One of the recurring claims of creationist apologetics is that mutations condemn living populations to relentless genetic deterioration — a supposedly inevitable decline which evolution cannot overcome. What this argument neglects is that mutations do not operate in isolation: selection influences which genetic variants pass to subsequent generations. Now, a long-running experiment with red flour beetles has provided direct genomic evidence that competition for mates can help remove harmful variants, leaving populations more resistant to extinction.
The research, led by Michael D. Pointer, of the University of East Anglia Department of Biological Sciences, described in a report in Proceedings of the National Academy of Sciences of the USA (PNAS), also addresses an interesting evolutionary question: why is sexual reproduction so widespread despite its considerable costs? Finding mates takes time and energy, competition can be costly, and reproduction requires contributions from individuals which do not themselves produce eggs. One possible compensating benefit is that competition for reproductive success helps prevent damaging mutations from accumulating.
The distinction matters. Genetic diversity is often used as an indicator of a population’s prospects, but the amount of variation cannot tell us everything about its effects. In this experiment, the estimated burden of harmful variants was a better predictor of extinction under inbreeding than diversity alone. Populations could retain similar amounts of genetic variation while differing in their vulnerability to genetic stress.
There is no foresight involved. Beetles do not select mates with the intention of protecting their distant descendants from extinction. Where harmful variants impair mating success, their carriers leave fewer offspring, making those variants less likely to pass on. A longer-term benefit to the population can emerge from differences in reproductive success in the present.
This does not establish that sexual selection is beneficial under all circumstances, nor does it provide a complete explanation for the origin or persistence of sex. It does, however, demonstrate a mechanism by which selection can counter the effects of harmful mutations — precisely the sort of process that claims of inevitable genetic decline need to confront. Here, evolutionary theory supplied a testable prediction, researchers followed populations across many generations, and genomic evidence revealed the resulting changes. No plan, magical intervention or intelligent guidance was required.
How sexual selection can remove harmful mutations. Evolutionary success involves more than survival. An organism must also reproduce to pass its genes to subsequent generations. Sexual selection arises when individuals differ in their success at obtaining mates or achieving fertilisation. It can involve competition for mates, mate choice and, after mating, competition between sperm.The paper in PNAS was accompanied by a news item from the University of East Anglia, Norwich:
How can this reduce harmful mutations?
Some mutations impair an animal’s development, physiology or general condition. Those effects may also reduce its reproductive success — for example, by weakening its ability to compete for mates or produce effective courtship signals. When carriers leave fewer offspring, the harmful genetic variants they carry are less likely to pass to the next generation.
This is one form of purifying selection: the removal of damaging variants from a population. Sexual selection can provide an additional route through which this happens, including when the effects of a variant are insufficient to prevent its carrier from surviving.
Why can selection on males benefit females?
Males and females share most of their genes. A harmful variant that reduces a male’s condition may also harm females that inherit it. If sexual selection reduces the transmission of such variants through males, both sons and daughters can benefit. This is not guaranteed, however: some variants have different, or even opposing, effects in the two sexes.
Genetic diversity is not the same as mutation load
Genetic diversity describes variation within a population. Mutation load concerns the reduction in fitness caused by harmful mutations. These are related but distinct properties: genetic differences can be harmful, beneficial or effectively neutral, depending on the variant and its circumstances.
Consequently, removing harmful variants need not cause a substantial loss of overall diversity. In the red flour beetle experiment, stronger sexual selection was associated with fewer predicted harmful variants while overall genetic diversity remained comparable between treatments.
Why does inbreeding expose hidden harm?
Many harmful variants are recessive: their effects are partly or largely masked when an individual also carries a functional copy of the gene. Close relatives are more likely to carry the same variants inherited from shared ancestors. Their offspring therefore face a greater chance of receiving two copies of a harmful recessive variant. The resulting loss of survival or reproductive success is called inbreeding depression.
No foresight — and no guarantee of perfection
Individuals do not need to recognise harmful mutations or anticipate extinction. Differences in reproductive success can change the frequencies of variants across generations, with population resilience emerging as a consequence.
Sexual selection also has costs, including injury, harassment and investment in costly displays. Its overall effects depend on the circumstances. The beetle findings demonstrate that it can reduce mutation load; they do not show that it always benefits populations or eliminates every harmful mutation.
Glossary
- Sexual selection
- Selection arising from differences in success at obtaining mates or achieving fertilisation.
- Allele
- An alternative version of a genetic sequence at a particular location in the genome.
- Fitness
- Reproductive contribution to subsequent generations, relative to other individuals in a particular environment.
- Mutation load
- The reduction in fitness attributable to harmful mutations.
- Recessive
- Describes a variant whose effect is masked or reduced when paired with a dominant alternative.
- Inbreeding depression
- Reduced survival or reproductive success resulting from mating between relatives, often because harmful recessive variants are exposed.
How sex can help save species from extinction
Giving females multiple males to mate with, rather than just one, could help make species more resistant to extinction – University of East Anglia research shows.
A new study reveals that when females have multiple males to mate with, their offspring inherit significantly fewer harmful genetic mutations. This, in turn, makes the entire population healthier and less likely to die out.
