How evolutionary history helps us understand what animals need from captive care
Every species brings an evolutionary history into captivity.
Species differ profoundly in how they perceive their surroundings, regulate their bodies, move through space, obtain and process food, communicate, respond to danger, reproduce and interact with other animals.
Those differences did not appear because animals were designed for particular environments.
They arose through evolutionary processes acting across many generations. Over generations the genes within the animal’s DNA changes, with only the animals that are able to survive and reproduce passing on their genes to their offspring.
Read on to find out why that history provides an essential starting point for understanding what an animal may need when the environment around it is controlled by people.
From Niche to Need
Genetics & Inheritance
From DNA to offspring
Most of an animal's genetic information is carried in DNA, organised into chromosomes within the nuclei of its cells. Small amounts of DNA are also found in mitochondria.
A gene is a region of DNA involved in producing a functional product or regulating biological processes. Different versions of a gene are called alleles. In many sexually reproducing animals, chromosomes occur in pairs, with one member of each pair inherited from each parent.
How alleles are passed between generations
In most sexually reproducing vertebrates and many invertebrates, specialised reproductive cells, such as eggs and sperm, are produced through meiosis.
During meiosis, chromosome pairs separate so that each reproductive cell receives only one chromosome from each pair. Recombination can also exchange sections of DNA between paired chromosomes, creating new combinations of existing alleles.
When egg and sperm combine at fertilisation, the offspring receives a new combination of genetic material from its parents.
This means siblings can share the same parents while inheriting different combinations of alleles.
This is the common pattern in many animals, but inheritance and reproductive systems vary. Some species reproduce differently, and mechanisms such as haplodiploidy, parthenogenesis and mitochondrial inheritance do not follow this simple two-parent pattern.
Genotype does not simply equal phenotype
The combination of genetic variants carried by an individual contributes to its genotype.
Its phenotype is the set of characteristics that are expressed, including aspects of anatomy, physiology, sensory function, behaviour and other biological traits.
Phenotype is not simply a direct readout of DNA. Gene expression, interactions between genes, development, physiology and environmental experience can all influence how genetic variation is expressed.
This is why two individuals can differ even when they share much of their genetic background, and why the same genotype may not produce exactly the same outcome in every environment.
Common genetics questions:
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DNA (Deoxyribonucleic acid) is the molecule that carries most of an animal's inherited genetic information. It is organised into chromosomes, usually found within the nuclei of cells, with a small amount of DNA also present in mitochondria.
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A gene is a region of DNA involved in producing a functional product or regulating biological processes. Genes contribute to characteristics throughout the animal, including aspects of development, anatomy, physiology, sensory function and behaviour.
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Genes occur along chromosomes. In many animals, chromosomes are present in pairs in most body cells, with one chromosome of each pair inherited from each parent.
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An allele is a version of a gene. Genetic variation within a population means that individuals may carry different versions of the same gene. In many sexually reproducing animals, an individual can inherit one allele from one parent and another allele from the other.
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In most sexually reproducing vertebrates and many invertebrates, eggs and sperm are produced through meiosis. Chromosome pairs separate and genetic material is reshuffled through recombination. When egg and sperm combine, the offspring receives a new combination of genetic material from its parents.
Not all animals reproduce in this way, however. Inheritance can differ in species with systems such as parthenogenesis or haplodiploidy.
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Genotype refers to the genetic variants an individual carries. Phenotype refers to the characteristics that are expressed.
Phenotype is not simply DNA made visible. Gene interactions, development, physiology, environmental conditions, learning and experience can all influence how inherited biology is expressed.
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No. The idea that one gene simply “codes for” one characteristic is useful for introducing genetics, but biological traits are often much more complex.
Genes contain information used to produce functional products, such as proteins, or to regulate biological processes. The characteristics we see in an animal arise from how those genetic processes interact during development and throughout life.
Some characteristics can show relatively simple Mendelian inheritance, where variation at a single gene or locus has a large and predictable effect on the phenotype. This can make it appear that one gene equals one trait.
But there are several important complications.
A single gene can influence more than one characteristic. This is called pleiotropy. A genetic variant selected because it produces a particular visible feature may therefore also affect another aspect of anatomy, physiology, development or behaviour.
Conversely, many characteristics are polygenic, meaning that variation in many genes contributes to the phenotype. Body size, body shape, many behavioural characteristics and numerous aspects of physiology can involve the combined effects of multiple genes rather than a single genetic switch.
Genes also interact with one another. Through epistasis, the effect of a variant at one gene can depend on the variants present at other genes.
And genotype is only part of the story. Development, nutrition, health, hormones, environmental conditions and experience can all influence how inherited biology is expressed.
