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For species to survive mass extinctions, having a high degree of genetic variation, which is facilitated by sexual reproduction, was more crucial than simply producing large numbers of offspring quickly, as it allowed for greater adaptability to changing environmental conditions and a higher chance of some individuals possessing traits advantageous for survival. 


Genetic diversity acts as a reservoir of traits that can be crucial for adapting to new and challenging environments. A diverse gene pool means that a population has a broader range of genetic traits. This diversity increases the likelihood that some individuals will possess advantageous traits that can help them survive in changing conditions. In environments that change rapidly, such as those following mass extinctions, individuals with traits that confer a survival advantage are more likely to survive and reproduce. This process, known as natural selection, leads to the propagation of beneficial traits in the population.



While producing large numbers of offspring quickly can be beneficial in stable environments, it is the genetic variation facilitated by sexual reproduction that provides the adaptability needed to survive and thrive in the face of mass extinctions and changing environmental conditions. The interbreeding between Homo sapiens and other hominin species is a testament to how genetic diversity can be enriched and the importance of this diversity for long-term survival.




Sexual reproduction involves the combination of genetic material from two parents, leading to offspring with a unique set of genes. This recombination can produce novel combinations of traits that might be advantageous in new environments. The process of meiosis during sexual reproduction, which involves genetic recombination and an independent assortment of chromosomes, increases genetic variation within a population. Furthermore, the interbreeding between Homo sapiens and archaic humans like Neanderthals and Denisovans is a prime example of how genetic exchange can enhance a population's genetic diversity. Studies have shown that modern humans carry small percentages of Neanderthal and Denisovan DNA, which may have conferred certain advantageous traits, such as resistance to infections or adaptations to cold climates.




When early Homo sapiens encountered and interbred with other hominin species like Neanderthals and Denisovans, they acquired new genes that had been shaped by different evolutionary pressures in different environments. This adaptive introgression allowed Homo sapiens to potentially adapt more quickly to new environments and challenges than relying solely on new mutations within their own population. For example, some Neanderthal genes are linked to immune function and adaptation to colder climates, which could have been beneficial as Homo sapiens migrated out of Africa.




Interbreeding, along with ongoing mutations and gene flow within Homo sapiens, led to a more diverse gene pool. This increased genetic diversity meant that different individuals within the population possessed a wider range of traits. When faced with new diseases, climate changes, or resource scarcity, it was more likely that some individuals would possess traits that allowed them to survive and reproduce successfully. In some cases, individuals with genes inherited from different hominin groups might have experienced heterozygote advantage, where having different versions of a gene (alleles) provided a survival benefit.




The combination of novel genes from other hominins and increased overall genetic diversity made Homo sapiens populations more resilient to environmental changes and diseases. The wider range of traits allowed different populations of Homo sapiens to adapt to and thrive in a greater variety of environments across the globe. Over time, natural selection would have favored individuals with the most beneficial genetic combinations, including those acquired through interbreeding. This would have further solidified the advantages conferred by this increased variation. 




While some introgressed genes were clearly beneficial, others might have been neutral or even slightly disadvantageous initially. Natural selection would have played a crucial role in sorting these out over time. The relationship between interbreeding, variation, and fitness is complex and involves many genes interacting with each other and the environment. The interbreeding events between early Homo sapiens and other hominins, coupled with the ongoing evolution of human variation, provided a significant advantage in terms of adaptability and resilience. This increased genetic diversity likely played a crucial role in the survival and successful reproduction of our species as we spread across the globe and encountered diverse challenges.

 

Recommended reading

 

 

What does it mean to have Neanderthal or Denisovan DNA?
https://medlineplus.gov/genetics/understanding/dtcgenetictesting/neanderthaldna/

What does it mean to have Neanderthal or Denisovan DNA?: MedlinePlus Genetics