Evolutionary Biology Quiz 1

What is cognition? What is social cognition? What is social learning?

- Cognition- simple rules followed by an organism that is not cognition. Example is the bird not looking for the worms they stored after a long period of time because they knew the worms were no longer fit to eat - Social cognition- recognizing potential thieves. If there were other birds in the area then this bird would move their stored food when the other had left or wasn't looking - Social learning- one culture learning something from one another and teaching each other how to do things in a certain way. An example is the observations of chimps and how different troops ate ants differently

What are three general approaches to testing hypotheses in Behavioral ecology studies? How do these three approaches differ? Can you identify examples of each?

1. Comparison between individuals within a species: individuals in groups may have greater success at feeding or avoiding predators than solitary individuals. Problem: the variation in strategies may reflect competitive ability (the most competitive group gets the best territory). Ex: mobbing behaviors in sea gulls, groups have lower egg predation 2. Controlled experimentation: in an experiment, we can vary one factor at a time (group size, etc) and see how this influences success under a set of conditions. Ex: spacing of nests and testing this, removing or adding egg shells to nests 3. Comparison among species: What behaviors are likely to evolve under specific ecological condition? This is difficult to do a comparative experiment on because different species behave differently. Ex: Kittiwakes vs Black sea gulls

What is a spandrel, preadaptation, and an exaptation?

1. Preadaptation: an adaptation which serves a different purpose from the one for which it evolved. 2. Spandrel: a phenotypic characteristic that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection. (appendix is a spandrel because it isn't necessary for our body to continue living but it must have served a purpose at some point in time) 3. Exaption: a trait that has been co-opted for a use other than the one for which natural selection has built it.

What are the three (or 5) criteria required for evolution by natural selection?

1. There is variation in a trait 2. Some portion of this variation is heritable (populations produce more young than can succeed resulting in competition) 3. Some variants will have more successful offspring (change in environment will favor new variants).

Know the criteria that must be met for natural selection to occur. KNOW the concepts underlying each of these: variation, heritability, differential reproductive success.

3 criteria for natural selection to occur 1. Trait variation in populations - Difference in height? Intelligence? 2. Heritability - Do offspring resemble their parents? 3. Differential reproductive Success - Do individuals with certain traits produce more successful offspring?

How were these competing hypotheses tested? Which hypothesis was rejected and which was supported?

3 ways the hypotheses were tested: 1. Free chicks: 2 extra nestlings were added to the nest 2. Free eggs: 2 extra eggs were added to the clutch 3. Full costs: the female was induced to lay 2 more eggs by removing the first 4 eggs on the day they were laid and returned to the clutch before incubation began. H1 was supported and H2 was rejected.

What is innate behavior? What is a releaser? What is an innate releasing mechanism? What is a fixed action pattern?

A behavior that an organism is born with and it is genetically determined. It is a response to environmental cues. Releaser= red spot Innate releasing mechanism= hormones that cause the fixed action pattern Fixed action pattern= pecking of the red dot

What is a good adaptive hypothesis that explains this reduced reproductive output? What are costs and benefits of this behavior?

A good adaptive hypothesis for this is that the birds that laid fewer eggs survived further into adulthood than those who laid more eggs, and also had a higher offspring survival rate than those who laid more eggs. The cost is risking some of the offspring dying from random causes and having too little offspring, but the benefit is not risking the life of the adult and therefore the life of all offspring if too many eggs are laid.

What is a reaction norm?

A reaction norm is the relationship between phenotype and the environment.

What form of logic are we using when we infer that natural selection must occur given that these three assumptions are met?

Abduction

What is abduction?

Abduction-inference to the best explanation. It is the explanations that best represents all of the data so it is assumed to be correct

How was optimization of this trait confirmed?

All three ways of testing resulted in the same number of chicks successfully being raised, but the full cost mothers had the lowest survival rate to the next breeding season.

What is the definition of altruism?

Altruism is the behavior of an animal that benefits another at its own expense.

What is an adaptive landscape? How do they relate to optimality theory? What are some key assumptions of optimality theory? What is required if populations are to find peaks of an adaptive landscape?

An adaptive landscape shows the relationship between fitness (vertical axis) and one or several traits or genes (horizontal axes).An adaptive landscape is necessary to obtain fitness optimum. Some key assumptions of the optimality theory is an adaptive landscape, stable environment for a long period of time, and mutation and variation.