So rather than thinking:
one gene → one trait
it is often more accurate to think:
many genes and their interactions → biological processes → development and environment → the phenotype of the individual animal
This is important when considering selective breeding. Selecting animals for one visible characteristic does not necessarily mean that only that characteristic is changing. The underlying genetics may affect several biological systems, or the selected phenotype may depend on combinations of genetic variants whose wider effects are not immediately obvious.
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Genes matter because DNA contributes to the production and regulation of molecules that build, maintain and control the animal's body.
Some genes provide information used to make proteins, including enzymes, receptors and structural proteins. Other DNA sequences influence when, where and how strongly genes are expressed during development and throughout life.
A genetic variant can therefore affect very different characteristics. It might alter pigment production and change coat, skin, feather or scale colour. It could influence the development of an eye, limb or other structure, alter the activity of an enzyme, change a receptor involved in sensory processing, or affect the regulation of metabolism, immunity or reproduction.
The effect may be obvious, subtle or have no detectable consequence at all.
How a variant is expressed can also depend on which other alleles are present, interactions with other genes, development and environmental conditions. Some variants are recessive and affect the phenotype only when two copies are inherited; others can influence the phenotype when only one copy is present.
This is why genotype does not translate into phenotype through a single simple pathway. Genetic variation acts within an interconnected biological system.
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Genetic differences matter because they can influence how an individual animal develops, functions and responds to its environment.
Some genetic variants may have little or no detectable effect. Others may alter visible characteristics such as coat, feather, skin or scale colour. But genetic differences can also affect much less visible aspects of biology, including sensory function, metabolism, enzyme activity, immunity, neurological development, reproductive function and the structure and function of organs, muscles or bones.
The consequences depend on which biological process is affected, how strongly it is affected, and how that change interacts with the rest of the animal's biology and environment.
A genetic difference might alter how well an animal can see or hear, coordinate its movements, digest and use nutrients, regulate internal processes, resist infection, grow and develop, reproduce or rear healthy offspring. Effects can range from subtle differences between individuals to substantial impairment.
Some variants may increase susceptibility to disease, reduce mobility or coordination, affect reproductive development or fertility, alter fecundity, litter or clutch size, influence the health or survival of offspring, or affect lifespan. In severe cases, a genetic change may disrupt an essential developmental or cellular process and be lethal.
Genetic effects also do not necessarily remain confined to a single characteristic. A variant may influence several traits because the gene or biological pathway involved contributes to more than one process. Its effects may also depend on other genes, developmental conditions, health and the environment in which the animal lives.
This is why genetic differences matter first at the level of the individual animal. They can influence what that individual is physically capable of doing, how it perceives and responds to its surroundings, its health and reproductive biology, the environmental conditions it can tolerate, and ultimately what it may need from captive care.
If those differences are heritable, their effects on individuals can also have consequences across generations. Variants that influence survival, reproductive development, fertility, fecundity, offspring viability or reproductive success may become more or less represented in subsequent generations.
This is where the term fitness is often encountered. In evolutionary biology, fitness has a specific meaning relating to an individual's reproductive success and contribution of genetic material to subsequent generations, usually considered relative to other individuals in the population. It does not simply mean that an animal is healthy, strong or experiencing good welfare. Health, survival, fertility, fecundity and offspring survival can all influence fitness, but fitness and welfare are not the same thing.
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Yes, but not every inherited difference is harmful.
Selective breeding can produce changes in colour, pattern, coat, scales, body shape, size or behaviour. Some of these changes may have little or no adverse effect on the animal. A genetic variant that changes skin or coat colour, for example, may be relatively neutral in captivity if it does not alter other biological functions. A colour that would affect camouflage, predator avoidance or mate choice in the wild may also have very different consequences when those pressures are absent or managed by people.
The important point is that we should not assume that a selected characteristic is either harmless or harmful simply because of how it looks.
Genes operate within an interconnected biological system. A variant selected for one visible characteristic may also influence other traits, interact with other genes, or be inherited alongside other genetic variants. Some of those effects may be obvious immediately. Others may affect physiology, development, immunity, sensory function, movement, reproduction or behaviour in ways that are much harder to see.
For the individual animal, these differences can sometimes change what appropriate care needs to provide. An inherited characteristic might alter skin protection, breathing, vision, balance, movement, feeding or susceptibility to injury or disease. Husbandry may then need to change, although adapting the environment cannot always remove an underlying impairment.