The findings, published today in the journal PNAS, emerged from a 15-year experiment involving thousands of red flour beetles.
But the team say it supports a long-standing evolutionary theory that could apply across much of the animal kingdom.
How the research happened
Researchers compared beetle populations in which females had just one male to mate with, with populations where females could mate in a competitive environment involving multiple males. After 156 generations, populations exposed to stronger sexual selection carried substantially fewer harmful genetic mutations. This was because females had greater choice of mates and males faced more competition to reproduce, compared with populations where mating opportunities were restricted.
Lead researcher Dr Michael Pointer, from UEA’s School of Biological Sciences, said: “In one type of population, females could mate with up to five males in each generation.
“In the other type, the opportunity for sexual selection was removed by pairing each female with just one male each generation.
“We then sequenced the genomes of multiple beetles from each population and identified the different mutations within those genomes, including those predicted to be harmful.
We found that when the females had more males to potentially mate with, those populations had fewer harmful mutations, but similar overall genetic diversity.
Dr Michael Pointer
Healthier genomes
“In simple terms, we found that populations of beetles where there were multiple males that the female could potentially mate with ended up with healthier genomes.
“This genetic advantage appeared to have real-world consequences because populations carrying higher levels of harmful mutations were far more likely to become extinct when subjected to inbreeding.
“Indeed, this mutation load proved a better predictor of extinction risk than the mating system itself,” he added.
Evidence for the ‘good genes’ hypothesis
The study offers evidence for a long debated evolutionary idea known as the ‘good genes’ hypothesis.
The theory suggests that successful males tend to be those with the best genes - in this case those with the fewest harmful mutations.
When females can choose between competing males, or when males compete intensely for matings, those with poorer genetic health are less likely to pass on their genes.
“Over many generations, this process acts like a biological quality-control system, helping purge damaging mutations from the population,” said Dr Pointer.
“Our work provides direct genomic evidence for this hypothesis.”
The researchers found that this genetic filtering occurred without reducing overall genetic diversity. Previous concerns had suggested that strong sexual selection could reduce the breeding population and lead to a loss of genetic variation.
But the beetles exposed to stronger sexual selection retained similar levels of genome-wide diversity to those in the low-selection population.
“This means that populations may be able to rid themselves of harmful mutations while still preserving the genetic variation needed to adapt to future challenges,” said Dr Pointer.
Important implications for conservation
Senior author Prof David Richardson, also from UEA’s School of Biological Sciences, said: “Many endangered species suffer from small population sizes and inbreeding, which allows harmful mutations to be expressed and lead to increased extinction risk.
“Conservation programmes, whether in the wild or captivity, should think carefully about restoring natural levels of sexual selection.
Allowing females multiple males to mate with could help populations to naturally weed out damaging genetic variants and improve their long-term chances of survival.
Prof David Richardson
“Experimental beetle populations allow us to test fundamental evolutionary principles over hundreds of generations, something that would be impossible in larger animals.
“The aim was not to understand the beetles themselves, but to investigate a broader question that has puzzled evolutionary biologists for decades – why sexual reproduction remains so widespread despite its enormous costs.
“One reason may be that sexual selection helps populations get rid of harmful mutations.
“The battle for mates may help nature battle against extinction.”
Publication:
The predictable creationist response is, of course, “But they’re still beetles!” This mistakes the persistence of a biological classification for the absence of evolutionary change and is the traditional disingenuous attempt to redefine 'evolution' having demanded evidence for it. Evolution is change in the inherited characteristics of populations across generations; it does not require descendants to cease belonging to their ancestral groups. Birds remain dinosaurs, humans remain apes, and these beetles remain beetles. Their continued membership of those groups is entirely consistent with evolution.
Nor does invoking an undefined “kind” rescue the argument. Unless creationists can provide a consistent biological definition and demonstrate a mechanism that prevents evolution beyond its supposed boundaries, the term supplies no testable alternative. This experiment was not a test of whether beetles could become something arbitrarily designated a different “kind”. It tested whether stronger sexual selection could reduce harmful genetic variation and improve population resilience. The genomic evidence supported that prediction.
That result directly challenges the claim that harmful mutations must accumulate unchecked, driving populations into inevitable genetic decline. After 156 generations, populations exposed to stronger sexual selection carried fewer predicted harmful variants without a comparable loss of overall genetic diversity. Their burden of harmful variants also helped explain their vulnerability to extinction under inbreeding. These are measurable biological differences, regardless of whether the insects retain the same name.
No beetle needed to understand genetics, plan for future environmental challenges or act for the preservation of its species. Differences in reproductive success were sufficient to produce a longer-term benefit. Evolutionary theory explained how that could happen and supplied a prediction that researchers could test. “Still beetles” does nothing to answer the evidence; it merely changes the subject.
Advertisement
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
All titles available in paperback, hardcover, ebook for Kindle and audio format.
Prices correct at time of publication. for current prices.
No comments :
Post a Comment
Obscene, threatening or obnoxious messages, preaching, abuse and spam will be removed, as will anything by known Internet trolls and stalkers, by known sock-puppet accounts and anything not connected with the post,
A claim made without evidence can be dismissed without evidence. Remember: your opinion is not an established fact unless corroborated.