Evolution and Adaptation by Natural Selection

1. Evolution and Adaptation by Natural Selection

2. A Puzzle • Unity of Life • Life arises only from preexisting life (vs. spontaneous generation) • All living organisms are composed of one or more cells, and cells come only from other cells • All organisms use the same DNA code (A T G C), which gets passed from cell to cell and generation to generation • Diversity of Life • Earth has been host to a staggering variety of life forms …penguins to petunias, dandelions to dinosaurs, ostriches to octopi, lobsters to lions, banana trees to bacteria, mushrooms to monkeys, sharks to saber-toothed cats How can life be so diverse yet still unified???

3. Solution: Life changes and diversifies over time Tree of Life Web Project Interpretation: All life is related, sharing a common ancestry – that is, a single DNA lineage. BUT… DNA sequences gradually change over time. Organisms past and present are connected by the flow of genes along branches on the “Tree of Life.” Living organisms are like leaves at the tips of twigs. Ancient species (now extinct) are back down the branches.

4. Evolution = a change in a population’s genes and traits over time, with increasing adaptation to the prevailing environment Curtis & Barnes Biology • Horse evolution (“equids”) • Superb 50 million year fossil record • Hyracotherium: dog-sized, adapted for browsing on leaves and fruit in tropical forests • Later species: increasingly adapted for life of grazing in grasslands • Molars became bigger and more durable, with broader grinding surface for tough grass • Larger size, longer legs, and reduction in toes to one big hoof for escaping predators in the open

5. Branching, not Linear Campbell et al. Biology “Speciation” (branching off of new species and lineages) -VS- “Extinction” (dead ends) Speciation rates usually exceed extinction rates, so diversity of life increases (exception: mass extinction events; e.g., dinosaurs)

6. Charles DarwinVoyage around South America aboard HMS Beagle, 1831-1836 Wikimedia Commons • Galapagos: young volcanic islands off Ecuador • 13 species of finch, with distinct varieties on different islands • Darwin later proposed that these finches all shared a common ancestor, a colonist from South America, but the lineages had “evolved” into different forms – a process he called “descent with modification” …BUT HOW??? • Later biologists would show that Darwin’s finches were adapted for the distinct foods on each island (even a “vampire” finch that parasitizes seabirds!) • (This was but one of many observations of plants, animals, fossils, and geology that Darwin made during the 5-year expedition) Lewis Life

7. Photos courtesy of Wikimedia Commons “Artificial” Selection Similarly, pigeon fanciers can create new varieties by “selective breeding” • Darwin – a pigeon breeder himself – noticed that no two members of the same species are perfectly identical. Each organism is born slightly different from its parents, from its brothers and sisters, and from other members of that species • (Today we know this stems from random reshuffling of genes during sexual reproduction, plus occasional mutations …things Darwin had no knowledge of) • Darwin reasoned that over many generations, a lot of little differences could add up to some enormous changes!

8. Try a little “artificial selection” yourself by creating your own “biomorphs” at www.annanardella.it/biomorph.html • Click Quick Start button (browser must be Java enabled) • Upper left: The “parent” biomorph, resembling a bush, whose shape is controlled by 9 “genes” (see table of genes on main page) • The other 18 biomorphsare the parent’s “mutant” offspring (9 genes mutated in the positive direction, 9 in the negative direction) • Simply click whichever mutant offspring you find most interesting. That now becomes the parent, and 18 new mutants appear. Repeat. • Advice: Be PATIENT and CHOOSY. Always review all 18 options, select one that you like best, and weed out the less interesting ones. Can you “evolve” the original bush into a bird-, bug-, or frog-like critter?