What's the difference between basic and applied research?

Basic research- investigate and uncover natural laws Applied science-manipulate the natural world (animal population management, impact of climate change, predicting mob behavior)

Why do we focus on evolutionary theory? Why don't we work with a low of evolution

Because ecologist use the theories to create, affirm and disprove laws. Laws are not always true and are often disproven over time

How do we know that meerkat teaching is not dependent on cognitive ability?

Because it follows rules. A meerkat pup call will elicit different responses in the adult. A certain younger age pup call will make the adult bring back dead prey with stingers removed while and older pup call will make the adult bring back a live scorpion with a stinger to teach the young how to remove it.

If cognitive abilities are valuable, why aren't there more highly intelligent species?

Because there is a cost to benefit ratio and to have a highly developed brain it takes a lot more developmental cost to produce it which renders the you vulnerable to predation for a much longer period

If cognitive abilities are valuable, why aren't there more highly intelligent species?

Because there is a cost to benefit ratio and to have a highly developed brain it takes a lot more developmental cost to produce it which renders the you vulnerable to predation for a much longer period. (Humans worry about brain development first and cannot walk until a year old, giraffes learn to walk first).

Why do some bees tend the hive while others search for food?

Bees possess a for gene, meaning they all have the same gene, but it tells different bees different things. It encourages some bees to leave the hive to search for food, and some bees to stay in the hive and feed there.

What is behavioral ecology?

Behavioral ecology is the response of an organism to a stimulus

Is mating behavior maintained by evolutionary constraints, or are they likely responsive to selective pressures? Given what you know about testis mass in primates, do you think there is much of a cost associated sperm competition?

Biggest primates have a breeding system that has one male mating with many females and their testis were smaller compared to a chimpanzee which had several males mating with each female and their testis were bigger. The alpha male is the only one impregnating the women of the group in the gorilla so he doesn't need a high sperm count, but the chimp males are competing to be the one that impregnates the female so they need a higher sperm count.

There are different approaches that can be used to test or address hypotheses in behavioral ecology. Which was used in the study of clutch size in great tits?

Both hypotheses used involve measuring further trade-offs. Empirical study

When comparing two functional models designed to explain what we see in nature, scientist will prefer the simplest model if all else is equal. Why is this reasonable? When we select the simpler model, what criterion are we applying?

Choosing a simpler model is applying the practice of parsimony. It will always make more sense that nature will follow this path of least resistance or the simplest path. It would not make more changes than necessary because this would not be practical.

Can you explain how phenotypic plasticity could be maladaptive as a result of ongoing climate change?

Climate change can cause mismatches between timing of breeding and peak of food availability.

What was the initial hypothesis that David Lack had to reject?

David Lack had to reject the predicted trade off between offspring number and quality.

What is deductivism? What is required for its use?

Deductivism- absolute proof based on basic assumptions; you must assume that the assumptions made are true

What's the difference between a fact, a hypothesis, a law, and a theory?

Definitions 1. Fact- shared observations 2. Hypothesis- proposed law 3. Law-describe patterns, capable of predicting future occurrences. 4. Theory-explain the nature of universe, mechanisms

What limits the effectiveness of natural selection to optimize behavioral traits for survival and other fitness related traits?

Environmental changes can limit the effectiveness of natural selection to optimize behavior traits.

Which is more important in determining behavior, genes or the environment?

Equally as important

What is a good way to use phylogenies when testing hypotheses associated with discrete traits?

Estimate Ancestral Character State Using Parsimony or Likelihood • Determine conditions likely to give rise to focal trait

What is evolutionary constraint? What is evolutionary lability?

Evolutionary constraints are restrictions, limitations, or biases on the course or outcome of adaptive evolution. Evolutionary lability means that environments are constantly going through changes that animals must adapt to.

In legal terms, what is special about evolutionary theory? Are there any legitimate scientific alternatives to evolutionary theory?

Evolutionary theory may be the only theory to be legally recognized as science. (not sure about part two of this question)

Why is evolutionary theory so important to the study of behavioral ecology?

Evolutionary theory may be the only theory to be legally recognized as science; it is also the bases of behavioral ecologist theories

What are some good common currencies to use for testing optimal foraging hypotheses? Be prepared to spot costs and benefits of different feeding strategies?

