Humans Bred with Unknown Species

Humans Bred with Unknown Species

Humans Bred with Unknown Species

A new study presented to the Royal Society meeting on ancient DNA in London last week has revealed a dramatic finding – the genome of one of our ancient ancestors, the Denisovans, contains a segment of DNA that seems to have come from another species that is currently unknown to science. The discovery suggests that there was rampant interbreeding between ancient human species in Europe and Asia more than 30,000 years ago. But, far more significant was the finding that they also mated with a mystery species from Asia – one that is neither human nor Neanderthal. 

Scientists launched into a flurry of discussion and debate upon hearing the study results and immediately began speculating about what this unknown species could be.  Some have suggested that a group may have branched off to Asia from the Homo heidelbernensis, who resided in Africa about half a million years ago. They are believed to be the ancestors of Europe’s Neanderthals. 

However others, such as Chris Stringer, a paleoanthropologist at the London Natural History Museum, admitted that they “don’t have the faintest idea” what the mystery species could be.

Traces of the unknown new genome were detected in two teeth and a finger bone of a Denisovan, which was discovered in a Siberian cave. There is not much data available about the appearance of Denisovans due to lack of their fossils’ availability, but the geneticists and researchers succeeded in arranging their entire genome very precisely.

“What it begins to suggest is that we’re looking at a ‘Lord of the Rings’-type world – that there were many hominid populations,” Mark Thomas, an evolutionary geneticist at University College London.

The question is now: who were these mystery people that the Denisovans were breeding with?



Evolution demographic schedule

Does Age Bring Death? Not For All Species:



Humans have a pretty straightforward view of aging: They’re born, they mature, they gradually become weaker and lose fertility, and eventually, they die.

But in nature, aging is far more diverse, new research finds. In fact, some animals are actually less likely to die the older they get — at least up to a point.

Understanding mortality

Evolutionary theorists working in the 1950s through 1970s explained the familiar pattern of increasing mortality with age as a trade-off between reproduction and survival. If an organism only has a certain number of resources, it has to decide whether to allocate them to creating offspring (searching for mates, wooing them and mating) or to surviving for another year.

“The question is how do you balance that,” Jones sad. “If you put everything into survival, you don’t reproduce very much or at all. If you put all your energy into reproduction, then you will have a low survival.”

No matter how healthy and resource-rich you are, there is always a slight chance that you’ll die. You could be hit by a bus, struck by lightning, or end up in the path of a rockslide. For this reason, Jones said, evolution favors those who reproduce early, before anything bad can befall them. Thus, genetic mutations that favor early reproduction, even at the expense of an organism’s later life, will be preserved.

Still, a few studies had revealed that some species don’t age as classical theory suggests, Jones said. Jellylike animals called hydras (Hydra magnipapillata) have low mortality rates that are constant throughout their lives. Hydra die so infrequently in laboratory conditions that researchers estimate it would take 1,400 years for 95 percent of a population to die of natural causes.

The desert tortoise (Gopherus agassizii) actually becomes less likely to die with age. The tortoises aren’t immortal, of course — they do still die. But their mortality rate in youth is actually higher than their mortality rate in old age. If they make it past their younger years, they’re likely to keep trucking until as old as 80 years of age.

A hydra, a small animal with constant mortality.

The diversity of aging

Most people who study aging focus on just a few species. Jones and his colleagues wanted a broader view, so they drew from across the tree of life, comparing aging patterns in 11 mammals, 12 other vertebrates (animals with backbones), 10 invertebrates, 12 plants and a green alga. They picked species for which there was good quality data on the life trajectory.

“We were restricting ourselves to the datasets which followed enough individuals that you had good pictures over the whole life course, which we defined as following 95 percent of the individuals until death,” Jones said.

The results highlighted the diversity between organisms, Jones said. “Mortality can go up [with age], it can stay constant, or it could go down,” he said. “And the same for fertility.”

At 102, the age at which 95 percent of humans are dead, a Japanese woman has 20 times the risk of mortality than the average for adult humans over the life span. In comparison, a white mangrove tree at the same so-called “terminal age” (123 years, for mangroves) is less than half as likely to die than the average adult of its species.