Examples occur across taxa. Extreme brachycephalic conformation in some dogs can affect breathing, thermoregulation and eye health. Silkback bearded dragons have greatly reduced scalation, altering the protection provided by the skin. The spider morph in ball pythons is associated with abnormalities of coordination and orientation. Bubble Eye goldfish have inherited morphological changes that can affect vision, swimming and vulnerability to injury.
But these examples should not imply that selective breeding itself is necessarily harmful. The welfare question is what biological consequences accompany the characteristic being selected.
There is also a longer-term issue. When animals showing a particular phenotype are repeatedly chosen for breeding, the genetic variants contributing to that phenotype can become increasingly common. At the same time, other associated or linked variants may also change in frequency, even though they were not deliberately selected.
Some consequences may therefore remain relatively hidden at first. A harmful recessive variant, for example, may be carried without affecting an individual when only one copy is present, but become expressed when offspring inherit two copies. Repeated breeding within a restricted population can also reduce genetic diversity and increase homozygosity, making some previously uncommon deleterious effects more likely to appear in later generations.
So selective breeding can produce exactly the characteristic people intended, while also changing aspects of the animal's biology that were not part of the original goal and may not be immediately visible.
This is why it is important to consider both the animal in front of us and the generations that may follow.
The question is not simply:
Can we breed for this characteristic?
but:
Does the characteristic affect the individual animal's health or welfare, what else may be changing alongside it, and what might repeated selection make more likely to appear in future generations?
When a new or unusual characteristic is being selected, useful questions include:
What genetic variant, variants or combination of genes underlies the characteristic?
Do those genetic changes influence other biological processes?
How does it interact with other genetic variants?
Are there consistent effects on health, behaviour, movement, reproduction or development?
Do those effects change what the animal needs from captive care?Selective breeding, through human choice of which animals reproduce, is itself an evolutionary process. The concern is therefore not that a characteristic has been “artificially” selected rather than having evolved naturally, but that human selection may strongly favour a particular phenotype without the broader biological consequences yet being fully understood.
These processes create and reshuffle variation between individuals. Across generations, natural selection, genetic drift, mutation, gene flow and other evolutionary processes can change that variation within populations.
Evolution across generations
Within every population, individuals vary.
Some of that variation is heritable because individuals carry different versions of genes, known as alleles, which can be passed from parents to offspring.
Natural selection acts on the characteristics expressed by individuals. Where heritable differences influence survival or reproductive success, individuals carrying some variants contribute proportionally more offspring to subsequent generations.
Across many generations, this can change the frequency of alleles within a population.
But natural selection is not the only process producing evolutionary change.
Mutation
Mutation creates new genetic variation through changes in DNA, the molecule that carries most of an animal's genetic information. Most mutations are neutral or have little effect, some are harmful, and occasionally a mutation may produce a characteristic that influences survival or reproductive success.
Genetic Drift
Allele frequencies can also change through chance, independently of whether those alleles improve survival or reproductive success. Those random changes can accumulate across generations, particularly in small populations. Because the effects of genes can depend on interactions with other genes, changes in allele frequencies can also alter combinations of alleles and their phenotypic effects. Through epistasis and other gene interactions, consequences may then extend to physiology, morphology, behaviour or other functions, which may subsequently influence survival and reproductive success.
Recombination
Sexual reproduction reshuffles existing genetic variation, producing new combinations of alleles in offspring.
Gene Flow
Movement and reproduction between populations can introduce alleles from one population into another.
Together, these processes mean that evolutionary history is more complex than simply asking whether a characteristic is “useful”.
Not every characteristic is an adaptation, and evolution does not work towards a predetermined outcome.
Genes do not act in isolation
The effect of an allele can depend on the other genetic variants present within an individual. Through epistasis, interactions between genes can alter how particular characteristics are expressed. Some genes also have pleiotropic effects, influencing more than one trait.
Changes in allele frequencies can therefore have consequences beyond a single visible characteristic. They may influence interacting aspects of anatomy, physiology, sensory processing, behaviour or other biological functions.
Gene expression also interacts with development and the environment, so an animal’s phenotype is not simply a direct readout of its DNA.
From alleles to the animal
Across evolutionary time, changes can therefore become apparent at many different biological levels.
They may influence:
External anatomy and morphology
Body form, limbs, skin, scales, fur, feathers, colouration, sensory structures and locomotor anatomy.
Sensory systems
How does the animal detect its world? This may include light and wavelengths beyond human vision, sounds and vibrations, chemical and olfactory cues, humidity, temperature, touch and other specialised sensory information. These cues may convey information about food, predators, territory and the identity of other animals, including species, individual familiarity, relatedness and potential mate compatibility, with MHC-associated cues contributing in some species.