Ex: cost of going far away to hunt using a lot of energy vs benefit of getting a large meal.

Be able to identify questions and statements that belong to each of the different levels of analysis proposed by Tinbergen. *see study guide Proximate cause: how is behavior possible and how is it achieved? (causation, development) Ultimate cause: why individuals act the way they do (adaptive advantage, evolutionary history)

Example of a causation proximate behavior: the prairie voles hormonal response in the brain encourages them to be monogamous. Example of a developmental or ontogeny proximate behavior: why do prairie voles and montane voles act different? prairie voles have an increased V1aR gene. Example of ultimate adaptive advantage behavior: maybe good, loving prairie vole mates are more likely to be reproductively successful. Example of ultimate evolutionary history or phylogeny behavior: mate guarding could occur in prairie voles due to low population density.

Do females ever commit infanticide? Why and why does this make sense from an adaptive perspective?

Females commit infanticide to make room for their own young when the male is doing the parental care. This makes sense from an adaptive perspective because the females kill off other offspring to ensure theirs make it and receive parental care from the male.

What two factors are critical to understand the development or ontogeny of an organism?

Genetic or hereditary influences

Why do great tits produce fewer young than they can successfully fledge?

Great tits produce fewer young than they can successfully fledge because they also must take into account taking care of themselves and their own survival, and having a full nest could take a toll on the adult survival rate.

What were the two hypotheses involving tradeoffs designed to explain smaller than predicted clutch sizes in great tits? Specifically, what were the tradeoffs?

H1: adult mortality trade off. The trade off lower than predicted optimal brood size because it helps to optimize lifetime reproduction output of the great tits. H2: offspring # quality trade off. Brood size is reduced because energy to feed chicks is high which causes reduced fledging success.

What factors can contribute to prey choice? What is handling time? What is the example from your text I used in class?

Highest rate of energy return is considered when choosing prey. Handling time is how long it takes and how difficult it is for an animal to eat. For example, crabs prefer medium sized mussels because the large ones are too hard to open and the small ones are easy to open but do not provide enough energy.

What is hypothetico-deductivism, and how does it differ from simple deductivism?

Hypothetico-deductivism- usage of hypothesis to make predictions and then testing the predictions - Normal deductivism takes a generalized premise and moves to a specific conclusion.

Why might we expect there to be a lag between a species exposure to a new environment, and the optimization of its behavior for that new environment?

In order for a species to obtain optimization, it must be in a stable environment for a very long time.

What do these comparative analyses suggest concerning sexual dimorphism for body size and tooth size in primates?

In primates males are usually larger than females. This can be explained by two hypothesis: 1. Sexual dimorphism could enable males and females to exploit different food niches and avoid competition. - It could have evolved through sexual selection, because larger males experienced increase success in competition for females (favored hypothesis) 2. Tooth size hypothesis: - Large teeth may have evolved in males for defence of the group against predators (favored hypothesis) - Males may have larger teeth for competition with other males for access to females

Of the three criteria, which were demonstrated in my cormorant example and what was missing? Could you pick out the missing criterion in other such examples?

In the cormorant example, the variation of parental control was not proven to be adaptive because the lack of parental control in some cormorants did not 100% mean this trait would be hereditary. The offspring with better parental control were more likely to survive.

What is a potential pitfall of inductivism?

Inductivism is incomplete and you may reach false hypothesis even if you have accurate data

What is inductivism and how does it relate to deductivism?

Inductivism- inference of natural laws (never seen a black swan so you assume they are all white) 1. Deductivism- information→ pattern→ hypothesis→ theory 2. Inductivism- theory→ hypothesis→ observation→ confirmation

Using this approach, what was learned regarding home range size in primates?

It is likely that the larger the animal the larger their home range size would be. Because of this they seperated animals based on diet and weight. They found that when you compare the leaf eater to specialized eaters( fruit only or insects only) that the specialized eaters had a larger home range than the leaf eaters. The theory is that the specialized eaters need to travel farther to find their specific food needs.

Is it possible to build optimality models using different costs and benefits? Can you only model energy collection and usage? What is actually most important to evolution?

It is not possible. You can model more than energy collection and usage, but whatever the two comparisons are they must be in correlation with one another. For example, you cannot model time vs calories.