9. Evolution by “Natural Selection”(Charles Darwin, The Origin of Species, 1859) Wikimedia Commons • In every population, more offspring are produced than can survive (they breed well beyond the environment’s “carrying capacity”) (ex) Not all goldfish will survive when released into the wild • Those offspring will compete with one another for survival and limited resources (ex) Goldfish race to escape predators, capture food, etc. (cont’d…) The Far Side by Gary Larson

10. A random variety of traits will appear among those offspring • Some traits are more favorable (or “adaptive”) than others for competing and surviving in that environment • Other traits may be “weeded out” (“Survival of the Fittest”)

11. Those offspring that happen to be born with more adaptive traits will have a better chance of surviving long enough to reproduce, thereby passing on their adaptive traits • In the next generation there will be a higher frequency of adaptive traits • Over many generations – aided by an occasional lucky mutation – the distribution of traits may shift dramatically (= evolution)

12. Galapagos ground finches: Catching evolution in the act(a study by Rosemary & Peter Grant and Peter Boag) Phenotypic Variation The Grants and colleagues collected data on Galapagos ground finches for many years. Here is the “beak depth” distribution for the 1976 population. Which important condition for natural selection does it reveal?

13. They also compared the beak depth of parents to that of their offspring. What important aspect of natural selection does this demonstrate? The differences are GENETIC (genotypic variation in the DNA): Parents with deep beaks tend to have offspring with equally deep beaks.

14. In 1977 a brutal drought struck the Galapagos. Vegetation was decimated and seeds became terribly scarce. Over 80% of the finch population starved to death. The birds quickly exhausted their supply of small, soft seeds. That left only the much larger, harder seeds of the Tribulus plant. Normally a finch would ignore Tribulus seeds, but now that was the only food available. A year later the Grants again surveyed beak depths. Interpretation? Birds with deeper beaks outcompeted birds with shallow beaks, probably because they could crack Tribulus seeds. And since the trait is genetic, this means the population EVOLVED a deeper beak!

15. Back to the crew of the Zostera on planet XK-714…who had the best plan?(one last chance to vote)

16. Cooper: Expose living plants to low but increasing doses of omicron radiation in the laboratory. This will allow them to adapt as needed by building an immunity or resistance to omicron radiation. Then transplant to the greenhouse. In this way, the greenhouse can be slowly but steadily stocked with omicron-tolerant plants. • Probably the SECOND best strategy …but unlikely to work • Flaw: She’s confusing short-term INDIVIDUAL “adaptation” with long-term EVOLUTIONARY adaptation …an easy mistake to make • True: Plants and animals do have a limited ability to “adapt” to certain changes in their environments, like adjusting to falling temperatures or stronger sunlight. Some can develop resistance to disease, poisons, etc. • BUT: The ABILITY to “adapt” to certain changes is itself an adaptation, produced by evolution through natural selection. Omicron radiation is a completely new and novel challenge. Thus there is no way taro’s ancestors could have evolved an ability to adjust to omicron. The Far Side by Gary Larson An excellent EVOLUTIONARY adaptation

17. Delano: Same as Cooper, but once an omicron-tolerant line of plants has been developed, collect their seeds and plant in the greenhouse. This will be a much faster way to populate the greenhouse. • Seems quite reasonable …but impossible • Flaw: He believes that changes acquired DURING an organism’s lifetime can be passed to its offspring …another common misunderstanding (even Darwin was prone to this error) • True: Organisms sometimes experience bodily changes during their own lifetimes • BUT: These changes CANNOT be inherited by their offspring (because DNA and genes were not changed) Bloom County by Berke Breathed

18. Eriksson: Expose taro seeds to low but increasing doses of omicron radiation. This will fundamentally alter them prior to development. Check growth rates, and once an optimal dosage is found, plant the now omicron-resistant seeds in the greenhouse. • Attractive idea …but incorrect • Flaw: She thinks it is the environmental conditions – namely omicron radiation – that alter DNA/genes, and only in a helpful, adaptive way. This is yet another common misunderstanding. The Far Side by Gary Larson • True: She has a good point that genetic alterations will not be helpful – nor inherited by offspring – unless they occur BEFORE development (though even the seed stage is usually too late) • BUT: (a) Omicron radiation doesn’t mutate DNA, and (b) even if it did, the mutations would be utterly RANDOM, unlikely to provide radiation resistance. Omicron radiation does not directly cause omicron tolerance. Mutations are RANDOM. A few are lucky, most aren’t.

