Natural Selection The AIDS Story Basketball Player Magic

Natural Selection The AIDS Story

Basketball Player “Magic” Johnson • 1991 at age 32 retires • He has AIDS and possibly just a few years to live (8 - 10 years) • Fast forward to 2007 - 16 years later and he is still alive • How and why • Medical advances and knowledge of evolution

HIV and AIDS • AIDS (acquired immune deficiency syndrome) • Killed 40 Million already and is on the increase! - worry baby! • Disease of the immune system • AIDS is caused by HIV virus • Virus infects and kill white blood cells • T cd 4 cells • Host loses immunity and dies from other infections

Course of HIV infection • • Virus invades Infects T cells and releases ‘babies’ Body fights Virus mutates Virus evolves and escapes detection

The Theory of Natural Selection • The Origin of Species by Charles Darwin – 1) Common descent – 2) Natural Selection • Common descent - we all appear to have descended from a common ancestor accepted easily • Natural Selection - How variety has come about since - hard to comprehend by many early scholars - it the greatest scientific theory of all.

Natural Selection is based on 4 general observation 1. Individuals in a population vary 1. Variation exist 2. Some variation is inherited 1. Genetic material involved 3. More offspring are produced then will survive 1. Multiple births 4. Survival and reproduction are not random 1. Those who are not suited have fewer offspring or not at all……

Testing Natural Selection • Artificial selection – Humans and Dogs – Dogs originated from the Grey Wolf – Breeding for physical traits – Many breeds of dogs - all one species – Human induced and not natural selection

Natural Selection in the Lab – High concentration of alcohol causes cell death – Fruit Flies tested by feeding them food with alcohol – As with any population there is variation in the natural population – Most flies find alcohol poisonous, but there are some (about 10% occurring naturally) who have a gene that can reduce to a less toxic form – Conducted experiment for 57 generations – Compared results

Wild populations • • No human interference Galapagos finches 1977 drought filled many Natural selection selected those that had the largest bills • Better at breaking tough seeds • In 1978 this finch population had a 5% greater bill size

Subtleties of Natural Selection • DODO • “The Dodo could not adapt to human hunters , so it went extinct” • Wrooooonnnnggg!!!! • Change and evolution do not work at the individual level - just at the population and gene frequency levels

Subtleties of Natural Selection • Natural selection does not result in perfection • Better adapted to the current circumstances • Bacteria example – Growth of bacteria under starvation conditions – Those that produce a toxin, which kills neighbours lives – Change to food-rich environment and these same bacteria lose out to the others – The normal bacteria do not waste time making the toxin

Natural Selection and HIV • 4 conditions are present for evolution of HIV virus 1. Virus in the bloodstream vary 1. Reproduction equals mutation 2. Variation is passed to offspring 1. Mutated RNA molecules infect new cells 3. More virus produced than can survive 1. Most HIV is eliminated by the antibodies of the host 4. Virus survival is not random 1. Antibodies do not recognize these and they will exist for longer

Evolutionary Arms Race • Virus is changing and so is the host – As each variant becomes more pronounced the host matches and makes new antibodies – HIV begins to be cleared from the blood – Virus mutates and other strains survive…

Medical Solutions • Drugs which interfere with the life cycle of the virus

AZT failure • No matter who took the AZT alone they sooner or later died of AIDS • The virus was mutating to become resistant to the AZT • Single drug therapy could give you some extra time but you would die. .

Combination drug therapy • Combining 3 or 4 drugs which act at different phases of the life cycle of the virus has worked extremely well • A single virus cannot (at least not easily) mutate simultaneously at all these parts of its life cycle • Resistance to multiple drugs is uncommon • Decreasing HIV replication decreases rate of evolution • Multiple drug resistance may be less deadly – 15% of patients develop drug-resistant HIV but it does not kill them as quickly - takes 3 -5 years longer

Problems with Combination Drug THerapy • Drug resistance • HIV seems less serious a disease • Therapy is expensive

Preventing AIDS • Can humans evolve resistance to HIV – In some Europeans there is a 1% chance you will never get AIDS – They carry a protein - CCR 5 - makes their T cells resistant to infection – Issues to many to accept • ABC – Abstinence – Be Faithful - monogamous – Condoms

Living with AIDS • ‘Magic’ Johnson is still alive and free of AIDS - why? • He is meticulous – Takes his medications on time! • and has access to the best medical care in the World – He is rich! • What will happen to him - will he die from being hit by a bus?