Physiological systems
Thermoregulation, metabolism, water and electrolyte balance, digestion and nutrient absorption, endocrine signalling, immune function, reproductive physiology, cell growth, repair and ageing all contribute to maintaining internal function. These systems interact with environmental conditions and resource availability, so factors such as nutrient deficiencies, inappropriate temperature, or inadequate UVB exposure in species dependent on UVB-mediated vitamin D synthesis can have consequences extending well beyond the immediately affected system.
Nervous system function
The brain and nervous system receive and integrate sensory information, coordinate movement and behaviour, and interact with endocrine and physiological systems. Neurotransmitters, neuromodulators and hormones contribute to the regulation of motivation, attention, learning, arousal, stress responses and affective state, influencing whether situations are experienced with positive or negative valence and how an animal responds to them.
Biological rhythms
Daily and seasonal patterns of activity, feeding, reproduction, migration, dormancy or torpor.
Behavioural systems and motivations
Patterns involved in finding food, seeking shelter, avoiding predators, defending resources, communicating, finding mates, caring for offspring, exploring and responding to changing circumstances. Some of these characteristics are immediately visible. Others operate largely unseen inside the animal. Behaviour is not the only legacy of evolution.
These systems do not operate independently. Nutrition can affect brain and endocrine function, light can influence biological rhythms and hormonal signalling; thermal conditions can alter metabolism and digestion; and prolonged physiological challenge can affect behaviour, cognition and affective state. What appears to be a single husbandry variable can therefore have effects throughout the animal.
Survival and reproduction require animals to solve problems
Every animal must somehow obtain the resources and skills required to live long enough to reproduce.
But different species solve those problems in very different ways.
They may need to:
find and obtain food
locate water
regulate body temperature
find shelter or refuge
detect and escape danger
compete for or defend resources
navigate through their environment
communicate with other animals
find and select compatible mates
reproduce successfully
rear or protect offspring
The ecological circumstances surrounding a species influence which characteristics encounter selection across generations.
The result is not a perfectly adapted animal.
It is a species with an inherited biological architecture arising from its particular evolutionary history.
Two species. Two very different evolutionary stories
Bearded dragon
Pogona vitticeps
Primarily diurnal.
Ectothermic.
Behaviourally thermoregulates using external heat.
Moves across the ground, climbs and digs.
Uses visual and chemical information about its surroundings.
Feeds on both plant and animal material.
Responds to environmental light, temperature and seasonal conditions.
A bearded dragon and a sugar glider face many of the same fundamental biological challenges.
Both need energy.
Both need to avoid danger.
Both need to reproduce.
Both need to regulate their internal state.
Both need to obtain information about their surroundings.
Yet they achieve these things in profoundly different ways.
Sugar glider
Petaurus breviceps
Nocturnal.
Endothermic.
Lives and moves within 3-D arboreal space.
Glides between supports using a patagium.
Uses tree hollows as daytime refuge.
Lives within social and scent-rich environment.
Feeds on seasonally changing plant exudates, nectar, pollen and invertebrates.
Same fundamental challenges. Different biological solutions.
Click on each poster to explore how ecology, anatomy, physiology, sensation and behaviour connect.
The animal brings its biology with it
Captivity can transform almost every aspect of an animal’s surroundings.
Humans may determine:
space
temperature
light
humidity
food
water
social companions
nest or refuge sites
substrate
opportunities for movement
daily routines
seasonal variation
reproduction
exposure to novelty
opportunities to choose or avoid
But changing the environment does not immediately remove the biological systems that evolved across the species’ history.
A captive-bred animal is still a member of the same species.
Its sensory systems still influence what it detects.
Its physiology still regulates its internal environment.
Its anatomy still influences how it can move.
Its digestive system still determines how food is processed.
Its nervous system and endocrine systems still respond to opportunities, challenges and threats.
Its behavioural systems can still generate motivations to seek, avoid, investigate, hide, forage, interact or reproduce.
Captive breeding can itself change populations over generations, particularly where humans deliberately or inadvertently select particular characteristics. Genetic drift and inbreeding can lead to considerable loss of genetic diversity and welfare implications in small captive populations.
But captive birth alone does not erase the evolutionary inheritance of the species.
When humans select for particular traits
Selective breeding occurs when people influence which animals reproduce because they want particular characteristics to appear in future generations. This is sometimes called artificial selection, but it is still an evolutionary process because heritable variation and the frequencies of genetic variants within a population can change across generations.
If a characteristic is heritable, repeatedly choosing animals that express it can make the genetic variants contributing to that phenotype more common. Over successive generations, the characteristic may become increasingly frequent, pronounced or predictable within a breeding line.