Be able to identify questions and statements that invoke group selection theory. How likely is it that group selection theory explains variation within a population?

It is unlikely that group selection explains the variation in a population.

What does the Integrative Theory of Development suggest concerning the relationship of genes and the environment? Can we ever ignore one or the other?

It suggests that we cannot ignore one or the other because even if the environment is constant, it does not mean that environmental influences are not present in an organism.

What are independent contrasts and who is credited with their first use?

Joe Felsenstein introduced independent contrasts. This is using phylogenies to identify independent evolutionary change

What was Karl Popper's contribution to the philosophy of science?

Karl Popper said that no hypothesis can be proven to be true but it can only be falsified. He stated that science progresses by eliminating alternate hypothesis

Who are the scientists recognized for establishing animal behavior as rigorous discipline?

Karl von Frisch, Konrad Lorenz, and Nikolaas Tinbergen

Are laws more important, or more informative than theories?

Laws are not more important than theories but they are more informative. Theories are more generalized statements about how the universe works while laws are used to predict future events.

What is learned behavior?

Learned behavior is one that is passed down or taught from the elders of the community or the parents of the offspring. Example is squirrell breaking into a bird feeder

Do lemmings commit suicide for the good of the species? Where did this myth come from?

Lemmings do not commit suicide, this myth came from the fact that lemmings would try to swim away during times of high population and low resources because they were starving and would end up dying in the process.

What are the confounding factors limiting the utility of simple comparisons among individuals within a species?

Nests that are in the middle of the colony have better protection for offspring than nests on the outside, therefore comparing reproductive success in the same colony may be uneffective.

What are Niko Tinbergen's four questions? What do they relate to?

Niko's four questions relate to behavior 1. mechanics/physiology 2. Genes and development 3. Adaptations 4. phylogeny

Does teaching require cognitive ability? What is required for a behavior to count as teaching?

No it does not require cognitive ability, instructor has to be showing another how to do something, it most cost time to teach how, also there must be a skill acquired by the trainee and teaching is rare.

If traits initially evolved for an alternative purpose, but are currently serving to increase fitness, is the adaptationist approach invalidated?

No, it is still valid.

How can optimality theory be applied to estimate the most productive trait values? What do I mean by the term "common currency" and why is it important?

Optimality theory applies to estimating the most productive trait values because only the strongest will survive. Common currency is the investment vs the return or cost vs benefit for different scenarios that involve animal survival.

Can phenotypic plasticity be adaptive?

Phenotypic plasticity can be adaptive because the ability to change phenotype in response to an environmental change can be an advantage.

Is phenotypic plasticity likely to evolve? When should we expect plasticity to be favored?

Phenotypic plasticity is likely to evolve and is favored when a species reacts well to an environmental change making it have an advantage in natural selection.

What is phenotypic plasticity?

Phenotypic plasticity is the ability of a single genotype to alter its phenotype in response to environmental conditions.

Can populations have reaction norms? Are all individuals expected to respond to environmental variation in the same way?

Populations can have reaction norms. Different populations from different places of the same species can react very differently to environmental variation (Great Tits Netherlands and UK).

Why are prairie voles monogamous and montane voles are polygynous?

Prairie voles have an increased V1aR gene causing them to be attached to the first partner they mate with, while montane voles do not have enough of this gene. They are monogamous due to their genes and the hormones in their brain that tells them to imprint on their mates.

Be able to list the assumptions of science. Know what they mean.

Primary assumptions 1. The universe is real 2. Our senses are accurate 3. Natural laws govern the universe 4. Natural laws are knowable 5. Uniformity: laws are constant

What are natural laws, and what distinguishes natural laws from the supernatural?

Principles that accurately describe the functioning of the observable universe; Natural laws are caused by nature and without thought while the supernatural would never do anything without conscious thought.

What are the two types of memory we discussed in class? What part of the brain is associated with spatial memory?

Procedural memory - Learning how to do things - squirrel and bird feeder Episodic memory - what, where and when - birds hide food and remember where it is The hippocampus is associated with spatial memory

Between the UK and Netherlands, which population of great tits is more likely to show an adaptive response with regard to climate change? Why?

The UK great tits are more likely to show an adaptive response to climate change because all the females in this population have similar reaction norms and respond similarly to climate change, and the netherlands group showed that females varied in their plasticity.

