Humans continue to evolve

Avatar of Saya Nabila.
Avatar of Saya Nabila.

Humans continue to evolve

Researchers have been looking into the evolution of human genetics.

They say they have discovered that human genes have continued to change after the evolutionary split from primate ancestors.

They acknowledge that genetic research is complicated and more study is needed.

New research is shedding new light on the evolution of modern humans — a process that continues, millions of years after the evolutionary split from our primate ancestors.

Researchers have now added to the existing body of knowledge to create a genetic map that compares human beings to other vertebrates, finding that a host of newly identified genes are entirely unique to humans.

Additionally, scientists say these findings could help them better understand the role that genetics play in certain diseases.

Their study was published todayTrusted Source in the life sciences journal Cell Reports.

While the study of specific genes can be challenging, scientists say this new dataset helps pave the way toward a more nuanced understanding of human genetics.

Genes: Life’s instruction book

According to Katie Sagaser, MS, CGC, the director of genetic counseling at Juno Diagnostics in San Diego, it’s helpful to think of genes as a set of instructions housed within the nucleus of each cell.

“I often liken genes to the chapters of a textbook,” Sagaser told Medical News Today. “If we think of each cell nucleus as a bookcase, holding the essential instructions for a complex project, then we expect the bookcase to hold 23 pairs of textbooks — 46 total. These textbooks represent human chromosomes inherited from each genetic parent.”

While each parent contributes one set of 23 “textbooks,” the instructions can vary significantly.

When researchers delve into the coils of DNA code embedded within chromosomes, they say they can identify these differences and begin to understand how they play out in the human body.

Genetics aren’t entirely predictable

Complicating matters is the fact that mutations — essentially variations or glitches within DNA sequencing — are entirely possible.

“This is the case when a baby is born with a de novo dominant gene mutation, meaning a single letter of the DNA code was randomly changed in such a way that it resulted in the individual having a unique diagnosis not inherited from either genetic parent,” explained Sagaser.

Another variable that can make genetics difficult to predict is the fact that variations in a person’s DNA code might occur during their lifetime – for instance, as a result of certain cancers.

“Thinking back to our bookcase example, if one were tasked with transcribing and reproducing each letter, sentence, chapter, and volume of a very dense stack of textbooks – it’s absolutely possible for a transcription error to occur,” said Sagaser. “Sometimes, spelling errors have very little consequence, if any. In other instances, however, spelling and other transcription errors can change the intended message altogether.”

Human evolution continues

A pair of scientists — Nikolaos Vakirlis, the new study’s first author and a junior researcher at the Alexander Fleming Biomedical Sciences Research Center in Greece, along with Aoife McLysaght, a senior author from Trinity College Dublin in Ireland — have been studying these “orphan” de novo genes for years.

Vakirlis told MNT that they started out by looking at short sequences of DNA in the human genome.

“These are elements of the genome that are not considered to be proper genes and were until relatively recently mostly left out of ‘mainstream’ genomics studies,” he explained. “However, a recent studyTrusted Source had shown that some of them seem to have important cellular roles.”

From there, Vakirlis and McLysaght sought to pinpoint when these sequences first evolved along the human lineage, along with the mechanisms that allowed them to emerge.

They were able to find a total of 155 de novo originated microproteins. Since de novo gene emergence is now an accepted evolutionary phenomenon, these microproteins could emerge into genes.

Vakirlis said that about a third of these 155 de novo originated microproteins were already known to be functional. However, two of them were strictly specific to humans and others also overlap with known mutations that cause disease.

“What we found is significant because it adds to our understanding of the human genome, including details of human-specific genetics, albeit small,” said Vakirlis. “Our findings also suggest that many more young but important microproteins could be hiding in human cells that can only be uncovered by careful experiments.”

The challenges of studying genes

While the findings shed new light on the human genome and create new avenues for research, it’s still a challenging area to study.

“I think the small size and the recent origins are very important for these genes because they combine to make them into the most difficult cases to study,” McLysaght told MNT. “They are on the edge of detectability both in comparative genomics studies and in genome annotation. And, as Nikos said, this work suggests a greater amount of unappreciated and undetected genes might exist.”

Vakirlis says that the next steps involved gaining a better understanding of how genes can evolve from scratch.

“We can now also conduct wider studies as new datasets of human microproteins are becoming available, in the hope to discover more evolutionarily novel ones,” he said.

Age vs. DNA: Which has more influence on how humans age?

A theory regarding evolution proposes that natural selection is less of a factor for people past their reproductive years since gene variations are not carried forward in offspring at that point in life.