The Southern fulmar (Fulmarus glacialoides), a seabird, becomes more likely to die with age. But it also becomes more fertile as it grows older. Hydras have constant fertility rates their entire lives. And many animals other than humans have life spans that continue past their reproductive years, including killer whales (Orcinus orca), mynah birds (Leucopsar rothschildi) and nematode worms (Caenorhabditis elegans).

The diversity of mortality and aging is independent of life span, Jones added. It’s not only long-lived creatures like the desert tortoise that show declining or constant mortality with age. The collared flycatcher (Ficedula albicollis), a migratory black-and-white bird, lives only about five years, maximum — at that age, 95 percent of collared flycatchers are dead. But the flycatcher’s mortality is fairly constant throughout adulthood, not rising with age.

Challenging theory

The findings challenge the assumptions of classical theory, suggesting the old ideas need a tweak, Jones said.

“In order to make sense of what we’re seeing, theoreticians need to figure out why it is that we’re seeing these patterns and make sense of it,” he said.

It’s likely that body size plays a role, he said. Organisms that grow with age without stopping at a certain size, like some trees, may be less vulnerable in old age to environmental fluctuations or other threats. Fish that outgrow all of their predators are likely to make it to a ripe old age, for example.

Jones and his colleagues plan to study wider populations of species and to get a sense of the reasons behind the varying life spans. For example, does it matter whether a plant is a tree or a shrub? Do certain environments promote longevity?

“There’s good evidence that a lot of these plants that live a very long time tend to live in arid regions,” Jones said. “Aridity might have some kind of effect.”

Bees outpace Orchids



Bees outpace orchids in evolution:


 Bees outpace orchids in evolution

Bees outpace orchids in evolution



Orchid bees aren’t so dependent on orchids after all, according to a new study that challenges the prevailing view of how plants and their insect pollinators evolve together.

A male orchid bee collects fragrance compounds from flowers of a Notylia orchid. Female orchid bees choose mates based upon the mix of these chemical compounds. (R. B. Singer photo)

A long-standing belief among biologists holds that species in highly specialized relationships engage in a continual back-and-forth play of co-evolution.

“What we found was that this reciprocal specialization did not exist for orchid bees and orchids,” said study lead author Santiago Ramirez, post-doctoral researcher in the lab of Neil Tsutsui, associate professor at the University of California, Berkeley’s Department of Environmental Science, Policy, and Management. “The bees evolved much earlier and independently, while the orchids appear to have been catching up.”

The bond between specific bees and the orchid plants they visited has been well-documented by botanists and naturalists, including Charles Darwin. Biologists discovered that male bees needed the specific perfume compounds produced by the flowering plants in order to mate with female bees.

In the study, published in the Sept. 23 issue of the journal Science, the researchers screened more than 7,000 individual male bees and sequenced DNA from 140 orchid pollinaria, which are small packages that contain all the pollen grains produced by a single flower. The researchers were able to infer the evolutionary history of both bees and orchids, and establish which species of bee pollinates what species of orchid. The researchers also quantified and analyzed the perfumes collected by orchid bees and compared them with the compounds produced by orchid flowers.

To their surprise, the scientists found that the bees evolved at least 12 million years earlier than their orchid counterparts. Additionally, they found that the compounds produced by the orchids only accounted for 10 percent of the compounds collected by their pollinators. The remaining 90 percent could be coming from other sources, including tree resins.

Male orchid bees can find the fragrance compounds they need for mating from decaying logs, as shown here, as well as from orchids. (B. Jacobi photo)

“It appears that the male bees evolved a preference to collect these compounds from all kinds of sources, and the orchids converged on that chemical preference millions of years later,” said Ramirez.

In essence, orchids need their bee pollinators more than the bees need them.

The findings have implications in conservation biology, particularly because of the alarming decline over the past 15 years of bee pollinators worldwide.

“Many plant species are extremely dependent on their pollinators,” said Ramirez, who began this work while he was a Ph.D. student in the lab of Naomi Pierce, Harvard University professor of biology. “If you lose one species of bee, you could lose three to four species of orchids. Many of these orchids don’t produce any other type of reward, such as nectar, that would attract other species of bee pollinators.”

“Our study is consistent with the emerging theory that insect sensory biases have played a major role in driving reproductive adaptations in flowering plants,” said Ramirez. “It highlights the ecological and evolutionary inter-dependence of flowering plants and their specialized pollinators, suggesting that new threats to insect pollinators may have profound effects on the ecosystems they inhabit.”