The genetics underlying the selected characteristic may be relatively simple, involving a variant at one major locus, or much more complex, involving many genes and their interactions. Traits such as body size, skull shape, behaviour and many aspects of physiology are often influenced by multiple genes as well as development and environmental conditions.
Selection does not act on one characteristic in isolation
When people select an animal because of a visible phenotype, they are selecting the whole genome carried by that animal, not only the genetic variant responsible for the characteristic they can see.
Several processes can therefore produce changes that were not intended.
A genetic variant may influence more than one trait, known as pleiotropy. The effect of one variant may also depend on variants at other genes, known as epistasis. Genes located close together on a chromosome may sometimes be inherited together, so selection for one variant can also change the frequency of nearby variants.
This means that selecting repeatedly for colour, pattern, body form or another characteristic can sometimes have consequences for other aspects of anatomy, physiology, sensory function, behaviour or health.
Some of those consequences may be immediately apparent. Others may remain difficult to detect for several generations.
Hidden variants can become visible
A deleterious recessive variant can be carried by an animal without producing an obvious effect when only one copy is present.
If related animals or animals from a restricted breeding population are repeatedly bred together, the probability that offspring inherit two copies of the same recessive variant can increase. A condition that was previously hidden in carriers may then begin to appear in offspring.
Repeated selection within a relatively small breeding population can also reduce genetic diversity and increase homozygosity, particularly if a small number of animals contribute disproportionately to subsequent generations.
This does not mean that every breeding line will develop genetic disease. It means that breeding decisions can influence not only the characteristic being deliberately selected, but also the genetic background in which that characteristic occurs.
Selection can make a phenotype increasingly established
Strong selection for a particular characteristic can progressively increase the frequency of contributing genetic variants. In some circumstances, an allele may eventually become fixed, meaning that all individuals in that population carry it.
Complex traits are less straightforward because several genes may contribute to the phenotype, but repeated selection can still make particular combinations increasingly common and the resulting phenotype more consistent.
This is why the consequences of a breeding decision may extend beyond one litter, clutch or generation.
Selection can also be used positively
Human-directed selection is not inherently detrimental.
Breeding programmes can select away from known deleterious variants, reduce extreme conformations, improve functional health and maintain or increase genetic diversity. Genetic testing, pedigree information, health screening and careful selection of breeding animals can all help inform these decisions.
The important issue is therefore what is being selected, what else may be changing alongside it, and how those changes affect the animals produced.
For welfare, the individual remains central. If a selected phenotype changes an animal's ability to breathe, move, see, feed, regulate its body, protect itself from injury or interact normally with its surroundings, those consequences matter whether the characteristic is rare, fashionable or firmly established within a breed or morph.
And across generations, responsible breeding means continuing to ask:
Are we only making the desired characteristic more predictable, or are we also changing other parts of the animal's biology?
Are previously hidden problems beginning to appear?
Can breeding decisions protect both the health and welfare of individual animals and the genetic diversity of the population that follows?
Species is the starting point, not the whole answer
Understanding a species tells us something fundamental about the biological system with which we are working.
But individuals are not interchangeable.
Genotype (DNA), development, early experience, health, age, reproductive state, learning, previous housing and individual temperament can all influence how an animal responds to its environment.
That is why Species First does not mean species alone.
The individual animal tells us how that biology is being expressed here and now.
From biology to need
Understanding evolutionary history does not mean trying to reproduce every feature of life in the wild.
Wild animals experience predation, hunger, disease, injury and competition, all of which can compromise welfare.
The important question is different:
What does the biology produced through that evolutionary history mean for the animal living in captivity today?
What environmental information does it need access to?
What conditions allow its body to function appropriately?
What is it motivated to seek or avoid?
What forms of movement matter?
What social conditions are biologically relevant?
What choices can it make?
Can it withdraw?
Can it regulate its own exposure to important environmental variables?
Can highly motivated behaviours find an appropriate outlet?
Explore the seven interconnected biological perspectives to find out more about how evolutionary history is expressed through the animal’s anatomy, physiology, sensory systems, behaviour and motivations..
From need to welfare
Understanding where needs originate is only the first step.
The next question is whether captive environments, husbandry practices and human decision-making allow those needs to be met.
A developing Species First resource
From Niche to Need will continue to expand through the six taxon routes, practical questions about keeping animals, the seven interconnected biological perspectives, further species examples and deeper exploration of the relationships between evolutionary history, ecology, sensory biology, anatomy, physiology, behaviour and welfare in captivity.
Every species brings a unique evolutionary history into captivity.
Species is the starting point. The individual animal is where welfare is experienced.
Understanding the animal helps us understand what its captive environment and care need to provide.