Evolution, Ancestry & Biodiversity — Chapter review · Life Science: Biology, Grade 10

Heritable variation, overproduction, competition for limited resources, and differential survival and reproduction.

(1) Heritable variation: individuals in a population differ in traits that can be passed to offspring. (2) Overproduction: populations produce more offspring than the environment can support. (3) Competition: because resources are limited, individuals compete to survive. (4) Differential survival and reproduction: individuals whose traits best suit the environment survive and reproduce more, so those heritable traits become more common over generations.

The dark-rock population will shift toward mostly dark-colored mice, because dark mice are camouflaged there and survive and reproduce more.

On the dark rock, light-colored mice stand out and are easily caught by owls, while dark-colored mice are camouflaged and survive better. Fur color is heritable, so the surviving dark mice pass the dark-color allele to more offspring. Generation after generation, the proportion of dark mice increases until the population on the dark rock is mostly dark — natural selection favoring the better-camouflaged variant. (This is a real, well-documented example.)

Because peahens prefer males with large, showy tails, those males reproduce more; the reproductive advantage outweighs the survival cost, so the trait spreads.

Natural selection favors whatever leads to the most surviving offspring overall, not merely the longest survival. This is a case of sexual selection: peahens tend to choose mates with larger, more impressive tails, perhaps because such tails signal a healthy, high-quality male. Males with showier tails therefore leave more offspring. As long as that reproductive advantage outweighs the increased risk of predation, the trait raises overall fitness and becomes more common — even exaggerated — over generations.

Example: the same bone plan in a human arm, bat wing, and whale flipper; this reveals they descend from a common ancestor.

Homologous structures share the same underlying anatomical plan in different species even when their functions differ. The human arm, bat wing, and whale flipper all contain one upper-arm bone, two forearm bones, and hand/finger bones in the same arrangement. This shared plan only makes sense if all three inherited the limb from a common ancestor and then modified it for grasping, flying, and swimming.

They are vestigial structures, suggesting whales evolved from four-legged land ancestors.

These reduced, nonfunctional leg and hip bones are vestigial structures — remnants of features that were fully functional in an ancestor. Since a structure with no current use rarely appears for the first time, their presence strongly suggests that whales descended from four-legged land mammals that walked on legs, and that over evolutionary time those legs were reduced as whales adapted to a fully aquatic life. Transitional whale fossils showing progressively smaller legs support this conclusion.

Most to least related: chimpanzee, cow, rattlesnake, tuna. Fewer amino-acid differences indicate a more recent common ancestor, matching the anatomical tree.

The fewer differences two species have in the same protein, the more recently they shared a common ancestor. Ordering by differences gives chimpanzee (0), cow (10), rattlesnake (22), tuna (31), so that is the order from most to least closely related to humans. This matches the tree built from anatomy: chimps are fellow mammals and primates (closest), cows are mammals but not primates, the rattlesnake is a more distant reptile, and the tuna is a still more distantly related fish. Because the molecular data and the anatomical data were gathered by completely independent methods yet produce the same tree, they strongly reinforce each other as evidence for common ancestry.

Speciation is one species splitting into two or more species that can no longer interbreed; reproductive isolation stops gene flow so the groups can diverge.

Speciation is the process by which one ancestral species becomes two or more distinct species that can no longer successfully interbreed. Reproductive isolation is essential because it halts gene flow between two groups. Once genes stop being exchanged, mutation, genetic drift, and natural selection can push each gene pool in its own direction until the groups become too different to interbreed.

Reduced gene flow can allow differences to accumulate; reproductive isolation requires evidence.

Mutation, drift, and selection can change separated populations. Separation or different appearances alone do not establish separate species under a reproductive-isolation model.

20 copies

The founders carry 25 x 2 = 50 total copies of the gene. If the striped allele makes up 40% of the gene pool, then 0.40 x 50 = 20 copies of the striped allele are present. (Because the founding group is small and carries only a random sample of the mainland gene pool, its allele frequencies can differ sharply from the source population — the founder effect.)

Homo sapiens; 'Homo' is the genus and 'sapiens' is the species.

In binomial nomenclature the scientific name has two parts. The first, capitalized word is the genus (Homo), a group of closely related species; the second word identifies the specific species (sapiens). The whole name is italicized: Homo sapiens. This two-word Latin system, devised by Linnaeus, gives every species a single unique name recognized worldwide.

