Humans are still evolving and we don’t know what will happen next
Evolutionary biology is not a slow-moving science. Just last month a new species of hominid (Homo naledi) was unveiled at a news conference in South Africa. When did modern humans branch off as an independent species? What have been our most important adaptations? And, most importantly, what is the next evolutionary step for humanity?
We reached out and spoke to five of the foremost experts on human evolution, who shared their expertise and predictions.
Professor of philosophy at Florida State University who has written extensively on the philosophy of biology. He founded the journal Biology and Philosophy and was a key witness in McLean v. Arkansas arguing against teaching creationism as science in public schools. He has published dozens of books on the philosophy of science, including The Philosophy of Human Evolution (2012) and Darwinism and Its Discontents (2006).
Associate dean of research at the Joint School of Nanoscience and Nanoengineering at North Carolina A&T State University and the University of North Carolina Greensboro. His work has included experimental evolution and studies in aging, as well as written works about racism, race, and biology. He has appeared in the New York Times, PBS, and his works include The Emperor's New Clothes: Biological Theories of Race at the Millennium (2005) and The Race Myth: Why We Pretend Race Exists in America (2004).
Research scientist and educator at the Smithsonian. Her work has included research on human origins and diet. She has contributed dozens of articles to publications including the Journal of Human Evolution and the Journal of Archaeological Science and has appeared on NPR as an expert.
Professor of ecology and evolutionary biology at Yale. He was a founding editor of the Journal of Evolutionary Biology, started several societies to promote biological research, and has written several books on biology including Evolution, An Introduction (2005) with Rolf Hoekstra.
Research Leader of Human Origins and the Natural History Museum in London. His work in across the globe has helped scientists understand the relationship between Homo sapiens and other Hominids during the emergence of our species. His works include The Origin of Our Species (2011) and Homo Britannicus: The Incredible Story of Human Life in Britain (2007).
The past is non-linear and messy
Anatomically modern Homo sapiens (us), are thought to have emerged as a distinct species around 200,000 years ago in Africa. While we often imagine one species of hominid handing the baton to the next in a neat, linear “evolution of man” progression, Homo sapiens lived simultaneously with several other hominid species—Homo neanderthalensis, Homo floresiensis, and the much older Homo erectus, whose geographic and temporal boundaries remain fuzzy.
They also had sex with each other, as evidenced by the amount of Neanderthal DNA in our genetic material (about 2.5% - 3% on average).
“The emergence of modern humans was a major evolutionary event, but it was not (in my view) sudden and punctuational,” Professor Chris Stringer, the research leader of human origins at the National History Museum in London, tells Hopes&Fears. “I think many of the changes were incremental, taking well over 100,000 years to develop… and introgression from other human species both within and outside of Africa added significantly to the story during the last 60,000 years.”
“In a sense, this inbreeding was actually anti-evolutionary,” argued Joseph L. Graves, the associate dean of research at the Joint School of Nanoscience and Nanoengineering at North Carolina A&T State University and the University of North Carolina Greensboro. “It resulted from a failure of reproductive isolation between the archaic humans and the modern humans.”
Professor Michael Ruse, a philosopher of biology and active defender of evolution against pseudoscience, noted the difficulty assigning a clean starting point for humans: “You could say getting up on our hind legs about 5 million years ago was a great event, but only to have others—like branching off as a species, losing our body hair, migrating towards different environments—seem equally as important. For example, the emergence of differences in skin color occurred in the past 15,000 years—very important socially, but not that big biologically,” he reflected. “Personally, I would stress the continuities and not the breaks.”
The present is changing
In the past 20,000 years (the last tenth of our existence as a species) humans have evolved our most immediately recognizable traits. Some changed happened slowly, and some in spurts.
“Over the course of our existence, selection intensities have been low, resulting in slow, gradual change," Joseph L. Graves explains. "However there have been periods of relatively rapid change in some traits in our species’ history, often in response to pathogens such as bubonic plague or falciparum malaria.”
While our resistance to leprosy and malaria are relatively new, we may not even be aware of our current adaptations.
“Humans are still evolving today,” says Dr. Briana Pobiner, a researcher at the Smithsonian’s Human Origins Program, who specializes in the diet of our progenitors.
“Only 10,000 years ago, like all mammals, our young lost the ability to digest milk sugar (lactose) after they stopped nursing, because the lactase enzyme which allows lactose to be digested was no longer produced,” Pobiner tells Hopes&Fears. “But now millions of adults have what is called lactase persistence, when the enzyme continues to be produced into adulthood. This varies around the world, but it is generally associated with populations that domesticated milk-producing animals like cows and goats, mainly in areas of Africa and Europe.”