What is the achilles heel of group selection theory? Who is credited with debunking the myth that group selection theory was a strong force?

The achilles heel is that mutant alleles conferring selfish behavior will spread if one selfish individual is brought into a group of altruists and the altruists will die out. Groups are not far enough spread out for a group of altruists to never be invaded by a selfish individual. George Williams and John Maynard are credited for the discredit of group selection, and individual selection is more powerful.

What are some advantages to the weaver bird example, and the ungulate example, to that of the comparative approach used for the gulls?

The advantages for the weaver birds is that they can adapt their diet to their environment. If they are in forest they will eat insects and in the savannah they eat seeds. They adapt to the resources that are the most plentiful in their environment. With the ungulates their environment controls their size. The smaller animals live in the trees and forest while the bigger animals live in herds in the wide open areas. Their body size also controls their diet.

What is the basic principle underlying group selection theory? Can it work?

The basic principle of group selection is that groups that work selflessly towards the better of the entire group will be more successful and groups of selfish individuals will die out. It can work, but only if assumptions are met. All it takes is one selfish individual to come into a group for group selection to no longer work.

What is the comparative method? Why is it sometimes the only approach we have left to us?

The comparative method is the comparison of animals among different species that gives us a feel for the range of strategies that animals adopt in nature.

What was the goal in the comparison of the black headed gulls and kittiwakes?

The comparison of black headed gulls and kittiwakes was meant to bring attention to the fact that these birds act very differently when it comes to breeding because the gulls nest on the ground and the kittiwakes nest on the side of cliffs where predation is very rare.

What are the criticisms of the adaptationist approach?

The criticisms to the adaptationist approach is that it is adaptive storytelling, and its unlikely that perfect fit is ever achieved. Adaptationist approach is the view that many physical and psychological traits of organisms are evolved adaptations.

What was the goal in comparing the different species of weaver birds?

The goal in comparing the different species of weaver birds was to explain that monogamous species are more likely to be monomorphic (female and male look the same) and polygamous species are more likely to be dimorphic (male usually more attractive than female because female normally chooses her mates). Monogamous are more likely to be in the forest and feed on insects and are solitary feeders, the polygynous are more likely to feed in flocks in the savannah and eat seeds. The forrest nests are more hidden, the savannah ones are less hidden.

What is the group selection argument for infanticide, and what is the individual selection argument?

The group selection argument is arguing that groups consisting of selfish individuals died out because they over-exploited their food resources but groups that restricted their birth rate had enough food and therefore survived. It favors the individuals that work for the better of the group. The individual selection is the idea that natural selection favors the individuals that do the best and have the most surviving young.

How is diet involved?

The theory is that the specialized eaters need to travel farther to find their specific food needs.

What is science?

The things we know; philosophy and process by which natural laws are described.

In addition to aggressive male behavior, was any other factor identified that could explain dimorphic dentition in primates?

The tooth size factor could simply be because males are naturally larger than females to begin with which means their teeth would be bigger as well.

What is an "optimal" trait value?

The trait value with the greatest benefit that exceeds the cost

What are two processes that limit the strength of group selection theory, making it such a weak force?

The two processes that limit the strength of group selection are 1. The fact that groups usually always die out faster than individuals and 2. Groups of altruists will rarely be isolated enough to keep out selfish individuals.

What are the drawbacks for these early comparative studies discussed in your text and in class? 1. What alternative hypotheses could explain differences in gull behavior? Correlation does not equal causation. 2. Is it really appropriate to classify ecological niches in a discrete fashion? Couldn't there be transition zones between forrest and grassland? Is being monomorphic discrete? 3. What is meant by confusing cause and effect in comparative studies? Could you turn your adaptationist hypotheses upside down? 4. What is the adaptationist approach to formulate hypotheses? What is meant by the term adaptationist story telling? Do all differences between species have to be adaptive? Can different lineages solve the same problem in different ways? 5. Can you really draw a strong conclusion by comparing only a few species or even just two? What is the number one concern regarding the independence of observations when c

There are always alternatives, lack of quantification, adaptationist story telling and phylogenetic independence. Correlation does not demonstrate causation. 1. The gulls live in a colony because there is not a lot of places to set up a nest. Because of this they are not as vicious. Also there is not as many predators on the side of a cliff compared to the ground. 2. I believe that it is not appropriate because there could be middle ground that is neither forest or grassland 3. Is flocking driven by food resources, or has predation favored flocking, forcing use of abundant food resources? This is an example of cause and effect. Because of this you can turn any hypothesis around and say the exact opposite of what you found to be "true" 4. All differences between species do not have to be adaptive. Different lineages solve the same problem in different. For example, deers used antlers derived from bone and sheep use horns derived from skin to fight off predators. 5. No, to have a good study you need to compare a lot of species and not just a few. The more species you have for comparison, the better formulated and supported your hypothesis is.

