Science: Will Climate Change Affect The Evolution of Humans?

Will Climate Change Affect The Evolution of Humans?

A Brief History Of Human Evolution:

 The earliest members of the genus Homo was the Homo habilis which evolved around 2.3 million years ago. The brains of our early ancestors were similar in dimensions to that of a modern day chimpanzee. However, over the course of the next million years encephalisation (an increase in brain mass in proportion to size) was initiated. This meant by the time the species Homo erectus was established cranial capacity had doubled in size. This encephalisation was indicative of a growing intelligence in progressive species of hominins as they developed the ability to use more complex tools which provided them with an evolutionary advantage over earlier ancestors. 

Archaic Homo sapiens, the precusor to of 'modern ' humans, evolved between 250,000-400,000 years ago. Neanderthals and other species of the genus homo may have contributed up to 6% of their genome to present-day humans. This suggests some interbreeding between these species. The transition to modern behaviours with the development of culture and language happened around 50,000 years ago.

 Are Humans Evolving Now?

Humans are perhaps unique in the fact that we have adapted to survive in almost all the worlds ecosystems. Humans live in tropical, temperate, desert and arctic conditions exploiting the resources of our natural surroundings and our proficiency with technology. Today over 40% of the earths land mass is adapted for agricultural or urban purposes and this figure is likely to increase as the human population grows. Since the advent of farming genetic evolution in humans has largely been confined to the development of resistance to various infectious diseases. 

One of the most notable of these genetic adaptations is the development of “Sickle Cell Anaemia” in areas in which malaria is widespread. Sickle Cell Anaemia provides an advantage to these populations in the event they become infected with malaria as it results in less severe symptoms. This is because the presence of malaria in haemoglobin of sickle cells causes the cell to rupture prematurely, meaning that the plasmodium is unable to reproduce. 

Although humans have alleles which code for genetic resistance to various diseases we are still susceptible to a vast array of other diseases, some of which we have no known cure for. However, through the use of medicines such as antibiotics, phage therapy and surgical procedures we can extend our lives or even cure us of many diseases. Through medical and technological advances the human population has been able to adapt to a spectrum of environments. As a result of our adaptability as a species and the fact that such technological developments will continue to increase rapidly in coming years.

How Will Climate Change Affect Humans?

In comparison to most other species humans are likely to fare favourably even if global warming does occur. This is a result of technologies conferring to our species the ability to survive in a number of different environments. It is also important to note that of the new species of hominid that evolved previously 13 out of 15, appeared during pulsed climate periods.Furthermore, despite the progressive encephalisation tin the Homo genus over 2 million years the majority of brain growth is believed to have taken place in the last 800,000 years. This time frame coincides a period noted for the strong fluctuation of global climate. Larger brains were necessary to process new information, to plan ahead and solve more abstract problems and there is still the potential for an increase in our cognitive abilities. Global Climate Change is cyclic and Homo sapiens and closely related but less evolved hominins have survived abrupt changes in climate before. A study by Stanford University on an African Yoruba tribe investigated the differences between the tribal genes for water retention and European gene pools. The team found that 85 per cent of the Yoruba had an identical sequence of genetic information that was longer than it would have been if it was a result of random recombination and genetic shuffling. This provides evidence that this gene had been naturally selected amongst the Yoruba. The length of the genetic signature suggests that the change occurred in the last 10,000 to 20,000 years, which coincided with the initial stages of the desertification of the Sahara. 

However, despite these previous trends of how climate change has impacted evolution there are reservations as to whether such trends will continue. Many palaeontologists support the idea of the “refugium” theory. A 'refugium' is a small area of relatively livable conditions that a population can use to survive the lethally harsh environmental conditions i.e. an ice age. In these isolated areas (such as caves) the founder effect can take place in these small groups of isolated individuals that contain only a small number of alleles of the whole population. The isolation of these individuals and interbreeding will cause them to become more genetically dissimilar from the main population due to the lack of gene flow until they can eventually be deemed a new species. This meant these groups, adapted to live in the more temperate conditions of their refugium had an evolutionary advantage over Neanderthaals when the environment became more hospitable. This is an aspect many tabloid scientists have over looked when detailing how humans are likely to evolve in future. The availability of flights and other technological advances in infrastructure the world is truly a “global community”. This has led mixing of different ethnicities (and thereby a variety of alleles) but also architectural improvements make the prospect of humans withstanding more extreme weather in caves unlikely. In a physiological sense humans are likely to evolve much slower for the foreseeable future due to the lack of isolation of groups of humans. Instead a more likely cause of evolution in humans in the future maybe as a result of the growing influence of technologies and the global community. Such a reliance on technology may result in such traits as humans developing weaker immune systems as a result of patients whose conditions may have previously rendered them unable to reproduce to be pass on genetically hereditary disease and other alleles which might not otherwise be selected by natural selection to their children. Improvements in modern medicine will reduce the selection pressure for humans to have strong immune systems to survive illness and are another area in which technologies have allowed us to supersede our biological weaknesses.

-Adam