Sheffield University. UK: Charles Darwin’s theory on evolution still holds true despite
lower mortality and fertility rates in the modern world, according to
new research by the University of Sheffield. Scientists looked at how cultural influences like easy access to
contraception and medical advances reducing infant mortality, effects
natural selection in modern human populations.
The study, carried out in Finland, observed that while only 67 per
cent of children born in the 1860s survived to adulthood the figure rose
to 94 per cent during the 1940s. At the same time, people went from
having an average of five children to 1.6 children during their
lifetime.
But despite artificial influences the study found genetic differences between humans are what continue to fuel evolution.
Dr Virpi Lummaa, from the Department of Animal and Plant Sciences at
the University of Sheffield, and Dr Elisabeth Bolund, now at the Uppsala
University in Sweden, used genealogical records collected from Finnish
churches starting at the beginning of the 18th century and still being
collected today. By assembling family trees over several generations of
over 10,000 individuals, they could sort out how much of the variation
in a trait is due to genetic influences and how much is due to
environmental influences, and how the determinants of key traits for
evolutionary success may have changed over the modernisation of society.
The study found that in the 18th and 19th centuries, about four to 18
per cent of the variation between individuals in lifespan, family size
and ages at first and last birth was influenced by genes, while the rest
of the variation was driven by differences in various aspects of their
environment.
“This is exciting because if genes
affected differences between individuals in these traits, it means they
could also change in response to natural selection,” said Dr Bolund.
“But we know that the environment has changed rapidly and dramatically,
so we investigated the genetic basis of such complex traits and their
ability to continue changing through evolution.”
The study showed that the genetic influence on timing of reproduction
and family size tended to actually be higher in recent times. This
means that modern human societies can still respond to selection, and
genetic differences between us continue to fuel evolution.
“It is possible that we in modern societies have more individual
freedom to express our genetic predispositions because social and
normative influences are more relaxed, and this leads to the genetic
differences among us explaining more of the reproductive patterns,” said
Dr Bolund.
Complex traits like the ones in the study are each influenced by many
different genes, while at the same time, several different traits can
be affected by the same genes. The authors found that the genetic basis
that is shared between the studied reproductive traits and longevity did
not change over time.
“This is reassuring if we want to use current patterns of natural
selection and genetic variation to make predictions of what will happen
in modern human populations over the next few generations,” added Dr
Bolund.
“Our results can help us when we want to predict population responses
in the face of global challenges such as prevailing epidemics, ageing
populations and decreasing fertility.”
The paper has been published online by the journal Evolution.