Organisms that are killed off, and don’t reproduce, have their DNA eliminated from the gene pool.
• Whatever works is kept until it eventually fails.
• Whatever doesn’t work is gotten rid of.

Evolution
• Gene mutations occur randomly.
–
–
–
–

One of the four base pairs is altered.
There are ~ 3.2 billion base pairs in the human genome.
There are ~ 25,000 genes in the human genome.
Nothing is perfect, and errors will happen.

• These affect either the structure of essential proteins, or the timing and expression of specific genes.
–
–
–
–

Many of these mutations will have a lethal effect.
A large number will have a non-lethal, but negative effect.
Many will have no effect, or a negligible effect.
A small percentage will have a beneficial effect.

Evolution
• Evolution works with what it’s got, so this is another factor making it an inherently conservative process.
– Drastic changes in structure/function can occur, but these are probably extremely rare events.
– A large number of genes is shared by large numbers of species. • But evolution may shape the timing and the frequency of their expression. We Belong to The Order Primates
The primates include the following:
• Prosimians such as lemurs and tarsiers
– Small brains, reliance on scent, nocturnal

• Anthropoids
– New World Monkeys
– Old World Monkeys
– Hominids
• Great apes
• Humans
– Including Neanderthals and related extinct species

Other Primate Species
Macaque
Chimpanzee

Gorilla
Orangutan

Evolution
• Survival of the fittest (probability of survival and capacity to pass on genes)
• Species are adapted to specific niches (polar bears,
Arctic plants, desert toads, extremophiles)
• Some live in a wide range of environments
(mosquitoes, humans)
• Darwin: “preservation of favourable individual differences and variations, and the destruction of those which are injurious”

Four Conditions for Natural Selection
• The individuals must be capable of reproducing.
• The offspring must inherit characteristics of their parents.
• There must be variation in individual traits
(characters) among members of the population.
• There is variation in the fitness of individual organisms. Variability: Intelligence
•
•
•
•
•
•
•
•
•

By definition, half the population is below average.
Height range: ~ 3 feet to ~ 8 feet tall
Weight range: ~ 40 pounds to ~ 1000 pounds
Normal distribution
Mean IQ: 100
84th percentile: 115
16th percentile: 85
98th percentile: 130
2nd percentile: 70

More on Evolution
• Most mutations either have no effect, or a deleterious one.
• Some mutations provide a survival advantage in current environment.
• Mutations may be problematic in other environments, however (e.g., sickle cell).
• Evolutionary adaptations aren’t necessarily efficient.
• Spandrels may produce unintended traits that have no apparent effect on survival.

Human Tails

Chimpanzees Have Cultures
• Variation among geographically distinct groups
• Gombe Stream (Tanzania) chimps use sticks to fish for termites, other chimps do not.
• Ivory Coast chimpanzees use stone hammers to break nuts, but in Gabon they do not.
• Mother chimps have been observed teaching their offspring to use certain types of tools.
• Chimpanzees use a variety of medicinal plants that are effective for intestinal parasites, headaches, and schistosomiasis. Language and Nonhuman Primates
• Washoe, taught ASL by the Gardners, taught her son
Loulis to sign.
• Chimps can combine words to make new words.
• Savage-Rumbaugh taught Austin & Sherman to solve problems that required sign language communication in planning (e.g., tool choice).
• Koko can express her emotions, and could refer to anger she experienced three days earlier.
• Koko