What is responsible for different feeding behaviors in the Drosophila discussed in class?

They have a for gene that tells indvididuals in the colony to feed different ways. Sitters remain in one area while rovers wander around. Individuals with the rover allele have a better short term memory while the ones with the sitting allele have better long term memory. Rovers move between feed patches so will benefit from fast learning, while sitters with a sedentary feeding style benefit from long term memory.

Why might thinking purely in terms of "innate" and "learned" be a false dichotomy?

This could be an artificial dichotomy because the line between a learned behavior and innate is sometimes unclear. Not every behavior has to be innate or learned but all behavior is influenced by the environment.

If we find evidence of convergent evolution it suggests that certain traits are likely to evolve in certain environments like fins in dolphins and fish. Clearly, fins are adaptive in an aquatic environment. Why else might species share traits? What is phylogenetic inertia?

This means that instead of there being many explanations for a single adaptation it could be due to something as simple as a common ancestry that passed the adaptation down. phylogenetic inertia refers to the limitations on the future evolutionary pathways that have been imposed by previous adaptations

In the pioneering work done by Clutton-Brock, Harvey and Pagel in the 1970s and 1980s, what improvements over simple comparative studies were achieved?

Three improvements to methodology over other comparative studies 1. They measured various aspects of behaviour and morphology on a continuous scale rather than categorizing primates into groups with different traits 2. They considered alternative hypotheses and used multivariate statistics to tease out the effects of different ecological variables on each trait 3. They used different genera as independent data points for analysis, rather than species, to reduce the problem of similarity through common ancestry

What are the two hypotheses I presented to explain the presence of infanticide in nature?

Two hypothesis of infanticide in nature is 1. to regulate the population and 2. due to sexual conflict

Why is it necessary to be aware of phylogeny when conducting comparative studies?

Two reasons: 1. To identify independent evolutionary transitions 2. To elucidate the order in which traits have evolved - The main reason for why we consider phylogenies is because species are not independent

Why is it important to discuss basic scientific principles in a course on behavioral ecology?

Two reasons: Behavioral ecology is explicitly hypothesis driven Most are dependent on evolutionary theory

What levels of analyses are most informative to behavioral ecology?

Ultimate causes of behavior

What is phenotypic plasticity? Can you explain the interactive theory of development?

When two organisms have the same set of genes but completely different phenotypes due to things like environment, diet, location

What is parsimony? Can you apply it?

When you have multiple options, the simplest of the two explanations are preferred. It can be applied to the trees we did in the homework. Also think about the planets. You could say that a planet revolves around earth but it is simpler to say that they all rotate the sun because the path is much easier to predict and is less complicated.

Who was the champion that promoted group selection theory in the mid 20th century?

Wynne- Edwards

Do humans have different sized teeth in males and females? Does this make sense knowing what you know about human ecology?

Yes male humans have larger teeth than females. This is predictable for ancestral species because humans are not monogamous but in contrast I could not see humans fighting each other or intimidating each other with their teeth.

Is there any evidence that humans require specific stimuli to develop normally?

Yes we need things like gravity to develop properly or we would develop osteoporosis and have bad joints. If you take away normal environmental factors such as these it could cause humans to develop abnormally and potentially live shorter lives. Also the barrel chest phenotype from living at high altitudes with low oxygen is an example of abnormal development due to environmental constraints. We also need social contact to live normal lives.(monkey and the boys kept in cells during the war)

How can you demonstrate that two species have independently acquired a discrete trait? Is it not possible that two species that share a trait do so because of common ancestry?

You can use a tree to compare the ancestry of species. If the earlier species do not have this trait it is much more likely,according to parasimony, that the species developed the trait separately rather than an ancestor who did not possess the trait.