The lizard is most closely related to the cat, because they share the most recent branch point (marked by the amniotic egg).

On a cladogram, the more recently two organisms share a common ancestor — and the more shared derived traits they have — the more closely related they are. The lizard and cat share the most recent derived trait on this tree, the amniotic egg, meaning they branch from a more recent common ancestor than the cat shares with the salamander or the shark. Therefore the lizard is the cat's closest relative among these four.

Natural selection adapts populations, reproductive isolation repeatedly splits them into new species (speciation), and over billions of years this branching produces the diversity that classification organizes into the tree of life.

Start with one process: natural selection acting on heritable variation, which adapts populations to their environments. When populations become reproductively isolated — by geography or other barriers — gene flow stops and mutation, drift, and selection push their gene pools apart until they become separate species (speciation). Repeat this splitting again and again across billions of years, and a single ancestral lineage radiates into millions of descendant species, each a twig on an ever-branching tree. Classification (taxonomy, cladograms, the three domains) is simply our attempt to map that tree, grouping organisms by the shared derived traits their common ancestors passed down. So the same basic mechanism, run over immense time, both generates biodiversity and gives it the nested, tree-like pattern that classification reveals — which is exactly what the unit's essential question asks.

16 percentage points

24/300 = 8 percent and 96/400 = 24 percent, a rise of 16 percentage points.

An individual's genotype is fixed at fertilization, so it cannot change its heritable characteristics during its life, and changes acquired during life are not passed to offspring. What evolves is the population: the proportions of alleles and of the traits they contribute to change across generations as some individuals leave more offspring than others. Evolution is therefore a property of populations over time, not a change within an individual.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

3

12 / 4 = 3 times as many differences suggests roughly three times as long since divergence, assuming a similar rate and no reversals.

All three contain the same set of bones in the same relative arrangement, differing in proportion rather than in plan, which indicates inheritance of a common underlying structure from a shared ancestor. The functions differ entirely — grasping, flight, swimming — so the comparison shows shared ancestry rather than shared function. What it does not show is when the lineages diverged or in what order; establishing that requires fossil evidence and molecular comparison.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.

Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

2 %

40 / 2,000 × 100 = 2 percent. Such a bottleneck leaves a gene pool whose composition reflects which few individuals survived rather than the original population's variety.

Speciation has occurred under the biological species concept. The populations can mate and produce offspring, but those offspring cannot reproduce, so no alleles pass between the populations through them; reproductive isolation is therefore complete in effect even though mating still happens. The sterility of hybrids is itself the reproductive barrier, and it indicates that genetic differences accumulated far enough during isolation to disrupt the hybrids' meiosis.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.

The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

5 %

5 / 100 × 100 = 5 percent. Reporting the distribution as well as the richness of 4 shows how unevenly individuals are spread.

A dichotomous key presents a series of paired choices about observable characteristics, and following the choices leads to a name. It is a tool for identifying an unknown specimen using features that are easy to see. Classification, by contrast, groups organisms to reflect evolutionary relationships, which may depend on evidence that is not visible, such as sequence data. A key may therefore use convenient features that do not indicate ancestry, so identifying an organism with a key says nothing about where it belongs in the hierarchy.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

Both have richness five and total 40, but the first is more even. Detection, area, timing and effort can affect observed richness; unobserved species are not automatically absent.

Both have richness five and total 40, but the first is more even. Detection, area, timing and effort can affect observed richness; unobserved species are not automatically absent.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

Both are present-day lineages with their own histories; a tree models branching ancestry, not ranked progress.

All tips of a cladogram are living or existing at the same time, so none has been evolving longer than another; each lineage has the same elapsed time since any shared ancestor. Left-to-right order is a drawing convention, and branches can be rotated at any node without changing the relationships shown. A tree represents branching order, not progress or rank, so there is no position on it that means more evolved.

Response criteria

• State a biologically accurate conclusion.
• Show the data, mechanism, or calculation that supports it.
• Include units, conditions, or limits where relevant.

1

Relatedness is judged by how recently lineages share a common ancestor. Node 4 is further from the root than node 2, so P and Q share a more recent ancestor and are more closely related.

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.