19. Alvarez: Keep the crops under ideal growing conditions in the greenhouse, but otherwise let the species adapt naturally to the new radiation on its own. It will slowly improve itself, eventually becoming omicron-tolerant. • Tempting …perhaps the most common misunderstanding of evolution • Flaw: He believes that species automatically progress and improve as needed, with offspring always a bit better adapted than their own parents The Far Side by Gary Larson • True: Many populations become better adapted to changing environments • BUT: Many populations also go extinct; there are no guarantees. Adaptation requires VARIATION plus SELECTION: Some varieties survive and reproduce, others don’t. Evolution is not a change in the WHOLE population; rather, it’s a change in a population’s MEMBERSHIP. Extinction – not progress – is the fate of most species

20. O’Brien: Raise plants in the greenhouse, but monitor their growth. If any grow faster than others, re-plant their seeds or stem cuttings. Remove slower-growing plants to make room. Repeat until plants are omicron-tolerant enough to sustain a mining colony. • The BEST strategy. She understands that to evolve an omicron-tolerant population, the crew will have to mimic natural selection. • True: Plants that happen to have some natural omicron tolerance – even a little bit – should be allowed to pass that trait on, while plants that seem especially vulnerable to omicron should be “weeded out,” thereby removing their DNA/genes from the population • BUT: It still might not work; there are no guarantees. There may not be enough variety to select from …or lucky mutations might never arise …or there may simply not be enough time (too few generations). Sometimes natural and artificial selection can yield quick results, but other times it is very slow and sluggish. The Far Side by Gary Larson

21. Three Pitfalls to Avoid • Evolution as effort-based or behavior-based: “Lamarckism” Jean Lamarck (1809) – a different model of evolution (now rejected): • Individuals can change their own bodies through use (or disuse) of body parts …thereby acquiring new traits during their lifetimes • Their offspring would then inherit these acquired traits Classic Lamarckian example: Lamarck suggested that early giraffes acquired longer necks by stretching for distant leaves. Their offspring inherited the additional length. They then stretched even more, and so on… NO! Even if an organism changes its body, its offspring will NOT inherit those changes. Organisms cannot alter their genes or DNA through behavior!

22. (Pitfalls cont’d) • Evolution as directional: Lamarck’s “ladder” of life Lamarck also thought life had a natural, “progressive” tendency to evolve from simple to complex, driven by unseen alchemical forces NO! Natural selection has no “foresight” into the future. It works only on genetic variations in the here-and-now, and direction depends only on immediate consequences. In fact, simpler forms are often more adaptive (e.g., bacteria still rule the Earth). Calvin & Hobbes by Bill Watterson • Evolution as need-based or environment-induced(not Lamarck) Organisms can sometimes “adapt” as needed to new circumstances through bodily reactions, behavioral responses, and even learning, but this is NOT the same as true genetic, evolutionary adaptation. Remember, evolution occurs not WITHIN individual lifetimes, but BETWEEN and ACROSS generations.

23. Naughty words to avoid(They’ll lead you into those 3 pitfalls) “Need” “Had To” “Try” “Want” “Learn”

24. Calvin & Hobbes by Bill Watterson • The ancestors of modern giraffes had short necks, but not equally short. Some happened to be born with slightly longer necks than others. How Darwin would explain giraffe necks: • In times of drought or famine, those with slightly longer necks could reach higher leaves, while those with shorter necks could not. Longer-necked giraffes thus outcompeted shorter-necked giraffes for food. • Giraffes with slightly longer necks survived longer and so left more offspring behind. Those offspring inherited the genes for longer necks. • Meanwhile, shorter-necked giraffes died young and did not reproduce, so genes for shorter necks died out with them. • Once in a while an offspring of two longer-necked giraffes would develop an even longer neck than either parent (perhaps due to a lucky mutation). This gave that giraffe a competitive edge over its neighbors, etc., etc. After many, many generations of weeding out shorter necks from longer ones, the exceptionally long neck of the modern day giraffe evolved.

25. C Q Jessens Practice Modern day flying fish have broad, wing-like pectoral fins that enable them to glide just above the water’s surface. Like many small fish, when a predator strikes from below, a flying fish leaps out of the water. Unlike most fish, however, it then spreads its fins (or “wings”) and glides as far as 100 yards, escaping its attacker! Suppose modern flying fish evolved from ancestors with “normal” pectoral fins. Explain how a flying fish’s wings might have gradually evolved through natural selection.