A new study supports this idea, finding that certain tissue types in older people are influenced more by aging itself and by environmental factors than by DNA.

These tissues, while critically important, can also lead to cancers, suggesting a limit to what evolution can achieve.

In 1952, Nobel-prize winner Dr. Peter Medawar put forward the hypothesis that aging processes may be a result of evolution’s natural selection not having that much to say about people past their child-bearing years.

A new study finds fresh support for Medawar’s hypothesis in an analysis of how roughly 20,000 human genes are expressedTrusted Source as we age.

The study suggests that our genes are less of an influence as we get older.

Study senior author Dr. Peter Sudmant, assistant professor in integrative biology at the University of California Berkeley tells Berkeley News, “Almost all human common diseases are diseases of aging: Alzheimer’s, cancers, heart disease, diabetes.”

“Massive amounts of public resources have gone into identifying genetic variants that predispose you to these diseases. What our study is showing is that, well, actually, as you get older, genes kind of matter less for your gene expression,” says Sudmant.

The study is published in Nature CommunicationsTrusted Source.

Evolutionary logic

Dr. Sudmant summarized Medawar’s hypothesis for Medical News Today:

“Genes that are turned on when we are young are more constrained by evolution because they are critical to making sure we survive to reproduce, while genes expressed after we reach reproductive age are under less evolutionary pressure.”

Dr. Giuseppe Passarino, professor of genetics at the University of Calabria in Italy, who was not involved in the study, explained to MNT how this works:

“It is evident that in order to have more children, you need to survive and to be fit [long enough to] reproduce yourself. To get this goal, you need to have no diseases while you are young, to be able to find food, to get a partner.”

“Evolution is based on the fact that individuals who have better fitness have more children. Thus, their genotypes will spread in the population more than those of subjects who have [fewer] children,” Dr. Passarino added.

Five problematic tissues

The researchers retrieved gene expression data for 27 different types of body tissues in almost 950 people from the GTEx web portal. Individuals were categorized as “young” if they were less than 55 years of age, and “old” if they were 55 or over.

In their analysis, the researchers found that genetics exerts about the same amount of influence over gene expression in almost all of our tissues until we cross into the “old” bracket.

At that point, aging plays a much more influential role for five critical tissue types — blood, colon, arteries, esophagus, and fat tissues — than does genetics.

As an influence on gene expression in the study, “aging” refers to the universal, progressive cellular aging processes associated with advancing years.

How our environment affects our aging

While it would theoretically be helpful if evolution would help select genes that keep us healthy even after we reproduce, according to Dr. Sudmant:

“The ‘limit of evolution’ here is that, late in life, you really should not have these sorts of genes turned on, and having them turned on actually makes you susceptible to cancer. However, because these are cell types in your body that need to keep turning over — blood! — there is no other option.”

Hence, aging and environmental factors are more influential in gene expression for these critical tissues.

In the study, environmental influences include factors not directly associated with those processes: the quality of the air and water we breathe and eat, our diet, and also our level of physical exercise.

The study finds that environmental factors account for about a third of gene expression in older people.

“This [study] does not imply that genetics is not important for aging. There are many studies showing that the similarities between relatives regarding the quality of aging (presence of diseases or inabilities) are very high. In fact, although the genes expressed later in life are not selected, still they are important for our life.”

— Dr. Giuseppe Passarino

“In other words, we are equipped with highly selected allelesTrusted Source for the first part of our life and with alleles [that] are less selected for the second part. However, in both cases, our phenotype is based on our genes,” Dr. Passarino added.

What this study means

According to Dr. Passarino, to better understand the complexity of how humans age and to learn how to slow down this process, researchers need to study the genes expressed later in life and improve them.

“One option may be to see how the genetic machinery works in long-lived subjects, and try to modulate the machinery of others accordingly,” said Dr. Passarino.

”For instance, it has been observed that long-lived subjects have limited ability to use proteins or sugar. Thus, we can use a limited amount of proteins and sugar to modulate our organism machinery as if we were equipped with the same genes of long-lived subjects,” he elaborated.

“When we do studies to identify the genetics underlying disease, we often end up with many genes that we could potentially target. Our study now quantifies how age impacts the expression of genes in the population. We argue that age-associated genes might be better therapeutic targets than the ones that vary in their expression as a function of human genetics,” Dr. Sudmant said.

“We think that genes that show consistence in age-associated changes in expression in humans are potentially really interesting targets to follow up on!” he concluded.