She added, “It turns out that multiple, independent genetic mutations facilitated this change, which speaks to strong (and recent) natural selection for the ability to digest lactose. Ancient DNA from skeletons in Europe demonstrates that this ability appeared less than 6,500 years ago in that area.”
Many physical traits are also recent introductions to the gene pool. Some of this is due to the pairing of natural selection with a phenomenon called genetic drift (which is, in the simplest terms, a process by which the frequency of alleles changes over time due to some organisms randomly surviving and leaving more offspring). Joseph Graves, whose work shows that there are no biologically significant races of humans, has a lot of data regarding the variations of humans from across the globe and the means by which they arose: “The migrants out of Africa were a small subset of the total human species. Their allele frequencies would have differed from their ancestral population due to random sampling. As these populations began to separate by geographical distance, some unique mutations appeared which influenced physical traits.”
Certain traits are responsive to our physical environment. Graves remarked, “Solar intensity has a predictable effect on skin pigmentation and loci associated with it such as Vitamin D binding locus. Yet, other traits such as disease resistance do not follow the solar intensity gradient, for example a schistosomiasis (worm) resistance gene. Thus human populations are mixes and matches of genes favored by non-correlated selection regimes.”
The future is uncertain
From H.G. Well’s grim terrestrial morlocks to Wall-E’s corpulent floating hedonists to the X-Men with flashy superpowers, it's tempting to speculate where we might end up in the future.
Stephen Stearns, a professor of ecology and evolutionary biology at Yale, was quick to point out how little we can predict about our future. Both our shift to agrarian lifestyles (8,000-10,000 years ago) and the Industrial Revolution were marked by major shifts in diet, exposure to infectious disease, and risks of chronic disease.
“We know that culture (agriculture, medicine, technology) now changes much faster than genes and traits can evolve,” he tells us, before adding, “We have therefore entered an era in which we are going to be permanently mismatched to a rapidly changing environment for as long as we can foresee.”
Stearns dwelled on being more humble about predicting the future generally: “Just ask yourself if you could have predicted, in 1920, vaccines, antibiotics, oral contraceptives, television, computers, space travel, and the Internet. No way. Now project 100 years into the future. I would claim that we do not have any idea what sorts of cultural changes and technological innovations will have taken place by then."
“I think before predicting the long-term we need to consider how well humans will survive the next 5,000 years of planetary change,” Chris Stringer adds, “on a scale we have never faced before.” This sentiment was shared by Ruse, who says evolution might happen “for other organisms, if there is time, to change in direction of better accommodation to a hot planet, but I would hesitate to say that this is something that will affect humans biologically.”
If post-industrial societies have complicated the picture of natural selection from the standpoint of survival and adaptation, one thing remains an active participant in our evolution: sexual selection. Certain traits can affect how many children someone is likely to have, thus minutely changing the next generation of humans.
“I doubt red hair or blue eyes will disappear from modern human populations altogether,” remarked Briana Pobiner, when asked if traits that come from recessive alleles would soon disappear. “Interestingly, a recent study indicates that Dutch men are becoming taller, on average, and not just because of good nutrition and health care – so yes, there is still evidence for evolution in our physical features.”
Dr. Pobiner also reminded me that infectious diseases still do have a role to play in our evolution. By some measurements bacteria and viruses are two of the most successful organisms (and quasi-organisms) on the planet and they will likely use us to their full advantage so long as we are around. “We control much of our physical environment now, but we will always be susceptible to infectious and other diseases,” argued Pobiner.
Malaria is one disease in particular that holds a lot of anxiety for us until we eradicate mosquitoes. “There is already evidence of adaptation to deal with malaria," Pobiner points out. “It turns out that having one copy of a mutation in one of the genes for hemoglobin confers some resistance to malaria. But two copies leads to sickle cell disease. This protection explains why the mutation persists, even though getting a double dose of the mutation is deadly.”
While the pace of cultural changes far outpaces our genetic ability to adapt to new circumstances, we can be reasonably sure that we will continue to evolve. After all, we have numbers on our side: each person has an average of 60 new mutations that their parents pass down to them. At a population of over 7 billion, there is a lot of room for uncertainty.
The scientists we spoke to uniformly withheld from making specific predictions, but they were all agreed that evolution hasn’t stopped.
“It’s definitely happening,” asserts Professor Graves, “but as human beings, we’re not in a lab setting. There are just too many complexities to make a scientifically meaningful prediction.”
This uncertainty has a thrill of its own. Not so much in imagining what it’s like to be telepathic, but in the anticipation of what scientists will inevitably discover about our species and our genome next. Our next big step could be into a warm, acidic, jellyfish-infested ocean (or into some other self-inflicted catastrophe), rather than into a bright future of mass immunity and hyperintelligence.